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Patent Analysis of

Hot-rolled steel sheet

Updated Time 12 June 2019

Patent Registration Data

Publication Number

US10000829

Application Number

US14/774249

Application Date

14 April 2014

Publication Date

19 June 2018

Current Assignee

NIPPON STEEL CORPORATION

Original Assignee (Applicant)

NIPPON STEEL & SUMITOMO METAL CORPORATION

International Classification

C22C38/32,C22C38/28,C22C38/26,C22C38/22,C22C38/18

Cooperative Classification

C22C38/32,C21D8/0263,C21D9/46,C22C38/00,C22C38/001

Inventor

TODA, YURI,AZUMA, MASAFUMI,UENISHI, AKIHIRO,SHIGESATO, GENICHI

Patent Images

This patent contains figures and images illustrating the invention and its embodiment.

US10000829 Hot-rolled steel sheet 1 US10000829 Hot-rolled steel sheet 2
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Abstract

A hot-rolled steel sheet includes a specified chemical composition and includes a steel structure represented by an area ratio of ferrite being 5% to 50%, an area ratio of bainite composed of an aggregate of bainitic ferrite whose grain average misorientation is 0.4° to 3° being 50% to 90%, and a total area ratio of martensite, pearlite, and retained austenite being 5% or less.

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Claims

1. A hot-rolled steel sheet comprising:a chemical composition represented by, in mass %, C: 0.02% to 0.15%, Si: 0.01% to 2.0%, Mn: 0.05% to 3.0%, P: 0.1% or less, S: 0.03% or less, Al: 0.001% to 0.01%, N: 0.02% or less, O: 0.02% or less, Ti: 0% to 0.2%, Nb: 0% to 0.2% Mo: 0% to 0.2% V: 0% to 0.2% Cr: 0% to 1.0%, B: 0% to 0.01%, Cu: 0% to 1.2%, Ni: 0% to 0.6%, Ca: 0% to 0.005%, REM: 0% to 0.02%, and the balance: Fe and an impurity; anda steel structure represented by an area ratio of ferrite: 5% to 50%, an area ratio of bainite composed of an aggregate of bainitic ferrite whose grain average misorientation is 0.4° to 3°: 50% to 95%, and a total area ratio of martensite, pearlite, and retained austenite: 5% or less.

2. The hot-rolled steel sheet according to claim 1, wherein the chemical composition satisfies one or more selected from the group consisting of, in mass %, Ti: 0.01% to 0.2%, Nb: 0.01% to 0.2%, Mo: 0.001% to 0.2%, V: 0.01% to 0.2%, Cr: 0.01% to 1.0%, B: 0.0002% to 0.01%, Cu: 0.02% to 1.2%, and Ni: 0.01% to 0.6%.

3. The hot-rolled steel sheet according to claim 1, wherein the chemical composition satisfies one or more selected from the group consisting of, in mass %, Ca: 0.0005% to 0.005% and REM: 0.0005% to 0.02%.

4. The hot-rolled steel sheet according to claim 2, wherein the chemical composition satisfies one or more selected from the group consisting of, in mass %, Ca: 0.0005% to 0.005% and REM: 0.0005% to 0.02%.

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Claim Tree

  • 1
    1. A hot-rolled steel sheet comprising:
    • a chemical composition represented by, in mass %, C: 0.02% to 0.15%, Si: 0.01% to 2.0%, Mn: 0.05% to 3.0%, P: 0.1% or less, S: 0.03% or less, Al: 0.001% to 0.01%, N: 0.02% or less, O: 0.02% or less, Ti: 0% to 0.2%, Nb: 0% to 0.2% Mo: 0% to 0.2% V: 0% to 0.2% Cr: 0% to 1.0%, B: 0% to 0.01%, Cu: 0% to 1.2%, Ni: 0% to 0.6%, Ca: 0% to 0.005%, REM: 0% to 0.02%, and the balance: Fe and an impurity
    • anda steel structure represented by an area ratio of ferrite: 5% to 50%, an area ratio of bainite composed of an aggregate of bainitic ferrite whose grain average misorientation is 0.4° to 3°: 50% to 95%, and a total area ratio of martensite, pearlite, and retained austenite: 5% or less.
    • 2. The hot-rolled steel sheet according to claim 1, wherein
      • the chemical composition satisfies one or more selected from the group consisting of,
    • 3. The hot-rolled steel sheet according to claim 1, wherein
      • the chemical composition satisfies one or more selected from the group consisting of,
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Description

TECHNICAL FIELD

The present invention relates to a hot-rolled steel sheet excellent in an elongation and a hole expandability.

BACKGROUND ART

Weight reduction of a body of an automobile using a high-strength steel sheet has been put forward, in order to suppress an emission amount of carbon dioxide gas from an automobile. A high-strength steel sheet has come to be often used for a body in order also to secure safety of a passenger. Further improvement of strength is important to further proceed with weight reduction of a body. On the other hand, some parts of a body require excellent formability. For example, an excellent hole expandability is required for a high-strength steel sheet for an underbody part.

However, attaining both of a strength improvement and a formability improvement is difficult. In general, the higher a strength of a steel sheet is, the lower a formability is, and an elongation, which is important in drawing and bulging, and a hole expandability, which is important in burring, are reduced.

Patent Literatures 1 to 11 describe high-strength steel sheets intended to improve formability or something. However, a hot-rolled steel sheet having a sufficient strength and a sufficient formability cannot be obtained by the conventional techniques.

Though a technique related to improvement of a hole expandability is described in Non Patent Literature 1, a hot-rolled steel sheet having a sufficient strength and a sufficient formability cannot be obtained by this conventional technique. Further, this conventional technique is hard to be applied to a manufacturing process on an industrial scale of a hot-rolled steel sheet.

CITATION LIST

Patent Literature

  • Patent Literature 1: Japanese Laid-open Patent Publication No. 2012-26032
  • Patent Literature 2: Japanese Laid-open Patent Publication No. 2011-225941
  • Patent Literature 3: Japanese Laid-open Patent Publication No. 2006-274318
  • Patent Literature 4: Japanese Laid-open Patent Publication No. 2005-220440
  • Patent Literature 5: Japanese Laid-open Patent Publication No. 2010-255090
  • Patent Literature 6: Japanese Laid-open Patent Publication No. 2010-202976
  • Patent Literature 7: Japanese Laid-open Patent Publication No. 2012-62561
  • Patent Literature 8: Japanese Laid-open Patent Publication No. 2004-218077
  • Patent Literature 9: Japanese Laid-open Patent Publication No. 2005-82841
  • Patent Literature 10: Japanese Laid-open Patent Publication No. 2007-314828
  • Patent Literature 11: Japanese Laid-open Patent Publication No. 2002-534601

Non Patent Literature

  • Non Patent Literature 1: Kato et al., Seitetsukenkyu (1984) vol. 312, p. 41

SUMMARY OF INVENTION

Technical Problem

A purpose of the present invention is to provide a hot-rolled steel sheet having a high strength and capable of obtaining excellent elongation and hole expandability.

Solution to Problem

The inventors of the present application, with an eye on a general manufacturing method of a hot-rolled steel sheet implemented in an industrial scale using a common continuous hot-rolling mill, have conducted keen studies in order to improve a formability such as an elongation and a hole expandability of the hot-rolled steel sheet while obtaining a high strength. As a result, a new structure quite effective in securing the high strength and improving the formability has been found out, the structure not having been formed by a conventional technique. This structure is bainite composed of an aggregate of bainitic ferrite whose grain average misorientation is 0.4° or more to 3° or less. This bainite hardly contains carbide and retained austenite in a grain. In other words, this bainite hardly contains what promotes development of a crack in hole expanding. Thus, this bainite contributes to securing of the high strength and improvement of the elongation and the hole expandability.

The bainite composed of the aggregate of bainitic ferrite whose grain average misorientation is 0.4° or more to 3° or less is not able to be formed by a conventional method such as methods described in above-described Patent Literatures 1 to 11. For example, the above bainite cannot be formed by a conventional technique intended to heighten a strength by forming martensite through making a cooling rate higher from the end of so called intermediate air cooling to coiling. For example, bainite included in a conventional steel sheet is composed of bainitic ferrite and an iron carbide, or composed of bainitic ferrite and retained austenite. Thus, in the conventional steel sheet, the iron carbide or retained austenite (or martensite having been transformed by being processed) promotes development of a crack in hole expanding. Accordingly, the bainite composed of the aggregate of bainitic ferrite whose grain average misorientation is 0.4° or more to 3° or less has a hole expandability superior to bainite included in a conventional steel sheet. This bainite is a structure different also from ferrite included in a conventional steel sheet. For example, a generating temperature of this bainite is equal to or lower than a bainite transformation start temperature estimated from a component of steel, and a grain boundary with a low angle exists inside a grain surrounded by a high-angle grain boundary of this bainite. This bainite has a feature different from that of ferrite at least in the above points.

With details being described later, the inventors of the present application have found that by making conditions of finish rolling, cooling thereafter, coiling thereafter, cooling thereafter, and something be appropriate, the bainite can be formed with a desired area ratio together with ferrite. By methods described in Patent Literatures 1 to 3, it is impossible to form bainite having a grain boundary with a low angle inside a grain surrounded by a high-angle grain boundary, since a cooling rate after the end of intermediate air cooling and before coiling, and a cooling rate in a state of coil are quite high.

The inventors of the present application have further conducted keen studies based on the above observation, and have conceived embodiments of the invention described below.

(1) A hot-rolled steel sheet including:

a chemical composition represented by, in mass %,

    • C: 0.02% to 0.15%,
    • Si: 0.01% to 2.0%,
    • Mn: 0.05% to 3.0%,
    • P: 0.1% or less,
    • S: 0.03% or less,
    • Al: 0.001% to 0.01%,
    • N: 0.02% or less,
    • O: 0.02% or less,
    • Ti: 0% to 0.2%,
    • Nb: 0% to 0.2%
    • Mo: 0% to 0.2%
    • V: 0% to 0.2%
    • Cr: 0% to 1.0%,
    • B: 0% to 0.01%,
    • Cu: 0% to 1.2%,
    • Ni: 0% to 0.6%,
    • Ca: 0% to 0.005%,
    • REM: 0% to 0.02%, and
    • the balance: Fe and an impurity; and

a steel structure represented by

    • an area ratio of ferrite: 5% to 50%,
    • an area ratio of bainite composed of an aggregate of bainitic ferrite whose grain average misorientation is 0.4° to 3°:50% to 95%, and
    • a total area ratio of martensite, pearlite, and retained austenite: 5% or less.

(2) The hot-rolled steel sheet according to (1), wherein the chemical composition satisfies one or more selected from the group consisting of, in mass %,

Ti: 0.01% to 0.2%,

Nb: 0.01% to 0.2%,

Mo: 0.001% to 0.2%,

V: 0.01% to 0.2%,

Cr: 0.01% to 1.0%,

B: 0.0002% to 0.01%,

Cu: 0.02% to 1.2%, and

Ni: 0.01% to 0.6%.

(3) The hot-rolled steel sheet according to (1) or (2), wherein the chemical composition satisfies one or more selected from the group consisting of, in mass %,

Ca: 0.0005% to 0.005% and

REM: 0.0005% to 0.02%.

Advantageous Effects of Invention

According to the present invention, it is possible to obtain excellent elongation and hole expandability while having a high strength.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a region representing a steel structure of a hot-rolled steel sheet; and

FIG. 2 is a view illustrating an outline of a temperature history from hot rolling to coiling.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described.

First, a steel structure of a hot-rolled steel sheet according to the present embodiment will be described. The hot-rolled steel sheet according to the present embodiment includes a steel structure represented by an area ratio of ferrite: 5% to 50%, an area ratio of bainite composed of an aggregate of bainitic ferrite whose grain average misorientation is 0.4° to 3°:50% to 95%, a total area ratio of martensite, pearlite, and retained austenite: 5% or less. The steel structure of the hot-rolled steel sheet may be represented by a steel structure in a region between ⅜ and ⅝ of a thickness of the hot-rolled steel sheet from a surface thereof. This region 1 is illustrated in FIG. 1. A cross section 2 being an object of steel structure observation is also illustrated in FIG. 1.

(Area Ratio of Ferrite: 5% to 50%)

Ferrite exhibits an excellent ductility and heightens a uniform elongation. When the area ratio of ferrite is less than 5%, a good uniform elongation cannot be obtained. Therefore, the area ratio of ferrite is 5% or more. When the area ratio of ferrite is over 50%, a hole expandability is considerably reduced. Thus, the area ratio of ferrite is 50% or less. The area ratio of ferrite is an area ratio in the cross section 2 parallel to a rolling direction in the region between ⅜ and ⅝ the thickness of the hot-rolled steel sheet from the surface thereof, and is an area ratio of ferrite in a microstructure observed at a magnification of 200 times to 500 times using an optical microscope.

(Area Ratio of Bainite Composed of Aggregate of Bainitic Ferrite Whose Grain Average Misorientation is 0.4° to 3°:50% to 95%)

Bainite composed of the aggregate of bainitic ferrite whose grain average misorientation is 0.4° or more to 3° or less is a new structure obtained by a later-described method. The grain average misorientation in a grain is obtained as below. First, crystal orientations of some points in the cross section 2 are measured by an electron back scattering diffraction (EBSD) method. Then, based on the measurement results by EBSD, it is assumed that a grain boundary exists between two points (pixels) which are adjacent to each other and between which a crystal misorientation is 15° or more. Then, within a region surrounded by the grain boundary, that is, within the grain, crystal misorientations between points adjacent to each other are calculated, and an average value thereof is calculated. The grain average misorientation within a crystal grain is obtained in this way.

As described above, it is found by inventors of the present application that bainite composed of the aggregate of bainitic ferrite whose grain average misorientation is 0.4° or more to 3° or less is a structure quite effective for securing of a high strength and improvement of a formability such as a hole expandability. This bainite hardly contains carbide and retained austenite in the grain. In other words, this bainite hardly contains what promotes development of a crack in hole expanding. Therefore, this bainite contributes to securing of the high strength and improvement of the elongation and the hole expandability.

When the area ratio of bainite composed of the aggregate of bainitic ferrite whose grain average misorientation is 0.4° or more to 3° or less is less than 50%, a sufficient strength cannot be obtained. Therefore, the area ratio of this bainite is 50% or more. When the area ratio of this bainite is over 95%, a sufficient elongation cannot be obtained. Therefore, the area ratio of this bainite is 95% or less. When the area ratio of this bainite is 50% or more to 95% or less, generally, a tensile strength is 590 MPa or more, a product (TS×λ) of the tensile strength (TS (MPa)) and a hole expansion ratio (λ(%)) is 65000 or more, and a product (EL×λ) of a total elongation (EL (%)) and the hole expansion ratio (λ(%)) is 1300 or more. These characteristics are suitable for a processing of an underbody part of an automobile.

A grain whose grain average misorientation is less than 0.4° may be regarded as ferrite. A grain whose grain average misorientation is over 3° is inferior in the hole expandability. The grain whose grain average misorientation is over 3° is generated in a lower temperature zone than the bainite composed of the aggregate of bainitic ferrite whose grain average misorientation is 0.4° or more to 3° or less, for example.

(Total Area Ratio of Martensite, Pearlite, and Retained Austenite: 5% or Less)

Martensite, pearlite, and retained austenite promote development of a crack at an interface with ferrite or bainite in hole expanding, and reduces the hole expandability. When the total area ratio of martensite, pearlite, and retained austenite is over 5%, such deterioration of the hole expandability is prominent. The area ratios of pearlite, martensite, and retained austenite are each area ratios in the cross section 2 and area ratios of perlite, martensite, and retained austenite in a microstructure observed at the magnification of 200 times to 500 times using the optical microscope. When a total of these structures is 5% or less, generally, the product (EL×λ) of the total elongation (EL (%)) and the hole expansion ratio (λ(%)) is over 1300, and suitable for a processing of the underbody part of the automobile.

It is a matter of course that a condition related to the aforementioned area ratio of each structure is preferable to be satisfied not only in the region 1 but also in a broader range, and the broader the range where this condition is satisfied is, the more excellent strength and workability can be obtained.

Next, a chemical composition of the hot-rolled steel sheet according to the embodiment of the present invention will be described. In description hereinafter, “%” being a unit of a content of each element contained in the hot-rolled steel sheet means “mass %” unless mentioned otherwise. The hot-rolled steel sheet according to the present embodiment includes a chemical composition represented by C: 0.02% to 0.15%, Si: 0.01% to 2.0%, Mn: 0.05% to 3.0%, P: 0.1% or less, S: 0.03% or less, Al: 0.001% to 0.01%, N: 0.02% or less, O: 0.02% or less, Ti: 0% to 0.2%, Nb: 0% to 0.2%, Mo: 0% to 0.2%, V: 0% to 0.2%, Cr: 0% to 1.0%, B: 0% to 0.01%, Cu: 0% to 1.2%, Ni: 0% to 0.6%, Ca: 0% to 0.005%, REM: 0% to 0.02%, and the balance: Fe and an impurity. As the impurity, there are exemplified what is included in a raw material such as ore and scrap and what is included in a manufacturing process.

(C: 0.02% to 0.15%)

C segregates in a grain boundary and has an effect to suppress peeling on an end surface formed by shearing or punch-cutting. C couples with Nb, Ti, or the like and forms a precipitate in the hot-rolled steel sheet, contributing to improvement of the strength by precipitation strengthening. When a C content is less than 0.02%, the effect to suppress peeling and an effect to improve the strength by precipitation strengthening cannot be obtained sufficiently. Therefore, the C content is 0.02% or more. On the other hand, C generates an iron-based carbide such as cementite (Fe3C), martensite, and retained austenite to be a starting point of a fracture in hole expanding. When the C content is over 0.15%, the sufficient hole expandability cannot be obtained. Therefore, the C content is 0.15% or less.

(Si: 0.01% to 2.0%)

Si contributes to improvement of the strength of the hot-rolled steel sheet. Si also has a role as a deoxidizing material of molten steel. Si suppresses precipitation of an iron-based carbide such as cementite and suppresses precipitation of cementite in a boundary of bainitic ferrite. When an Si content is less than 0.01%, above effects cannot be obtained sufficiently. Therefore, the Si content is 0.01% or more. When the Si content is over 2.0%, the effect to suppress precipitation of cementite is saturated. Further, when the Si content is over 2.0%, generation of ferrite is suppressed, so that a desired steel structure in which the area ratio of ferrite is 5% or more cannot be obtained. Therefore, the Si content is 2.0% or less.

(Mn: 0.05% to 3.0%)

Mn contributes to improvement of the strength by solid solution strengthening. When a Mn content is less than 0.05%, the sufficient strength cannot be obtained. Therefore, the Mn content is 0.05% or more. When the Mn content is over 3.0%, a slab fracture occurs. Therefore, the Mn content is 3.0% or less.

(P: 0.1% or Less)

P is not an essential element and is contained as an impurity in steel, for example. In view of a workability, a weldability, and a fatigue characteristic, a P content as low as possible is preferable. In particular, when the P content is over 0.1%, deterioration of the workability, the weldability, and the fatigue characteristic is prominent. Therefore, the P content is 0.1% or less.

(S: 0.03% or Less)

S is not an essential element and is contained as an impurity in steel, for example. A higher S content makes it easier for an A-based inclusion leading to deterioration of the hole expandability to be generated, and thus, the S content as low as possible is preferable. In particular, when the S content is over 0.03%, deterioration of the hole expandability is prominent. Therefore, the S content is 0.03% or less.

(Al: 0.001% to 0.01%)

Al has an action to deoxidize molten steel. When an Al content is less than 0.001%, sufficient deoxidation is difficult. Therefore, the Al content is 0.001% or more. When the Al content is over 0.01%, the elongation is easy to be reduced due to increase of non-metal inclusions. Therefore, the Al content is 0.01% or less.

(N: 0.02% or Less)

N is not an essential element and is contained as an impurity in steel, for example. In view of the workability, an N content as low as possible is preferable. In particular, when the N content is over 0.02%, deterioration of the workability is prominent. Therefore, the N content is 0.02% or less.

(O: 0.02% or Less)

O is not an essential element and is contained as an impurity in steel, for example. In view of the workability, an O content as low as possible is preferable. In particular, when the O content is over 0.02%, deterioration of the workability is prominent. Therefore, the 0 content is 0.02% or less.

Ti, Nb, Mo, V, Cr, B, Cu, Ni, Ca, and REM are not essential elements but arbitrary elements, which may be properly contained in the hot-rolled steel sheet to limits of predetermined contents.

(Ti: 0% to 0.2%, Nb: 0% to 0.2%, Mo: 0% to 0.2%, V: 0% to 0.2%, Cr: 0% to 1.0%, B: 0% to 0.01%, Cu: 0% to 1.2%, Ni: 0% to 0.6%)

Ti, Nb, Mo, V, Cr, B, Cu, and Ni contribute to further improvement of the strength of the hot-rolled steel sheet by precipitation hardening or solid solution strengthening. Therefore, one or more kinds selected from the group consisting of these elements may be contained. However, with regard to Ti, Nb, Mo, and V, when a content of any one thereof is over 0.2%, generation of ferrite is suppressed, so that the desired steel structure in which the area ratio of ferrite is 5% or more cannot be obtained. Therefore, a Ti content, an Nb content, an Mo content, and a V content are each 0.2% or less. When a Cr content is over 1.0%, an effect to improve the strength is saturated. Further, when the Cr content is over 1.0%, generation of ferrite is suppressed, so that the desired steel structure in which the area ratio of ferrite is 5% or more cannot be obtained. Therefore, the Cr content is 1.0% or less. When a B content is over 0.01%, generation of ferrite is suppressed, so that the desired steel structure in which the area ratio of ferrite is 5% or more cannot be obtained. Therefore, the B content is 0.01% or less. When a Cu content is over 1.2%, generation of ferrite is suppressed, so that the desired steel structure in which the area ratio of ferrite is 5% or more cannot be obtained. Therefore, the Cu content is 1.2% or less. When an Ni content is over 0.6%, generation of ferrite is suppressed, so that the desired steel structure in which the area ratio of ferrite is 5% or more cannot be obtained. Therefore, the Ni content is 0.6% or less. In order to secure a more excellent strength of the hot-rolled steel sheet, the Ti content, the Nb content, the V content, the Cr content, and the Ni content are each preferably 0.01% or more, the Mo content is preferably 0.001% or more, the B content is preferably 0.0002%, and the Cu content is preferably 0.02% or more. In other words, it is preferable that at least one of “Ti: 0.01% to 0.2%”, “Nb: 0.01% to 0.2%”, “Mo: 0.001% to 0.2%”, “V: 0.01% to 0.2%”, “Cr: 0.01% to 1.0%”, “B: 0.0002% to 0.01%”, “Cu: 0.02% to 1.2%”, and “Ni: 0.01% to 0.6%” is satisfied.

(Ca: 0% to 0.005%, REM: 0% to 0.02%)

Ca and REM change a form of a non-metal inclusion which may be a starting point of destruction or deteriorate the workability, and make the non-metal inclusion harmless. Therefore, one or more kinds selected from the group consisting of the above elements may be contained. However, when a Ca content is over 0.005%, the form of the non-metal inclusion is elongated, and the non-metal inclusion may be the starting point of destruction or deteriorate the workability. When a REM content is over 0.02%, the form of the non-metal inclusion is elongated and the non-metal inclusion may be the starting point of destruction or deteriorate the workability. Therefore, the Ca content is 0.005% or less and the REM content is 0.02% or less. In order to make an effect of making the non-metal inclusion harmless more excellent, the Ca content and the REM content are each preferable 0.0005% or more. In other words, it is preferable that at least one of “Ca: 0.0005% to 0.005%” and “REM: 0.0005% to 0.02%” is satisfied.

REM (rare earth metal) indicates elements of 17 kinds in total of Sc, Y, and lanthanoid, and the “REM content” means a content of a total of these 17 kinds of elements. Lanthanoid is industrially added in a form of misch metal, for example.

Next, an example of a method for manufacturing the hot-rolled steel sheet according to the present embodiment will be described. Though the hot-rolled steel sheet according to the present embodiment can be manufactured by the method described here, a method for manufacturing the hot-rolled steel sheet according to the present embodiment is not limited thereto. In other words, even if a hot-rolled steel sheet is manufactured by another method, as long as the hot-rolled steel sheet includes the above-described steel structure and chemical composition, the hot-rolled steel structure can be regarded as being within the scope of the embodiment. For example, though a hot-rolling facility of seven passes is used in the following method, a hot-rolled steel sheet manufactured using a hot-rolling facility of six passes may sometimes fall within the scope of the present embodiment.

In this method, following steps are carried out in sequence. FIG. 2 illustrates an outline of a temperature history from hot rolling to coiling.

(1) A steel ingot or slab including the above-described chemical composition is casted, and reheating 11 is carried out as necessary.

(2) Rough rolling 12 of the steel ingot or slab is carried out. The rough rolling is included in the hot rolling.

(3) Finish rolling 13 of the steel ingot or slab is carried out. The finish rolling is included in the hot rolling. In the finish rolling, rolling of one pass before rolling of a final stage is carried out at a temperature of 850° C. or more to 1150° C. or less and at a reduction of 10% or more to 40% or less, and the rolling of the final stage is carried out at a temperature (T1(° C.)) of 850° C. or more to 1050° C. or less and at a reduction of 3% or more to 10% or less.

(4) Cooling is carried out on a run out table to a temperature (T2(° C.)) of 600° C. or more to 750° C. or less. A time from the end of the finish rolling to the start of the cooling is indicated as t1 (second).

(5) Air cooling 14 for a time (t2 (second)) of 1 second or more to 10 seconds or less is carried out. During this air cooling, ferrite transformation in a two-phase region occurs, and an excellent elongation can be obtained.

(6) Cooling 15 at a cooling rate of P (° C./second) to a temperature of 400° C. or more to 650° C. or less is carried out. The cooling rate P satisfies (formula 1) below.

(7) Coiling 16 at the temperature of 400° C. or more to 650° C. or less is carried out.

(8) A hot-rolled coil is cooled at a cooling rate of 0.15° C./minute or less, while a temperature of the hot-rolled coil is T3(° C.)-300° C. or more to T3(° C.) or less. T3(° C.) is represented by (formula 2) below.

(9) Cooling is carried out from a temperature of less than T3(° C.)-300° C. to 25° C. at a cooling rate of 0.05° C./minute or less.

P(° C./second)≥1/{1.44×1012exp(−3211/(T1+273))×t11/3}×2×1011+(C)×1/{1−(1.44×1012exp(−3211/(T2+273))×t21/3}×(−3)×1013  (formula 1)

T3(° C.)=830−270×(C)−90×(Mn)−37×(Ni)−70×(Cr)−83×(Mo)  (formula 2)

Here, (C), (Mn), (Ni), (Cr), and (Mo) indicate a C content, an Mn content, an Ni content, a Cr content, and an Mo content of a hot-rolled steel sheet, respectively.

In casting of the steel ingot or slab, molten steel whose components are adjusted to have a chemical composition within a range described above is casted. Then, the steel ingot or slab is sent to a hot rolling mill. On this occasion, the casted steel ingot or slab having a high temperature may be directly sent to the hot rolling mill, or may be cooled to a room temperature and thereafter reheated in a heating furnace, and sent to the hot rolling mill. A temperature of reheating is not limited in particular. When the reheating temperature is 1260° C. or more, an amount of scaling off increases and sometimes reduces a yield, and thus the reheating temperature is preferably less than 1260° C. Further, when the reheating temperature is less than 1000° C., an operation efficiency is sometimes impaired significantly in terms of schedule, and thus the reheating temperature is preferably 1000° C. or more.

When a rolling temperature of the final stage of rough rolling is less than 1080° C., that is, when the rolling temperature is lowered to less than 1080° C. during rough rolling, an austenite grain after finish rolling becomes excessively small and transformation from austenite to ferrite is excessively promoted, so that desired bainite is sometimes hard to be obtained. Therefore, rolling of the final stage is preferably carried out at 1080° C. or more. When the rolling temperature of the final stage of rough rolling is over 1150° C., that is, when the rolling temperature exceeds 1150° C. during rough rolling, an austenite grain after finish rolling becomes large and ferrite transformation in a two-phase region to occur in later cooling is not sufficiently promoted, so that a desired steel structure is sometimes hard to be obtained. Therefore, rolling of the final stage is preferably carried out at 1150° C. or less.

When a cumulative reduction of the final stage and a previous stage thereof of rough rolling is over 65%, an austenite grain after finish rolling becomes excessively small, and transformation from austenite to ferrite is excessively promoted, so that desired bainite is sometimes hard to be obtained. Therefore, the cumulative reduction is preferably 65% or less. When the cumulative reduction is less than 40%, the austenite grain after finish rolling becomes large and ferrite transformation in the two-phase region to occur in later cooling is not sufficiently promoted, so that the desired steel structure is sometimes hard to be obtained. Therefore, the cumulative reduction is preferably 40% or more.

The finish rolling is important to generate bainite composed of an aggregate of bainitic ferrite whose grain average misorientation is 0.4° or more to 3° or less. The bainitic ferrite can be obtained as a result that austenite which includes a strain after being processed is transformed to bainite. Therefore, it is important to carry out finish rolling under a condition which makes a strain remain in austenite after finish rolling.

In the finish rolling, rolling of one pass before rolling of the final stage, the rolling of the final stage being rolling carried out in a final stand of a finish rolling mill, is carried out at a temperature of 850° C. or more to 1150° C. or less and at a reduction of 10% or more to 40% or less. When the rolling temperature of the above rolling is over 1150° C. or the reduction is less than 10%, an austenite grain after finish rolling becomes large and ferrite transformation in the two-phase region to occur in later cooling is not sufficiently promoted, so that the desired steel structure cannot be obtained. When the rolling temperature of the above rolling is less than 850° C. or the reduction is over 40%, the strain remains excessively in austenite after finish rolling, and the workability is deteriorated.

In the finish rolling, rolling of the final stage is carried out at a temperature of 850° C. or more to 1050° C. or less and at a reduction of 3% or more to 10% or less. The temperature (finish rolling end temperature) of rolling of the final stage is indicated as T1(° C.). When the temperature T1 is over 1050° C. or the reduction is less than 3%, a residual amount of the strain in austenite after finish rolling becomes insufficient, so that the desired steel structure cannot be obtained. When the temperature T1 is less than 850° C. or the reduction is over 10%, the strain remains excessively in austenite after finish rolling, so that the workability is deteriorated.

After the finish rolling, cooling is carried out on a run out table (ROT) to a temperature of 600° C. or more to 750° C. or less. A reaching temperature of the above cooling is indicated as T2(° C.). When the temperature T2 is less than 600° C., ferrite transformation in the two-phase region becomes insufficient, so that a sufficient elongation cannot be obtained. When the temperature T2 is over 750° C., ferrite transformation is excessively promoted, so that the desired steel structure cannot be obtained. An average cooling rate on the run out table is 20° C./second to 200° C./second, for example. This is for obtaining the desired steel structure stably.

Once the cooling on the run out table ends, air cooling for one second or more to ten seconds or less is carried out. A time of the air cooling is indicated as t2 (second). When the time t2 is less than one second, ferrite transformation in the two-phase region becomes insufficient, so that the sufficient elongation cannot be obtained. When the time t2 is over 10 seconds, ferrite transformation in the two-phase region is excessively promoted, so that the desired steel structure cannot be obtained.

A time from the end of finish rolling to the start of cooling on the run out table is indicated as t1 (second). The time t1 is not limited in particular, but is preferably 10 seconds or less in order to prevent coarsening of austenite after finish rolling. Air cooling is substantially carried out from the end of finish rolling to the start of cooling on the run out table.

Once the air cooling for the time t2 ends, cooling to a temperature of 400° C. or more to 650° C. or less at a predetermined cooling rate is carried out. The cooling rate is indicated as P(° C./second). The cooling rate P satisfies a relation of (formula 1). When the cooling rate P satisfies the relation of (formula 1), generation of pearlite in the air cooling can be suppressed, and area ratios of martensite, pearlite, and retained austenite can be made 5% or less in total. On the other hand, when the cooling rate P does not satisfy the relation of (formula 1), pearlite is generated in great amount, for example, so that the desired steel structure cannot be obtained. Therefore, the cooling rate P satisfying the relation of (formula 1) is quite important in order to obtain the desired steel structure.

The cooling rate P is preferably 200° C./second or less from a viewpoint of suppression of a warp due to a thermal strain and so on. The cooling rate P is more preferably 30° C./second or less from a viewpoint of further suppression of the warp and so on.

Thereafter, the coiling at a temperature of 400° C. or more to 650° C. or less is carried out. When the coiling temperature is over 650° C., ferrite is generated and sufficient bainite cannot be obtained, so that the desired steel structure cannot be obtained. When the coiling temperature is less than 400° C., martensite is generated and sufficient bainite cannot be obtained, so that the desired steel structure cannot be obtained.

While a temperature of a hot-rolled coil obtained by the coiling is T3(° C.)-300° C. or more to T3(° C.) or less, the hot-rolled coil is cooled at a cooling rate of 0.15° C./minute or less. When the cooling rate is 0.15° C./minute or less, bainite transformation can be promoted, and the area ratios of martensite, pearlite, and retained austenite can be made to be 5% or less in total. On the other hand, when the cooling rate is over 0.15° C./minute, bainite transformation is not sufficiently promoted and the area ratios of martensite, pearlite, and retained austenite exceed 5% in total, so that the workability is deteriorated. Therefore, the cooling rate being 0.15° C./minute or less is quite important in order to obtain the desired steel structure.

When the temperature of the hot-rolled coil exceeds the temperature T3(° C.), transformation from austenite to pearlite occurs, so that the desired steel structure cannot be obtained.

When the temperature of the hot-rolled coil is less than T3(° C.)-300° C., the hot-rolled coil is cooled at a cooling rate of 0.05° C./minute or less. When the cooling rate is 0.05° C./minute or less, transformation from untransformed austenite to martensite can be suppressed, so that a superior workability can be obtained. On the other hand, when the cooling rate is over 0.05° C./minute, transformation from austenite to martensite occurs, the area ratios of martensite, pearlite, and retained austenite exceed 5% in total, so that the workability is deteriorated. Further, during cooling, when the temperature of the hot-rolled coil rises to exceed T3(° C.)-300° C. due to heat generation concurrent with phase transformation from austenite to bainite, transformation from austenite to pearlite occurs and a structural fraction of pearlite exceeds 5%, so that the workability is deteriorated.

Even if the hot-rolled steel sheet according to the present embodiment is subjected to a surface treatment, effects to improve a strength, an elongation, and a hole expandability can be obtained. For example, electroplating, hot dipping, deposition plating, organic coating formation, film laminating, organic salts treatment, inorganic salts treatment, non-chroming treatment, or the like may be performed.

The above-described embodiment merely illustrates concrete examples of implementing the present invention, and the technical scope of the present invention is not to be construed in a restrictive manner by these embodiments. That is, the present invention may be implemented in various forms without departing from the technical spirit or main features thereof.

Examples

Next, an experiment the inventors of the present application carried out will be described. In this experiment, using a plurality of steels (steel symbols A to MMM) having chemical compositions listed in Table 1 and Table 2, samples of hot-rolled steel sheets having steel structures listed in Table 3 to Table 5 were manufactured, and their mechanical characteristics were investigated. The balance of each of the steels is Fe and an impurity. Further, an “area ratio of bainite” in Table 3 to Table 5 is an area ratio of bainite composed of an aggregate of bainitic ferrite whose grain average misorientation is 0.4° or more to 3° or less. A plating layer of the sample No. 29 is a hot-dip plating layer.

An area ratio of ferrite was specified by observing a cross section parallel to a rolling direction in a region between ⅜ and ⅝ of a thickness of the hot-rolled steel sheet from a surface at a magnification of 200 times to 500 times using an optical microscope. The area ratio of bainite composed of the aggregate of bainitic ferrite whose grain average misorientation is 0.4° or more to 3° or less was specified through measuring crystal directions of a plurality of points in the cross section parallel to the rolling direction in the region between ⅜ and ⅝ of the thickness of the hot-rolled steel sheet from the surface by the EBSD method. Each area ratio of pearlite, martensite, retained austenite was specified by observing the cross section parallel to the rolling direction in the region between ⅜ and ⅝ of the thickness of the hot-rolled steel sheet from the surface at the magnification of 200 times to 500 times using an optical microscope.

Then, a tensile test and a hole expansion test of each hot-rolled steel sheet were carried out. The tensile test was carried out using a No. 5 test piece, which is described in Japan Industrial Standard (JIS) Z 2201, fabricated from each hot-rolled steel sheet in accordance with a method described in Japan Industrial Standard (JIS) Z 2241. The hole expansion test was carried out in accordance with a method described in Japan Industrial Standard (JIS) Z 2256. Results of the above are also listed in Table 3 to Table 5.

As listed in Table 3 to Table 5, only in the samples within the scope of the present invention, the excellent elongation and hole expandability could be obtained while the high strength being obtained. In evaluation of the mechanical characteristic, it was targeted that a tensile strength was 590 MPa or more, that a product (TS×λ) of the tensile strength (TS (MPa)) and a hole expansion ratio (λ(%)) was 65000 or more, and that a product (EL×λ) of a total elongation (EL (%)) and the hole expansion ratio (λ(%)) was 1300 or more. In the sample No. 60, since the steel (steel symbol F) contained Mn excessively, a slab fracture occurred and a hot-rolled steel sheet was not able to be manufactured.

Each hot-rolled steel sheet was manufactured as below under a condition listed in Table 6 to Table 9. After smelting in a steel converter and continuous casting were carried out, reheating at a heating temperature listed in Table 3 to Table 6 was carried out, and hot-rolling including rough rolling and finish rolling of 7 passes was carried out. A temperature and a cumulative reduction of a final stage of the rough rolling are listed in Table 3 to Table 6. Further, a rolling end temperature and a reduction of the sixth pass, and a rolling end temperature (T1) and a reduction of the seventh pass (final stage) of the finish rolling are listed in Table 3 to Table 6. A thickness after hot rolling was 1.2 mm to 5.4 mm. After a time t1 (second) elapsed from the end of the finish rolling, cooling to a temperature T2 listed in Table 3 to Table 6 was carried out on a run out table. Then, once the temperature reached the temperature T2, air cooling was started. A time t2 of the air cooing is listed in Table 3 to Table 6. After the air cooling for the time t2, cooling was carried out to a coiling temperature listed in Table 3 to Table 6 at a cooling rate P (° C./second) listed in Table 3 to Table 6, and coiling was carried out at the coiling temperature, so that a hot-rolled coil was fabricated. Thereafter, cooling of two stages of first cooing and second cooling was carried out. The first cooling started at a starting temperature listed in Table 3 to Table 6, and ended at an end temperature listed in Table 3 to Table 6. A cooling rate during the first cooling is listed in Table 3 to Table 6. The second cooling started at a starting temperature listed in Table 3 to Table 6, and ended at 25° C. A cooling rate during the second cooling is listed in Table 3 to Table 6. Further, in manufacture of the hot-rolled steel sheet of the sample No. 29, hot dipping was performed after the second cooling ended.


TABLE 1
STEEL
SYMBOL
C
Si
Mn
P
S
Al
N
B
O
Ti
A
0.041
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
B
0.008
0.855
1.260
0.007
0.001
0.0046
0.0038
0.0002
0.0030
0.125
C
0.210
0.855
1.260
0.007
0.001
0.0046
0.0038
0.0002
0.0030
0.125
D
0.040
0.007
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
E
0.041
0.954
0.001
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
F
0.041
0.954
6.900
0.007
0.001
0.0045
0.0038
0.0002
0.0032
0.123
G
0.040
0.854
1.250
0.500
0.001
0.0450
0.0036
0.0002
0.0032
0.123
H
0.041
0.954
1.250
0.007
0.080
0.0050
0.0036
0.0002
0.0032
0.123
I
0.038
0.954
1.250
0.007
0.001
0.0005
0.0038
0.0002
0.0032
0.123
J
0.041
0.854
1.250
0.007
0.001
0.1000
0.0038
0.0002
0.0032
0.123
K
0.042
0.854
1.250
0.007
0.001
0.0045
0.0800
0.0002
0.0032
0.123
L
0.041
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.1400
0.123
M
0.042
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.001
N
0.041
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
O
0.039
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
P
0.038
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0001
0.0032
0.123
Q
0.041
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
R
0.085
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
S
0.065
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
T
0.025
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
U
0.039
1.500
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
V
0.040
0.800
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
W
0.041
0.050
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
X
0.038
0.854
2.300
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
Y
0.039
0.854
1.000
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
Z
0.041
0.954
0.700
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
AA
0.041
0.854
1.250
0.080
0.001
0.0045
BB
0.040
0.854
1.250
0.008
0.001
0.0045
0.0036
0.0032
CC
0.041
0.954
1.250
0.004
0.001
0.0045
0.0036
0.0032
DD
0.038
0.854
1.250
0.007
0.010
0.0045
0.0036
0.0002
0.0032
0.123
EE
0.042
0.854
1.250
0.007
0.002
0.0045
0.0036
0.0002
0.0032
0.123
STEEL
T3
SYMBOL
Nb
Mo
Cu
Ni
V
Cr
Ca
REM
(° C.)
A
0.036
0.005
0.0010
708
B
0.037
0.040
0.0008
711
C
0.037
0.040
0.0008
657
D
0.036
0.005
0.0010
706
E
0.036
0.005
0.0010
818
F
0.036
0.005
0.0010
188
G
0.036
0.005
0.0010
706
H
0.036
0.005
0.0010
706
I
0.036
0.005
0.0010
707
J
0.036
0.005
0.0010
706
K
0.036
0.005
0.0010
706
L
0.036
0.005
0.0010
708
M
0.036
0.005
0.0010
706
N
0.001
0.005
0.0010
706
O
0.036
0.0001
0.0010
707
P
0.036
0.005
0.0010
707
Q
0.036
0.005
0.0001
706
R
0.036
0.005
0.0010
694
S
0.036
0.005
0.0010
700
T
0.036
0.005
0.0010
710
U
0.036
0.005
0.0010
707
V
0.036
0.005
0.0010
706
W
0.036
0.005
0.0010
706
X
0.036
0.005
0.0010
612
Y
0.036
0.005
0.0010
728
Z
0.036
0.005
0.0010
812
AA
706
BB
707
CC
0.0010
706
DD
0.036
0.005
707
EE
0.036
0.005
0.0010
0.0010
706


TABLE 2
STEEL
SYMBOL
C
Si
Mn
P
S
Al
N
B
O
Ti
FF
0.041
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
GG
0.041
0.954
1.250
0.007
0.001
0.0045
0.0100
0.0002
0.0032
0.123
HH
0.039
0.854
1.250
0.007
0.001
0.0045
0.0040
0.0002
0.0032
0.123
II
0.040
0.954
1.250
0.007
0.001
0.0045
0.0010
0.0002
0.0032
0.123
JJ
0.041
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0100
0.123
KK
0.039
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0040
0.123
LL
0.039
0.854
1.250
0.500
0.001
0.0045
0.0036
0.0002
0.0020
0.123
MM
0.041
0.854
1.250
0.007
0.001
0.0080
0.0036
0.0002
0.0032
0.123
NN
0.041
0.954
1.250
0.007
0.001
0.0050
0.0036
0.0002
0.0032
0.123
OO
0.040
0.854
1.250
0.007
0.001
0.0020
0.0036
0.0002
0.0032
0.123
PP
0.041
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.144
QQ
0.390
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.110
RR
0.041
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.150
SS
0.041
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
TT
0.040
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
UU
0.041
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
VV
0.039
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
WW
0.041
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
XX
0.042
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
YY
0.041
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
ZZ
0.042
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
AAA
0.040
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
BBB
0.039
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
CCC
0.038
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
DDD
0.041
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
EEE
0.041
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0060
0.0032
0.123
FFF
0.041
0.954
1.250
0.080
0.001
0.0045
0.0036
0.0003
0.0032
0.123
GGG
0.038
0.954
1.250
0.008
0.001
0.0045
0.0036
0.0001
0.0032
0.123
HHH
0.041
0.854
1.250
0.004
0.001
0.0045
0.0036
0.0002
0.0032
0.123
III
0.041
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
JJJ
0.040
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
KKK
0.041
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
LLL
0.038
0.854
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
MMM
0.041
0.954
1.250
0.007
0.001
0.0045
0.0036
0.0002
0.0032
0.123
STEEL
T3
SYMBOL
Nb
Mo
Cu
Ni
V
Cr
Ca
REM
(° C.)
FF
0.036
0.005
0.0010
706
GG
0.036
0.005
0.0010
708
HH
0.036
0.005
0.0010
707
II
0.036
0.005
0.0010
708
JJ
0.036
0.005
0.0010
706
KK
0.036
0.005
0.0010
707
LL
0.036
0.005
0.0010
707
MM
0.036
0.005
0.0010
708
NN
0.036
0.005
0.0010
706
OO
0.036
0.005
0.0010
708
PP
0.036
0.005
0.0010
706
QQ
0.036
0.005
0.0010
707
RR
0.036
0.005
0.0010
706
SS
0.144
0.005
0.0010
708
TT
0.108
0.005
0.0010
706
UU
0.054
0.005
0.0010
708
VV
0.036
0.139
0.0010
695
WW
0.036
0.106
0.0010
698
XX
0.036
0.048
0.0010
702
YY
0.036
0.005
0.145
0.0010
706
ZZ
0.036
0.005
0.105
0.0010
706
AAA
0.036
0.005
0.045
0.0010
706
BBB
0.036
0.005
0.143
0.0010
687
CCC
0.036
0.005
0.102
0.0010
700
DDD
0.036
0.005
0.034
0.0010
704
EEE
0.036
0.005
0.0010
706
FFF
0.036
0.005
0.0010
708
GGG
0.036
0.005
0.0010
707
HHH
0.036
0.005
0.800
0.0010
706
III
0.036
0.005
0.080
0.0010
708
JJJ
0.036
0.005
0.040
0.0010
706
KKK
0.036
0.005
0.350
0.0010
693
LLL
0.036
0.005
0.080
0.0010
703
MMM
0.036
0.005
0.020
0.0010
705


TABLE 3
TOTAL
AREA
RATIO
AREA
OF MAR-
AREA
RATIO
TENSITE,
AREA
RATIO
OF
PEARITE
RATIO
AREA
OF
AREA
RE-
AND RE-
OF
RATIO
MAR-
RATIO
TAINED
TAINED
SAM-
STEEL
FER-
OF
TEN-
OF
AUS-
AUS-
PLE
SYM-
RITE
BAINITE
SITE
PEARITE
TENITE
TENITE
TS
EL
λ
TS ×λ
EL ×λ
PLATING
No.
BOL
(%)
(%)
(%)
(%)
(%)
(%)
(MPa)
(%)
(%)
(MPa · %)
(% · %)
LAYER
1
A
32
66.6
0.10
1.00
0.10
1.20
810.00
18
85
68850
1530
WITHOUT
2
A
20
78.9
0.10
0.90
0.10
1.10
811.00
17
101
81911
1717
WITHOUT
3
A
48
50.9
0.10
1.10
0.10
1.30
815.00
18
85
69275
1530
WITHOUT
4
A
39
59.9
0.10
0.90
0.10
1.10
798.00
19
81
64638
1539
WITHOUT
5
A
21
77.8
0.10
1.00
0.10
1.20
799.00
16
102
81498
1632
WITHOUT
6
A
48
50.6
0.10
1.10
0.10
1.30
810.00
18
84
68040
1512
WITHOUT
7
A
39
60.0
0.10
0.90
0.10
1.10
811.00
19
81
65691
1539
WITHOUT
8
A
39
60.1
0.10
1.00
0.10
1.20
809.00
18
82
66338
1476
WITHOUT
9
A
32
66.7
0.10
1.00
0.10
1.20
804.00
18
86
69144
1548
WITHOUT
10
A
21
77.6
0.10
0.90
0.10
1.10
812.00
16
102
82824
1632
WITHOUT
11
A
21
77.7
0.10
1.10
0.10
1.30
805.00
16
103
82915
1648
WITHOUT
12
A
32
66.8
0.10
1.10
0.10
1.30
800.00
18
87
69600
1566
WITHOUT
13
A
39
60.1
0.10
1.00
0.10
1.20
801.00
19
82
65682
1558
WITHOUT
14
A
39
60.2
0.10
1.10
0.10
1.30
809.00
19
81
65529
1539
WITHOUT
15
A
21
77.7
0.10
1.00
0.10
1.20
799.00
18
85
67915
1530
WITHOUT
16
A
21
78.0
0.10
0.90
0.10
1.10
794.00
16
101
80194
1616
WITHOUT
17
A
29
69.9
0.10
1.00
0.10
1.20
798.00
19
81
64638
1539
WITHOUT
18
A
32
66.8
0.10
0.90
0.10
1.10
810.00
18
85
68850
1530
WITHOUT
19
A
21
77.9
0.10
1.00
0.10
1.20
811.00
16
101
81911
1616
WITHOUT
20
A
21
77.8
0.10
1.00
0.10
1.20
811.00
16
102
82722
1632
WITHOUT
21
A
32
66.5
0.10
1.10
0.10
1.30
812.00
18
85
69020
1530
WITHOUT
22
A
39
59.8
0.10
1.10
0.10
1.30
810.00
19
81
65610
1539
WITHOUT
23
A
39
59.8
0.10
1.00
0.10
1.20
810.00
19
82
66420
1558
WITHOUT
24
A
32
66.9
0.10
0.90
0.10
1.10
809.00
18
85
68765
1530
WITHOUT
25
A
21
77.8
0.10
0.90
0.10
1.10
806.00
16
100
80600
1600
WITHOUT
26
A
32
63.6
3.20
1.00
0.10
4.30
830.00
18
80
66400
1440
WITHOUT
27
A
32
66.7
0.10
1.10
0.10
1.30
812.00
18
84
68208
1512
WITHOUT
28
A
32
66.4
0.10
1.10
0.10
1.30
810.00
18
85
68850
1530
WITHOUT
29
A
32
66.4
0.10
1.00
0.10
1.20
810.00
18
86
69660
1548
WITH
30
A
4
94.8
0.10
0.90
0.10
1.10
809.00
12
65
52585
780
WITHOUT
31
A
71
27.9
0.10
0.90
0.10
1.10
775.00
20
45
34875
900
WITHOUT
32
A
71
28.0
0.10
1.00
0.10
1.20
769.00
20
46
35374
920
WITHOUT
33
A
4
94.7
0.10
0.90
0.10
1.10
841.00
12
65
54665
780
WITHOUT
34
A
4
94.6
0.10
1.10
0.10
1.30
838.00
12
66
55308
792
WITHOUT
35
A
4
94.4
0.10
1.10
0.10
1.30
840.00
12
65
54600
780
WITHOUT
36
A
4
94.9
0.10
1.00
0.10
1.20
839.00
12
66
55374
792
WITHOUT
37
A
4
94.6
0.10
1.00
0.10
1.20
840.00
12
65
54600
780
WITHOUT
38
A
71
27.7
0.10
0.90
0.10
1.10
771.00
20
45
34695
900
WITHOUT
39
A
71
27.6
0.10
0.90
0.10
1.10
772.00
20
44
33968
880
WITHOUT


TABLE 4
TOTAL
AREA
RATIO
AREA
OF MAR-
AREA
RATIO
TENSITE,
AREA
RATIO
OF
PEARITE
RATIO
AREA
OF
AREA
RE-
AND RE-
OF
RATIO
MAR-
RATIO
TAINED
TAINED
SAM-
STEEL
FER-
OF
TEN-
OF
AUS-
AUS-
PLE
SYM-
RITE
BAINITE
SITE
PEARITE
TENITE
TENITE
TS
EL
λ
TS ×λ
EL ×λ
PLATING
No.
BOL
(%)
(%)
(%)
(%)
(%)
(%)
(MPa)
(%)
(%)
(MPa · %)
(% · %)
LAYER
40
A
71
27.9
0.10
1.00
0.10
1.20
768.00
20
45
34560
900
WITHOUT
41
A
71
27.9
0.10
1.00
0.10
1.20
770.00
20
44
33880
880
WITHOUT
42
A
71
27.7
0.10
0.90
0.10
1.10
771.00
20
45
34695
900
WITHOUT
43
A
4
94.7
0.10
1.10
0.10
1.30
838.00
12
65
54470
780
WITHOUT
44
A
71
27.7
0.10
1.00
0.10
1.20
771.00
20
43
33153
860
WITHOUT
45
A
4
94.8
0.10
0.90
0.10
1.10
839.00
12
64
53696
768
WITHOUT
46
A
32
36.6
0.10
31.10
0.10
31.30
768.00
18
45
34560
810
WITHOUT
47
A
30
41.2
0.10
28.90
0.10
29.10
770.00
18
45
34560
810
WITHOUT
48
A
32
36.2
0.10
31.50
0.10
31.70
768.00
18
45
34560
810
WITHOUT
49
A
71
27.8
0.10
1.10
0.10
1.30
770.00
20
44
33880
880
WITHOUT
50
A
32
39.6
27.20
1.00
0.10
28.30
838.00
12
55
46090
660
WITHOUT
51
A
32
37.0
0.10
30.90
0.10
31.10
773.00
18
45
34785
810
WITHOUT
52
A
32
40.2
26.90
1.00
0.10
28.00
837.00
12
56
46872
672
WITHOUT
53
A
32
43.6
20.90
0.90
2.90
24.70
773.00
18
44
34012
792
WITHOUT
54
A
32
36.4
0.10
31.40
0.10
31.60
771.00
18
46
35466
828
WITHOUT
55
A
32
39.8
27.00
1.00
0.10
28.10
837.00
12
57
47709
684
WITHOUT
56
B
32
66.4
0.10
1.00
0.10
1.20
342.00
18
45
15390
810
WITHOUT
57
C
32
40.0
27.00
1.00
0.10
28.10
840.00
12
57
47880
684
WITHOUT
58
D
32
37.0
0.10
31.00
0.11
31.21
772.00
18
44
33968
792
WITHOUT
59
E
32
67.0
0.10
1.00
0.10
1.20
341.00
18
45
15345
810
WITHOUT
60
F
61
G
32
66.7
0.10
1.00
0.10
1.20
851.00
11
37
31487
407
WITHOUT
62
H
32
67.0
0.10
0.90
0.10
1.10
811.00
18
29
23519
522
WITHOUT
63
I
32
67.1
0.10
0.90
0.10
1.10
810.00
6
85
68850
510
WITHOUT
64
J
32
67.1
0.10
1.00
0.10
1.20
809.00
6
86
69574
516
WITHOUT
65
K
32
66.7
0.10
1.10
0.10
1.30
851.00
18
14
11914
252
WITHOUT
66
L
32
66.6
0.10
1.10
0.10
1.30
811.00
18
15
12165
270
WITHOUT
67
M
32
66.4
0.10
1.00
0.10
1.20
346.00
18
45
15570
810
WITHOUT
68
N
32
67.0
0.10
0.90
0.10
1.10
346.00
18
46
15916
828
WITHOUT
69
O
32
67.0
0.10
0.90
0.10
1.10
341.00
18
45
15345
810
WITHOUT
70
P
32
67.0
0.10
1.00
0.10
1.20
342.00
18
46
15732
828
WITHOUT
71
Q
32
66.8
0.10
0.90
0.10
1.10
811.00
18
21
17031
378
WITHOUT
72
R
20
78.8
0.10
1.10
0.10
1.30
1030.00
28
75
77250
2100
WITHOUT
73
S
35
63.9
0.10
1.10
0.10
1.30
820.00
18
85
69700
1530
WITHOUT
74
T
45
53.8
0.10
1.00
0.10
1.20
610.00
18
120
73200
2160
WITHOUT
75
U
32
66.7
0.10
1.00
0.10
1.20
851.00
18
85
72335
1530
WITHOUT
76
V
32
67.0
0.10
0.90
0.10
1.10
830.00
18
86
71380
1548
WITHOUT
77
W
32
67.1
0.10
0.90
0.10
1.10
790.00
18
86
67940
1548
WITHOUT
78
X
32
67.1
0.10
1.00
0.10
1.20
852.00
18
85
72420
1530
WITHOUT


TABLE 5
TOTAL
AREA
RATIO
AREA
OF MAR-
AREA
RATIO
TENSITE,
AREA
RATIO
OF
PEARITE
RATIO
AREA
OF
AREA
RE-
AND RE-
OF
RATIO
MAR-
RATIO
TAINED
TAINED
SAM-
STEEL
FER-
OF
TEN-
OF
AUS-
AUS-
PLE
SYM-
RITE
BAINITE
SITE
PEARITE
TENITE
TENITE
TS
EL
λ
TS ×λ
EL ×λ
PLATING
No.
BOL
(%)
(%)
(%)
(%)
(%)
(%)
(MPa)
(%)
(%)
(MPa · %)
(% · %)
LAYER
79
Y
32
66.8
0.10
1.00
0.10
1.20
830.00
18
86
71380
1548
WITHOUT
80
Z
32
66.8
0.10
0.90
0.10
1.10
792.00
18
85
67320
1530
WITHOUT
81
AA
32
66.3
0.10
1.10
0.10
1.30
813.00
18
85
69105
1530
WITHOUT
82
BB
32
66.9
0.10
1.00
0.10
1.20
810.00
19
96
77760
1824
WITHOUT
83
CC
32
67.0
0.10
0.90
0.10
1.10
815.00
21
101
82315
2121
WITHOUT
84
DD
32
67.0
0.10
1.00
0.10
1.20
806.00
18
85
68510
1530
WITHOUT
85
EE
32
66.6
0.10
1.00
0.10
1.20
802.00
19
95
76190
1805
WITHOUT
86
FF
32
67.1
0.10
0.90
0.10
1.10
814.00
21
100
81400
2100
WITHOUT
87
GG
32
67.1
0.10
1.00
0.10
1.20
815.00
18
85
69275
1530
WITHOUT
88
HH
32
66.8
0.10
1.00
0.10
1.20
816.00
19
95
77520
1805
WITHOUT
89
II
32
66.8
0.10
0.90
0.10
1.10
812.00
21
102
82824
2142
WITHOUT
90
JJ
32
66.3
0.10
1.10
0.10
1.30
811.00
18
85
68935
1530
WITHOUT
91
KK
32
66.8
0.10
1.10
0.10
1.30
812.00
19
95
77140
1805
WITHOUT
92
LL
32
66.9
0.10
1.00
0.10
1.20
813.00
21
102
82926
2142
WITHOUT
93
MM
32
66.5
0.10
1.10
0.10
1.30
813.00
18
85
69105
1530
WITHOUT
94
NN
32
66.6
0.10
1.00
0.10
1.20
815.00
19
95
77425
1805
WITHOUT
95
OO
32
66.8
0.10
0.90
0.10
1.10
809.00
21
100
80900
2100
WITHOUT
96
PP
32
66.7
0.10
1.00
0.10
1.20
847.00
18
85
71995
1530
WITHOUT
97
QQ
32
66.8
0.10
0.90
0.10
1.10
829.00
18
86
71294
1548
WITHOUT
98
RR
32
66.9
0.10
1.00
0.10
1.20
811.00
17
85
68935
1445
WITHOUT
99
SS
32
67.0
0.10
1.00
0.10
1.20
853.00
18
86
73358
1548
WITHOUT
100
TT
32
67.0
0.10
1.10
0.10
1.30
834.00
18
85
70890
1530
WITHOUT
101
UU
32
66.7
0.10
1.10
0.10
1.30
814.00
18
85
69190
1530
WITHOUT
102
VV
32
66.7
0.10
1.00
0.10
1.20
855.00
17
86
73530
1462
WITHOUT
103
WW
32
66.5
0.10
0.90
0.10
1.10
828.00
18
86
71208
1548
WITHOUT
104
XX
32
67.0
0.10
0.90
0.10
1.10
809.00
17
86
69574
1462
WITHOUT
105
YY
32
66.9
0.10
1.00
0.10
1.20
842.00
18
85
71570
1530
WITHOUT
106
ZZ
32
67.0
0.10
1.00
0.10
1.20
825.00
18
86
70950
1548
WITHOUT
107
AAA
32
66.6
0.10
1.00
0.10
1.20
809.00
17
86
69574
1462
WITHOUT
108
BBB
32
67.0
0.10
1.00
0.10
1.20
841.00
18
86
72326
1548
WITHOUT
109
CCC
32
67.0
0.10
1.10
0.10
1.30
827.00
17
85
70295
1445
WITHOUT
110
DDD
32
66.8
0.10
1.00
0.10
1.20
809.00
17
85
68765
1445
WITHOUT
111
EEE
32
66.8
0.10
0.90
0.10
1.10
855.00
17
86
73530
1462
WITHOUT
112
FFF
32
66.4
0.10
1.00
0.10
1.20
829.00
18
86
71294
1548
WITHOUT
113
GGG
32
67.0
0.10
0.90
0.10
0.10
809.00
18
85
68765
1530
WITHOUT
114
HHH
32
66.9
0.10
1.00
0.10
1.20
851.00
18
85
72335
1530
WITHOUT
115
III
32
66.7
0.10
1.00
0.10
1.20
832.00
17
86
71552
1462
WITHOUT
116
JJJ
32
66.7
0.10
1.10
0.10
1.30
809.00
17
86
69574
1462
WITHOUT
117
KKK
32
66.5
0.10
1.10
0.10
1.30
841.00
18
85
71485
1530
WITHOUT
118
LLL
32.1
66.71
0.10
1.00
0.09
1.19
829.00
17
86
71294
1462
WITHOUT
119
MMM
31.8
67.12
0.09
0.90
0.09
1.08
808.00
18
86
69488
1548
WITHOUT


TABLE 6
COOL-
FINISH ROLLING
ING
ROUGH
END
END
AIR
AFTER
SECOND
RE-
ROLLING
TEM-
RE-
TEM-
RE-
E-
COOLING
AIR
COIL-
FIRST COOLING
COOLING
HEAT-
FINAL
PER-
DUC-
PER-
DUC-
LAPSED
START
RIGHT
COOL-
ING
START
END
START
ING
TEM-
CUMU-
A-
TION
ATURE
TION
TIME
TEM-
SIDE
ING
TEM-
TEM-
TEM-
TEM-
TEM-
PER-
LATIVE
TURE
OF
OF
OF
TO
PER-
IN
COOL-
PER-
PER-
PER-
COOL-
PER-
COOL-
SAM-
STEEL
PER-
A-
REDUC-
OF 6TH
6TH
7TH
7TH
COOL-
A-
FOR-
ING
A-
A-
A-
ING
A-
ING
PLE
SYM-
ATURE
TURE
TION
PASS
PASS
PASS
PASS
ING
TURE
TIME
MULA
RATE
TURE
TURE
TURE
RATE
T3-300
TURE
RATE
No.
BOL
(° C.)
(° C.)
(%)
(° C.)
(%)
T1 (° C.)
(%)
t1 (s)
T2 (° C.)
(s)
1
P (° C./s)
(° C.)
(° C.)
(° C.)
(° C./s)
(° C.)
(° C.)
(° C./s)
1
A
1200
1100
55
950
15
900
8
2
670
4
18
18
606
596
412
0.10
406
391
0.02
2
A
1206
1105
54
1100
14
890
7
2
677
3
19
25
601
581
409
0.12
406
388
0.03
3
A
1203
1104
54
960
13
908
6
2
664
6
16
24
605
595
409
0.08
406
388
0.02
4
A
1201
1102
55
990
14
904
5
2
665
5
17
21
601
581
413
0.08
406
390
0.03
5
A
1200
1107
56
951
30
902
7
2
667
4
18
19
588
589
411
0.09
406
387
0.03
6
A
1206
1102
54
951
17
906
7
2
668
6
16
18
598
588
409
0.11
406
381
0.02
7
A
1209
1108
56
954
11
895
8
2
662
3
20
21
603
593
412
0.12
406
380
0.03
8
A
1203
1109
55
955
16
1020
6
2
669
4
18
28
601
581
413
0.09
406
387
0.03
9
A
1206
1107
55
951
15
910
6
2
671
5
17
19
588
588
412
0.08
406
386
0.02
10
A
1203
1105
55
956
14
860
5
2
678
3
19
21
603
593
411
0.12
406
384
0.02
11
A
1204
1103
55
957
15
880
9
2
675
6
16
17
605
595
410
0.11
406
386
0.02
12
A
1203
1102
55
953
15
908
7
2
670
5
17
21
601
591
413
0.10
406
388
0.03
13
A
1206
1105
54
954
14
905
4
2
671
4
18
18
600
590
408
0.09
406
381
0.03
14
A
1206
1108
55
955
16
896
8
2
730
6
13
19
598
589
409
0.08
406
381
0.02
15
A
1208
1102
56
957
13
887
6
2
660
3
20
21
588
588
410
0.11
406
388
0.03
16
A
1208
1104
54
953
12
901
5
2
620
4
21
23
602
582
412
0.10
406
391
0.02
17
A
1203
1102
53
951
15
904
7
2
664
8
14
28
601
591
409
0.12
406
890
0.03
18
A
1204
1103
56
952
16
903
5
2
665
5
17
19
600
590
411
0.09
406
381
0.02
19
A
1203
1106
57
953
15
896
6
2
667
2
23
25
606
596
410
0.09
406
382
0.03
20
A
1201
1109
54
958
14
895
7
2
668
4
18
21
640
630
408
0.08
406
383
0.02
21
A
1200
1102
55
946
13
906
6
2
662
6
16
23
580
580
413
0.07
406
380
0.03
22
A
1206
1103
54
956
12
903
5
2
669
5
17
18
450
440
410
0.09
406
387
0.02
23
A
1209
1102
57
950
14
902
8
2
671
7
15
21
601
591
409
0.13
406
386
0.02
24
A
1203
1104
54
953
15
907
8
2
678
6
16
18
605
595
412
0.09
406
390
0.03
25
A
1203
1105
53
952
16
901
8
2
675
4
18
19
601
591
412
0.04
406
388
0.03
26
A
1206
1104
56
954
15
904
6
2
671
5
17
21
599
589
413
0.08
406
387
0.04
27
A
1206
1108
57
851
14
906
7
2
679
6
16
19
598
588
412
0.09
406
385
0.02
28
A
1208
1102
54
952
14
905
5
2
668
4
18
18
603
593
411
0.11
406
384
0.01
29
A
1208
1103
56
954
13
904
8
2
665
5
17
19
601
591
410
0.12
406
386
0.03


TABLE 7
COOL-
FINISH ROLLING
ING
ROUGH
END
END
AIR
AFTER
SECOND
RE-
ROLLING
TEM-
RE-
TEM-
RE-
E-
COOLING
AIR
COIL-
FIRST COOLING
COOLING
HEAT-
FINAL
PER-
DUC-
PER-
DUC-
LAPSED
START
RIGHT
COOL-
ING
START
END
START
ING
TEM-
CUMU-
A-
TION
ATURE
TION
TIME
TEM-
SIDE
ING
TEM-
TEM-
TEM-
TEM-
TEM-
PER-
LATIVE
TURE
OF
OF
OF
TO
PER-
IN
COOL-
PER-
PER-
PER-
COOL-
PER-
COOL-
SAM-
STEEL
PER-
A-
REDUC-
OF 6TH
6TH
7TH
7TH
COOL-
A-
FOR-
ING
A-
A-
A-
ING
A-
ING
PLE
SYM-
ATURE
TURE
TION
PASS
PASS
PASS
PASS
ING
TURE
TIME
MULA
RATE
TURE
TURE
TURE
RATE
T3-300
TURE
RATE
No.
BOL
(° C.)
(° C.)
(%)
(° C.)
(%)
T1 (° C.)
(%)
t1 (s)
T2 (° C.)
(s)
1
P (° C./s)
(° C.)
(° C.)
(° C.)
(° C./s)
(° C.)
(° C.)
(° C./s)
30
A
1203
1290
57
951
15
906
6
2
669
6
16
21
598
588
413
0.09
406
384
0.03
31
A
1204
1220
54
950
16
908
7
2
661
4
19
20
603
593
408
0.08
406
386
0.02
32
A
1203
1008
78
950
14
902
5
2
772
5
13
18
605
595
408
0.12
406
381
0.03
33
A
1201
1107
31
954
15
901
6
2
670
6
16
21
601
591
410
0.11
406
389
0.03
34
A
1200
1105
54
1180
13
902
7
2
670
4
18
22
600
580
412
0.10
406
391
0.02
35
A
1203
1103
54
920
12
905
8
2
667
6
16
20
599
589
409
0.09
406
390
0.02
36
A
1204
1102
55
954
58
904
8
2
668
5
17
19
598
588
409
0.08
406
381
0.02
37
A
1203
1005
56
955
6
901
6
2
662
7
16
18
602
592
413
0.11
406
382
0.03
38
A
1206
1109
54
951
16
1080
7
2
669
6
15
17
601
591
411
0.10
406
383
0.03
39
A
1206
1002
56
956
15
910
6
2
671
4
19
21
600
590
409
0.10
406
390
0.02
40
A
1200
1104
55
958
14
905
15
2
678
5
16
18
606
596
412
0.10
406
387
0.03
41
A
1206
1102
55
953
15
904
2
2
675
6
16
19
606
596
412
0.10
406
386
0.02
42
A
1208
1103
55
954
15
906
6
2
810
5
17
21
606
596
413
0.08
406
390
0.03
43
A
1203
1106
55
955
14
908
5
2
540
7
15
18
520
510
412
0.12
406
388
0.02
44
A
1203
1108
55
957
16
902
7
2
668
18
12
19
606
596
411
0.11
406
387
0.03
45
A
1206
1107
54
953
13
901
7
2
665
0.4
37.4
17
606
596
410
0.10
406
391
0.02
46
A
1206
1105
55
951
12
906
8
2
669
6
16
6
606
596
412
0.11
406
391
0.03
47
A
1206
1105
55
951
12
906
8
2
669
5
17
4
606
596
412
0.11
406
391
0.03
48
A
1206
1105
55
951
12
906
8
2
669
6
16
2
606
596
412
0.11
406
391
0.03
49
A
1200
1103
56
950
15
903
6
2
661
4
19
20
710
700
412
0.12
406
391
0.03
50
A
1200
1102
54
951
16
902
6
2
670
5
17
18
310
300
397
0.09
406
390
0.02
51
A
1210
1105
53
956
15
907
7
2
668
6
16
19
606
605
410
0.08
406
388
0.03
52
A
1208
1103
56
957
14
901
5
2
685
4
18
21
606
596
474
0.10
406
387
0.02
53
A
1205
1102
57
953
13
904
6
2
669
6
16
23
606
596
412
0.50
406
391
0.03
54
A
1202
1106
54
954
12
906
7
2
661
5
17
28
606
596
412
0.10
406
420
0.03
55
A
1203
1108
55
955
14
905
8
2
670
7
15
17
606
596
413
0.10
406
391
0.16
56
B
1200
1102
54
957
15
904
8
2
670
6
5
18
611
601
412
0.09
411
396
0.02
57
C
1200
1104
57
950
15
906
6
2
670
4
85
90
557
547
412
0.08
357
342
0.03
58
D
1202
1105
54
955
13
908
7
2
670
4
18
21
606
596
412
0.11
406
391
0.02


TABLE 8
COOL-
FINISH ROLLING
ING
ROUGH
END
END
AIR
AFTER
SECOND
RE-
ROLLING
TEM-
RE-
TEM-
RE-
E-
COOLING
AIR
COIL-
FIRST COOLING
COOLING
HEAT-
FINAL
PER-
DUC-
PER-
DUC-
LAPSED
START
RIGHT
COOL-
ING
START
END
START
ING
TEM-
CUMU-
A-
TION
ATURE
TION
TIME
TEM-
SIDE
ING
TEM-
TEM-
TEM-
TEM-
TEM-
PER-
LATIVE
TURE
OF
OF
OF
TO
PER-
IN
COOL-
PER-
PER-
PER-
COOL-
PER-
COOL-
SAM-
STEEL
PER-
A-
REDUC-
OF 6TH
6TH
7TH
7TH
COOL-
A-
FOR-
ING
A-
A-
A-
ING
A-
ING
PLE
SYM-
ATURE
TURE
TION
PASS
PASS
PASS
PASS
ING
TURE
TIME
MULA
RATE
TURE
TURE
TURE
RATE
T3-300
TURE
RATE
No.
BOL
(° C.)
(° C.)
(%)
(° C.)
(%)
T1 (° C.)
(%)
t1 (s)
T2 (° C.)
(s)
1
P (° C./s)
(° C.)
(° C.)
(° C.)
(° C./s)
(° C.)
(° C.)
(° C./s)
30
E
1203
1102
53
950
12
900
6
2
673
5
17
18
685
675
525
0.10
518
503
0.03
31
F
32
G
1200
1103
53
955
16
880
8
2
661
6
16
17
595
595
409
0.08
395
380
0.03
33
H
1200
1106
56
951
15
908
6
2
772
5
13
21
606
596
412
0.09
406
390
0.03
34
I
1210
1109
57
956
14
905
5
2
670
4
17
18
607
597
413
0.11
406
387
0.02
35
J
1209
1107
54
957
15
896
7
2
670
6
16
18
601
591
412
0.12
407
386
0.03
36
K
1205
1105
55
953
15
897
7
2
667
3
20
21
605
595
411
0.09
406
390
0.03
37
L
1202
1103
55
954
14
901
8
2
668
4
18
23
601
591
410
0.08
406
388
0.02
38
M
1203
1102
55
955
16
904
6
2
662
5
18
28
599
589
413
0.12
406
387
0.02
39
N
1201
1105
55
957
13
903
6
2
669
3
19
21
598
588
406
0.11
406
385
0.02
40
O
1202
1103
55
953
12
896
7
2
671
6
15
18
603
583
409
0.10
406
384
0.03
41
P
1206
1102
55
951
15
895
5
2
678
5
15
21
601
581
410
0.08
407
386
0.03
42
Q
1209
1106
54
950
16
906
6
2
675
4
18
23
598
588
412
0.08
407
384
0.02
43
R
1208
1109
54
951
15
903
7
2
671
6
31
34
603
593
409
0.11
406
386
0.03
44
S
1205
1102
55
956
14
902
8
2
679
3
29
33
605
595
411
0.10
394
381
0.02
45
T
1202
1104
56
957
13
907
8
2
668
4
12
18
601
591
410
0.10
400
388
0.03
46
U
1204
1105
54
953
12
901
6
2
665
5
16
19
600
590
411
0.10
410
395
0.02
47
V
1204
1102
56
954
14
904
7
2
668
6
16
21
599
589
413
0.10
407
390
0.03
48
W
1207
1103
55
955
15
906
8
2
661
4
19
21
598
588
412
0.08
406
381
0.02
49
X
1210
1102
55
957
16
905
6
2
670
6
15
18
602
592
409
0.12
406
382
0.03
50
Y
1202
1106
55
950
15
904
5
2
668
5
16
17
601
591
412
0.11
312
383
0.03
51
Z
1209
1102
55
955
14
906
7
2
665
7
16
21
600
590
436
0.10
429
390
0.02
52
AA
1204
1103
55
950
14
908
5
2
669
6
16
19
606
596
527
0.08
512
387
0.03
53
BB
1205
1102
54
957
13
902
6
2
661
4
18
21
606
596
412
0.09
406
386
0.02
54
CC
1203
1104
55
953
15
901
7
2
670
4
18
21
606
596
411
0.11
406
390
0.03
55
DD
1201
1105
56
954
16
902
6
2
665
5
16
22
606
586
408
0.12
406
388
0.03
56
EE
1207
1104
54
955
14
905
5
2
667
6
16
20
607
587
408
0.09
407
387
0.03
57
FF
1206
1108
53
957
15
904
8
2
668
4
18
19
605
595
410
0.08
406
391
0.02
58
GG
1205
1102
56
953
13
901
8
2
662
5
17
18
601
591
412
0.12
406
391
0.03


TABLE 9
COOL-
FINISH ROLLING
ING
ROUGH
END
END
AIR
AFTER
SECOND
RE-
ROLLING
TEM-
RE-
TEM-
RE-
E-
COOLING
AIR
COIL-
FIRST COOLING
COOLING
HEAT-
FINAL
PER-
DUC-
PER-
DUC-
LAPSED
START
RIGHT
COOL-
ING
START
END
START
ING
TEM-
CUMU-
A-
TION
ATURE
TION
TIME
TEM-
SIDE
ING
TEM-
TEM-
TEM-
TEM-
TEM-
PER-
LATIVE
TURE
OF
OF
OF
TO
PER-
IN
COOL-
PER-
PER-
PER-
COOL-
PER-
COOL-
SAM-
STEEL
PER-
A-
REDUC-
OF 6TH
6TH
7TH
7TH
COOL-
A-
FOR-
ING
A-
A-
A-
ING
A-
ING
PLE
SYM-
ATURE
TURE
TION
PASS
PASS
PASS
PASS
ING
TURE
TIME
MULA
RATE
TURE
TURE
TURE
RATE
T3-300
TURE
RATE
No.
BOL
(° C.)
(° C.)
(%)
(° C.)
(%)
T1 (° C.)
(%)
t1 (s)
T2 (° C.)
(s)
1
P (° C./s)
(° C.)
(° C.)
(° C.)
(° C./s)
(° C.)
(° C.)
(° C./s)
88
HH
1204
1103
57
951
12
900
8
2
669
6
15
17
598
589
408
0.11
406
391
0.02
89
II
1203
1108
54
952
15
900
6
2
671
4
18
21
598
588
411
0.10
407
390
0.03
90
JJ
1201
1102
55
953
15
900
7
2
678
6
16
18
603
583
410
0.10
406
387
0.03
91
KK
1207
1104
54
958
14
902
5
2
675
5
16
18
601
591
409
0.09
406
386
0.02
92
LL
1206
1105
57
946
15
905
8
2
670
7
15
18
598
588
413
0.08
407
390
0.03
93
MM
1204
1102
54
956
15
904
6
2
671
6
16
18
603
593
408
0.11
407
388
0.02
94
NN
1208
1103
53
950
14
901
7
2
670
4
18
21
605
595
409
0.10
406
387
0.03
95
OO
1206
1102
56
953
16
902
5
2
670
5
17
18
601
591
412
0.10
406
391
0.03
96
PP
1203
1106
57
952
13
901
6
2
670
6
16
18
600
590
412
0.10
406
391
0.03
97
QQ
1201
1102
55
954
12
906
7
2
670
5
16
21
598
589
413
0.10
406
391
0.02
98
RR
1200
1103
55
951
15
903
8
2
661
7
16
22
598
588
412
0.08
406
392
0.03
99
SS
1206
1104
55
956
16
902
8
2
670
4
18
20
602
592
412
0.12
407
391
0.02
100
TT
1209
1105
55
957
15
907
6
2
668
4
18
19
601
591
412
0.11
406
391
0.03
101
UU
1203
1102
54
953
14
901
7
2
665
4
18
21
600
580
412
0.10
406
391
0.02
102
VV
1205
1103
57
954
15
904
8
2
669
5
16
17
585
585
412
0.08
406
391
0.03
103
WW
1203
1102
54
955
15
906
8
2
661
6
16
21
585
585
412
0.08
395
380
0.03
104
XX
1204
1106
53
957
15
905
5
2
670
4
18
21
598
588
412
0.11
398
383
0.02
105
YY
1203
1102
56
950
15
804
8
2
665
5
17
19
602
592
412
0.12
402
387
0.03
106
ZZ
1206
1103
57
955
15
900
6
2
667
6
17
21
606
596
412
0.08
406
391
0.02
107
AAA
1206
1101
55
950
14
900
7
2
668
4
18
21
606
596
413
0.08
406
391
0.03
108
BBB
1208
1103
55
957
16
900
5
2
662
6
16
19
606
596
412
0.12
406
391
0.03
109
CCC
1209
1102
55
953
13
902
6
2
669
5
16
17
597
587
412
0.10
387
392
0.03
110
DDD
1203
1107
55
954
12
907
7
2
671
7
15
18
600
590
412
0.10
400
385
0.03
111
EEE
1204
1102
54
955
15
901
8
2
678
6
16
18
604
594
412
0.10
404
389
0.03
112
FFF
1204
1105
56
957
16
904
8
2
675
4
18
22
606
596
412
0.10
406
391
0.03
113
GGG
1205
1104
54
953
15
906
6
2
670
5
16
18
605
595
412
0.08
406
391
0.03
114
HHH
1206
1102
55
951
14
905
7
2
671
6
16
18
601
591
412
0.12
407
387
0.02
115
III
1208
1107
57
952
15
904
8
2
670
5
17
20
598
589
413
0.11
408
386
0.03
116
JJJ
1209
1108
54
953
15
900
8
2
670
7
15
21
598
588
412
0.08
406
390
0.02
117
KKK
1202
1102
53
950
15
900
8
2
670
4
18
21
803
593
411
0.08
406
388
0.03
118
LLL
1204
1108
52
950
14
900
8
2
670
4
17
19
801
591
408
0.11
403
378
0.02
119
MMM
1201
1104
55
951
15
903
6
2
671
5
17
18
598
588
409
0.10
403
388
0.03

INDUSTRIAL APPLICABILITY

The present invention may be used in an industry related to a hot-rolled steel sheet used for an underbody part of an automobile, for example.

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Patent Valuation

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22.97/100 Score

Market Attractiveness

It shows from an IP point of view how many competitors are active and innovations are made in the different technical fields of the company. On a company level, the market attractiveness is often also an indicator of how diversified a company is. Here we look into the commercial relevance of the market.

100.0/100 Score

Market Coverage

It shows the sizes of the market that is covered with the IP and in how many countries the IP guarantees protection. It reflects a market size that is potentially addressable with the invented technology/formulation with a legal protection which also includes a freedom to operate. Here we look into the size of the impacted market.

64.21/100 Score

Technology Quality

It shows the degree of innovation that can be derived from a company’s IP. Here we look into ease of detection, ability to design around and significance of the patented feature to the product/service.

53.0/100 Score

Assignee Score

It takes the R&D behavior of the company itself into account that results in IP. During the invention phase, larger companies are considered to assign a higher R&D budget on a certain technology field, these companies have a better influence on their market, on what is marketable and what might lead to a standard.

21.74/100 Score

Legal Score

It shows the legal strength of IP in terms of its degree of protecting effect. Here we look into claim scope, claim breadth, claim quality, stability and priority.

Citation

Patents Cited in This Cited by
Title Current Assignee Application Date Publication Date
溶接熱影響部の耐軟化性に優れたバーリング性高強度鋼板およびその製造方法 新日本製鐵株式会社 04 December 2003 05 August 2004
高强度热轧钢板及其制造方法 新日铁住金株式会社 09 March 2011 11 June 2014
穴拡げ加工性に優れた高強度熱延鋼板およびその製造方法 株式会社神戸製鋼所 28 March 2005 12 October 2006
穴拡げ性と延性のバランスが極めて良好な高強度鋼板の製造方法と亜鉛めっき鋼板の製造方法 新日鐵住金株式会社 28 April 2008 12 November 2009
耐水素脆化特性に優れた超高強度鋼板及びその製造方法 株式会社神戸製鋼所 07 January 2005 18 August 2005
See full citation <>

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US10000829 Hot-rolled steel sheet 1 US10000829 Hot-rolled steel sheet 2