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Hot-rolled steel sheet and manufacturing method therefor

A technology of hot-rolled steel plate and manufacturing method, which is applied in the direction of manufacturing tools, heat treatment furnaces, heat treatment equipment, etc., can solve problems such as cracking, unsuitable running parts, poor hole expansion, etc., and achieve improved fuel efficiency, shortened processing procedures, and reduced manufacturing costs. Reduced effect

Active Publication Date: 2020-02-11
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, the DP steel plate has the problem of poor hole expandability because voids may be generated at the interface of two phases with significantly different hardnesses to cause cracks, and it is not suitable for applications requiring high hole expandability, such as running parts.

Method used

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  • Hot-rolled steel sheet and manufacturing method therefor
  • Hot-rolled steel sheet and manufacturing method therefor
  • Hot-rolled steel sheet and manufacturing method therefor

Examples

Experimental program
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Effect test

Embodiment

[0102] The steel containing the composition shown in Table 1 is cast using continuous equipment from casting to rolling. After casting a slab, rough rolling and finish rolling are performed, followed by primary cooling, intermediate air cooling and secondary cooling, and coiling. Taken, a hot-rolled steel sheet was produced. The rest other than the components shown in Table 1 are Fe and impurities. In addition, the component composition obtained by analyzing the sample collected from the produced hot-rolled steel sheet was equivalent to the component composition of the steel shown in Table 1.

[0103]

[0104]

[0105] Table 2 shows the codes of the steel types used, the finish rolling conditions, and the thicknesses of the steel sheets. In Table 2, "F3 load factor", "F4 load factor" and "F5 load factor" refer to the respective rolling loads of the last three rolling stands in the rolling mill having five consecutive finishing stands The ratio of the rolling load to th...

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PUM

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Abstract

Provided is a hot-rolled steel sheet that has a prescribed composition and that includes a two-phase structure in which a martensite phase has a structural fraction of 10-40% in terms of area fraction, and in which a ferrite phase has a structural fraction of at least 60%, wherein ferrite grains have an average grain diameter of at most 5.0 um, and the coverage factor of martensite grains by the ferrite grains is more than 60%. Also provided is a hot-rolled steel sheet manufacturing method comprising: a step for achieving, in the last three rolling stands, a rolling load of at least 80% of that of an immediately-preceding rolling stand, and an average rolling temperature of 800-950 deg c; and a step for forced-cooling a steel sheet and then rolling up the steel sheet, wherein the forced cooling starts within 1.5 seconds of the termination of rolling to cool down the steel sheet to 600-750 deg c at an average cooling rate of at least 30 deg c / sec, and then the steel sheet is subjected to spontaneous cooling for 3-10 seconds, and then further cooled down to 200 deg c or lower at an average cooling rate of at least 30 deg c / sec.

Description

technical field [0001] The present invention relates to a hot-rolled steel sheet having a tensile strength of 980 MPa or more having an excellent balance between toughness and hole expandability, and a method for producing the same. Background technique [0002] In recent years, for the purpose of improving the fuel efficiency and crash safety of automobiles, efforts have been made to reduce the weight of automobile bodies by using high-strength steel sheets. Securing press formability becomes important when applying a high-strength steel sheet. It is generally known that a dual phase steel sheet (hereinafter referred to as DP steel sheet) is composed of a composite structure of a soft ferrite phase and a hard martensite phase, and has good press formability. However, the DP steel sheet has a problem of poor hole expandability because voids may be generated at the interface of two phases with significantly different hardnesses to cause cracks, and it is not suitable for app...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/06C22C38/38C21D8/02C21D9/46
CPCC21D8/02C21D9/46C22C38/06C22C38/38C21D8/021C22C38/02C22C38/04C22C38/001C22C38/00C22C38/12C22C38/002C22C38/18C21D8/0205C21D8/0226C21D6/005C21D6/008C22C38/14C21D6/00C21D8/0426C21D2211/008C22C38/34C22C38/44C22C38/48C22C38/50
Inventor 豊田武平岛哲矢冈本力
Owner NIPPON STEEL CORP
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