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Ultra high-strength steel sheet having excellent hole expandability and manufacturing method therefor

An ultra-high-strength, hole-expanding technology, used in manufacturing tools, chemical instruments and methods, coatings, etc., can solve problems such as high investment costs and increased processing costs, and achieve protection of the global environment, inhibition of CO2 production, and excellent yield. Effects of strength and hole expandability

Inactive Publication Date: 2018-08-21
POHANG IRON & STEEL CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, there is a need to develop materials that allow low-cost cold press forming due to limitations such as high equipment investment costs, increased heat treatment and processing costs

Method used

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  • Ultra high-strength steel sheet having excellent hole expandability and manufacturing method therefor
  • Ultra high-strength steel sheet having excellent hole expandability and manufacturing method therefor
  • Ultra high-strength steel sheet having excellent hole expandability and manufacturing method therefor

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0087] Steel having the composition shown in Table 2 below was vacuum-melted with 30 kg of ingot, then kept at a temperature of 1200° C. for 1 hour, and then hot-rolled to complete finish rolling at 900° C. and the finish-rolled steel was loaded into 600 °C preheated oven for 1 hour. Thereafter, the steel is furnace cooled and its coiling simulated for hot rolling. Next, the steel was cold-rolled at a reduction ratio of 50%, then annealed at 900°C, cooled to the cooling termination temperature listed in Table 3, and then maintained at the heat treatment temperature listed in Table 3 for 400 °C. seconds for reheating.

[0088]Yield strength (YS), tensile strength (TS), elongation (TE), retained austenite fraction, and yield ratio (YR) of the samples were measured and shown in Table 3 below.

[0089] [Table 2]

[0090]

[0091] In Table 2, the unit of content of each element is % by weight.

[0092] [table 3]

[0093]

[0094]

[0095] As shown in Table 3, when a s...

Embodiment 2

[0100] Further experiments were conducted by applying the same conditions as in Example 1 and the same heat treatment temperatures as in Table 4 below. Inventive Examples 1-3 and Comparative Example 2 are the same as in Example 1 above.

[0101] The mechanical properties, hole expandability and austenite amount before and after the tensile test were measured and are shown in Table 4 below. By calculating the difference in the fraction of austenite in the system before and after the tensile test, the amount of transformed martensite formed during the transformation can be predicted.

[0102] The hole expandability is expressed by the ratio of the expansion of the circular hole to the initial hole size. The expansion of the circular hole is when a circular hole is formed in the sample and then expanded with a conical drill until the cracks generated at the edge of the hole have at least The amount of expansion until one point penetrates in the thickness direction. Hole expanda...

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Abstract

An aspect of the present invention comprises, by weight, 0.15-0.30% of C, 1.0-3.0% of Si, 3.0-5.0% of Mn, 0.020% or less of P, 0.010% or less of S, 0.01-3.0% of Al, 0.020% or less (0% exclusive) of N,and a balance amount of Fe and inevitable impurities, with a microstructure having retained austenite at an area fraction of 5-20 % and ferrite, bainite and fresh martensite at a balance area fraction.

Description

technical field [0001] The present invention relates to an ultrahigh-strength steel sheet excellent in hole expandability and a method for producing the same. Background technique [0002] In order to control the carbon dioxide emission of automobiles and improve fuel efficiency, automobile manufacturers have been requiring the weight reduction of automobile bodies. At this time, there is a contradiction in that the thickness of the steel plate needs to be reduced in order to reduce the thickness of the steel plate for automobiles, and the thickness of the steel plate needs to be increased in order to ensure collision safety. [0003] In order to solve this contradiction, it is necessary to increase the plasticity of the material while increasing the strength of the material, and this is possible by using various types of automotive steel sheets, such as dual-phase (DP) steel sheets, transformation-induced plasticity (TRIP) steel sheets, and composite-phase steel sheets. (C...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C22C38/04C22C38/06C22C38/02C22C38/00C22C38/38C23C2/40C21D8/02C23C2/06
CPCC21D8/02C23C2/06C23C2/40C22C38/00C22C38/02C22C38/04C22C38/06C22C38/38C21D8/0263C21D9/46C21D2211/001C22C38/001C22C38/12C22C38/14C23C2/0224C22C38/48C22C38/18C23C30/005B32B15/013B32B15/043B32B15/01C22C38/28B32B15/04C22C38/26C22C38/22C22C38/46C22C38/24B32B15/18C23C30/00C22C38/44C22C38/50Y10T428/12958Y10T428/12972Y10T428/12799Y10T428/12979Y10T428/12951C22C38/08
Inventor 李世雄李圭荣柳朱炫李源辉
Owner POHANG IRON & STEEL CO LTD
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