Ultrahigh-strength steel sheet and manufacturing method therefor

Patent metadata

Field	Value
Publication number	US-10144986-B2
Application number	US-201314911709-A
Country	US
Kind code	B2
Filing date	Aug 14, 2013
Priority date	Aug 14, 2013
Publication date	Dec 4, 2018
Grant date	Dec 4, 2018

Abstract

The present invention relates to an ultrahigh-strength steel sheet and a manufacturing method therefor. More specifically, the present invention can provide an ultra-high strength steel sheet which can ensure weldability and a delayed fracture resistance property by controlling the contents of elements affecting platability along with the contents of austenite-stabilizing elements and increasing twin formation through re-rolling, and simultaneously improve impact characteristics and workability by ensuring excellent yield strength and ductility.

First claim

The invention claimed is:

1. An ultrahigh-strength steel sheet comprising, by wt %, carbon (C): 0.4% to 0.7%, manganese (Mn): 12% to 24%, aluminum (Al): 0.01% to 3.0%, silicon (Si): 0.3% or less, phosphorus (P): 0.03% or less, sulfur (S): 0.03% or less, nitrogen (N): 0.04% or less, nickel (Ni): 0.05% to 1.0%, chromium (Cr): 0.05% to 1.0%, and tin (Sn): 0.01% to 0.03%, and a balance of iron (Fe) and inevitable impurities, wherein the ultrahigh-strength steel sheet comprises single phase austenite as a microstructure.

2. The ultrahigh-strength steel sheet of claim 1 , wherein the microstructure of the ultrahigh-strength steel sheet comprises grains in an amount of 70% or greater that have an aspect ratio of 2 or greater in a rolling direction by an effect of work hardening.

3. The ultrahigh-strength steel sheet of claim 1 , further comprising titanium (Ti): 0.005% to 0.10%, boron (B): 0.0005% to 0.0050%.

4. The ultrahigh-strength steel sheet of claim 3 , wherein the microstructure of the ultrahigh-strength steel sheet has an average grain size within a range of 2 μm to 10 μm by an effect of work hardening.

5. The ultrahigh-strength steel sheet of claim 1 , wherein the steel sheet has a tensile strength of 1300 MPa or greater and a yield strength of 1000 MPa or greater.

6. The ultrahigh-strength steel sheet of claim 1 , wherein the ultrahigh-strength steel sheet is one of a cold-rolled steel sheet, a hot-dip plated steel sheet, a hot-dip alloy plated steel sheet, and an electroplated steel sheet.

7. A method for manufacturing an ultrahigh-strength steel sheet, the method comprising:
heating a steel ingot or a continuously cast slab to 1050° C. to 1300° C. for homogenization, the steel ingot or continuously cast slab comprising, by wt %, carbon (C): 0.4% to 0.7%, manganese (Mn): 12% to 24%, aluminum (Al): 0.01% to 3.0%, silicon (Si): 0.3% or less, phosphorus (P): 0.03% or less, sulfur (S): 0.03% or less, nitrogen (N): 0.04% or less, nickel (Ni): 0.05% to 1.0%, chromium (Cr): 0.05% to 1.0%, and tin (Sn): 0.01% to 0.03%, and a balance of iron (Fe) and inevitable impurities;
hot rolling the homogenized steel ingot or continuously cast slab at a finish hot rolling temperature of 850° C. to 1000° C. so as to form a hot-rolled steel sheet;
coiling the hot-rolled steel sheet within a temperature range of 200° C. to 700° C.;
cold rolling the coiled steel sheet at a reduction ratio of 30% to 80% to form a cold-rolled steel sheet;
continuously annealing the cold-rolled steel sheet within a temperature range of 400° C. to 900° C.; and
re-rolling the continuously annealed steel sheet.

8. The method of claim 7 , wherein the steel ingot or continuously cast slab further comprises titanium (Ti): 0.005% to 0.10%, boron (B): 0.0005% to 0.0050%.

9. The method of claim 7 , wherein the re-rolling is performed through one of a skin pass milling process, a double reduction rolling process, a hot rolling finishing process, and a continuous rolling process.

10. The method of claim 7 , wherein the re-rolling is performed at a reduction ratio of 30% to 50%.

11. The method of claim 7 , wherein after the continuous annealing, the method further comprises electroplating or hot-dip plating the continuously annealed steel sheet.

Assignees

• Posco

Inventors

• Kim Sung-Kyu
• Cho Won-Tae
• Kim Tai-Ho
• Chin Kwang-Geun
• Han Sang-Ho

Classifications

• C21D8/04

  to produce plates or strips for drawing, e.g. for deep-drawing · CPC title

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C21D8/0226

  Hot rolling · CPC title

• C21D7/02

  by cold working · CPC title

• C21D8/0426

  Hot rolling · CPC title