US 12,338,506 B2
Cold rolled heat treated steel sheet and a method of manufacturing thereof
Jean-Marc Pipard, Vaux (FR); and Artem Arlazarov, Blenod les Pont A Mousson (FR)
Assigned to ArcelorMittal, Luxembourg (LU)
Filed by ArcelorMittal, Luxembourg (LU)
Filed on Jan. 3, 2023, as Appl. No. 18/149,270.
Application 18/149,270 is a division of application No. 16/761,319, granted, now 11,572,599, previously published as PCT/IB2018/058664, filed on Nov. 5, 2018.
Claims priority of application No. PCT/IB2017/057041 (WO), filed on Nov. 10, 2017.
Prior Publication US 2023/0141152 A1, May 11, 2023
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 9/46 (2006.01); C21D 6/00 (2006.01); C21D 8/02 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/06 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01); C22C 38/46 (2006.01); C22C 38/48 (2006.01); C22C 38/50 (2006.01); C22C 38/54 (2006.01); C22C 38/58 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 6/004 (2013.01); C21D 6/005 (2013.01); C21D 6/007 (2013.01); C21D 6/008 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (2013.01); C21D 8/0236 (2013.01); C21D 8/0263 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/02 (2013.01); C22C 38/06 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01); C22C 38/48 (2013.01); C22C 38/50 (2013.01); C22C 38/54 (2013.01); C22C 38/58 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/008 (2013.01)] 11 Claims
 
1. A method of production of a cold rolled heat treated steel sheet comprising the following successive steps:
providing a semi-finished product with a steel composition comprising the following elements, expressed in percentage by weight:
0.10%≤Carbon≤0.5%
1%≤Manganese≤3.4%
0.5%≤Silicon≤2.5%
0.03%≤Aluminum≤1.5%
0%≤Sulfur≤0.003%
0.002%≤Phosphorus≤0.02%
0%≤Nitrogen≤0.01%
and optionally one or more of the following elements
0.05%≤Chromium≤1%
0.001%≤Molybdenum≤0.5%
0.001%≤Niobium≤0.1%
0.001%≤Titanium≤0.1%
0.001%≤Copper≤2%
0.01%≤Nickel≤3%
0.0001%≤Calcium≤0.005%
0%≤Vanadium≤0.1%
0%≤Boron≤0.003%
0%≤Cerium≤0.1%
0%≤Magnesium≤0.010%
0%≤Zirconium≤0.010%
a remainder being iron and unavoidable impurities caused by processing;
reheating the semi-finished product to a temperature between 1200° C. and 1280° C.;
rolling the semi-finished product in the austenitic range wherein the hot rolling finishing temperature is above Ac3 to obtain a hot rolled steel sheet;
cooling the hot rolled steel sheet at a cooling rate above 30° C./s to a coiling temperature below 600° C.; and coiling the hot rolled steel sheet;
cooling the hot rolled sheet to room temperature;
cold rolling the hot rolled steel sheet with a reduction rate between 35 and 90% to obtain a cold rolled steel sheet;
performing a first annealing by heating the said cold rolled steel sheet at a rate greater than 3° C./s to a soaking temperature between Ac3 and Ac3+100° C. and holding the cold rolled sheet for a time of 10 to 500 seconds;
cooling the cold rolled sheet at a rate greater than 20° C./s to a temperature below 500° C. to define an annealed steel sheet;
performing a second annealing by heating the annealed steel sheet at a rate greater than 3° C./s to a soaking temperature between Tsoaking and Ac3 and holding the annealed steel sheet for a time of 10 to 500 seconds;
cooling the annealed steel sheet at a rate greater than 20° C./s to a temperature range between Tcmax and Tcmin:
TCmax=565-601*(1−Exp(−0.868*C))−34*Mn−13*Si−10*Cr+13*Al−361*Nb
TCmin=565-601*(1−Exp(−1.736*C))−34*Mn−13*Si−10*Cr+13*Al−361*Nb wherein C, Mn, Si, Cr, Al and Nb are in wt. % of the elements in the steel composition; and
bringing the annealed steel sheet to a temperature range between 350° C. and 550° C., holding the annealed steel sheet for a time of 5 to 500 seconds and cooling the annealed steel sheet down to room temperature with a cooling rate of at least 1° C./s to obtain the cold rolled heat treated steel sheet;
wherein Tcmax, Tcmin Ac3, and Tsoaking, are in ° C.