US 11,834,727 B2
Hot rolled coated steel sheet having high strength, high formability, excellent bake hardenability and method of manufacturing same
Hyun-Taek Na, Gwangyang-si (KR); and Sung-Il Kim, Gwangyang-si (KR)
Assigned to POSCO CO., LTD, Pohang-si (KR)
Filed by POSCO Co., Ltd, Pohang-si (KR)
Filed on Jan. 31, 2023, as Appl. No. 18/103,718.
Application 18/103,718 is a division of application No. 17/253,284, granted, now 11,591,666, previously published as PCT/KR2019/008378, filed on Jul. 8, 2019.
Claims priority of application No. 10-2018-0081086 (KR), filed on Jul. 12, 2018.
Prior Publication US 2023/0167523 A1, Jun. 1, 2023
Int. Cl. C21D 9/46 (2006.01); B32B 15/01 (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 38/48 (2006.01); C22C 38/50 (2006.01); C22C 38/58 (2006.01); C23C 2/06 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01)
CPC C21D 9/46 (2013.01) [B32B 15/013 (2013.01); C21D 6/002 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (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 38/48 (2013.01); C22C 38/50 (2013.01); C22C 38/58 (2013.01); C23C 2/06 (2013.01); C23C 2/28 (2013.01); C23C 2/40 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 12 Claims
 
1. A method of manufacturing a hot-rolled coated steel sheet, comprising operations of:
reheating a steel slab including in wt %, C: 0.05 to 0.14%, Si: 0.1 to 1.0%, Mn: 1.0 to 2.0%, P: 0.001 to 0.05%, S: 0.001 to 0.01%, Al: 0.01 to 0.1%, Cr: 0.005 to 1.0%, Ti: 0.005 to 0.13%, Nb: 0.005 to 0.03%, N: 0.001 to 0.01%, and a balance of Fe and inevitable impurities,
hot rolling the reheated steel slab at a temperature of Ar3 or higher to 1000° C. to obtain a hot-rolled steel sheet;
primary cooling the hot-rolled steel sheet to a temperature of 550 to 700° C.;
ultra-slow cooling the primary cooled hot-rolled steel sheet to satisfy the following Equation 2;
secondary cooling the ultra-slow cooled hot-rolled steel sheet to a temperature of 300 to 500° C., and then winding the same;
charging the wound hot-rolled steel sheet into a heating table of 350 to 550° C., heating the hot-rolled steel sheet, and then extracting the same;
introducing the heated hot-rolled steel sheet into a hot-dip plating bath of 450 to 550° C. to form a plating layer on a surface of the hot-rolled steel sheet; and
temper rolling the hot-rolled steel sheet on which the plating layer is formed,
wherein the following Equation 3 is satisfied in the heating operation and the temper rolling operation,
|T−TR|≤2
TR=241+109[C]+16.9[Mn]+22.7[Cr]−11.1[Si]−5.4[Al]−0.87Temp+0.00068Temp2  [Equation 2]
where T is an actual ultra-slow cooling time, TR is a theoretical ultra-slow cooling time, Temp is an intermediate temperature during ultra-slow cooling, and the [C], [Mn], [Cr], [Si], and [Al] is a content of each alloy element,
15≤(1000−TH)×ElSPM≤250  [Equation 3]
TH is an average temperature of a charging temperature of a heating table of the hot-rolled steel sheet before being charged into a hot-dip plating bath and an extraction temperature of the same, and ElSPM is a difference in length of the hot-rolled steel sheet before temper rolling and immediately after temper rolling.