US 12,188,105 B2
Steel material for welding steel pipe having excellent low-temperature toughness, steel material that has undergone weld heat treatment, and method for manufacturing same
Hwan-Gyo Jung, Pohang-si (KR)
Assigned to POSCO CO., LTD, Pohang-si (KR)
Appl. No. 16/760,170
Filed by POSCO, Pohang-si (KR)
PCT Filed Nov. 2, 2018, PCT No. PCT/KR2018/013261
§ 371(c)(1), (2) Date Apr. 29, 2020,
PCT Pub. No. WO2019/088762, PCT Pub. Date May 9, 2019.
Claims priority of application No. 10-2017-0145686 (KR), filed on Nov. 3, 2017.
Prior Publication US 2020/0255920 A1, Aug. 13, 2020
This patent is subject to a terminal disclaimer.
Int. Cl. C21D 6/00 (2006.01); C21D 8/02 (2006.01); C21D 9/08 (2006.01); C21D 9/46 (2006.01); C21D 9/50 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (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 9/50 (2013.01) [C21D 6/004 (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); C21D 9/08 (2013.01); C21D 9/46 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (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 2211/002 (2013.01); C21D 2211/005 (2013.01)] 8 Claims
OG exemplary drawing
 
1. A steel material for a welded steel pipe, the steel material comprising:
by weight %, 0.03-0.10% of carbon (C), 0.1-0.5 of silicon (Si), 1.0-2.0% of manganese (Mn), 0.01-0.05% of aluminum (Al), 0.05-0.30% of molybdenum (Mo), 0.05-0.30% of chromium (Cr), 0.05-0.50% of nickel (Ni), 0.02-0.08% of niobium (Nb), 0.005-0.020% of titanium (Ti), 0.001-0.007% of nitrogen (N), 0.020% or lower of phosphorous (P), 0.0030% or lower of sulfur(S), 0.0005-0.005% of calcium (Ca), and a balance of Fe and inevitable impurities,
wherein, the steel material has a microstructure consisting of a low-temperature transformation phase of 30% or lower excluding 0% by area fraction and a balance of ferrite, and the low-temperature transformation phase includes at least one of acicular ferrite and bainite,
wherein the microstructure of the steel material includes acicular ferrite of 5 to 10% by area fraction.