Thick steel plate and production method for thick steel plate

Patent metadata

Field	Value
Publication number	US-2016010193-A1
Application number	US-201414770897-A
Country	US
Kind code	A1
Filing date	Feb 25, 2014
Priority date	Feb 28, 2013
Publication date	Jan 14, 2016
Grant date	—

Abstract

Provided are a steel plate having high tensile strength, high yield strength, and excellent low-temperature toughness and a method for manufacturing the steel plate.
A steel plate contains 0.04% to 0.15% C, 0.1% to 2.0% Si, 0.8% to 2.0% Mn, 0.025% or less P, 0.020% or less S, 0.001% to 0.100% Al, 0.010% to 0.050% Nb, and 0.005% to 0.050% Ti and further contains Cu, Ni, Cr, Mo, and N on a mass basis such that 0.5%≦Cu+Ni+Cr+Mo≦3.0% and 1.8≦Ti/N≦4.5 are satisfied, the remainder being Fe and inevitable impurities. The area fraction of polygonal ferrite is less than 10%. The effective grain size at the through-thickness center is 15 μm or less. The standard deviation of the effective grain size is 10 μm or less.

First claim

1 . A steel plate containing 0.04% to 0.15% C, 0.1% to 2.0% Si, 0.8% to 2.0% Mn, 0.025% or less P, 0.020% or less S, 0.001% to 0.100% Al, 0.010% to 0.050% Nb, and 0.005% to 0.050% Ti on a mass basis, the steel plate further containing Cu, Ni, Cr, Mo, and N on a mass basis such that 0.5%≦Cu+Ni+Cr+Mo≦3.0% and 1.8≦Ti/N≦4.5 are satisfied, a remainder being Fe and inevitable impurities,
wherein an area fraction of polygonal ferrite is less than 10%, the effective grain size at the through-thickness center is 15 μm or less, and a standard deviation of the effective grain size is 10 μm or less.

2 . The steel plate according to claim 1 , further containing one or more of 0.01% to 0.10% V, 0.01% to 1.00% W, 0.0005% to 0.0050% B, 0.0005% to 0.0060% Ca, 0.0020% to 0.0200% of a REM, and 0.0002% to 0.0060% Mg on a mass basis.

3 . A method for manufacturing the steel plate according to claim 1 , comprising:
a heating step of heating a steel plate having a composition specified in claim 1 to a temperature of 950° C. to 1,150° C.; a recrystallization temperature region rolling step of performing rolling with a rolling shape factor of 0.5 or more and a rolling reduction of 6.0% or more per pass at a through-thickness center temperature of 930° C. to 1,050° C. three or more passes after the heating step; a non-recrystallization temperature region rolling step of performing rolling with a rolling shape factor of 0.5 or more and total rolling reduction of 35% or more at the through-thickness center temperature of lower than 930° C. one or more passes after the recrystallization temperature region rolling step; and a cooling step of performing cooling under conditions where cooling is started at the through-thickness center temperature of Ar 3 +15° C. or more and an average cooling rate of the through-thickness center from 700° C. to 500° C. is 3.5° C./sec or more after the non-recrystallization temperature region rolling step.

4 . The method for manufacturing the steel plate according to claim 3 , further comprising a tempering step of tempering at a temperature of 700° C. or lower after the cooling step.

Assignees

• Jfe Steel Corp

Inventors

• Terazawa Yusuke
• Ichimiya Katsuyuki
• Hayashi Kenji

Classifications

• C22C38/14

  containing titanium or zirconium · CPC title

• C22C38/12

  containing tungsten, tantalum, molybdenum, vanadium, or niobium · CPC title

• C21D2201/05

  Grain orientation · CPC title

• C21D2211/008

  Martensite · CPC title

• C21D2211/005

  Ferrite · CPC title