Fire-resistant steel superior in weld joint reheat embrittlement resistance and toughness and method of production of same
View Patent ↗The present invention provides high temperature strength and fire-resistant steel superior in weld joint reheat embrittlement resistance and toughness which is produced using steel of a room temperature strength of the 400 to 600N/mm 2 class containing as main ingredients C: 0.010% to less than 0.05%, Si: 0.01 to 0.50%, Mn: 0.80 to 2.00%, Cr: 0.50% to less than 2.00%, V: 0.03 to 0.30%, Nb: 0.01 to 0.10%, N: 0.001 to 0.010%, and Al: 0.005 to 0.10%, limiting the contents of Ni, Cu, Mo, and B, and satisfying the relationship of 4Cr[%]-5Mo[%]-10Ni[%]-2Cu[%]-Mn[%]>0.
1. A fire-resistant steel having weld joint reheat embrittlement resistance and toughness and a room temperature strength of 400 to 600N/mm 2 class, consisting of, by mass %,
C: 0.010% to less than 0.05%,
Si: 0.01 to 0.50%,
Mn: 0.80 to 2.00%,
Cr: 0.50% to less than 2.00%,
V: 0.03 to 0.30%,
Nb: 0.01 to 0.10%,
N: 0.001 to 0.010%, and
Al: 0.005 to 0.10%,
limiting contents of Ni, Cu, Mo, and B to
Ni: less than 0.10%,
Cu: less than 0.10%,
Mo: 0.10% or less, and
B: less than 0.0003%,
further limiting contents of impurity ingredients of P, S, and O to
P: less than 0.020%,
S: less than 0.0050%, and
O: less than 0.010%, and
a balance of iron and unavoidable impurities, wherein
Cr, Mo, Ni, Cu, and Mn satisfy the following formula (1):
4Cr[%]-5Mo[%]-10Ni[%]-2Cu[%]-Mn[%]>0 (1)
where, in formula (1), the units of the concentrations of the elements are mass %, wherein a dislocation density in a ferrite phase of said steel material is 10 10 /m 2 or more, said steel material structure has an occupancy of bainite or martensite in a structure viewed under an optical microscope of 20% or more and is comprised of a quenched structure, and in said steel material, carbides or nitrides comprising one or more of Nb, V, and Cr are precipitated by a 2/μm 2 or higher density.
2. A fire-resistant steel having weld joint reheat embrittlement resistance and toughness as set forth in claim 1 , wherein the steel has a high temperature yield strength at 600° C. of at least ½ of the prescribed yield strength at room temperature.
3. A fire-resistant steel having weld joint reheat embrittlement resistance and toughness and a room temperature strength of 400 to 600N/mm 2 class, consisting of, by mass %,
C: 0.010% to less than 0.05%,
Si: 0.01 to 0.50%,
Mn: 0.80 to 2.00%,
Cr: 0.50% to less than 2.00%,
V: 0.03 to 0.30%,
Nb: 0.01 to 0.10%,
N: 0.001 to 0.010%, and
Al: 0.005 to 0.10%,
limiting contents of Ni, Cu, Mo, and B to
Ni: less than 0.10%,
Cu: less than 0.10%,
Mo: 0.10% or less, and
B: less than 0.0003%,
further limiting contents of impurity ingredients of P, S, and O to
P: less than 0.020%,
S: less than 0.0050%,
O: less than 0.010%,
one or both of Ti: over 0.005% to less than 0.050% and
Zr: 0.002 to 0.010%, and
a balance of iron and unavoidable impurities,
wherein Cr, Mo, Ni, Cu, and Mn satisfy the following formula (1):
4Cr[%]-5Mo[%]-10Ni[%]-2Cu[%]-Mn[%]>0 (1)
where, in formula (1), the units of the concentrations of the elements are mass %, wherein a dislocation density in a ferrite phase of said steel material is 10 10 /m 2 or more, said steel material structure has an occupancy of bainite or martensite in a structure viewed under an optical microscope of 20% or more and is comprised of a quenched structure, and in said steel material, carbides or nitrides comprising one or more of Nb, V, Cr, Ti, and Zr are precipitated by a 2/μm 2 or higher density.
4. A fire-resistant steel having weld joint reheat embrittlement resistance and toughness as set forth in claim 3 , wherein the steel has a high temperature yield strength at 600° C. of at least ½ of the prescribed yield strength at room temperature.
5. A fire-resistant steel having weld joint reheat embrittlement resistance and toughness and a room temperature strength of 400 to 600N/mm 2 class, consisting of, by mass %,
C: 0.010% to less than 0.05%,
Si: 0.01 to 0.50%,
Mn: 0.80 to 2.00%,
Cr: 0.50% to less than 2.00%,
V: 0.03 to 0.30%,
Nb: 0.01 to 0.10%,
N: 0.001 to 0.010%, and
Al: 0.005 to 0.10%,
limiting contents of Ni, Cu, Mo, and B to
Ni: less than 0.10%,
Cu: less than 0.10%,
Mo: 0.10% or less, and
B: less than 0.0003%,
further limiting contents of impurity ingredients of P, S, and O to
P: less than 0.020%,
S: less than 0.0050%,
O: less than 0.010%,
one or more of
Mg: 0.0005 to 0.005%,
Ca: 0.0005 to 0.005%,
Y: 0.001 to 0.050%,
La: 0.001 to 0.050%, and
Ce: 0.001 to 0.050%, and
a balance of iron and unavoidable impurities,
wherein Cr, Mo, Ni, Cu, and Mn satisfy the following formula (1):
4Cr[%]-5Mo[%]-10Ni[%]-2Cu[%]-Mn[%]>0 (1)
where, in formula (1), the units of the concentrations of the elements are mass %, wherein a dislocation density in a ferrite phase of said steel material is 10 10 /m 2 or more, said steel material structure has an occupancy of bainite or martensite in a structure viewed under an optical microscope of 20% or more and is comprised of a quenched structure, and in said steel material, carbides or nitrides comprising one or more of Nb, V, and Cr are precipitated by a 2/μm 2 or higher density.
6. A fire-resistant steel having weld joint reheat embrittlement resistance and toughness as set forth in claim 5 , wherein the steel has a high temperature yield strength at 600° C. of at least ½ of the prescribed yield strength at room temperature.