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CN-122029299-A - Steel material and pressure vessel

CN122029299ACN 122029299 ACN122029299 ACN 122029299ACN-122029299-A

Abstract

A steel material having a specific chemical composition in which alpha is 5.0 to 16.0 inclusive and beta is 0.017 inclusive, the microstructure of a portion 1/4 of the thickness from the surface thereof having a tensile strength of 615MPa to 930MPa inclusive includes lower bainite and martensite, the sum of the area ratios of the lower bainite and the martensite is 15.0% or more, the sum of the area ratios of the upper bainite, the lower bainite and the martensite is 90.0% or more, and the area ratio of residual austenite is lower than 1.7%.α=0.50×√[C]×（1+0.64[Si]）×（1+4.10[Mn]）×（1+0.27[Cu]）×（1+0.52[Ni]）×（1+2.33[Cr]）×（1+3.14[Mo]）,β=[Mn]×[P]-[Mo]/100.

Inventors

  • Uchiyama Koya
  • NAKANISHI DAISUKE
  • USUKI HIROKAZU
  • SHIRAHATA HIROYUKI

Assignees

  • 日本制铁株式会社

Dates

Publication Date
20260512
Application Date
20241011
Priority Date
20231011

Claims (11)

  1. 1. A steel material having a chemical composition of, in mass%, C is 0.03% to 0.20%, Si is 0.01% to 0.50%, Mn is 0.10% to 2.00%, P is below 0.025%, S is less than 0.0250%, Ni is 4.51% or more and less than 6.10%, Al is 0.001% to 0.100%, 0.0100% Or less of O, N is less than 0.0100%, Cu:0~1.50%、 Cr:0~3.00%、 Mo:0~2.00%、 B:0~0.0050%、 Nb:0~0.050%、 Ti:0~0.050%、 V:0~0.10%、 Mg:0~0.0200%、 Ca:0~0.0200%、 REM:0~0.0200%、 The rest part of Fe and impurities, And alpha represented by the following formula (1) is 5.0 to 16.0, and beta represented by the following formula (2) is 0.017, The steel has a tensile strength of 615MPa to 930MPa, The microstructure of a portion 1/4 of the thickness in the thickness direction from the surface of the steel material includes lower bainite and martensite, the total area ratio of the lower bainite and the martensite is 15.0% or more, the total area ratio of the upper bainite, the lower bainite and the martensite is 90.0% or more, the area ratio of retained austenite is less than 1.7%, α=0.50×√[C]×(1+0.64[Si])×(1+4.10[Mn])×(1+0.27[Cu])×(1+0.52[Ni])×(1+2.33[Cr])×(1+3.14[Mo]) (1) β=[Mn]×[P]-[Mo]/100 (2) Wherein [ element symbol ] in the formulas (1) and (2) represents the content (mass%) of each corresponding element contained in the steel material, and zero is substituted when the element is not contained.
  2. 2. The steel product as claimed in claim 1 wherein the chemical composition comprises group A, [ Group A ] 1 Or 2 or more selected from the group consisting of: cu is 0.01-1.50%, Cr is 0.01-3.00%, Mo is 0.01% to 2.00% and B is 0.0003% or more and 0.0050% or less.
  3. 3. The steel product as claimed in claim 1 or claim 2 wherein the chemical composition comprises group B, [ Group B ] 1 Or 2 or more selected from the group consisting of: Nb is 0.001% or more and 0.050% or less, 0.001% To 0.050% of Ti, and V is 0.01% or more and 0.10% or less.
  4. 4. A steel product as claimed in any one of claims 1 to 3 wherein the chemical composition comprises group C, [ Group C ] 1 Or 2 or more selected from the group consisting of: mg 0.0003% or more and 0.0200% or less Ca is 0.0003% or more and 0.0200% or less, and REM is 0.0003% or more and 0.0200% or less.
  5. 5. The steel product as claimed in any one of claims 1 to 4, wherein an average crystal grain size of a microstructure of a portion 1/4 of a thickness in a thickness direction from a surface of the steel product is 20.0 μm or less.
  6. 6. The steel product as claimed in any one of claims 1 to 5 wherein the aspect ratio of prior austenite grains at a position 1/4 of the thickness in the thickness direction from the surface of the steel product is 1.5 or more.
  7. 7. The steel product as claimed in any one of claims 1 to 6 wherein the charpy impact absorption energy at-110 ℃ of a portion of 1/4 of the thickness is 150J or more.
  8. 8. The steel product as set forth in any one of claims 1 to 7 wherein, when the steel product is subjected to heat treatment at a temperature range of 425 ℃ or higher at a temperature rise rate and a temperature fall rate of 55 ℃/h and held at 600 ℃ for 2 hours, the charpy impact absorption energy at-110 ℃ of a portion 1/4 of the thickness at the position where the heat treatment is performed is 150J or higher.
  9. 9. The steel material according to any one of claims 1 to 8, wherein a thermal cycle simulating welding of 2kJ/mm is applied to a portion of 1/4 of the thickness of the steel material, and when the steel material is subjected to heat treatment at a temperature range of 425 ℃ or higher at a temperature rise rate and a temperature fall rate of 55 ℃/h and at 600 ℃ for 2 hours, the P concentration in the prior austenite grain boundaries is 3.0% or less in atomic percent concentration, and the grain boundary carbide coating rate is 40% or less.
  10. 10. The steel material according to any one of claims 1 to 9, wherein a thermal cycle simulating welding of 2kJ/mm is applied to a portion of 1/4 of the thickness of the steel material, and when the steel material is subjected to heat treatment at a temperature range of 425 ℃ or higher at a temperature rise rate and a temperature fall rate of 55 ℃/h and at 600 ℃ for 2 hours, the charpy impact absorption energy at-110 ℃ of the portion subjected to the heat treatment is 50J or higher.
  11. 11. A pressure vessel comprising the steel product as claimed in any one of claims 1 to 10.

Description

Steel material and pressure vessel Technical Field The present disclosure relates to steel and pressure vessels. Background The steel material can be used for welded structures such as buildings, bridges, ships, pipeline pipes, offshore structures, and pressure vessels (tanks). Steels excellent in strength and low-temperature toughness and stress are effective for use at low temperatures. Low-temperature steel is used for a pressure vessel for low temperature such as a liquefied gas storage tank. For low-temperature steel, there are Al killed steel, nickel steel, high Mn steel, austenitic stainless steel, and the like depending on the use temperature. For example, nickel steel such as 3.5% ni steel is used as a material for mounting a tank for liquefied ethane or liquefied ethylene at a temperature of about-100 ℃. As in the 3.5% Ni steel, ni is often contained in steel materials, typified by pressure vessels for low temperatures, which require securing low-temperature toughness. For example, patent document 1 proposes a nickel-containing steel sheet for low temperature, which has a specific chemical composition containing 3.0% or more and less than 5.0% of Ni, an alumina cluster index (cluster index) of 0.030 or less, an effective crystal grain size of 12.0 μm or less, an average value of tensile strength of 540MPa to 610MPa, and a charpy impact absorption energy of 150J or more at-140 ℃. Patent document 2 proposes a nickel-containing steel for low temperature having excellent toughness, which has a specific chemical composition containing Ni of 2.7% or more and 5.0% or less, has a prior austenite grain size of 20 μm or less when heated for quenching, has an effective crystal grain size of 12 μm or less after heat treatment, and has a tensile strength of 450MPa to 690 MPa. Patent document 3 discloses a method for producing a high-strength and high-toughness steel, which comprises heating a steel slab having a specific chemical composition and containing 1.0 to 8.0% ni to a temperature of 1000 to 1250 ℃, then subjecting the steel slab to 20 to 60% reduction in a temperature region where austenite is recrystallized during hot rolling, then subjecting the steel slab to 30 to 70% reduction in a temperature region where austenite is not recrystallized, after finishing rolling at 650 ℃ or more, subjecting the steel slab to quenching treatment in which water cooling is started from a temperature of Ar 3 point or more and stopped at a temperature of 150 ℃ or less, then further reheating from Ac 3 point to Ac 3 +100 ℃, then quenching, and then subjecting the steel slab to tempering treatment at a temperature of Ac 1 point or less. Patent document 1 Japanese patent No. 6610352 Patent document 2 Japanese patent No. 6984319 Patent document 3 Japanese patent laid-open No. 1-230713 Disclosure of Invention Problems to be solved by the invention For low-temperature steel used in a low-temperature pressure vessel, it is desired to ensure both high strength and low-temperature toughness. In addition, the low-temperature pressure vessel is manufactured by welding steel materials, and in order to remove residual stress generated by welding, post heat treatment (Post WELD HEAT TREATMENT, sometimes referred to as PWHT) is sometimes performed. Recently, the low-temperature toughness after PWHT of steel has been further improved. The present disclosure addresses the problem of providing a steel material and a pressure vessel which have high tensile strength and can obtain good low-temperature toughness regardless of the heat treatment after welding and which are suitable for low-temperature applications. Means for solving the problems The gist of the present disclosure is as follows. <1> A steel material having a chemical composition of, in mass%, C is 0.03% to 0.20%, Si is 0.01% to 0.50%, Mn is 0.10% to 2.00%, P is below 0.025%, S is less than 0.0250%, Ni is 4.51% or more and less than 6.10%, Al is 0.001% to 0.100%, 0.0100% Or less of O, N is less than 0.0100%, Cu:0~1.50%、 Cr:0~3.00%、 Mo:0~2.00%、 B:0~0.0050%、 Nb:0~0.050%、 Ti:0~0.050%、 V:0~0.10%、 Mg:0~0.0200%、 Ca:0~0.0200%、 REM:0~0.0200%、 The rest part of Fe and impurities, And alpha represented by the following formula (1) is 5.0 to 16.0, and beta represented by the following formula (2) is 0.017, The steel has a tensile strength of 615MPa to 930MPa, The microstructure of the portion 1/4 of the thickness in the thickness direction from the surface of the steel material includes lower bainite and martensite, the total area ratio of the lower bainite and the martensite is 15.0% or more, the total area ratio of the upper bainite, the lower bainite and the martensite is 90.0% or more, and the area ratio of the retained austenite is less than 1.7%. α=0.50×√[C]×(1+0.64[Si])×(1+4.10[Mn])×(1+0.27[Cu])×(1+0.52[Ni])×(1+2.33[Cr])×(1+3.14[Mo]) (1) β=[Mn]×[P]-[Mo]/100 (2) Wherein the symbol of element in the formulas (1) and (2) represents the content (mass%) of the corresponding element cont