Search

CN-122003514-A - Steel material and pressure vessel

CN122003514ACN 122003514 ACN122003514 ACN 122003514ACN-122003514-A

Abstract

A steel material having a specific chemical composition represented by the following formula (1) wherein Ceq is 0.350 or more, a tensile strength is 490MPa to 720MPa, a total area ratio of a microstructure of a region having a thickness of 1/4 from the surface to a low-temperature-generated phase change structure is 70.0% or more, and an average crystal grain diameter is 25.0 [ mu ] m or less. Ceq= [ C ] + [ Mn ]/6+ [ Ni ]/15+ [ Cu ]/15+ [ Cr ]/5+ [ Mo ]/5+ [ V ]/5 (1).

Inventors

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

Assignees

  • 日本制铁株式会社

Dates

Publication Date
20260508
Application Date
20241011
Priority Date
20231011

Claims (10)

  1. 1. A steel material having the following chemical composition in mass%: C:0.03%~0.20%、 Si:0.10%~0.50%、 Mn:1.25%~2.00%、 P is below 0.025%, S is less than 0.0100%, Al:0.005%~0.100%、 0.0100% Or less of O, N is less than 0.0100%, Ni:0~1.30%、 Cu:0~0.90%、 Cr:0~0.90%、 Mo:0~1.00%、 B:0~0.0050%、 Nb:0~0.020%、 Ti:0~0.050%、 V:0~0.10%、 Mg:0~0.015%、 Ca:0~0.015%、 REM:0~0.015%、 The rest part is Fe and impurities, And Ceq represented by the following formula (1) is 0.350 or more, The tensile strength of the steel is 490 MPa-720 MPa, The total area ratio of the microstructure of the portion 1/4 of the thickness in the thickness direction from the surface of the steel material to the low-temperature-generated phase-change structure is 70.0% or more, and the average crystal grain diameter is 25.0 μm or less, Ceq=[C]+[Mn]/6+[Ni]/15+[Cu]/15+[Cr]/5+[Mo]/5+[V]/5 (1) Wherein the symbol of element in the formula (1) represents the content in mass% of each corresponding element contained in the steel material, and zero is substituted when the corresponding 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 more than 2 elements selected from the following elements: Ni:0.01%~1.30%、 Cu:0.01%~0.90%、 Cr:0.01%~0.90%、 0.01% -1.00% of Mo B:0.0003%~0.0050%。
  3. 3. The steel product as claimed in claim 1 or claim 2 wherein the chemical composition comprises group B, [ Group B ] 1 Or more than 2 elements selected from the following elements: Nb:0.001%~0.020%、 0.001% -0.050% Ti V:0.01%~0.10%。
  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 more than 2 elements selected from the following elements: Mg:0.0003%~0.015% ca 0.0003% -0.015% REM:0.0003%~0.015%。
  5. 5. The steel product as claimed in any one of claims 1 to 4 wherein the charpy impact absorption energy at-90 ℃ of the portion of 1/4 of the thickness is 150J or more.
  6. 6. The steel product as set forth in any one of claims 1 to 5 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-90 ℃ of a portion 1/4 of the thickness of the heat treated portion is 150J or higher.
  7. 7. The steel product according to any one of claims 1 to 6, wherein in a cross section parallel to a rolling direction and a thickness direction of the steel product, an aspect ratio of prior austenite grains at a portion 1/4 of a thickness in the thickness direction from a surface of the steel product is 3.5 or less.
  8. 8. The steel product according to any one of claims 1 to 6, wherein an aspect ratio of prior austenite grains at a portion 1/4 of a thickness in a thickness direction from a surface of the steel product in a cross section parallel to a rolling direction and the thickness direction of the steel product is less than 1.5.
  9. 9. The steel product as claimed in any one of claims 1 to 8, having a yield ratio of 80.0% or less.
  10. 10. A pressure vessel comprising the steel product of any one of claims 1 to 9.

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, line pipes, marine structures, pressure vessels (tanks), and the like. 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. Among the low-temperature steels, there are Al killed steels, nickel steels, high Mn steels, austenitic stainless steels, and the like, depending on the use temperature. For example, for LPG cans with a service temperature of around-50 ℃, al-killed steel is applied. In addition, various steels and methods for producing steels have been proposed in which the chemical composition and microstructure (metal structure) are defined for the purpose of low-temperature toughness and high strength (for example, refer to patent documents 1 to 9). Patent document 1 Japanese patent laid-open No. 61-207512 Patent document 2 Japanese patent application laid-open No. 2013-245360 Patent document 3 Japanese patent laid-open publication No. 2016-148105 Patent document 4 Japanese patent application laid-open No. 2021-088753 Patent document 5 Japanese patent laid-open No. 2-254118 Patent document 6 Japanese patent laid-open No. 3-264615 Patent document 7 Japanese patent laid-open No. 5-263132 Patent document 8 Japanese patent laid-open No. 2021-070862 Patent document 9 Japanese patent laid-open No. 9-020921 Disclosure of Invention Problems to be solved by the invention For low-temperature steel used in a pressure vessel for low temperature, both high strength and securing of low-temperature toughness are desired. In addition, the low-temperature pressure vessel is manufactured by welding steel materials, and in order to remove residual stress generated by welding, 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. On the other hand, in general, if a steel sheet is manufactured by directly performing Direct Quenching (DQ) by water cooling after hot rolling or further performing tempering (T) after DQ, toughness in a width direction (sometimes referred to as C direction) perpendicular to a rolling direction is significantly deteriorated compared to toughness in the L direction due to anisotropy in the rolling direction (sometimes referred to as L direction). However, for example, in the case of a steel sheet for LPG tank, toughness in not only the L direction but also the C direction is sometimes required. The object of the present disclosure is to provide a steel material which has high tensile strength, can obtain good low-temperature toughness both before and after heat treatment after welding, and is suitable for low-temperature applications, and in which the difference between the low-temperature toughness in the direction parallel to the rolling direction and the low-temperature toughness in the direction perpendicular to the rolling direction is small. Means for solving the problems The gist of the present disclosure is as follows. <1> A steel material having the following chemical composition in mass%: C:0.03%~0.20%、 Si:0.10%~0.50%、 Mn:1.25%~2.00%、 P is below 0.025%, S is less than 0.0100%, Al:0.005%~0.100%、 0.0100% Or less of O, N is less than 0.0100%, Ni:0~1.30%、 Cu:0~0.90%、 Cr:0~0.90%、 Mo:0~1.00%、 B:0~0.0050%、 Nb:0~0.020%、 Ti:0~0.050%、 V:0~0.10%、 Mg:0~0.015%、 Ca:0~0.015%、 REM:0~0.015%、 The rest part is Fe and impurities, And Ceq represented by the following formula (1) is 0.350 or more, The tensile strength of the steel is 490 MPa-720 MPa, The total area ratio of the microstructure of the portion 1/4 of the thickness in the thickness direction from the surface of the steel material to the low-temperature-generated phase-change structure is 70.0% or more, and the average crystal grain diameter is 25.0 μm or less. Ceq=[C]+[Mn]/6+[Ni]/15+[Cu]/15+[Cr]/5+[Mo]/5+[V]/5 (1) Wherein the symbol of element in the formula (1) represents the content (mass%) of each corresponding element contained in the steel material. Substituting zero without the inclusion of the corresponding element. <2> The steel material according to <1>, wherein the chemical composition comprises the following group A. [ Group A ] 1 Or more than 2 elements selected from the following elements: Ni:0.01%~1.30%、 Cu:0.01%~0.90%、 Cr:0.01%~0.90%、 0.01% -1.00% of Mo B:0.0003%~0.0050%。 <3> The steel material according to <1> or <2>, wherein the chemical composition comprises the following group B. [ Group B ] 1 Or more than 2 elements selected from the following elements: Nb:0.001%~0.020%、 0.001% -0.050% Ti V:0.01%~0.10%。 <4> The steel material according to any one of <1> to <3>, wherein the chemical composition comprises the following group C. [ Group C