BR-112021012379-B1 - Steel material suitable for use in acidic environments.

BR112021012379B1BR 112021012379 B1BR112021012379 B1BR 112021012379B1BR-112021012379-B1

Abstract

STEEL MATERIAL SUITABLE FOR USE IN ACIDIC ENVIRONMENTS. To provide a steel material with a yield strength of 110 ksi and excellent SSC resistance. A steel material according to the present disclosure has a chemical composition consisting of, in % by mass: C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr: 0.55 to 1.10%, Mo: 0.70 to 1.00%, Ti: 0.002 to 0.020%, V: 0.05 to 0.30%, Nb: 0.002 to 0.100%, B: 0.0005 to 0.0040%, N: 0.0100% or less, O: less than 0.0020%, and the balance being Fe and impurities, and satisfying Formula (1) described in the descriptive report. A grain diameter of an austenitic grain a priori is 15.0 micrometers or less, and an average area of precipitate that is precipitated at an austenitic grain boundary a priori is 12.5 x 10 to the power of -3 square micrometers or less. A yield strength is 758 to 862 MPa.

Inventors

Yohei Otome
Hiroki KAMITANI
Atsushi Soma
Taro OE
NOBUAKI KOMATSUBARA
Yuji Arai
Hideki Takabe

Assignees

NIPPON STEEL CORPORATION

Dates

Publication Date: 20260317
Application Date: 20200213
Priority Date: 20190215

Claims (6)

1. Steel material characterized by comprising: a chemical composition consisting of, in % by mass: C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr: 0.55 to 1.10%, Mo: 0.70 to less than 1.00%, Ti: 0.002 to 0.020%, V: 0.07 to 0.30%, Nb: 0.002 to 0.100%, B: 0.0005 to 0.0040%, N: 0.0100% or less, O: less than 0.0020%, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, Zr: 0 to 0.0100%, rare earth metal: 0 to 0.0100%, Cu: 0 to 0.50%, Ni: 0 to 0.50%, Co: 0 to 0.50%, and W: 0 to 0.50%, with the balance being Fe and impurities, and satisfying Formula (1), wherein in the steel material, a grain diameter of an austenitic grain a priori is 4.5 to 15.0 μm, an average precipitate area that is precipitated at an austenitic grain boundary a priori is 3.0x10-3 to 12.5x10-3 μm2, and a yield strength is 758 to 862 MPa: Mo/Cr > 0.90 (1) where the content (% by mass) of a corresponding element is replaced by each element symbol in Formula (1).
2. Steel material, according to claim 1, characterized in that its chemical composition contains one or more types of elements selected from the group consisting of: Ca: 0.0001 to 0.0100%, Mg: 0.0001 to 0.0100%, Zr: 0.0001 to 0.0100%, and rare earth metal: 0.0001 to 0.0100%.
3. Steel material, according to claim 1 or claim 2, characterized by its chemical composition containing one or more types of elements selected from the group consisting of: Cu: 0.02 to 0.50%, and Ni: 0.02 to 0.50%.
4. Steel material, according to any one of claim 1 to claim 3, characterized by the chemical composition containing one or more types of elements selected from the group consisting of: Co: 0.02 to 0.50%, and W: 0.02 to 0.50%.
5. Steel material, according to any one of claim 1 to claim 4, characterized by the steel material being in an oil well steel pipe.
6. Steel material, according to any one of claim 1 to claim 5, characterized in that the steel material is a seamless steel tube.

Description

TECHNICAL FIELD [001] This disclosure relates to a steel material, and more particularly to a steel material suitable for use in an acidic environment. PREVIOUS TECHNIQUE [002] Due to the deepening of oil and gas wells (in this document, oil and gas wells are collectively referred to as “oil wells”), there is a demand for increased strength of oil well steel materials represented by oil well steel pipes. Specifically, 80 ksi grade oil well steel pipes (yield strength is 80 to less than 95 ksi, i.e., 552 to less than 655 MPa) and 95 ksi grade oil well steel pipes (yield strength is 95 to less than 110 ksi, i.e., 655 to less than 758 MPa) are being widely used, and recently, orders for 110 ksi steel pipes (yield strength is 110 to 125 ksi, i.e., 758 to 862 MPa) are also beginning to be placed. [003] Most deep wells are in an acidic environment containing corrosive hydrogen sulfide. In the present description, an acidic environment means an environment that contains hydrogen sulfide and is acidified. Note that an acidic environment may contain carbon dioxide. Steel oil well pipes used in a corrosive environment must have not only high strength but also resistance to sulfide stress cracking (referred to in this document as “SSC strength”). [004] A technique for increasing the SSC strength of a steel material, such as an oil well steel pipe, is disclosed in Japanese Patent Application Publication No. 62-253720 (Patent Literature 1), Japanese Patent Application Publication No. 59-232220 (Patent Literature 2), Japanese Patent Application Publication No. 06-322478 (Patent Literature 3), Japanese Patent Application Publication No. 08-311551 (Patent Literature 4), Japanese Patent Application Publication No. 2000-256783 (Patent Literature 5), Japanese Patent Application Publication No. 2000297344 (Patent Literature 6), Japanese Patent Application Publication No. 2005-350754 (Patent Literature 7), National Publication of International Patent Application No. 2012-519238 (Patent Literature 8) and Publication of Japanese Patent Application No. 2012-26030 (Patent Literature 9). [005] Patent Literature 1 proposes a method for increasing the SSC strength of oil well steel by reducing impurities such as Mn and P. Patent Literature 2 proposes a method for increasing the SSC strength of steel by performing double quenching to make the grain fine. [006] Patent Literature 3 proposes a method for increasing the SSC strength of a 125 ksi grade steel material by finer-fining the steel microstructure through induction heat treatment. Patent Literature 4 proposes a method for increasing the SSC strength of a 110 to 140 ksi grade steel tube by increasing the hardenability of the steel using a direct quenching process and also increasing a tempering temperature. [007] Patent Literature 5 and Patent Literature 6 propose a method for increasing the SSC strength of low-alloy steel for petroleum tubular products with a grade of 110 to 140 ksi by controlling carbide morphology. Patent Literature 7 proposes a method for increasing the SSC strength of a steel material with a grade of 125 ksi or higher by controlling the dislocation density and a hydrogen diffusion coefficient to predetermined values. Patent Literature 8 proposes a method for increasing the SSC strength of 125 ksi grade steel by performing multiple quenching cycles on low-alloy steel containing 0.3 to 0.5% C. Patent Literature 9 proposes a method for controlling carbide morphology and number by adopting a two-stage heat treatment tempering process. More specifically, in Patent Literature 9, a large M3C or M2C number density is suppressed to increase the SSC strength of 125 ksi grade steel. LIST OF CITATIONS PATENT LITERATURE [Patent Literature 1] Publication of Japanese Patent Application No. 62-253720. [Patent Literature 2] Publication of Japanese Patent Application No. 59-232220. [Patent Literature 3] Publication of Japanese Patent Application No. 06-322478. [Patent Literature 4] Publication of Japanese Patent Application No. 08-311551. [Patent Literature 5] Publication of Japanese Patent Application No. 2000-256783. [Patent Literature 6] Publication of Patent Application Japanese Patent No. 2000-297344.[Patent Literature 7] Publication of Japanese Patent Application No. 2005-350754.[Patent Literature 8] National Publication of International Patent Application No. 2012-519238.[Patent Literature 9] Publication of Japanese Patent Application No. 2012-26030. SUMMARY OF THE INVENTION TECHNICAL PROBLEM [008] However, a steel material (an oil well steel pipe, for example) exhibiting a yield strength of 110 ksi (758 to 862 MPa) and excellent SSC strength can be obtained by a technique different from the techniques disclosed in Patent Literatures 1 to 9 mentioned above. [009] It is an objective of the present disclosure to provide a steel material that has a yield strength of 758 to 862 MPa (grade 110 ksi) and also has excellent SSC resistance in an acidic environment. SOLUTION TO TH