655 Mpa Grade Martensitic Stainless Steel Having High Toughness and Method for Manufacturing the Same

Abstract

A martensitic stainless steel for inexpensive seamless pipe having 655 MPa yield strength, high toughness and excellent corrosion resistance in high CO 2 environments, and a method for manufacturing thereof is provided. The steel comprises C:0.005-0.05%, Si:0.1-0.5%, Mn: 0.1-2.0% P: −0.005%, S: −0.005%, Cr: 10.0-12.5%, Mo: 0.1-0.5%, Ni: 1.5-3.0%, N: −0.02%, Al: 0.01-0.1%, by weight, while FI value defined by the formula [FI=Cr+Mo−Ni−30 (C+N)] being 5.00 to 8.49, and balance of substantially Fe. The method comprises the steps of reheating the cooled steel at temperatures from 780° C. to 960° C., quenching the reheated steel, and then tempering the quenched steel at temperatures from 550° C. to 650° C.

1 . A 655 MPa grade martensitic stainless steel having high toughness, comprising C:0.005-0.05%, Si:0.1-0.5%, Mn: 0.1-2.0%, P: −0.05%, S: −0.005%, Cr: 10.0-12.5%, Mo: 0.1-0.5%, Ni: 1.5-3.0%, N: −0.02%, Al: 0.01-0.1% by weight, while FI value defined by the formula [FI=Cr+Mo−Ni−30(C+N)] being 5.00 to 8.49, and balance of substantially Fe. 
     
     
         2 . The 655 MPa grade martensitic stainless steel having high toughness according to  claim 1 , further comprising at least one chemical composition selected from the group consisting of Cu: −0.5%, Nb: −0.05%, V: −0.1%, B: −0.00 5 %, Ca: −0.005%, by weight. 
     
     
         3 . A method for manufacturing a 655 MPa grade martensitic stainless steel having high toughness, comprising the steps of: hot-rolling a steel, comprising C:0.005-0.05%, Si:0.1-0.5%, Mn: 0.1-2.0%, P: −0.05%., S: 0.005%, Cr: 10.0-12.5%, Mo: 0.1-0. 5%, Ni: 1.5-3.0%, Ni: −0.02%, Al: 0.01-0.1%, by weight, while FI value defined by the formula [FI=Cr+Mo−Ni−30(C+N) ] being 5.00 to 8.49, and balance of substantially Fe, cooling the hot-rolled steel; reheating the cooled steel at temperatures from 780° C. to 960° C.; quenching the reheated steel; and then tempering the quenched steel at temperatures from 550° C. to 650° C. 
     
     
         4 . The method for manufacturing the 655 MPa grade stainless steel having high toughness according to  claim 3 , comprising the steps of: hot-rolling the steel further comprising at least one chemical composition selected from the group consisting of Cu: −0.5%, Nb: −0.05%, V: −0.1%, B: −0.005%, Ca: −0.005%, flyweight; cooling the hot-rolled steel; reheating the cooled steel at temperatures from 780° C. to 960° C.; quenching the reheated steel; and then tempering the quenched steel at temperatures from 550° C. to 650° C.