Martensitic Stainless Steel with High Strength, High Toughness and High Corrosion Resistance

Abstract

A method of producing a high performance stainless steel exhibiting corrosion resistance even under a very severe corrosion environment at temperatures of equal to or higher than 180° C., for example, 220° C., while maintaining strength and toughness by improving the corrosion resistance of a conventional martensitic stainless steel with high strength. The martensitic stainless steel includes, in mass %, C: 0.005% to 0.05%, Si: equal to or less than 1.0%, Mn: equal to or less than 2.0%, Cr: 16 to 18%, Ni: 2.5 to 6.5%, Mo: 1.5 to 3.5%, W: equal to or less than 3.5%, Cu: equal to or less than 3.5%, V: 0.01 to 0.08%, Sol.Al: 0.005 to 0.10%, N: equal to or less than 0.05%, and Ta: 0.01 to 0.06%, and the balance Fe with inevitable impurities.

1 . A method of producing a martensitic stainless steel comprising:
 providing a steel comprising in mass %, C: 0.005% to 0.05%, Si: equal to or less than 1.0%, Mn: equal to or less than 2.0%, Cr: 16 to 18%, Ni: 2.5 to 6.5%, Mo: 1.5 to 3.5%, W: equal to or less than 3.5%, Cu: equal to or less than 3.5%, V: 0.01 to 0.08%, Sol.Al: 0.005 to 0.10%, N: equal to or less than 0.05%, and Ta: 0.01 to 0.06%, and the balance Fe with inevitable impurities;   hot-working the steel;   heating the hot-worked steel to form austenite in the hot-worked steel at a temperature equal to or higher than 800° C. and equal to or lower than 980° C.;   quenching and cooling the heated steel at a temperature equal to or lower than 100° C.; and   tempering the quenched steel at a temperature equal to or higher than 500° C. and equal to or lower than 700° C.   
     
     
         2 . The method according to  claim 1 , wherein the steel further comprises, in mass %, Nb: equal to or less than 0.1%. 
     
     
         3 . The method according to  claim 1 , wherein an absorbed energy of the martensitic stainless steel in a Charpy full size test at −20° C. is equal to or higher than 100 J. 
     
     
         4 . The method according to  claim 1 , wherein a 0.2% proof stress of the martensitic stainless steel is equal to or higher than 758 MPa and equal to or lower than 965 a, an absorbed energy of the martensitic stainless steel in a Charpy full size test at −20° C. is equal to or higher than 100 J, and a corrosion rate of the martensitic stainless steel under an environment of a 20% NaCl aqueous solution at 220° C. and 10 atmospheric pressure-CO 2  is equal to or lower than 0.5 mm/year. 
     
     
         5 . A method of producing a martensitic stainless steel pipe for an oil well, a gas well, or a line pipe comprising providing the martensitic stainless steel produced by the method according to  claim 1 . 
     
     
         6 . The method according to  claim 2 , wherein an absorbed energy of the martensitic stainless steel in a Charpy full size test at −20° C. is equal to or higher than 100 J. 
     
     
         7 . The method according to  claim 2 , wherein a 0.2% proof stress of the martensitic stainless steel is equal to or higher than 758 MPa and equal to or lower than 965 MPa, an absorbed energy of the martensitic stainless steel of in a Charpy full size test at −20° C. is equal to or higher than 100 J, and a corrosion rate of the martensitic stainless steel under an environment of a 20% NaCl aqueous solution at 220° C. and 10 atmospheric pressure-CO 2  is equal to or lower than 0.5 mm/year. 
     
     
         8 . A method of producing a martensitic stainless steel pipe for an oil well, a gas well, or a line pipe comprising providing the martensitic stainless steel produced by the method according to  claim 2 . 
     
     
         9 . A method of producing a martensitic stainless steel pipe for an oil well, a gas well, or a line pipe comprising providing the martensitic stainless steel produced by the method according to  claim 3 . 
     
     
         10 . A method of producing a martensitic stainless steel pipe for an oil well, a gas well, or a line pipe comprising providing the martensitic stainless steel produced by the method according to  claim 4 . 
     
     
         11 . A method of producing a martensitic stainless steel pipe for an oil well, a gas well, or a line pipe comprising providing the martensitic stainless steel produced by the method according to  claim 6 . 
     
     
         12 . A method of producing a martensitic stainless steel pipe for an oil well, a gas well, or a line pipe comprising providing the martensitic stainless steel produced by the method according to  claim 7 .