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

Abstract

The present invention provides a high performance-stainless steel exhibiting a corrosion resistance even under very severe corrosion environments at temperatures of equal to or higher than 180° C., for example, 220° C. while maintaining strength and a toughness by improving a corrosion resistance of a conventional martensitic stainless steel with high strength. The present invention provides a martensitic stainless steel containing, 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 martensitic stainless steel containing, 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. 
     
     
         2 . The martensitic stainless steel according to  claim 1 , further containing, in mass %, Nb: equal to or less than 0.1%. 
     
     
         3 . The martensitic stainless steel according to  claim 1 , wherein a 0.2% proof stress thereof is equal to or higher than 758 MPa and equal to or lower than 965 MPa, an absorbed energy thereof in a Charpy full size test at −20° C. is equal to or higher than 100 J, and a corrosion rate thereof under an environment of a 20% NaCl aqueous solution, 220° C., 10 atmospheric pressure-CO 2  is equal to or lower than 0.5 mm/year. 
     
     
         4 . A martensitic stainless steel pipe for an oil well, a gas well, or a line pipe comprising the martensitic stainless steel according to  claim 1 . 
     
     
         5 . A method of producing a martensitic stainless steel comprising the steps of subjecting the martensitic stainless steel having a composition as defined in  claim 1  to hot working,
 thereafter forming austenite in the steel at a temperature of equal to or higher than 800° C. and equal to or lower than 980° C. and successively quenching and cooling the steel at a temperature of equal to or lower than 100° C., 
 followed by tempering the steel at a temperature of equal to or higher than 500° C. and equal to or lower than 700° C. 
 
     
     
         6 . The martensitic stainless steel according to  claim 2 , wherein a 0.2% proof stress thereof is equal to or higher than 758 MPa and equal to or lower than 965 MPa, an absorbed energy thereof in a Charpy full size test at −20° C. is equal to or higher than 100 J, and a corrosion rate thereof under an environment of a 20% NaCl aqueous solution, 220° C., 10 atmospheric pressure-CO 2  is equal to or lower than 0.5 mm/year. 
     
     
         7 . A martensitic stainless steel pipe for an oil well, a gas well, or a line pipe comprising the martensitic stainless steel according to any one of  claim 2 . 
     
     
         8 . A martensitic stainless steel pipe for an oil well, a gas well, or a line pipe comprising the martensitic stainless steel according to any one of  claim 3 . 
     
     
         9 . A martensitic stainless steel pipe for an oil well, a gas well, or a line pipe comprising the martensitic stainless steel according to any one of  claim 6 . 
     
     
         10 . A method of producing a martensitic stainless steel comprising the steps of:
 subjecting the martensitic stainless steel having a composition as defined in  claim 2  to hot working,   thereafter forming austenite in the steel at a temperature of equal to or higher than 800° C. and equal to or lower than 980° C. and successively quenching and cooling the steel at a temperature of equal to or lower than 100° C.,   followed by tempering the steel at a temperature of equal to or higher than 500° C. and equal to or lower than 700° C.