Martensitic stainless steel seamless pipe for oil country tubular goods and method for manufacturing the same

Abstract

A seamless steel pipe for oil country tubular goods which simultaneously has a high strength of a 110 ksi grade of yield strength and a superior low temperature toughness and a method for manufacturing the same are provided. A quenching treatment is performed on a stainless steel seamless pipe having a composition which contains on a mass percent basis, less than 0.010% of C, 1.0% or less of Si, 0.1% to 2.0% of Mn, 0.020% or less of P, 0.010% or less of S, 0.10% or less of Al, 10% to 14% of Cr, 0.1% to 4.0% of Ni, 0.05% or less of N, and the balance being Fe and inevitable impurities in which after heating is performed to a heating temperature for quenching equivalent to or more than the Ac 3 transformation point, cooling is performed to a temperature range of 100° C. or less at a cooling rate equivalent to or more than that of air cooling; and following the quenching treatment, a tempering treatment is performed in which heating is performed to a tempering temperature in the range of more than 450° C. to 550° C., and cooling is then performed.

1 . A martensitic stainless steel seamless pipe for oil country tubular goods comprising:
 a composition which contains on a mass percent basis,   less than 0.010% of C, 1.0% or less of Si,   0.1% to 2.0% of Mn, 0.020% or less of P,   0.010% or less of S, 0.10% or less of Al,   10% to 14% of Cr, 0.1% to 4.0% of Ni,   0.05% or less of N, and   the balance being Fe and inevitable impurities,   and has a high strength of a 110 ksi grade of yield strength and a superior low temperature toughness having a fracture transition temperature vTrs of −60° C. or less in a Charpy impact test.   
     
     
         2 . The martensitic stainless steel seamless pipe according to  claim 1 , wherein the composition further comprises on a mass percent basis, at least one selected from the group consisting of 2.0% or less of Cu and 2.0% or less of Mo. 
     
     
         3 . The martensitic stainless steel seamless pipe according to  claim 1 , wherein the composition further comprises on a mass percent basis, at least one selected from the group consisting of 0.10% or less of V, 0.10% or less of Nb, and 0.10% or less of Ti. 
     
     
         4 . A method for manufacturing a martensitic stainless steel seamless pipe for oil country tubular goods has a high strength of a 110 ksi grade of yield strength and a superior low temperature toughness, the method comprising:
 performing a quenching treatment on a stainless steel seamless pipe having a composition which contains on a mass percent basis,   less than 0.010% of C, 1.0% or less of Si,   0.1% to 2.0% of Mn, 0.020% or less of P,   0.010% or less of S, 0.10% or less of Al,   10% to 14% of Cr, 0.1% to 4.0% of Ni,   0.05% or less of N, and   the balance being Fe and inevitable impurities   the stainless steel pipe to a heating temperature for quenching equivalent to or more than the Ac 3  transformation point,   cooling the stainless steel pipe from the heating temperature for quenching to a temperature range of 100° C. or less at a cooling rate equivalent to or more than that of air cooling; and   performing a tempering treatment in which following quenching treatment, heating is performed to a tempering temperature in the range of more than 450° C. to 550° C., and cooling is then performed.   
     
     
         5 . The method according to  claim 4 , wherein the composition further contains on a mass percent basis, at least one selected from the group consisting of 2.0% or less of Cu and 2.0% or less of Mo. 
     
     
         6 . The method according to  claim 4 , wherein the composition further comprises on a mass percent basis, at least one selected from the group consisting of 0.10% or less of V, 0.10% or less of Nb, and 0.10% or less of Ti. 
     
     
         7 . The method according to  claim 4 , wherein in the cooling of the tempering treatment, a correctional treatment is performed in a temperature range of 400° C. or more. 
     
     
         8 . The martensitic stainless steel seamless pipe according to  claim 2 , wherein the composition further comprises on a mass percent basis, at least one selected from the group consisting of 0.10% or less of V, 0.10% or less of Nb, and 0.10% or less of Ti. 
     
     
         9 . The method according to  claim 5 , wherein the composition further comprises on a mass percent basis, at least one selected from the group consisting of 0.10% or less of V, 0.10% or less of Nb, and 0.10% or less of Ti. 
     
     
         10 . The method according to  claim 5 , wherein in the cooling of the tempering treatment, a correctional treatment is performed in a temperature range of 400° C. or more. 
     
     
         11 . The method according to  claim 6 , wherein in the cooling of the tempering treatment, a correctional treatment is performed in a temperature range of 400° C. or more.