Martensitic stainless steel for oil wells and method for manufacturing martensitic stainless steel pipe for oil wells

Abstract

A martensitic stainless steel for oil wells, which comprises specified quantities of C, Si, Mn, P, S, Cr, Al, Ni, Cu, Mo, Ti and N, and the balance being Fe and impurities, has not only a satisfactory SSC resistance in the coexistence of chloride ion, wet carbon dioxide and trace hydrogen sulfide but also an excellent low temperature toughness. Therefore, it can be used in an environment containing hydrogen sulfide, carbon dioxide and chloride ion in cold areas. This steel pipe stands good for a use in the above-mentioned severe environment can be easily manufactured by the present invention method.

1 . A martensitic stainless steel for oil wells, which comprises by mass percent, C: 0.16 to 0.22%, Si: 0.1 to 0.8%, Mn: 0.25 to 1.00%, P: not more than 0.025%, S: not more than 0.010%, Cr: 12.0 to 13.5%, Al: not more than 0.010%, Ni: 0 to 0.2%, Cu: 0 to 0.10%, Mo: 0 to 0.20%, Ti: 0 to 0.050% and N: 0.01 to 0.1%, with the balance being Fe and impurities.  
   
   
       2 . The martensitic stainless steel for oil wells according to  claim 1 , which further contains either one or more elements selected from Nb: 0.020 to 0.045% and V: 0.01 to 0.2% in lieu of part of Fe.  
   
   
       3 . The martensitic stainless steel for oil wells according to  claim 1 , which further contains one or more elements selected from among Ca: 0.0002 to 0.005%, Mg: 0.0002 to 0.005%, La: 0.0002 to 0.005% and Ce: 0.0002 to 0.005% in lieu of part of Fe.  
   
   
       4 . The martensitic stainless steel for oil wells according to  claim 1 , which further contains either one or both elements selected from Nb: 0.020 to 0.045% and V: 0.01 to 0.2%, and one or more elements selected from among Ca: 0.0002 to 0.005%, Mg: 0.0002 to 0.005%, La: 0.0002 to 0.005% and Ce: 0.0002 to 0.005% in lieu of part of Fe.  
   
   
       5 . A method for manufacturing a martensitic stainless steel pipe for oil wells, which comprises: 
 heating the martensitic stainless steel pipe, having the chemical composition according to  claim 1 , to a temperature range of 920 to 1050° C. followed by air cooling; and then,    performing tempering treatment at a temperature ranging from not lower than 625° C. to not higher than the Ac 1  point.    
   
   
       6 . A method for manufacturing a martensitic stainless steel pipe for oil wells, which comprises: 
 heating the martensitic stainless steel pipe, having the chemical composition according to  claim 2 , to a temperature range of 920 to 1050° C. followed by air cooling; and then,    performing tempering treatment at a temperature ranging from not lower than 625° C. to not higher than the Ac 1  point.    
   
   
       7 . A method for manufacturing a martensitic stainless steel pipe for oil wells, which comprises: 
 heating the martensitic stainless steel pipe, having the chemical composition according to  claim 3 , to a temperature range of 920 to 1050° C. followed by air cooling; and then,    performing tempering treatment at a temperature ranging from not lower than 625° C. to not higher than the Ac 1  point.    
   
   
       8 . A method for manufacturing a martensitic stainless steel pipe for oil wells, which comprises: 
 heating the martensitic stainless steel pipe, having the chemical composition according to  claim 4 , to a temperature range of 920 to 1050° C. followed by air cooling; and then,    performing tempering treatment at a temperature ranging from not lower than 625° C. to not higher than the Ac 1  point.