Method of producing high-carbon steel pipe having superior cold workability and induction hardenability

Abstract

The invention provides a high-carbon steel pipe having superior cold workability and induction hardenability, and a method of producing the steel pipe. The method comprises the steps of heating or soaking a base steel pipe having a composition containing C: 0.3 to 0.8%, Si: not more than 2%, and Mn: not more than 3%, and then carrying out reducing rolling on the base steel pipe at least in the temperature range of (Ac 1 transformation point—50° C.) to Ac 1 transformation point with an accumulated reduction in diameter of not less than 30%. A structure in which the grain size of cementite is not greater than 1.0 μm is obtained, thus resulting in improved cold workability and induction hardenability.

What is claimed is:  
     
         1 . A high-carbon steel pipe having superior cold workability and induction hardenability, wherein said steel pipe has a composition containing, by mass %, 
 C: 0.3 to 0.8%,    Si: not more than 2%, and    Mn: not more than 3%,    the balance consisting of Fe and inevitable impurities, and said steel pipe has a structure with the grain size of cementite being not greater than 1.0 μm at any positions including a seam.    
     
     
         2 . A high-carbon steel pipe according to  claim 1 , wherein said steel pipe further contains in addition to said composition, by mass %, one or more selected from among Cr: not more than 2%, Mo: not more than 2%, W: not more than 2%, Ni: not more than 2%, Cu: not more than 2%, and B: not more than 0.01%.  
     
     
         3 . A high-carbon steel pipe according to  claim 1  or  2 , wherein said steel pipe further contains in addition to said composition, by mass %, one or more selected from.among Ti: not more than 1%, Nb: not more than 1%, and V: not more than 1%:  
     
     
         4 . A high-carbon steel pipe accordingto any one of  claims 1  to  3 , wherein an r-value is not less than 1.2 in the longitudinal direction of said steel pipe at any positions including the seam.  
     
     
         5 . A method of producing a high-carbon steel pipe having superior cold workability and induction hardenability, said method comprising the steps of: 
 preparing a base steel pipe having a composition containing, by mass %,    C: 0.3 to 0.8%,    Si: not more than 2%, and    Mn: not more than 3%; and    carrying out reducing rolling on said base steel pipe at least in the temperature range of (Ac 1  transformation point—50° C.) to Ac 1  transformation point with an accumulated reduction in diameter of not less than 30%.    
     
     
         6 . A method of producing a high-carbon steel pipe according to  claim 5 , wherein said base steel pipe is a seam welded steel pipe produced by the steps of slitting a steel strip into a predetermined width, removing droops in slit surfaces, and joining the slit surfaces to each other by electrical resistance seam welding.