Method for Producing High-Alloy Seamless Steel Pipe

Abstract

Pipe-swelling can be prevented by piercing-rolling a high-alloy steel billet heated to a temperature range from 900 to 1250° C. with a piercing mill equipped with main rolls having a surface roughness R max of 150 to 500 μm. A ratio (the gap W G of guide rolls/the gap W R of the main rolls) is preferably at 1.10 to 1.20. The difference (θ P −θ R ) is preferably set at 0 to 3.0°, where θ R is an angle between an exit-side face of each of the main rolls of the piercing mill and the pass line; and θ P is an angle between a rolling face of the piercing plug and the pass line.

1 . A method for producing a high-alloy seamless steel pipe, including steps of:
 billet-heating process;   piercing-rolling process, wherein surface roughness R max  of main rolls used in the piercing-rolling process is set at 150 to 500 μm; and   elongation-rolling process.   
     
     
         2 . The method for producing a high-alloy seamless steel pipe according to  claim 1 ,
 wherein a ratio W G /W R ) is set at 1.10 to 1.20 in the piercing-rolling process, where:
 W R  is the gap of the main rolls of the piercing mill and 
 W G  is the gap of the guide rolls of the piercing mill. 
   
     
     
         3 . The method for producing a high-alloy seamless steel pipe according to  claim 1  or  2 ,
 wherein surface temperature of a workpiece during the piercing-rolling process is set at 900 to 1250° C. 
 
     
     
         4 . The method for producing a high-alloy seamless steel pipe according to  claim 1 ,
 wherein a difference (θ P −θ R ) is set at 0 to 3.0°,   where:
 θ R  is an angle between an exit-side ace of each of the main rolls of the piercing mill and the pass line and 
 θ P  is an angle between a rolling face of the piercing plug and the pass line. 
   
     
     
         5 . The method for producing a high-alloy seamless steel pipe according to  claim 3 ,
 wherein a difference (θ P −θ R ) is set at 0 to 3.0°,   where:   θ R  is an angle between an exit-side face of each of the main rolls of the piercing mill and the pass line and
 θ P  is an angle between a rolling face of the piercing plug and the pass line. 
   
     
     
         6 . The method for producing a high-alloy seamless steel pipe to  claim 1 ,
 wherein the main rolls that have been used for piercing a seamless steel pipes of ordinary steel are used.   
     
     
         7 . The method for producing a high-alloy seamless steel pipe according to  claim 3 ,
 wherein the main rolls that have been used for piercing a seamless steel pipes of ordinary steel are used.   
     
     
         8 . The method for producing a high-alloy seamless steel pipe according to  claim 4 .
 wherein the main rolls that have been used for piercing a seamless steel pipes of ordinary steel are used.   
     
     
         9 . The method for producing a high-alloy seamless steel pipe according to  claim 5 ,
 wherein the main rolls that have been used for piercing a seamless steel pipes of ordinary steel are used.   
     
     
         10 . The method for producing a high-alloy seamless steel pipe according to  claim 6 ,
 wherein the flow rate of the roll-cooling water at the time of piercing the seamless steel pipes of ordinary steel is set at 1000 to 1500 l/min.   
     
     
         11 . The method for producing a high-alloy seamless steel pipe according to  claim 7 ,
 wherein the flow rate of the roll-cooling water at the time of piercing the seamless steel pipes of ordinary steel is set at 1000 to 1500 l/min.   
     
     
         12 . The method for producing a high-alloy seamless steel pipe according to  claim 8 ,
 wherein the flow rate of the roll-cooling water at the time of piercing the seamless steel pipes of ordinary steel is set at 1000 to 1500 l/min.   
     
     
         13 . The method for producing a high-alloy seamless steel pipe according to  claim 9 ,
 wherein the flow rate of the roll-cooling water at the time of piercing the seamless steel pipes of ordinary steel is set at 1000 to 1500 l/min.