Process for Manufacturing Cold-Formed Precision Steel Pipes

Abstract

The invention relates to a process for manufacturing cold-formed, in particular cold-drawn, precision steel pipes for application in particular as pressure-operated cylinder pipes with optimum addition of one or several alloying elements as well as impurities caused by melting. A seamless, hot-formed pipe blank or welded pipe blank made from a hot strip with defined starting condition is hereby drawn in one pass or in several passes into a finished pipe, and the pipe undergoes a heat treatment before the finishing pass.

1 - 10 . (canceled) 
   
   
       11 . A process for manufacturing a precision steel pipe having the following chemical composition (in weight-%): 
     
       
         
               
               
               
             
                   
                   
               
                   
                 C = 
                 0.05-0.25 
               
                   
                 Si = 
                 0.15-1.0  
               
                   
                 Mn = 
                 1.0-3.5 
               
                   
                 Al = 
                 0.020-0.060 
               
                   
                 V 
                 max. 0.20   
               
                   
                 N 
                 max 0.150 
               
                   
                 S 
                 max 0.030 
               
                   
                   
               
           
              
             
             
              
              
              
              
              
              
              
              
             
          
         
       
     
     and impurities caused by melting, said process comprising the steps of:
 drawing a pipe blank with defined starting condition in at least one pass; 
 subjecting the pipe blank to a heat treatment; and 
 subjecting the pipe blank to a finishing drawing step to produce a finished pipe. 
 
   
   
       12 . The process of  claim 11 , wherein the pipe blank is a seamless, hot-formed pipe blank. 
   
   
       13 . The process of  claim 11 , wherein the pipe blank is welded pipe blank made from a hot strip. 
   
   
       14 . The process of  claim 11 , further comprising the step of adding at least one alloying element selected from the group consisting of Cr, Mo, Ni, W, Ti, and Nb. 
   
   
       15 . The process of  claim 11 , further comprising the step of adding alloying elements in a following composition (in weight-%): 
     
       
         
               
               
               
             
                   
                   
               
                   
                 Cr 
                 max. 0.80 
               
                   
                 Mo 
                 max. 0.65 
               
                   
                 Ni 
                 max. 0.90 
               
                   
                 W 
                 max. 0.90 
               
                   
                 Ti 
                 max. 0.20 
               
                   
                 Nb 
                 max. 0.20 
               
                   
                   
               
           
              
             
             
              
              
              
              
              
              
              
             
          
         
       
     
   
   
       16 . The process of  claim 11 , wherein the heat treatment comprises the step of heating the pipe blank to a temperature of in a range of 910-940° C., cooling the pipe blank, and exposing the pipe blank to a tempering treatment. 
   
   
       17 . The process of  claim 16 , wherein the cooling step comprises accelerated cooling. 
   
   
       18 . The process of  claim 17 , wherein the accelerated cooling step comprises quenching. 
   
   
       19 . The process of  claim 11 , wherein the quenching step is implemented by means of a water shower. 
   
   
       20 . The process of  claim 16 , wherein the cooling step comprises exposure to static air. 
   
   
       21 . The process of  claim 16 , wherein the tempering treatment is carried out at a temperature range of 540 to 720° C. 
   
   
       22 . The process of  claim 11 , further comprising the step of subjecting the finished pipe to a final annealing. 
   
   
       23 . The process of  claim 22 , wherein the final annealing step is carried out at a temperature range of 500 to 700° C.