Dual seam-welded air hardenable steel tubing and structural members

Abstract

The present invention provides seam-welded, air hardenable steel tubes, methods of manufacturing seam-welded air hardenable steel tubes, tube mills for practicing such methods and applications for using seam-welded, air hardenable steel tubing of the present invention.

1 . A steel tube comprising air hardenable steel and dual longitudinal welded seams  
   
   
       2 . The steel tube of  claim 1 , wherein the air hardenable steel is stainless.  
   
   
       3 . The steel tube of  claim 2 , wherein the air hardenable stainless steel is a martensitic stainless steel.  
   
   
       4 . The steel tube of  claim 3 , wherein the martensitic stainless steel is a 400 series stainless steel.  
   
   
       5 . The steel tube of  claim 4 , wherein the 400 series stainless steel is 410.  
   
   
       6 . The steel tube of  claim 1  further comprising transverse members.  
   
   
       7 . The steel tube of  claim 6 , wherein the transverse members are tubes.  
   
   
       8 . A method of producing an air hardenable steel tube, the method comprising: 
 selecting a strip stock of air hardenable steel;    forming two workpieces each with two weld edges that would produce a tube form if the weld edges were adjacent;    welding said adjacent edges to form two seams;    and controlling the cooling rate of the welded seams.    
   
   
       9 . The method of  claim 8 , wherein the air hardenable steel strip stock is stainless steel.  
   
   
       10 . The method of  claim 9 , wherein the stainless steel is a martensitic stainless steel.  
   
   
       11 . The method of  claim 9 , wherein the stainless steel is a 400 series stainless steel.  
   
   
       12 . The method of  claim 9 , wherein the stainless steel is 410.  
   
   
       13 . The method of  claim 9 , wherein the air hardenable steel strip stock is in an annealed state prior to being formed into a workpiece.  
   
   
       14 . The method of  claim 9  further comprising heat-treating the seam-welded air hardenable steel tube to a high strength condition.  
   
   
       15 . The steel tube of  claim 1  further comprising at least one seam-welded air hardenable steel tube to form a structure, wherein the entire structure is subjected to heat treating after assembly to induce a high strength condition in the air hardenable parts of the structure.  
   
   
       16 . The structure of  claim 15 , wherein said at least one seam-welded steel tube is of a stainless steel.  
   
   
       17 . The structure of  claim 15 , wherein said at least one seam-welded stainless steel tube is of a martensitic stainless steel.  
   
   
       18 . The structure of  claim 17 , wherein the martensitic stainless steel is of the 400 series stainless steels.  
   
   
       19 . The structure of  claim 18 , wherein the 400 series stainless steel is 410.  
   
   
       20 . The structure of  claim 15 , wherein the structure is load bearing member of a a motor vehicle.