Method for laser welding one or more workpieces of hardenable steel in a butt joint

Abstract

A method for laser welding of one or more workpieces made from press hardenable steel, in a butt joint, in which the workpiece or the workpieces have a thickness of at least 1.8 mm and/or a jump in thickness of at least 0.4 mm arises at the butt joint including supplying filler wire into a molten bath generated by a laser beam. In order to ensure that the weld seam can reliably harden into a martensitic structure during the hot forming (press hardening), the filler wire contains at least one alloy element from the group of manganese, chromium, molybdenum, silicon and nickel, wherein the at least one alloy element is present in the filler wire with a mass proportion that is larger by at least 0.1% by weight than the mass proportion of the element in the press hardenable steel of the workpiece or the workpieces.

The invention claimed is: 
     
       1. A method for laser welding of one or more workpieces made from press hardenable steel in a butt joint, in which the workpiece or the workpieces have a thickness of at least 1.8 mm and/or a jump in thickness of at least 0.4 mm arises at the butt joint, comprising supplying filler wire into a molten bath generated exclusively by a laser beam, wherein the filler wire contains at least one alloy element from the group consisting of manganese, chromium, molybdenum, silicon and nickel, the element promoting the formation of austenite in the molten bath generated using the laser beam, wherein the at least one alloy element is present in the filler wire with a mass proportion that is larger by at least 0.1% by weight than a mass proportion of the element in the press hardenable steel of the workpiece or the workpieces, wherein the filler wire has a carbon mass proportion that is lower by at least 0.1% by weight than the mass proportion of carbon in the press hardenable steel of the workpiece or the workpieces, and wherein the workpiece used or the workpieces used are uncoated or, by removing in the edge region along the abutting edges to be welded to one another before the laser welding, are partly de-layered. 
     
     
       2. The method according to  claim 1 , wherein the steel of the workpiece or the workpieces has the following composition:
 0.10-0.50% by weight C, 
 max. 0.40% by weight Si, 
 0.50-2.00% by weight Mn, 
 max. 0.025% by weight P, 
 max. 0.010% by weight S, 
 max. 0.60% by weight Cr, 
 max. 0.50% by weight Mo, 
 max. 0.050% by weight Ti, 
 max. 0.0008-0.0070% by weight B, and 
 min. 0.010% by weight Al, 
 remainder Fe and unavoidable impurities. 
 
     
     
       3. The method according to  claim 1 , wherein the filler wire has the following composition:
 0.05-0.15% by weight C, 
 0.5-2.0% by weight Si, 
 1.0-2.5% by weight Mn, 
 0.5-2.0% by weight Cr+Mo, and 
 1.0-4.0% by weight Ni, 
 remainder Fe and unavoidable impurities. 
 
     
     
       4. The method according to  claim 1 , herein wherein the filler wire is supplied to the molten bath in a heated state. 
     
     
       5. The method according to  claim 4 , wherein the filler wire is heated to a temperature of at least 50° C., at least in a length section, before supply into the molten bath. 
     
     
       6. The method according to  claim 1 , wherein the molten bath is loaded with protective gas during the laser welding. 
     
     
       7. The method according to  claim 6 , wherein pure argon or a mixture of argon and carbon dioxide is used as the protective gas. 
     
     
       8. The method according to  claim 1 , wherein the partly de-layered workpiece or the partly de-layered workpieces have a surface layer comprising aluminium or aluminium/silicon. 
     
     
       9. The method according to  claim 1 , wherein the press hardenable steel is a manganese-boron steel.