Fastening element made of carbon-containing steel and method for the production thereof

Abstract

A fixing element which comprises carbon-bearing steel and has a hardened functional tip is overall heated to the austenitisation temperature, held at that temperature and then quenched and is then subjected to an annealing operation which is effected by inductive heating and limited to the region of the fixing element, which lies outside the functional tip. In that way the structure of the fixing element comprises in part martensite and in part annealed martensite, wherein the functional tip comprises throughout martensite and the remainder of the fixing element comprises a martensite which is annealed by short-term inductive heating.

1 . A process for the production of a fixing element which has a hardened functional tip and comprises a carbon-bearing steel which after heating to austenitisation temperature and subsequent quenching forms martensite, wherein the fixing element is heated overall to the austenitisation temperature, held at that temperature and then quenched and is then subjected to an annealing operation, characterised in that the annealing operation is effected by inductive heating to a temperature above annealing brittleness and is restricted to the region of the fixing element, which lies outside the functional tip.  
     
     
         2 . A process according to  claim 1  characterised in that a low-alloyed carbon steel is used as the carbon-bearing steel.  
     
     
         3 . A process according to  claim 1  characterised in that a high-alloyed carbon steel is used as the carbon-bearing steel.  
     
     
         4 . A process according to  claim 2  characterised in that at least the functional tip is recarburised or carbonitrided during the operation of heating to the austenitisation temperature.  
     
     
         5 . A process according to one of  claims 1  to  4  characterised in that the inductive heating operation is effected in a continuous mode through a line inductor.  
     
     
         6 . A process according to one of  claims 1  to  5  characterised in that the functional tip is cooled during inductive heating of the rest of the fixing element.  
     
     
         7 . A process according to one of  claims 1  to  6  characterised in that the fixing element is a screw and the functional tip is a screwthread-forming and possibly hole-forming shaping zone.  
     
     
         8 . A process according to one of  claims 1  to  6  characterised in that the fixing element is a firing nail or setting bolt.  
     
     
         9 . A process according to one of  claims 1  to  6  characterised in that the fixing element is a rivet, in particular a stamping rivet.  
     
     
         10 . A fixing element which comprises a carbon-bearing steel and has a hardened functional tip and whose structure comprises in part martensite and in part annealed martensite, characterised in that the functional tip comprises martensite throughout and the remainder of the fixing element comprises a martensite annealed by short-term inductive heating to a temperature above annealing brittleness.  
     
     
         11 . A fixing element according to  claim 8  characterised in that the edge region at least of the functional tip is case-hardened as a result of recarburisation or carbonitriding.  
     
     
         12 . A fixing element according to  claim 8  or  claim 9  characterised in that it is a screw and the functional tip is a screwthread-forming and possibly hole-forming shaping zone.  
     
     
         13 . A fixing element according to  claim 8  or  claim 9  characterised in that it is a firing nail or setting bolt.  
     
     
         14 . A fixing element according to  claim 8  or  claim 9  characterised in that it is a rivet, in particular a stamping rivet.