Method of producing a painted steel shaft product of high strength

Abstract

A high-strength product of sheet steel is produced in the press hardening process. A blank is heated to reach austenite structure and hot-stamped in a pair of cooled tools. The product is kept in the tools to rapidly be cooled to harden with the tools as a fixture. The blank has a surface of black oxide before it is shaped and the shaped product is painted directly on the black surface.

1 . A method of producing a painted high strength product of sheet steel, wherein a sheet steel blank is heated to austenitic state and hot stamped and hardened in a cooled pair of tools, characterised in that a blank is used that has a black oxide layer of 1-5 μm, and the shaped and hardened product is painted on the black oxide layer. 
     
     
         2 . A method according to  claim 1 , characterised in that the blank is cut from a strip having a surface of black oxide, and the blank is heated in a furnace with inert or slightly oxidising atmosphere. 
     
     
         3 . A method according to  claim 1 , characterised in that the blank is cut from an unoxidised band and the blank is heated in a furnace with a slightly oxidising atmosphere.