Process for the production of a composite metal part and products thus obtained

A process for producing a composite cold rolling roll or roller by coating or hard-surfacing a metal core of low-alloy structural steel with a harder metal layer composed of a high-speed steel containing chromium in a concentration from about 2% to about 14%, and at least one metal selected from the group consisting of tungsten in a concentration from about 10% to about 20%, molybdenum in a concentration from about 3% to about 12%, and cobalt in a concentration from about 2.5% to about 16%, wherein this high-speed steel is so selected as to exhibit a hardness higher than 57 Rockwell C and contains the following elements in a concentration range as follows:

• C=0.5% to 2.6%
• Mn=0.2% to 1.7%
• Si=0.2% to 1.4%
• S=at most 0.2%
• V=at most 10%
• with Mo%+W%+V%+Co% at least equal to 3, wherein the low-alloy structural steel forming the metal core is so selected as to ensure a non-fragile connection to the high-speed steel and to be compatible with the utilisation stresses of the part, and has a composition within the range defined below:
• ______________________________________ C = 0.2% to 1% Ni = 0% to 2.5% Mn = 0.2% to 1.5% Cr = 0.5% to 6% Si = 0.2% to 1% Mo = 0% to 2% S = 0.005% to 0.200% V = 0% to 0.5%, ______________________________________
• wherein the said high-speed steel is added solely in the form of a prealloyed powder, and the coating of hard-surfacing of the core with this powder is effected by welding the high-speed steel to the metal core by means of one of the welding processes of the following group:
• welding by means of a transferred or semi-transferred arc plasma torch, or welding by means of a laser torch, the operation of coating or hard-surfacing by welding being followed by tempering heat treatment, or by hardening and tempering heat treatment adapted to the nature of the powder used.