INVESTIGATING THE EFFECTS OF LASER STELLITE PAD WELDING ON THE SERVICE PROPERTIES OF VALVE STEELS

In the work the results of tests on 50H21G9N4 and H9S2 valve steels with pad welded stellite layers are presented. Basic properties such as tribological and erosion resistance as well as high temperature oxidation resistance were determined. Testing conditions were accepted with certain simplification owing to the complexity of mechanical and thermal load exhaust valves and, therefore, they do not reflect real operating conditions accurately. Specimens with and without laser, plasma and TIG pad welded stellite layers were subject to tests. The conducted tests showed the highest tribological resistance of stellite layers under the conditions of dry friction in comparison with the material in the initial state as well as plasma and TIG pad welded stellite layers. The main mechanism of the abrasive wear of the surface layer is an adhesive wear by breaking the connections and adhesions that are being formed. The research on wear by abrasive erosion showed a smaller decrease in the mass of specimens with pad welded stellite layers in comparison with plasma and TIG pad welded stellite layers as well as the material in the initial form without the pad welded stellite layer. The resistance of stellite layers to high temperature oxidation was showed in the research on heat resistance. Moreover, it was found that pad welding does not have any significant influence on the heat resistance of stellite layers