HSS deposition by PTA – feasibility and properties

High speed steels (HSS) as iron alloys reinforced by carbides of tungsten, chromium, vanadium and/or cobalt are known for more than 100 years. HSS is commonly used for cutting tools fabrication because of their high hardness, ductility, and strength and temperature resistance. Recently many different kinds of thin layers are often deposited on HSS tools in order to increase their lifetime. HSS are produced by conventional metallurgical methods and the tools are hardened by quenching and tempering. Recently, large part of HSS tools are produced by powder metallurgy (i.e. HIP-hot isostatic pressing). There are also some studies about thermal spraying of HSS but there is no evidence about Plasma Transfer Arc cladding of HSS. Two powders of HSS 23, resp. HSS30 grade were selected and deposited by Plasma Transfer Arc (PTA) and pulsed PTA on to mild steel substrate. In order to find the ability of thick layer forming, four layers cladding were used. To minimize heat input the influence of 76 Hz pulsation was also studied. Vickers hardness was measured on cross section and metallography of coatings was done. It was found that with selected parameters thick layer of HSS can be deposited. Pulsation increases the hardness of coatings in comparison with layers produced by direct current PTA. PTA and pulsed PTA methods of HSS parts fabrication can be used for both manufacturing and reparation of cutting tools and also for 3D additive manufacturing process.