Thick tool steel coatings with laser cladding

This paper concentrates on thick and crack-free laser clad coatings (up to 3 mm). The coating material is a chromium-molybdenum-tungsten-vanadium alloyed high-speed steel that shows high wear resistance, high compressive strength, good toughness, very good dimensional stability on heat treatment and very good temper resistance. It will be demonstrated that laser cladding of MicroMelt 23 powder offers a relatively wide processing window resulting in the formation of thick, microstructurally uniform, hard, crack- and defect- free coating on ordinary steel substrates. Microstructural observations using light and field emission gun scanning electron microscopy with EDS and EBSD attachments together with internal strain measurements using diffraction of X-rays revealed the reason for low susceptibility to crack formation. An intensive martensitic transformation inside small austenitic cells surrounded by hard carbides following the rapid solidification process compensates the tensile strain and finally results in cornpressive stresses at the coating surface. Laser cladding on different steels substrate geometries will be demonstrated together with hardness profiles and their dependence on cladding conditions.