Microstructural development in the heat-affected zone of a laser-cladded steel

The surface of a medium carbon steel sheet was laser cladded with a Co-Cr alloy in two layers by a multi-pass technique. This study is concerned with the heat-affected zone (HAZ) created. Within this zone, austenitisation and martensite formation take place repeatedly twice or three times followed by later tempering. This change in microstructure is associated with a hardening and a softening. The microstructure consists of tempered martensite close to the heat source, an intermediate zone of tempered martensite/bainite and a partially transformed zone. However, the hardness is constant throughout the HAZ and decreases in the partially transformed zone to the substrate hardness. The analysis of the microstructure and the hardness are used to re-establish the temperature history encountered by the material in the HAZ. It could be shown that the HAZ has a translational symmetry that can be approximated by a 2-D sheet structure. © 2005 Carl Hanser Verlag, München.