Characterisation of the Thermal Damage in a Martensitic Steel Substrate Consequent to Laser Cladding Process

The paper deals with the study of the thermal damage of the substrate during the laser cladding process. The laser cladding process is known as a process which causes small thermal damage in the base material situated directly below the deposited powder. However when the laser cladding process is applied to martensitic steels, that have been previously treated in order to obtain well balanced hard and tough structures, the deposition of the heated powder as well as the interaction of the laser beam with the surface can modify the base material properties beneath the cladding layer. As a consequence uncontrolled, different and variable in hardness microstructures are produced. A 1 kW fiber laser source transmitted trough a 50 μm delivery fiber was employed to deposit a common Co-base powder over a martensitic stainless steel. Different process conditions were tested in order to reproduce different temperature fields in the base material. The temperature field in the substrate was measured making use of micro-thermocouples able to capture the fast heating and cooling thermal cycles during the deposition process. The microstructure analysis of the heat affected zones beneath the cladding layer together with the microhardness measurements allowed the thermal damage in terms of extension and intensity to be characterized and compared with the corresponding thermal cycles