Post-heat treatment of Nd:YAG laser welded high carbon steels

Abstract

Rapid cooling associated with laser welding can lead to poor component fatigue life. In general, the cooling rate of the welding process determines the weld quality and is dependent on: the weld geometry, laser parameters, beam profile at the workpiece and the material’s thermal and optical properties. Cooling of the workpiece leads to a tranformation of the austenite phase to martensite. It is the presence of martensite that increases the hardness and produces brittle welds. Often, however, spatial hardness discontinuities are induced in the fusion and heat affected zones and for samples subjected to cyclic loading this can lead to cracking. In the present case, a dual-beam delivery system was used to implement a post-heating technique, simultaneously with the welding process. The weld quality for the post-heating geometry was compared to that achieved with normal welding (single-beam delivery system) for a range of system parameters. The weld quality was quantified by measuring and comparing: the weld width, penetration, hardness profiles and tensile strengths for a range of selected weld parameters, including pulse length and pulse repetition frequency. The post-heating technique was effective in controlling the cooling rate to achieve the desired weld characteristics. For example: reducing the hardness profile, improving the microstructure, producing a weld with higher tensile strength and eliminating cracking.Rapid cooling associated with laser welding can lead to poor component fatigue life. In general, the cooling rate of the welding process determines the weld quality and is dependent on: the weld geometry, laser parameters, beam profile at the workpiece and the material’s thermal and optical properties. Cooling of the workpiece leads to a tranformation of the austenite phase to martensite. It is the presence of martensite that increases the hardness and produces brittle welds. Often, however, spatial hardness discontinuities are induced in the fusion and heat affected zones and for samples subjected to cyclic loading this can lead to cracking. In the present case, a dual-beam delivery system was used to implement a post-heating technique, simultaneously with the welding process. The weld quality for the post-heating geometry was compared to that achieved with normal welding (single-beam delivery system) for a range of system parameters. The weld quality was quantified by measuring and comparing: the weld w...