Characterisation of quasi-stationary temperature fields in laser welding by infrared thermography

摘要

In this work, high-speed thermography is shown to effectively capture quasi-stationary temperature fields during the laser welding of steel plates. This capability is demonstrated for two cases, with one involving the addition of a ferritic-bainitic filler wire, and the other involving the addition of a low-transformation-temperature (LTT) filler wire. The same welding parameters are used in each case, but the temperature fields differ, with the spacing between isotherms being greater in the case where the low-transformation-temperature filler material is added. This observation is consistent with the differences in the extent of the heat-affected zone in each sample, and the shape of the weld pool ripples on the weld bead surfaces. The characterization of temperature fields in this way can greatly assist in the development of novel methods for reducing residual stresses, such as the application of low-transformation-temperature filler materials through partial-metallurgical injection (PMI). This technique reduces or eliminates tensile residual stresses by controlling the temperature fields so that phase transformations take place at the optimum times, and success can only be guaranteed through precise knowledge of the temperature fields in the vicinity of the welding heat source in real time.