Optimizing Temper Bead Welding by CWM and DOE

Abstract

Temper bead welding has been developed by the judicious positioning of weld beads and the control of heat input with the objective of reduce the peak hardness within the weld HAZ and ultimately improve the fracture toughness. This is usually done by experiment, i.e., trial and error. This paper describes a computational weld mechanics model to compute the transient temperature and transient microstructure evolution in temper bead welds. It is shown that the micro-structure in welds in low-alloy steels can be computed with useful accuracy and resolution for multi-pass welds. Furthermore by combining this analysis with a Design of Experiment (DOE) methodology, this approach has the potential to optimize the design of temper bead weld procedures. Comparison with experimental measurements are used to validate the model. Because hardness can be measured easily, quickly and economically, there is a particular focus on hardness as the most important criterion required in practice. Hardness is a function of carbon equivalent, austenite grain size and cooling rate between 800 to 600 °C. The micro structure can not be characterized by the power per unit length of weld or heat input. This is shown by running tests with different values of speed and current while the heat input is kept unchanged. On the other hand, the parameters in power are not fixed in practice and vary along the weld. This motivates a DOE perturbation analyses for two main parameters in the power; current and speed. The result shows the upper and lower bound expected for hardness due to the variations of each parameter.