Calculation of hardness distribution in the HAZ of micro-alloyed steel

This study describes a method for the determination of hardness based on Vickers micro-hardness of the phase constituents in the heat-affected zone (HAZ) of single-layered metal active gas (MAG) and electron beam (EB)-welded components. The finite element (FE) simulation was performed incorporating of austenite grain size (AGS)-dependent gamma-alpha decomposition during cooling from an austenitizing temperature in the HAZ. In this simulation, a 2D symmetric thermo-metallurgical model was conducted using SYSWELD software version 2013. Two welding continuous cooling transformation (CCT) diagrams were incorporated which were experimentally determined for 1000 and 1300 degrees C peak temperatures using dilatometry. The implementation of CCT diagrams was performed as the function of the calculated austenite grain sizes (AGS). It was found that the phase constituents themselves had the most significant contribution to the hardness. An increase in hardness was predicted in the electron-beam-welded HAZ, whereas the MAG welding showed a reduction in hardness. The amount of reduction was depending on heat input during welding. The prediction of the hardness distribution in the HAZ was found in good accordance with experimental results.