Temperature Control During the Process Combination Welding and Rolling for Enabling Full Recrystallization with Homogenized Grain Size Distribution

Welding with an electric arc is mainly used as a joining technology, where a high energy input is required locally for the joining process. Due to the heat input, the welded bead is characterized by a heat affected zone, that consists of an inhomogeneous microstructure of different phases and grain sizes. This leads to non-optimal mechanical properties. One way to improve the microstructure is to induce plastic deformation (e.g. by rolling), which can enable recrystallization mechanisms, that homogenize the microstructure and therefore can optimize the material properties. Yet, the recrystallization mechanisms require a minimum temperature to be activated. On one hand, the in-situ heat input during welding can be used for this in a process combination of welding and rolling but might not be enough, to reach or hold this recrystallization temperature during rolling. An excessive heat input on the other hand leads to too high temperatures, causing significant grain growth, that also negatively affect the mechanical properties. In any case, a certain temperature range over time has to be maintained. The temperature can be controlled by burners for pre-heating and post-heating, and the heating power can be controlled separately. In this numerical study, burner heat models are used to simulate the temperature-controlled process combination of welding one single bead with a subsequent rolling step for the mild steel St37/S235JR. The influence of the pre- and post-heating could be numerically proven and suitable heating combinations were found, that allow a full recrystallization with a nearly homogenous grain size distribution.