5th International High Manganese Steel Conference - HMNS 2022

In the last decade, the academic community extensively researched medium-Mn steels. This steel class has proved their position as one of the possible successor to classic AHSS due to excellent mechanical properties paired with still reasonable alloying costs. Nevertheless, several technical issues have to be resolved in order to enable a successful application of medium-Mn steels in a vehicle, which is the main target of this contribution. In this context, all presented results were acquired by a large-scale produced material, fulfilling the requirements for a batch-annealed medium-Mn steel with the strength level of 780 MPa, manufactured at the voestalpine steel plant in Linz, Austria.
The first presented topic is that of the often-observed presence of extensive yield point elongation (YPE). This work clearly shows that YPE can be avoided by a two-step heat treatment, altering the microstructural features such as morphology, effective grain size and texture by a simultaneous improvement of mechanical properties.
Concerning the robustness of the manufacturing process, the issue of the sensitivity of mechanical properties to the intercritical annealing temperature was referred to as a concern towards industrial scale production. Based on the large-scaled material, this work can emphasize that by a precise temperature control during a batch annealing cycle stable mechanical properties throughout an entire coil can be achieved since the sensitivity to annealing time is low.
The third addressed topic is the necessary suitability of the material for resistance spot welding process. In our first investigations, the material revealed rather low cross tension strength (CTS) after welding with standard parameters. Therefore, the chemical composition was adjusted and a double-pulse regime was established to vastly increase CTS.
Considering all the above-mentioned aspects, this contribution represents a compilation of critical points and possible solutions towards the large-scale implementation and subsequent use of the present material by the automotive industry.