Analysis of the rapid tempering treatment on a high-strength boron steel in the martensitic state through physical simulation

In recent years, high-strength boron steels have become increasingly important in the automotive industry, particularly for structural components such as the B-pillar. These steels, when in a martensitic state, provide excellent safety performance while enabling the use of thinner sheets, which contributes to reducing the overall weight of vehicles. However, the inherent brittleness of martensite poses difficulties during the mechanical assembly process with other car body parts. One potential solution to enhance ductility is the application of rapid tempering, which is also valued for its lower energy consumption when compared to conventional tempering treatments. This study focuses on analyzing the softening behavior and associated microstructural evolution of martensitic 37MnB4 steel when subjected to rapid tempering cycles. Three distinct heating rates (10K/s, 100K/s, and 250K/s) and two holding times (0 s and 8 s) were considered. The findings indicate that rapid tempering leads to notable softening of the steel, with the highest degree of softening observed at tempering temperatures close to, specifically a few dozen degrees higher than, the eutectoid point at equilibrium, depending on both the heating rate and the holding time applied.