Abstract:

As a third-generation automobile steel, the enhancement of mechanical properties and formability for the medium-Mn steel is becoming a cutting-edge topic. In this research, a warm-hot stamping process for the medium-Mn steel is proposed. The methods of orthogonal experiments, range analysis and comprehensive evaluation are used to investigate the optimal process parameters. The warm-hot stamping process with austenization temperature of 810 ℃, soaking time of 7 minutes and deformation temperature of 550 ℃ are optimal. Tear tests show that the fracture morphologies are uniformly distributed and fine-grained martensite laths with the average size of 2-3 μm are observed when the optimal process parameters are applied. Moreover, an automotive B-pillar is warm-stamped to examine the new process. The excellent comprehensive performance including strength, plasticity and fracture toughness is achieved. As a result, the warm-hot forming process for the medium-Mn steel is proved to be effective and will promote the industrial application of the third-generation automobile steels.

Key words: ductility, orthogonal experiment, tear strength, warm-hot stamping, medium-Mn steel