Investigation of 22MnB5 formability in hot stamping operations

In the automotive industry, the hot forming of high strength steels offers the possibility to obtain significant reduction of weight without affecting the structural performances of final products. The main reason of its restricted application in the industry lies however in the lack of basic knowledge about mechanical and microstructural characteristics of sheets at elevated temperature, boundary conditions (i.e. friction and heat transfer), sensitivity of the formed component geometrical and mechanical characteristics to all the process parameters. To partially overcome this limitation, this paper presents a novel test based on the Nakazima concept which is able to evaluate the material formability at elevated temperature. Thermal tests with the aid of a dilatometer device were utilised to generate phase transformation data while uni-axial tensile tests, performed simultaneously with quenching, provided flow stress data at different temperatures and strain rates. The effective thermal cycle to apply during the formability test was optimized through numerical simulations of the test itself suitably calibrated through the above data.