Speaker
Description
The manganese-boron alloy 22MnB5 is particularly used for structural and safety-relevant parts in the automotive industry. Parts made from this alloy are usually produced using the hot stamping process. In this process, the sheet is heated to over 950 °C using an industrial roller hearth furnace. The heated sheet is then simultaneously formed and quenched in a cooled tool with a temperature gradient of more than 27 K/s. This leads to the formation of a martensitic microstructure with a hardness value of over 450 HV10 and an elongation at break of less than 6%. The small strain potential of such components make them difficult to form after they are press-hardened. Due to high temperature gradients of resistance heating a sheet can get a local heat-treatment without a large temperature transition zone. This can be used to locally soften already press-hardened components for subsequent operations such as bending. Within the scope of this paper, resistance heating with direct current is used to soften a press-hardened 22MnB5+AlSi sheet stripe of 3 mm width. The sheet could consequently be bent over an angle of 90° without cracking the substrate.