Investigation of the impact of process parameters on the layer formation of AlSi coated boron-manganese steel

Abstract

Hot stamping has established itself as a technology for manufacturing safety-relevant car body components. Its usage has found increased importance due to rising political and social pressure e.g. for improved fuel conservation. Due to reduced sheet thickness, hot stamping parts offer lightweight solutions while at the same time providing improved crash performance due to their high strength. Boron-manganese steel is commonly used in hot stamping processes. Due to hot scale formation during heat treatment and the subsequent forming process, additional coatings, typically AlSi-coatings, are applied. Since hot stamped parts are formed at temperatures of 600 °C to 800 °C no suitable lubricants have yet been found. This leads to increased friction and severe wear in the process, which negatively affect tool lifetime and overall part quality. Additionally, process temperatures influence the layer formation and surface roughness due to diffusion processes. A deeper process understanding is needed to acquire detailed knowledge of the resulting impact on tribological behavior. Within this study, the effect of coating thickness on the resulting layer is analyzed by comparing the resulting material composition and surface roughness. To this end, the layer formation and surface roughness are analyzed for two different layer thicknesses (AS150 and AS80) in relation to furnace temperature, holding time and heat up rate. Both are characterized by means of heating experiments conducted on an annealing furnace. The change in layer composition and surface roughness are determined via metallographic investigation and tactile measurement. The results of this study help to improve the process understanding of the tribological conditions within the hot stamping process and to develop future measures for reducing tool wear.