Avaliação da ausência de revestimento em aços endurecidos por estampagem a quente: estudo sobre blanks soldados a laser

Abstract

Advances in the study of steels and their alloys have enabled the production of advanced, high-strength steels. Combined with the hot stamping process, these steels have led to gains in vehicle safety and weight reduction. Often, hot forming requires coating the steels to prevent oxidation and decarburization caused by high temperatures and an oxidizing environment. This study evaluates the influence of the coating layer on components produced by hot stamping using press-hardened and press-quenched steels joined by laser welding. PHS 1500 steel can reach a strength limit of 1500 MPa after forming and has a microstructure composed mainly of acicular martensite. It is often used in safety components that resist intrusion in the event of an impact. PQS 500, with a yield strength of approximately 500 MPa, is used in components requiring greater energy absorption. Combining both materials through laser welding led to the development of laser-welded blanks (LWB). Materials coated with aluminum and silicon layers were evaluated to determine their presence or absence. The study was therefore carried out on samples of a vehicle component that uses LWB technology to verify the final microstructure after hot forming through optical microscopy (OM) and to evaluate the mechanical properties through Vickers microhardness testing. The PQS 500 regions were found to have a ferritic matrix, while the PHS 1500 regions were found to have a predominantly martensitic matrix. The expected average values were observed for the properties after forming: PQS 500 was 179.22 HV, the laser-welded region was 229.44 HV, and PHS was 445 HV. Completely removing the coating from the samples demonstrated the impact of the absence of this protection, evidenced by decarburization regions and reduced hardness where carbon diffusion occurred. Decarburization of the component was confirmed by the hardness of the PHS 1500 region, where a hardness of 216 HV was measured. This indicates a reduction in mechanical strength after stamping.