BIW Lightweight Potential Applying Uncoated UHS Hot Forming Steel with Increased Tensile Strength

Weight reduction and safety are key factors on the automotive market. Lightweight materials have been widely discussed as an alternative to reduce CO2 emissions levels and fuel efficiency. Press-hardened steels (PHS), such as 22MnB5 steel, are known to combine high ultimate strength resistance and low thickness. To improve this correlation, new generations of ultra-high strength (UHS) hot forming steel grades are under development. Once the mechanical properties improve after the hot forming process it is possible to decrease the thickness keeping the same performance. An example is the 37MnB5 steel which has some adjustments in terms of chemical composition, increasing its hardenability and providing a more refined quenched martensite. A simulation study of weight reduction for a body in white (BIW) application will be presented considering a 37MnB5 steel grade. Additionally, some preliminar results of this steel are discussed. The heat treatment, performed in laboratorial scale, results in as expected phase transformation, being the microstructure composed by a martensitic matrix. The studied grade shows high potential as lightweight solution once it offers ultimate strength values up to 1900 MPa, allowing studies of thickness optimization, keeping the ductility of the first-generation of PHS steels. Depending on the application the weight reduction could reach approximately 10 to 15 percent, compared to parts produced using 22MnB5.