Progress of press hardening steels： strengthening and toughening, oxidation resistance and hydrogen embrittlement resistance

With the increasing demand for lightweighting and safety in the automotive industry, press hardening steels have been widely used in key structural components of automobiles due to their excellent mechanical properties and formability. However, press hardening steels still face three key challenges at present. They are the trade-off between strength and toughness, surface oxidation after forming, and the hydrogen embrittlement. These challenges restrict the further promotion and application of press hardening steels. To address these challenges, numerous researchers have delved deeply into two major technical paths in recent years, alloy composition design and process optimization. In terms of strengthening and toughening, new techniques such as press hardening-quenching and partitioning steels and medium manganese steels have achieved a product of strength and ductility exceeding 20 GPa·% by regulating the content and distribution of retained austenite, and significantly improved the toughness at the same time. Regarding oxidation resistance, in addition to conventional surface coatings, Cr-Si alloyed uncoated press hardening steels have made a breakthrough. Meanwhile, new processes such as rapid heating and pre-oxidation have also been proven to effectively alleviate surface oxidation during the forming process. Concerning hydrogen embrittlement resistance, researchers have dedicated to clarifying the interaction mechanism between hydrogen and coatings, grain boundaries, precipitates, and retained austenite, etc. By adding microalloying elements such as Nb and Ti, the microstructure is refined and hydrogen traps are induced to reduce the content of diffusible hydrogen. This paper systematically reviews the recent progress in strengthening and toughening, oxidation resistance and hydrogen embrittlement resistance of press hardening steels, focusing on alloy composition design and process optimization. With the development of artificial intelligence and the increasing demand for heavy-gauge press hardening steels, press hardening steels will continue to advance in the direction of multi-performance collaboration as well as intelligent research and development in the future.