Production of shaped semi-products from AHS steels by internal pressure

The constant evolution of industry brings demands for components of ever-higher quality, complex shapes and excellent mechanical properties, with reduced operating costs and with improved reliability in service. Such demands can be met by processing high-strength, low-alloyed steels using novel heat-treatment methods. One of such methods is the quenching and partitioning (Q&P) process, which can lead to high strengths of about 2000 MPa at elongation levels of more than 10 %. The Q&P process can be combined with unconventional procedures for making complex-shaped parts to manufacture components with excellent mechanical properties and an intricate shape. This paper describes the sequence of internal high-pressure forming, hot stamping and the Q&P process used for making a functional product with good mechanical properties and a complex shape. The purpose of the experimental programme was to employ a production chain for processing hollow, thin-walled stock. Using a step-by-step optimization, commercially usable products were obtained. The microstructure of the products consisted primarily of martensite and a small fraction of bainite. Such a microstructure guarantees a high ultimate strength. The strength level throughout the part was not less than 1950 MPa, combined with an excellent elongation of approximately 15 %.