The Effect of Chromium on Microstructure Development During Q-P Process

Martensitic microstructures with a controlled fraction of retained austenite have the potential to reach high tensile strength above 1900-2000 MPa with ductility higher than 10 %. These microstructures can be obtained by using the Q&P process. The Q&P process with integrated incremental deformation was tested and optimized for two high-strength steels 42SiCr and 42SiMn with 0.43 % C. The 42SiCr steel contained an additional 1.3 % of Cr. A suitable austenitization temperature was determined in the first step and then quenching and partitioning temperatures and cooling rate after deformation were optimized. The results suggest that the addition of Cr has a significant influence on the mechanical properties. Tensile strength of 1367 MPa with ductility A5mm = 7 % were obtained in 42SiMn without Cr (sample geometry: 2x1.5 mm, 5 mm active length). However, the Cr content of 1.33 % in the 42SiCr steel was responsible for the increase in its strength up to 1965 MPa and for the very good ductility A5mm =21 %.