Strengthening mechanism and precipitate evolution of a multi-application special engineering steel designed based on a hybrid idea

Abstract

Special engineering steel that combined the attractive properties of composite maraging steel, tool steel, structural steel, and stainless steel was designed as a hybrid steel (0.20 C-10.9 alloy elements wt%) based on a hybrid idea. The hybrid steel underwent solid solution treatment at 1020 °C, followed by different aging treatments. The best combination of properties and heat treatments was determined by analyzing the evolution of precipitates and mechanical properties. The strengthening mechanism was quantitatively elucidated. The results showed that the size of martensite slats and the diameter and number of precipitates increased upon increasing the aging temperature and time. The higher proportion of large-angle grain boundaries toughened the hybrid steel. The precipitate evolution occurred from a single Cr2VC2 to the gradual appearance of intermetallic phases such as CrNbN, MoNbN, and Cr2Nb. Dislocation strengthening and precipitation strengthening were the main strengthening mechanisms, which accounted for 80–92% of the yield strength. The contributions of dislocation strengthening and precipitation strengthening to the yield strength could be adjusted by changing the microstructure by using different aging treatments. The strength and plasticity were optimally matched. The mechanical properties of the hybrid steel aged at 540 °C for 8 h were the best due to the combined effect of multiple strengthening mechanisms. The ultimate tensile strength reached a peak of 2009 ± 30 MPa with an elongation of 9.5 ± 0.8%. This hybrid idea may be applied to any other steels and provides a pathway for the development of special steel.