Mechanical Behavior of Fresh and Tempered Martensite in a CrMoV-Alloyed Steel Explained by Microstructural Evolution and Strength Modeling

Abstract

AbstractThe mechanical behavior of a wear-resistant CrMoV-alloyed martensitic steel in quenched and tempered conditions has been investigated and correlated with the microstructure. The steel has a combination of ultra-high tensile strength of 2065 MPa and total elongation of 7.4 pct in the as-quenched condition. The strength and ductility of the steel change initially during tempering and thereafter remain quite stable during tempering at either 450 °C or 550 °C. A good combination of yield strength and total elongation is achieved after tempering at 550 °C for 2 to 8 hours (about 1300 MPa and 14 pct). The evolution of the mechanical properties can be mainly related to an initial condition with high density of dislocations (in the order of 1015) and carbon in solid solution, while quite early during tempering, dislocations will start to annihilate and carbide precipitates form. On the other hand, there is a negligible evolution of the effective grain size during tempering. Modeling of the individual strengthening mechanisms and the overall yield strength is in good agreement with the tensile test results, in particular for the tempered samples. Finally, the relatively low yield strength of the fresh martensite, significantly lower than for the tempered conditions, is discussed in relation to the two available theories.