Tempering Behavior of Novel Low-Alloy High-Strength Steel

The effect of tempering on the mechanical properties, structure, and dispersion of secondary phase particles is studied in 0.4%C-2%Si-1%Cr-1%Mo-VNb steel. This steel austenitized at 900 degrees C with subsequent water quenching exhibits a yield stress of 1445 MPa and a lath martensite structure with MX particles of similar to 40 nm located in matrix and boundary M6C carbides of similar to 210 nm. Tempering in the temperature interval of 200-400 degrees C provides a yield stress of 1625 MPa due to the precipitation of epsilon-carbide and cementite within laths. The yield stress decreases to 1415 and 1310 MPa after tempering at 500 and 650 degrees C, respectively, due to the replacement of matrix carbides by boundary M23C6 carbide. A Charpy V-notch impact energy of similar to 12 J/cm(2) is almost independent from tempering temperatures of up to 400 degrees C and increases up to similar to 33 J/cm(2) after tempering at 650 degrees C due to decreased yield stresses and increased plasticity.