Tempering Behavior of Novel Low-Alloy High-Strength Steel

Abstract

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 °C with subsequent water quenching exhibits a yield stress of 1445 MPa and a lath martensite structure with MX particles of ~40 nm located in matrix and boundary M6C carbides of ~210 nm. Tempering in the temperature interval of 200–400 °C provides a yield stress of 1625 MPa due to the precipitation of ε-carbide and cementite within laths. The yield stress decreases to 1415 and 1310 MPa after tempering at 500 and 650 °C, respectively, due to the replacement of matrix carbides by boundary M23C6 carbide. A Charpy V-notch impact energy of ~12 J/cm2 is almost independent from tempering temperatures of up to 400 °C and increases up to ~33 J/cm2 after tempering at 650 °C due to decreased yield stresses and increased plasticity.

Effect of Tempforming on Strength and Toughness of Medium-Carbon Low-Alloy Steel

“…The microstructure after quenching and tempering at 600 °C was described in a previous paper [ 11 ] in detail. The tempered martensite lath structure (TMLS) with a size of prior austenite grains of ~12 μm, a distance between high-angle boundaries (HABs) of 0.84 μm, a lattice dislocation density of ~6 × 10 14 m −2 , and a lath thickness of ~200 nm evolved after tempering at 600° [ 11 ]. Tempering at T > 500 °C produces M 6 C and M 23 C 6 carbides located on HABs and low-angle boundaries (LABs) and a dispersion of MX carbonitrides located in a ferritic matrix [ 11 ].…”

“…The tempered martensite lath structure (TMLS) with a size of prior austenite grains of ~12 μm, a distance between high-angle boundaries (HABs) of 0.84 μm, a lattice dislocation density of ~6 × 10 14 m −2 , and a lath thickness of ~200 nm evolved after tempering at 600° [ 11 ]. Tempering at T > 500 °C produces M 6 C and M 23 C 6 carbides located on HABs and low-angle boundaries (LABs) and a dispersion of MX carbonitrides located in a ferritic matrix [ 11 ]. M 6 C, M 23 C 6 , and MX particles exhibit a round shape and dimensions of ~210, ~50, and ~45 nm, respectively [ 11 ].…”

“…Tempering at T > 500 °C produces M 6 C and M 23 C 6 carbides located on HABs and low-angle boundaries (LABs) and a dispersion of MX carbonitrides located in a ferritic matrix [ 11 ]. M 6 C, M 23 C 6 , and MX particles exhibit a round shape and dimensions of ~210, ~50, and ~45 nm, respectively [ 11 ].…”

“…The lattice dislocation density increases by 40% in comparison with quenched and tempered steel [ 11 ] ( Table 4 ). Spacing between LABs, which roughly corresponds to transverse lath size, decreases by a factor of ~2 compared with the thickness of the initial laths in quenched and tempered steel [ 11 ] ( Table 4 , Figure 3 ).…”

“…The lattice dislocation density increases by 40% in comparison with quenched and tempered steel [ 11 ] ( Table 4 ). Spacing between LABs, which roughly corresponds to transverse lath size, decreases by a factor of ~2 compared with the thickness of the initial laths in quenched and tempered steel [ 11 ] ( Table 4 , Figure 3 ). At tempforming temperatures of 600 and 650 °C, the spacing between HABs decreases by a factor of more than 2 and 1.3, respectively.…”