Effect of molybdenum on microstructure and mechanical properties of intercritically annealed and isothermally transformed low carbon steel

Abstract

The effects of Mo on microstructure and deformation behaviour of intercritically annealed (760°C) and isothermally transformed (400 and 450°C) steels were studied using three alloys containing from 0 to 0·14 wt-%Mo and 0·1 wt-%C, 1·2 wt-%Si, and 1·5 wt-%Mn. Tensile specimens were tested at temperatures between −80 and 120°C. With the addition of Mo, hardenability increases and constant amounts (about 8 vol.-%) of austenite are retained in the microstructure independent of heat treatment conditions. A range of mechanical properties, which depended on alloying, microstructure, and testing temperature, was achieved. The optimum combinations of ultimate tensile strength and elongation, 700 MN m⁻² and 34% and 620 MN m⁻² and 39%, for the 0·14 wt-%Mo and Mo free steels, respectively, were obtained when significant amounts of retained austenite transform by strain induced mechanisms at high strains, increasing strain hardening and deferring necking to higher strains.

MST/1508