EFFECT OF MOLYBDENUM ON MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF INTERCRITICALLY ANNEALED AND ISOTHERMALLY TRANSFORMED LOW-CARBON STEEL

The effects of Mo on microstructure and deformation behaviour of inter critically annealed (760-degrees-C) and isothermally transformed (400 and 450-degrees-C) steels were studied using three alloys containing f rom 0 to 0.14 wt-%Mo and 0.1 wt-%C, 1.2 wt-%Si, and 1.5 wt-% Mn. Tensi le specimens were tested at temperatures between -80 and 120-degrees-C . With the addition of Mo, hardenability increases and constant amount s (about 8 vol.-%) of austenite are retained in the microstructure ind ependent of heat treatment conditions. A range of mechanical propertie s, 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 0.1 4 wt-%Mo and Mo free steels, respectively, were obtained when signific ant amounts of retained austenite transform by strain induced mechanis ms at high strains, increasing strain hardening and deferring necking to higher strains.