Effects of Alloying Element on Strength and Toughness of Microalloyed Steels

Microalloyed steels have been widely used as substitutes for hardened and tempered carbon steels since they can remarkably reduce production costs of machined parts by saving heat treatment, logistics cost and lead time of production process. Recently, this trend of microalloyed steels is extending to the field of alloy steels. It is most important to minimize toughness drop over 1000MPa range of tensile strength for achieving high strength comparable to alloy steels[1]*. High strength microalloyed steel has not been used for machine parts due to the lack of toughness.

The purpose of this study, for future practical use, is to clarify the strength-toughness balance of high strength microalloyed steel and to compare them with conventional carbon and alloy steels. The relationship between strength-toughness and wide variety of alloying element for microalloyed steel was investigated. These factors have a consistent relationship when they have discussed among the same carbon content level. We also found that hardness and microstructure were mostly consistent in various forging conditions in microalloyed steel. Taking these advantages, this high strength microalloyed steel is expected to be applied to automobile parts.