Medium-carbon, microalloyed forging steels represent a cost effective replacement of quenched and tempered grades. Their strength properties are derived from precipitation during cooling from the forging temperature. Because of the relatively high carbon content, vanadium is the most suitable addition to achieve precipitation strengthening. The effectiveness of vanadium is enhanced by the presence of nitrogen. For components subjected to impact loading, improvement in toughness is achieved by refining austenitic grains, pinning their boundaries by means of dispersed titanium nitrides.
Precipitation strengthened ferrite-pearlite steels exhibit superior machinability compared to that of quenched and tempered alloy steels. As a result, the total machining costs are substantially reduced compared to the costs of machining heat-treated steels. The frequency of tool breakage and tool changes decrease dramatically, virtually eliminating line scrap and unnecessary downtime. Improved machinability features greatly increase the economic advantages of microalloyed steels.
The incorporation of microalloyed forging steels into industrial production requires close cooperation between the steel mill, forge shop, machine shop and component designer. Experience gained in the past decades provides a solid foundation for the safe application of microalloyed forging steels in a variety of critical automotive components. The resulting cost reduction provides the driving force for a rapid adoption of this relatively new class of steels.