Method for producing an ausferritic steel austempered during continuous cooling followed by annealing

摘要

Method for producing an austempered steel, characterized in that it comprises the steps of subjecting a steel alloy having a silicon content of 1.5 to 4.4 weight percent and a carbon content of 0.3 to 0.8 weight percent to continuous cooling followed by annealing, where the continuous cooling begins from a fully austenitic temperature that is achieved as a result of casting of one or more steel components, or hot forging or hot rolling of one or more semi-finished steel products. The cooling rate during said continuous cooling is initially sufficiently fast to prevent predominant formation of proeutectoid ferrite or pearlite, while subsequently at intermediate temperatures, the cooling rate is sufficiently slow to allow a transformation of the austenite to mainly ausferrite during cooling, before the austenite being enriched in carbon during growth of acicular ferrite has reached a temperature below its continuously decreasing Mtemperature, thereby limiting the amount of martensite being formed if cooled to ambient temperature or lower, and where the annealing is able to complete the transformation of carbon enriched austenite to ausferrite and to temper any martensite previously formed. The method results in the cost-efficient production of one or more continuously cooled and annealed austempered steel components or semi-finished products having mainly an ausferritic microstructure.