Effects of composition and processing on development of grain coarsening resistance in cold forged and carburised steel

AbstractA series of high nitrogen 0·2 wt-%C steels was melted to evaluate the effects of composition and processing on the isochronal austenite grain coarsening resistance of cold forged compression specimens during simulated carburising. Steels containing aluminium or combinations of aluminium and vanadium exhibit good grain coarsening resistance in the presence of a sufficiently high content of grain refining precipitates, whereas steels containing niobium and aluminium exhibit an extremely high degree of microstructural stability as a result of the relative thermodynamic independence with which Nb(C,N) and AlN coexist in austenite. In addition to the effects of grain refining precipitates, the evolution of the ferrite—carbide microstructure and the elimination of microstructural strain before austenitisation have a significant effect on grain coarsening resistance independent of steel composition. Grain coarsening resistance in this context is beneficially affected by reheating and hot rolling at high ...