Precipitation in the austenite of microalloyed low carbon steel

A. K. Ibraheem

Abstract The morphology and chemical compositions of Ti–rich cube and lath, Nb–rich, Al–rich and sulphide particles, were investigated on reheating Nb–Ti microalloyed, low carbon steels. A commercial steel containing 0.065% C, 0.037% Al, 0.026% Nb, 0.014% Ti and 0.005% N, and as–cast steel containing 0.096% C, 0.027% Nb, 0.007% Ti and 0.0035% N, were reheated between 850 and 1400C, and either quenched or cooled slowly. The precipitation in a few HDR specimens was also examined. The HDR specimens contained 0.065% C, 0.027% Nb, 0.005% N and 0.005–0.021% Ti, and had been hot direct rolled above 1100 degC. In the commercial steel, laths were richer in Ti than cubes and both were richer in Ti than predicted by a model of the solution thermodynamics. The composition of cubes approached that of laths on reheating at high temperatures. The cast steel contained only Nb–rich particles,...