Some tests on acicular or bainitic alloy cast steels

This preliminary study indicates that sub-critically heat treated acicular steels can show good mechanical properties in 30 × 38mm sections for applications where high strength, ductility and toughness are required. The best combination of properties obtained were TS 1071 N/mm2, 0.2% proof strength 847 N/mm2, 14% elongation and an average 38J CVN impact after treating for 4h/320°C. The best tensile properties were achieved with carbon contents in the range 0.175 - 0.33%. Impact values were improved with low sulphur and phosphorus levels. High (1.8%) silicon content adversely affects tensile ductility. At 368 - 400HV, hardness was not significantly affected by composition. Variations in sub-critical heat treatment temperatures had little effect up to 320°C but above this, impact properties were impaired. As-cast bainitic structures were obtained in sections of up to 40 × 75mm by alloying with about 2.8%Ni, 1%Cu and 0.6%Mo, but the heavier-section castings showed inferior impact values.