Effect of Intercritical Heat Treatment on Microstructure and Mechanical Properties of Sn Bearing 33MnCrB5 Steel

With the recycling of scrap steel, the accumulation of Sn deteriorates the properties of high-strength low-alloy structural steel. The effect of intercritical heat treatment (IHT) on microstructure and the mechanical properties of Sn bearing 33MnCrB5 steel has been studied. Results indicated that a composite microstructure of ferrite and martensite was obtained by adding the intercritical quenching to the conventional quenching and tempering. Compared with the conventional heat-treated samples, the impact energy increased evidently from 30 J to 77 J and the strength decreased slightly. The loss of strength resulting from the IHT is reduced by the modification of tempering conditions. Furthermore, AES showed that the grain boundary segregation of Sn can be alleviated via the IHT. Based on different heat treatment results, the optimum heat treatment technology, that is, 910 °C normalizing, 860 °C pre-quenching, 770 °C intercritical quenching, 450 °C tempering, was obtained to balance the strength and toughness.