Properties of cast steels of low hardening capacity

This work concerns the mechanical properties of low-hardenability steel 50PPL in comparison with standard steel 45L after quenching and low-temperature annealing, and rolled steels 45 and 55PP. The mechanical properties (strength, bending, hardness) of cast and forged low-hardenability steel 50PPL after quenching are similar to those of steels 45 and 55PP. the strength of cast steel 50PPL is somewhat higher after quenching (about 14%) than that of steel 45L. The high strength of low-hardenability steel 50PPL in the cast and wrought conditions, especially that of basic steel 50PPL, is due to fine-grained austenite (grade 11-12), which reduces the size of martensite crystals formed in induction hardening. Other conditions being equal, refining of martensite is the main reason for the high strength. The properties of steel 50PPL and 45L depend on the quenching temperature. With quenching temperatures of 1100-1150degC the strength and ductility increase in forged samples of steels 45L and 50PPL despite austenite grain growth, which is evidently explained by the solution of hard-to-dissolve particles of second phase, creating conditions for development of the aging process during subsequent low-temperature tempering. Electron microscopic studies of fracture surfaces after static bending tests showed that the percentage of ductile components (dimples) increases in formed samples of steels 45L and 50PPL quenched from high temperatures (1100-1150degC)