Investigation on Microstructure and Mechanical Properties of a Low Alloyed Ultra-High Strength Steel

With Thermo-Calc software the equilibrium phases of a low alloyed ultrahigh strength steel 30Cr3 for engine case were studied.By mechanical test,transmission electron microscopic(TEM),scanning electron microscopic(SEM) and XRD observation the performance of 30Cr3 steel was investigated.The results showed that at room temperature the structure components of 30Cr3 steel after equilibrium phase transformation are α-Fe and carbides(MC、M23C6、M7C3).30Cr3 steel has good hardenability after normalization,of which microstructure is mainly martensite.During tempering e-carbide is precipitated in martensite laths.The tension strength and yield strength of 30Cr3 steel first rise up with a max.Tension strength of 1 870 MPa at 250 ℃,then decline with tempering temperature;the impact energy and fracture toughness decline with increase of tempering temperature.