Effect of Solidification Pressure on Phase Transformation and Precipitated Phases of 30Cr15Mo1N Ingot

In this research, the effect of solidification pressure on phase transformation temperature and sequence, amount of proeutectoid ferrite, characteristics of pearlite and carbonitrides have been investigated by microstructure observation, crystal structure and component analysis, and thermodynamic calculation. The microstructure of 30Cr15Mo1N ingot is mainly composed of martensite, austenite, pearlite, ferrite, M 23 (C,N) 6 and M 2 (C,N). With increasing solidification pressure, M 23 (C,N) 6 precipitation temperature, austenite (γ) and ferrite (δ) formation temperature increase, and M 2 (C,N) precipitation temperature and ferrite (α) formation temperature decrease. Under 0.5 MPa, the precipitation sequence during solidification process of 30Cr15Mo1N ingot is “L → δ → γ → M 2 (C,N) → M 23 (C,N) 6 → α + martensite/retained austenite → pearlite”. There is a negligible change in phase transformation sequence with increasing solidification pressure from 0.5 to 2 MPa. In addition, the increment in solidification pressure is beneficial to significantly increase the amount of proeutectoid ferrite and reduce pearlite lamellar spacing by enhancing cooling of 30Cr15Mo1N ingot. Meanwhile, with increasing solidification pressure from 0.5 to 2 MPa, the size of M 2 (C,N) and the amount of precipitated phases (pearlite and carbonitrides) have a decreasing trend, and the change in the size of M 23 (C,N) 6 can be neglected.