Stress induced phase transition on the medium-high carbon alloy steel hardfacing coating during the work hardening process: Experiments and first-principles calculation

The stress induced phase transition on the medium-high carbon alloy steel hardfacing coating during the work hardening process was studied by experiments and first-principles calculation. The experimental results show that, the hardness of the specimens tempered for 2 h and 8 h at 480 °C before fatigue cycle are HRC 50.3 and HRC 50.1. The amounts of the retained austenite are 26.7 vt% and 7.3 vt%, respectively. With increase of the fatigue cycle, the amounts of the retained austenite in the tempered specimens decrease while their hardness increase constantly, until the amount of the retained austenite is decreased to 4.9 vt%. After fatigue cycle, the increments of the martensite grains with [001] and [101] orientations are much more than those with other orientations, which indicates that, during the work hardening process, the austenite grain transforms to the [001] and [101] oriented martensite grain preferentially. The calculated results show that, when pressure is 0 GPa, the face-centered cubic austenite supercell is stable, while the body-centered tetragonal martensite supercell is unstable. With increase of the pressure, the stabilities of the austenite and the martensite both increase gradually. When the pressure is larger than 18 GPa, the martensite is more stable than the austenite. For the austenite supercell, the stable limit pressure is 39 GPa. The critical pressure of the stress-induced phase transition is 36 GPa.