Improvement in Mechanical Properties of a Surface-Carburized Ferrite–Martensite Dual-Phase Steel by Intercritical Annealing

This study investigated the effects of ferrite volume fraction and morphology on the mechanical properties and rolling contact fatigue life of surface-carburized G20CrNi2Mo-Al steel with ferrite–martensite dual-phase microstructures. Compared with full austenitization treatment, intercritical annealing treatment optimized the properties, and the microstructural evolution of different heat treatment processes was explored. The experimental results indicated that after austenitizing at 900 °C for 30 min and intercritical annealing at 805 °C for 40 min, the steel had 6.9 vol.% continuous grain boundary ferrite in the center, and the mechanical properties reached their maxima. Under the optimal heat treatment conditions, the hardness value, impact toughness and tensile strength increased by 4.0, 11.1 and 2.4%, respectively; the rolling contact fatigue life increased by 76.1% compared with that after conventional full austenitization treatment.