Effect of Carburizing and Carbonitriding Temperatures on the Microstructure and Wear Resistance of 18Cr2Ni4WA Steel with Carburizing–Carbonitriding Heat Treatment

This study systematically investigates the effects of carburizing and carbonitriding temperatures on the microstructural evolution and wear resistance of 18Cr2Ni4WA steel. The surface layer after carburizing–carbonitriding treatment comprises acicular/lath martensite, residual austenite, and dispersed carbides, with microstructural gradients dependent on processing parameters. Elevated carburizing temperatures (930–970 °C with 850 °C carbonitriding) marginally reduce surface microhardness and harden layer depth, while increasing carbonitriding temperature to 880 °C (930 °C carburizing) significantly decreases hardness and accelerates softening at depth. Microstructural analysis reveals that higher carbonitriding temperature (880 °C) promotes grain coarsening, reduces carbide fraction, and increases residual austenite content, attributed to altered carbon/nitrogen diffusion kinetics and solute supersaturation. Wear resistance correlates strongly with carbide dispersion and grain refinement, and the 930 °C carburizing and 850 °C carbonitriding sample exhibiting the lowest wear rate, 61.5% lower than conventional carburized specimens, due to optimized nitrogen‐containing martensite and dislocation pinning by fine carbides. These findings demonstrate that synergistic control of carburizing and carbonitriding temperatures enables tailored surface engineering, achieving enhanced wear resistance through nanoscale carbide distribution and stabilized martensitic matrices, offering critical insights for manufacturing high‐performance gears and aerospace components.