EFFECT OF HEAT TREATMENT REGIMES ON THE MICROSTRUCTURE AND SERVICE PROPERTIES OF HIGH WEAR-RESISTANT CR–MN–MO–NI CAST STEELS

Abstract

The present study investigates the influence of systematic variations in austenitizing temperature (950, 1000, and 1050 °C), holding time (1–2 h), and oil-quench tempering temperature (200, 400, and 600 °C) on the microstructural evolution and service properties of a Cr–Mn–Mo–Ni alloyed wear-resistant cast steel. Nine experimental conditions were evaluated against an as-cast reference state using optical microscopy, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), Vickers microhardness (HV0.5), Rockwell hardness (HRC), and dry-sand abrasive wear testing (ASTM G65 Procedure B). Statistical significance of all measured responses was assessed by one-way analysis of variance (ANOVA). Austenitizing at 1050 °C combined with tempering at 200 °C yielded the optimal combination of properties: martensite fraction 93 ± 2 %, matrix microhardness 791 ± 16 HV0.5, bulk hardness 63.7 ± 0.5 HRC, volumetric wear rate 2.09 × 10⁻⁶ mm³/N·m, and a Wear Resistance Index (WRI) of 1.55 relative to a 950 °C–200 °C baseline. Increasing austenitizing temperature promoted greater carbide dissolution, reduced retained-austenite content, and refined undissolved secondary carbide particles from 6.8 µm (as-cast) to 1.1 µm, with a concomitant increase in alloying-element supersaturation of the martensite matrix. Tempering above 400 °C triggered secondary carbide precipitation, recovery of dislocation substructure, and partial bainitic transformation, collectively reducing hardness and wear resistance. ANOVA confirmed that both austenitizing temperature (p < 0.001) and tempering temperature (p < 0.001) are statistically significant factors. The findings provide quantitative metallurgical guidance for designing heat treatment protocols for cast steel components in mining, comminution, and mineral-processing applications.