Effect of Austenitizing Temperature on The Structural Evolution of Hot Forged Steel Grinding Balls

This paper reports the influence of heat treatment temperature on the microstructural changes that may occur in an XC38 forged steel grinding ball. Three austenitizing temperatures (870°C, 950°C and 1150°C) were used and a tempering at 250 °C followed by air cooling was carried out. Optical and scanning electron microscopies, as well as X-ray diffraction, were performed to investigate the microstructure and phase of the different samples. Microstructural analysis using the Rietveld method was conducted to access, for each temperature, the type and proportion of phases as well as crystallites size and microstrain. The obtained results were compared to those recorded on as forged steel. The effect brought by the variation of the austenitization temperature was well highlighted by the obtained results. The nature and proportion of microstructural phases were significantly affected by the increase of the austenitization temperature which was in favour of the increase of martensite content in a mixed microstructure consisting of bainite and martensite. A rising amount of martensite is noticed, with the increase of temperature, at the expense of the bainite content. An effect was also noticed on phase’s proportions, microstructural parameters, crystallites size and mircostrain.