Effect of Austempering on the Microstructure, Mechanical Properties and Tribological Performance of EN-GJS-800-8 Ductile Iron Castings

This study evaluated the effect of austempering on the microstructure, mechanical properties, and dry-sliding wear performance of EN-GJS-800-8 ductile iron produced as cross-step castings with wall thicknesses of 8, 17, 38, and 48 mm. As-cast and heat-treated specimens were examined by optical microscopy and quantitative image analysis, Brinell hardness, tensile and Charpy impact testing, ball-on-disk testing, and three-dimensional confocal profilometry. Austenitization at 880–890 °C for 2.5 h followed by austempering at 370–380 °C for 2 h produced an optically homogeneous acicular matrix consistent with ausferrite in all investigated sections and reduced the wall-thickness-related variation in hardness. The average hardness reached 296.4 HBW, the ultimate tensile strength 935 MPa, and elongation 8.6%. The mean Charpy impact energy increased from 5.12 to 10.06 J. The wear-track cross-sectional area decreased from approximately 2.98 × 104 to 210 μm2, while the maximum track depth decreased from 43.5 to 3 μm. The selected heat-treatment cycle therefore improved strength, impact-energy absorption, and wear resistance while promoting a more uniform response across the casting sections.