Rolling contact fatigue study of chilled and quenched/tempered ductile iron compared with AISI 1080 steel

Both ductile iron and steel are widely used to build rolling elements. As ductile irons generally cost less than steels, this study was conducted to evaluate its rolling contact fatigue (RCF) performance by comparing with that of the AISI 1080 steel. The RCF resistance of two ductile iron variants, chilled ductile iron (CDI) and quenched and tempered ductile iron (Q&T DI), was evaluated. RCF testing was performed using a 3-ball and rod rig. The CDI and Q&T DI results were compared to those of Q&T 1080 steel. The three groups of specimens were processed to ensure a consistent surface hardness of 60 HRC prior to testing. Q&T DI exhibits a much lower RCF loading capacity (2.1 GPa) compared with CDI (3.6 GPa). Under the same loading condition, CDI demonstrated a significantly lower RCF resistance compared with Q&T 1080 steel. Failures in CDI was found to be independent of graphite, which explains CDI’s improved RCF life compared to Q&T DI. This improvement is attributed to higher micro-hardness and less variation throughout the material. The microstructure of tested CDI was analyzed with electron backscatter diffraction (EBSD) from the specimen surface to the core. These observations on carbide volume fraction and growth preference correlated to cooling rate differences between the material groups. This study paves the way for mechanistically based process design of ductile iron variants to achieve comparable RCF life of steels. •Similar surface hardness in the range 57.3–60.4HRC were achieved with three materials.•Quenched and tempered 1080 steel outperformed cast irons in rolling contact fatigue.•Chilled ductile outperformed quenched and tempered ductile iron even with lower surface hardness.•Improved microstructure consistency was found to benefit fatigue life of cast irons.•RCF performance of iron may be further improved by optimization of microconstituent volume and morphology.