Influence of graphite nodules on the wear resistance of nodular cast iron in reciprocal sliding against deep-drawing Interstitial-Free (IF) steel

Nodular cast iron stamping dies are extensively applied in the automotive industry to manufacture low carbon steel bodywork components. During the process, a flat steel plate is typically stamped by deep drawing in a defined die shape, causing wear to the entry radius of the nodular cast iron die. Although the graphite nodules present in the die microstructure are indicated to improve wear resistance due to its solid lubricant capability, few studies have investigated how the microstructure characteristics affect die wear. Therefore, this study investigates the influence of the number, size, as well amount of pearlite and ferrite in the wear resistance of a nodular cast iron in reciprocal sliding against a commercial Interstitial-Free (IF) deep-drawing steel. The reciprocal sliding tribology tests were conducted according to ASTM G133-05 standard in a ball-on-flat configuration. The nodular cast iron pins were extracted from a round bar obtained by FUCO^® continuous casting in three different radial positions, which produces pins with distinct microstructures. A commercial zinc-aluminum coated flat IF steel plate was selected as the counter body. The coefficient of friction and wear rate were accessed for the three tribo-pair configurations. Also, the pin’s microstructure and hardness were evaluated by means of Scanning Electron Microscopy (SEM) and Brinell hardness, respectively. The results reveal that the volume of graphite nodules is constant; it reduces the friction coefficient while not interfering with the wear rate of the pins extracted from the three different positions of the FUCO bar. The wear rate is abrasive followed by oxidative wear. The most wear resistant nodular casting iron pin was the one from the surface, which presented the smallest amount of pearlite.