Effect of Treatment Temperature on the Cyclic Spherical Contact Behavior of Plasma Nitrided and Nitrocarburized AISI 321 Steel

This work studied the cyclic spherical contact behavior of plasma nitrided (N) and nitrocarburized (NC) AISI 321 steel. The temperature and exposition time were 400 and 500 °C for 6 h in each treatment. A superficial hardness between ~10 (NC 400 °C) and ~17 GPa (NC 500 °C) was found by instrumented indentations; moreover, plastic and total work of indentation were analyzed. In cyclic spherical contact assessment, a critical load was first determined by applying tests between 100 and 1000 N. Next, cyclic tests were conducted with three subcritical loads (120, 150, and 180 N) and up to 10⁵ cycles. A detrimental effect of treatment temperature was observed, 500 °C treatments presented worse failures than 400 °C, which is explained by the decomposition of expanded austenite. Between 400 °C treatments, nitrocarburizing presented a better performance, its higher plastic work of indentation is associated with a better energy absorption capacity.

Keywords:
Nitriding; nitrocarburizing; expanded austenite; contact fatigue; cyclic load; spherical contact