Oxidation of Ferrous Alloys and Coatings Under Isothermal, Impulse Heating, and Diesel Engine Operation: Part I—4140 Steel

The oxidation resistance of 4140 steel was evaluated for use in the next generation of high-output diesel engines at temperatures up to 900 °C using isothermal furnace testing, a novel highly transient combustion-based laboratory test, and direct high temperature engine exposure. Isothermal tests were used both to evaluate the temperature capability of the alloy and to derive oxidation kinetics. An anisothermal model was then applied to predict oxide growth during impulse cyclic heating tests (ICHT), where the steel is directly exposed to combustion. Isothermal oxidation kinetics are shown to accurately predict scale growth in this scenario despite the presence of the flame, large thermal transients, and thermal gradients present in the alloy. This is found to not translate well to oxidation observed on the 4140 piston after engine testing, where the observed oxidation is significantly thicker than expected. Several potential error sources are discussed including the role of in-cylinder pressure, combustion interactions, and engine build-to-build variability.