Modeling of as-tempered hardness in steel is essential to understanding final properties of heat-treated components. Most of the tempering mathematical models derive a tempering parameter using Hollomon-Jaffe formulation. Some recent models incorporate chemical composition into the general Hollomon-Jaffe relationship. This paper compares model predictions with a substantial set of actual tempered Jominy End Quench bars and the hardness data from them. Improvements to the models and direction for future work are discussed.

The cooling history of carburized heat-treated gears plays a significant role in developing microstructure, hardness, and residual stress in the tooth that influences the fatigue performance of the gear. Evaluating gear carburizing heat treatment should include a microstructure and hardened depth evaluation. This can be done on an actual part or with a test piece. The best practice for a test piece is to use a section size that closely approximates the cooling rate at the gear flank of the actual gear. This study furthers work already presented showing the correct test piece size that should be used for different gear modules (tooth thicknesses). Metallurgical comparisons between test pieces, actual gears, and FEA simulations are shown.

Surface hardening by nitriding is a commonly used heat treatment to enhance tribological characteristics, fatigue, and corrosion resistance of ferrous components. Nitrided white layer is known for its high hardness but also for its brittle nature. It is not uncommon to see white layer chipping or breakaway during metallurgical sample preparation that may complicate the analysis of the ‘true’ white layer characteristics in the microstructure of the nitrided load. This paper discusses the results of the several studies performed to evaluate the effect of cutting and polishing operation, polishing pressure, use of foils, and Ni plating. Best practice procedure has been developed for metallurgical sample preparation to minimize uncertainty in parts quality evaluation.

Nitriding surface hardening is commonly used on steel components for high wear, fatigue and corrosion applications. Case hardening results from white layer formation and coherent alloy nitride precipitates in the diffusion zone. This paper evaluates the microstructure development in the nitrided case and its effects on the hardness in both the white layer and the substrate for two industry nitriding materials, Nitralloy 135M and AISI 4140. Computational thermodynamic calculations were used to identify the type and amount of stable alloy nitrides precipitation and helped explain the differences in the white layer hardness, degree of porosity at the surface, and the hardening effect within the substrate. Some initial insights toward designing nitriding alloys are shown.