Across all industries, material specifications are tightening beyond previously understood process capabilities. Slight shifts in material grade, microstructure, heat treatment, or alloy composition can significantly impact long term material integrity. This study examines the feasibility of noncontact, 100% inline magneto-inductive testing on materials and components to ensure material quality standards. To investigate the hypothesis that material grade, carbon content, density, and alloy composition can be accurately tested in real time during production, an experiment was conducted using magneto-inductive test instrumentation and an encircling coil. The results of the investigation confirmed that 100% of the material in a component could be thus tested, accurately, efficiently, and autonomously verifying that the specified material grade with the proper composition and properties had been used.

Carburization is a common method of hardening steel surfaces to be wear-resistant for a wide range of mechanical processes. One critical characteristic of the carburization process is the increase in carbon content that leads to the formation of martensite in the surface layer. Combustion and spark-OES are two common methods for determination of carbon in steels. However, these techniques do not effectively separate carbon from near surface contaminants, carburized layers, and base material composition. Careful consideration of glow discharge spectroscopy as a method of precisely characterizing carbon concentration in surface layers as part of a production process should be evaluated in terms of how the resulting data align with other common analytical and metallurgical measurements. When used together, glow discharge spectroscopy, optical microscopy, and microhardness testing are all useful, complementary techniques for characterizing the elemental composition, visually observable changes in material composition, and changes in surface hardness throughout the hardened case, respectively. Close agreement between related measurements can be used to support the use of each of these techniques as part of a strong quality program for heat treatment facilities.

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.

AISI 8620 low carbon steel is widely used due to its relatively low cost and excellent case hardening properties. The nominal chemistry of AISI 8620 can have a large range, affecting the phase transformation timing and final hardness of a carburized case. Different vendors and different heats of steel can have different chemistries under the same AISI 8620 range which will change the result of a well-established heat treatment process. Modeling the effects of alloy element variation can save countless hours and scrap costs while providing assurance that mechanical requirements are met. The DANTE model was validated using data from a previous publication and was used to study the effect of chemistry variations on hardness and phase transformation timing. Finally, a model of high and low chemistries was executed to observe the changes in hardness, retained austenite and residual stress caused by alloy variation within the validated heat treatment process.

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.

High entropy alloys (HEA) are an exciting new class of alloys composed of several metallic elements with equiatomic or near-equiatomic composition to maximize configurational entropy, leading to desirable properties. However, during solidification, as in casting or welding processes, elements segregate, creating local regions of distinct composition. In conventional alloy systems, homogenization heat treatments are used to remove this segregation effect. This study examines the conditions of the heat treatment needed in HEA alloys. First, the solidification behavior of equiatomic alloy composition AlCoCrCuFeNi is modeled using the Scheil module within Thermo-Calc along with the TCHEA2 database. Energy dispersive spectroscopy (EDS) is performed across the dendrite arms of the as-melted HEA to compare with the Scheil calculations. The resulting dendritic and interdendritic compositions are used as inputs in Thermo- Calc to determine the stable phases as a function of temperature. Selected heat treatments are conducted on the as-melted HEA to compare with the calculation results.