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Development of Surface Treatment Solutions for Stamping Tools Fabricated via Additive Manufacturing

Oak Ridge National Laboratory (ORNL) and H.E.F. USA, Inc. (HEF) partnered to develop wear resistant surface treatment of additive manufactured steels for stamping die applications under CRADA agreement NFE-19-07909. This project aimed at evaluating the ARCOR® process, developed by HEF, to improve the surface behavior of 410SS (stainless steel), 410NiMo SS, 630 SS, and Maraging 250 steel coupons and demo components, fabricated via wire arc additive manufacturing (WAAM), with and without post print heat treatment. The peak hardness achieved was ~1000 HV and above (Up to 1300 HV) for all materials under proper processing parameters, and far exceeded the target hardness of 746 HV (60 HRC). Finally, stamping tools were printed and nitrocarburized with the optimum parameters, and then went through 500 fabrication cycles. Characterization of the used 17-4PH stamping tool discovered no crack or delamination in the nitrocarburized layer and the interface between the nitrocarburized layer and substrate.

36 MATERIALS SCIENCE↗

Rapid Alloy Surface Engineering through Closed-Vessel Reagent Pyrolysis

For rapid surface engineering of Cr-containing alloys by low-temperature nitrocarburization, we introduce a process based on pyrolysis of solid reagents, e.g., urea, performed in an evacuated closed vessel. Upon heating to temperatures high enough for rapid diffusion of interstitial solute, but low enough to avoid second-phase precipitation, the reagent is pyrolyzed to a gas atmosphere containing molecules that (i) activate the alloy surface by stripping away the passivating Cr 2 O 3 -rich surface film (diffusion barrier) and (ii) rapidly infuse carbon and nitrogen into the alloy. We demonstrate quantitatively that this method can generate a subsurface zone with concentrated carbon and nitrogen comparable to what can be accomplished by established (e.g., gas-phase- or plasma-based) methods, but with significantly reduced processing time. As another important difference to established gas-phase processing, the interaction of gas molecules with the alloy surface can have auto-catalytic effects by altering the gas composition in a way that accelerates solute infusion by providing a high activity of HNCO. The new method lends itself to rapid experimentation with a minimum of laboratory equipment.

36 MATERIALS SCIENCE↗

Tribology and Tribocorrosion of Case-Hardened Steels: A Review

This report reviews the tribological and tribocorrosion performance of steels that are case-hardened via boriding, chromizing, carburizing, nitriding, nitrocarburizing, and carbonitriding. Case-hardening is commonly used to improve the hardness, impact durability, wear resistance, and corrosion resistance of steel alloys and has been successfully applied in various industries, providing a cost-effective, high-throughput solution for applications involving contact and sliding interfaces in complex service environments. This article summarizes the literature results of the wear and friction behavior of common case-hardening methods for steel alloys under various conditions, including corrosive environments. Special attention is given to the influences of case-hardening process parameters and alloy composition on tribological performance. Furthermore, by discussing key findings from the literature, this review provides insights into optimizing case-hardening processes for improving the tribological and tribocorrosion performance of steel alloys.

Alloys↗