Abstract
The effect of plastic deformation applied to AISI 316L in low-temperature vacuum carburizing without surface activation was investigated. To create a difference in the deformation states of each specimen, solution and stress-relieving heat treatment were performed using plastically deformed AISI 316L, and the deformation structure and the carburized layer were observed with EBSD and OM. The change in lattice parameter was confirmed with XRD, and the natural oxide layers were analyzed through TEM and XPS. In this study, the carburized layer on the deformed AISI 316L was the thinnest and the dissolved carbon content of the layer was the lowest. The thickness and composition of the natural oxide layer on the surface were changed due to the deformed structure. The natural oxide layer on the deformed AISI 316L was the thickest, and the layer was formed with a bi-layer structure consisting of an upper Cr-rich layer and a lower Fe-rich layer. The thick and Cr-rich oxide layer was difficult to decompose due to the requirement for lower oxygen partial pressure. In conclusion, the oxide layer is the most influential factor, and its thickness and composition may determine carburizing efficiency in low-temperature vacuum carburizing without surface activation.
Highlights
Published: 2 November 2021Austenitic stainless steels (ASSs) are the materials used in various industries due to their formability and weldability based on excellent corrosion resistance
The heat treatment was respectively conducted to compare the state of the plastic deformation and the gradually relieving stress, because diffusion, the driving force behind low-temperature vacuum carburizing, is affected by the state of the material
316L specimens subjected to either plastic deformation, solution heat-treatment, or stressrelieving treatment (623 K, 973 K) were measured by Electron Backscatter Diffraction (EBSD) to observe the microstructure and strain distribution
Summary
Published: 2 November 2021Austenitic stainless steels (ASSs) are the materials used in various industries due to their formability and weldability based on excellent corrosion resistance. While conventional thermochemical treatment methods such as carburizing and nitriding have been applied, the inherent corrosion resistance of ASSs is impaired due to precipitates such as carbide and nitride [3,4] To overcome this problem, a low-temperature hardening process, which is carried out below precipitate formation temperature, has been developed [5]. The interstitial atoms can be supersaturated due to the influence of alloying elements, thereby increasing surface hardness, wear resistance, and fatigue resistance, because those induced the compressive stress at the surface as the lattice expands due to supersaturation For this reason, the low-temperature hardening layer, which is supersaturated by the interstitial atoms, is called expanded austenite (or the supersaturated layer), and the inherent corrosion resistance of ASSs can be maintained
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