Behavior of Carbon and Nitrogen after Low Temperature Thermochemical Treatment on Austenitic and Duplex Stainless Steel

摘要

This paper explores carbon and nitrogen behavior after low temperature thermochemical hybrid treatments in conventional tube furnace which introduce nitrogen and carbon simultaneously to form a dual layer structure and to achieve much enhanced surface properties of AISI 316L and Duplex 2205. The expected layer is a structure termed expanded austenite which is supersaturated with nitrogen and carbon. This structure is responsible to the higher hardness without impairing its corrosion resistance. Characterization of this expanded austenite layers were performed by FESEM (Field Emission Scanning Electron Microscope) and USPM (Universal Scanning Probe Microscope) which were used to reveal the characters of the produced thin layers. These treatments give rise to alloyed layers with a common feature of being precipitation-free and supersaturated with nitrogen, or carbon or both in the austenite lattice which is known as S Phase or expanded austenite. Unfortunately, there is not a uniform layer thickness in all specimen and we could get an effective layer after duration of 9 h treatment. The result of the hybrid treatment for 316L gives a thicker layer than 2205. EDS line scan in the cross-section treated layers reveal a decrease of Fe and corresponding slight increase of N and C at the compound layer, which suggests the existence of iron nitrides/carbides in the compound layer. Such distributions of nitrogen and carbon in the surface layer are likely to produce some beneficial influences upon the properties of hybrid treated layers on 316L and 2205.