The Effect of Surface Finish on Low-Temperature Acetylene-Based Carburization of 316L Austenitic Stainless Steel

The Effect of C₂H₂/H₂ Gas Mixture Ratio in Direct Low-Temperature Vacuum Carburization

“…Also, it is consistent with the study that flowing high C2H2 with nearly infinite carbon activity is expected to increase the carbon concentration in ASS, but the actual carburization efficiency is very low [16]. The reason why the efficiency of carburization is lowered when the ratio of C2H2 is greatly increased can be expected as follows [16,17]: a) difficult to increase to para-equilibrium carbon solubility limit due to a lack of free radicals generated depending on the amount of introducing H2 gas, b) the interruption of the transfer of soluble carbon species from the gas atmosphere into the solid because of the soot and metal dust formed by the high activity of C2H2 gas.…”

“…However, alternative ways are demanded to solve the environmental problems which those gases are very toxic. So, the acetylene gas (C2H2) as a carbon source is recently studied to remove the natural oxide layer and improve carburization efficiency in carburization [16][17][18]. The mechanism of carburization in acetylene is elucidated as follows: first, adsorption and decomposition of C2H2 gas on the solid surface at the certain temperature and it subsequently the carbon species to be a development of radical [19,20], those can be soluble into iron.…”

“…Such low-temperature carburization with C2H2 gas has been researched about the effects of activity and diffusion rate by changing of process temperature and time [17,21,22]. In carburization, C2H2 gas causes the sufficient reactions even with a small amount for carburization in a vacuum and a decrease of the oxygen partial pressure so that the natural oxide layer can be naturally decomposed [17,22]. Due to the characteristic of acetylene at the low-temperature regime, carburization in a vacuum was proposed to control soot and/or metal dusting easily.…”

“…[16] And in another study has been researched the change of the carbon activity and the partial pressure of oxygen according to the ratio of the process gas. [17] Nevertheless, it is lack of studies on the effect of the C2H2 gas ratio of total process gases in low-temperature vacuum carburization. Therefore, the theoretical and experimental studies are essentially demanded because the process gas ratio, an important experimental parameter that affects the carburization efficiency, produces radicals that cause strong reaction of the hydrocarbons and determines thermodynamic activity by vacuum degree and gas ratio [16,20].…”

Low-Temperature Carburization of AL-6XN Enabled by Provisional Passivation

“…Another potential obstacle to carbon or nitrogen infusion into alloy parts can originate from machining-induced severe plastic deformation, poor crystallinity, and contamination in a zone directly below the surface, known as the "Beilby" layer ( Figure 1) [13]. This has been confirmed by the results of Ge et al [14,15] on acetylene-based low-temperature carburization of AISI-316L.…”