Study On The Process Of Hollow Cathode Plasma Source Carburizing AISI 304L Austenitic Stainless Steel

In this paper,AISI 304 L austenitic stainless steel was carburized by three kinds ofprocesses at the temperature of 450 ℃,air pressure of 300 Pa and cathode potential,andγC-phase carburized layers were obtained.Process L₁: Hollow cathode plasma source carburization,using the graphite screen,its cylinder wall was distributed with through holes,the atmosphere is composed of methane and hydrogen.Process L₂: Carburizing using the graphite screen,its through holes was embedded with stainless steel tubes.Process L₃:Carburizing using the graphite screen,at the atmosphere of hydrogen.The micro-structure,carbon concentration-depth distribution and phase structure of the carburized layer obtained were observed and measured by metallographic microscope,electron probe micro-analyzer and X-ray diffractometer.The presence of supersaturated carbon in the carburized layers were research by X-ray photoelectron spectroscopy analysis.The hardness gradient,the surface roughness and abrasion resistance of the carburized layers obtained were measured and analyzed by Vickers micro-hardness tester,surface profiler and ball-disc wear instrument.The thickness of the carburized layers obtained by L₁ is 8 mm,the surface micro-hardness is HV0.25 N 5.7 GPa,and the hardness gradient is gentle.The thickness of the carburized layer obtained by L₂ is 17 mm,and the surface micro-hardness is HV0.25 N 10.3 GPa,the hardness gradient is also gentle.The thickness of the carburized layer obtained by L₃ is 6mm,the surface micro-hardness is HV0.25 N 8.2 GPa,and the micro-hardness gradient is steep.X-ray photoelectron spectroscopy analysis shows that the supersaturated carbon in theγC-phase carburized layers is existed as a mixture of Cr Cx bonded with C-Fe bonds and Fe Cx bonded with C-Cr bonds.Under the conditions of load 2 N and grinding speed of 0.16 m/s,the Si3N4 ceramic ball was used as the grinding mill to grind with the sample.When grinded,the carburized layers obtained by L₁ and L₃,its wear marks appear abrasive wear characteristics.The carburized layer obtained by L₂ shows the characteristics of oxidation wear.The specific wear rate of the carburized layers after treatment with L₁,L₂ and L₃ is 1.34×10-6 mm3/N·m,1.08×10-6 mm3/N·m,1.13×10-6 mm3/N,respectively.Specific wear rate is 1/7¹/5 of the original AISI 304 Laustenitic stainless steel.The wear resistance of the carburized layers obtained by these three processes were much better than original AISI 304 L austenitic stainless steels.