Study On Austenite Nitriding Process In Gas Nitriding Furnace

Nitrocarburizing is a chemical heat treatment process that mainly uses nitriding and simultaneously diffuse carbon to improve its hardness,wear resistance,fatigue strength and corrosion resistance.According to different temperatures,it can be divided into ferrite nitrocarburizing and austenite nitrocarburizing.At present,ferrite nitrocarburizing is mainly used in industrial production.After austenite nitrocarburizing treatment,?phase compound layer is formed on the surface,and austenite quenching layer is obtained on the subsurface.After aging,the compound layer has aging effect,and the hardness can reach 1000 HV_0.1.The residual austenite in the quenching layer can also be decomposed,and the hardness is also significantly improved.After treatment,the parts have good wear resistance,small deformation,and can overcome the shortcomings of shallow ferrite nitrocarburizing layer.However,for a long time,due to the high treatment temperature,the strength of the core of the part is reduced and the surface is easy to have looseness,and quenching treatment is required after nitrocarburizing The traditional well furnace does not have the automatic quenching function,which also limits the application of this process.In this paper,the heat treatment process of austenitrocarburizing and artificial aging on SPCC low carbon steel by UNB-1000 box nitride furnace manufactured by Jiangsu Fengdong was studied.The effects of process parameters such as diffuse temperature,diffuse time,methanol flow rate,ammonia flow rate,and aging temperature and time on the layer were studied.The optimum production process was determined and the microstructure was characterized.The use effect of the parts in practical production was tracked and confirmed.The main results are as follows:(1)SPCC low carbon steel was austenitic nitrocarburized at 650°C×120 min(methanol flow rate 30 m L/min,ammonia flow rate 150 L/min),and artificial aging at 250°C×240 min.The thickness of the nitrocarburized layer was about0.035?0.04mm,and the highest hardness near the surface reached 1000 HV_0.1.(2)The aging temperature and time have great effect on the precipitation hardening of the?phase near the inner side.The larger the difference of nitrogen content is,the more obvious the effect of precipitation hardening is.The compound layer depth and austenite quenching layer depth are both reduced when the nitrocarburizing time is shortened.With the increase of nitrocarburizing temperature,the depth of layer increases.However,the surface quality of the compound layer is decreased and the degree of looseness is increased.The increase of methanol content has little effect on the depth of the nitrocarburizing layer and can reduce the looseness of the compound layer.With the decrease of ammonia flow,the depth of compound layer decreases,the range of aging hardening increases,the surface hardness increases,and the looseness can also be improved.(3)After austenitic nitrocarburizing,the surface microstructure of SPCC low carbon steel is mainly?phase,and the subsurface is mainly residual austenite.After aging,the microstructure of compound layer is?phase+??phase,and the subsurface is?-Fe+??phase.(4)For the shell of agricultural harvester parts,the average service life was increased by about 30%by austenitic nitrocarburizing process.