Research On Low Temperature Carburizing Of Austenite Stainless Steels

With the development of the society and economy,as a material with excellent corrosion resistance,stainless steel is playing an increasingly important role.Because of the better corrosion resistance,austenite stainless steel has become the most widely applied material of all stainless steels(about 65%`～70%of the stainless steel production).But austenite stainless steel has low strength,which is reflected in low hardness(250HV-300HV),poor wear appearance and fatigue resistance performance.Carburizing is a process which has simple operation,wide operation range,and obvious surface hardening effect,but normal carburizing treatments need a high temperature(above 900℃).Although the infiltration of carbon atom enhances the surface strength,the formation of chromium carbide in substrate induces a dramatic decrease in corrosion resistance.So the chemical heat treatment is the key factor to enhance the surface corrosion and strength of austenite stainless steel without formation of chromium carbide.Austenite stainless steel low temperature carburizing technology can achieve this target.We have designed and produced the dedicated device for the research on austenite stainless steel low carburizing technology by our own,.This device has passed practical running test,and its technical indicators meet the technological requirements.This dedicated device was used to carry out the research on austenite stainless steel low temperature carburizing technology.As representative models of austenite stainless steels,AISI304、AISI316 and AISI321 were applied in this experiment.To deal with these materials,we use electroplating pretreatment and fluoride pretreatment.AISI304 and AISI316 were treated by electroplating pretreatment,and then carburized at 550℃ for 24h、48h、72h and 96h or at 565℃ for 24h and 48h.Carburized layer can be observed obviously in both of these two treated samples.After been treated at 550℃ for 24h,the surface hardness of AISI316 is about 650HV,and those of AISI304 is about 600HV.The carburized layer can be observed obviously from AISI304、AISI316 and AISI321 samples treated by fluoride treatment and following carburizing treatment.The surface hardness was enhanced after been treated,too.It was confirmed that both of these two pretreatments are benefit to the following low temperature carburizing process.Chromium carbide have not been observed obviously by XRD in carburizing layer.Electrochemical and corrosion rate tests were used to analyze the changes of the samples treated by low temperature carburizing.By electrochemical experiment,we had found that the samples carburized at 550℃ not more than 48h had a better corrosion resistance than those without low temperature carburizing.But the samples treated at 550℃ for 72h had a slightly lower corrosion resistance.The result of corrosion rate experiment was basically identical with that of electrochemical experiment.