Effects Of Heat Treatment Technology On Properties Of Carbidic Austempered Ductile Iron

Carbidic austempered ductile iron (CADI) which has wear resistanceproperty is derived from austempered ductile iron (ADI) in recent years. CADIalmost have many of the excellent mechanical properties of ADI, and the wearresistance property is better than that of ADI. Research shows that the wearresistance property of ADI is better than that of steel under the same hardnessin the abrasive wear conditions. However, the toughness of ADI is low athome and abroad now. αKof sample without notch usually is only5~27J/cm2,the toughness tends to lower limit when the hardness tends to higher. Forexample, corresponding to HRC49~54,αKcan reach7~11J/cm2. The lowertoughness of CADI restricts the application scope undoubtedly. In order toimprove the mechanical properties and break the limit of lower toughness,thepaper researched the effect of different Heat treatment process methods andparameters on the properties of CADI.Main contents in this paper were asfollowed:1, this paper focused on the novel methods of obtaining higher toughnessCADI under ultra-high austenited temperature. The effect laws of propertiesinfluenced by the ultra-high austenited temperature and the austemperingtemperature of heat treatment process parameters were systematic researched;The contrast of CADI samples under different content of Cr was researched;The effects of “process—property” were analysed in theory combined withorganization. The results showed that microstructure was further improved,corresponding the limits of hardness HRC39~50, CADI obtained the limits oftoughness93~28J/cm2under960~1000℃ultra-high austenited temperature,the toughness was widely improved, these had a positive meaning to expandthe application field of CADI.2, the effect laws of the toughness and hardness properties of CADIinfluenced by“higher temperature prepare process”, austenited temperature(Tγ)and austempering temperature(TA) were researched. The results and lawswere analysed by using the basic principle of heat treatment of ADI with themicrostructure under different conditions. The results showed that thetoughness was rising when austenited temperature and austemperingtemperature were increased by the method of “higher temperature prepareprocess”, but the hardness reduced,under the condition of “higher temperature prepare process”, the effect of Tγ and TA for the properties of CADI wasconsistent with that of ADI by the traditional process conditions, however,After a certain range, the effect of increasing TA did not play a significantrole. The toughness of CADI can increase by the method of “highertemperature prepare process”. Corresponding the limits of hardnessHRC51~56, CADI can obtain the limits of toughness38~18J/cm2. TheVolume percentage of carbide increased gradually with increasing the contentof chromium under the same conditions of heat treatment, moreover, thehardness increased and the toughness reduced.3, in the impact of abrasive wear test conditions，the relationships betweenaustenited temperature, austempering temperature and the wear-resistingperformance of Cr0.5%CADI were researched by the method of “highertemperature prepare process”. The results showed that the wear resistance ofCADI can increase in a range of reducing the temperature of Tγand TA. Theabrasion mechanism of CADI was different under different heat treatment. Thewear surface was smooth and flat, the adhesion was less, and the abrasionmechanism mainly was microcutting when the temperature of Tγand TAwas low;the degree of smooth significantly became worse by rising the temperature of TγandTA, the abrasion mechanism mainly was adhesion and microploughing. Moreover,the hardness of CADI obviously increased after impact wear, this indicatedthat the work hardening of CADI was produced, and the wear resistance ofCADI further was improved, these had great significance in enlarging theapplication of CADI.The principles and effects of different processes on mechanical properties,wear-resisting property of CADI were also discussed. Discussion and analysiswere carried out about the phenomenon and principles from theoretical viewwith the matrix organization and the change characteristics of carbide.