Effect Of Stress On Microstructure And Properties Of Working Layer Of Carbide Austempered Ductile Iron(CADI)

Carbidic austempered ductile iron(CADI) is a new kind of wear-resistant material,which is widely concerned because of its high hardness,good wear resistance and high strength.When the CADI structure is affected by external force,it will produce work hardening phenomenon and form a stable working layer.At present,the research mainly focuses on the wear resistance under static load,but in practice,the CADI working layer will be affected by the external force of dynamic load.In this paper,the austempering treatment is carried out for CADI,and the impact wear performance of the heat treated CADI is studied.The friction wear performance and abrasive wear performance of CADI are analyzed.The corrosion mechanism of CADI in different corrosive media is studied,and the influence of impact stress on the structure and performance change of CADI is explored.The austempering of CADI shows that acicular ferrite forms in austenite grain after heat treatment,and the white bright zone is formed by the remaining austenite and martensite.The content of ferrite,retained austenite and martensite in CADI is affected by different quenching temperature.The higher the isothermal temperature is,the fuller the ferrite structure grows,the higher the relative content of austenite,the higher the content of austenite and the lower the content of martensite in the white bright zone.The impact wear experiment shows that under the impact stress,the work hardening phenomenon of CADI occurs,forming a stable working layer with a certain thickness.With the increase of isothermal temperature,the hardness of CADI decreased,and the impact stress increased,the thickness of working layer increased from 3mm at 200 ? to 4mm at 260 ?.The further away from the impact surface,the smaller the impact on the structure of CADI,the less obvious the work hardening phenomenon.The impact stress causes the transformation of retained austenite from face centered cubic lattice to body centered cubic lattice in CADI.With the increase of isothermal temperature,the transformation amount of austenite increases gradually,and the hardness increases more obviously.The results of friction and wear experiments show that the hardness of the surface of CADI increases after impact wear,and the plastic deformation of the wear surface decreases compared with that before impact wear.At 200 ?,work hardening increases the brittleness of the surface structure and the wear rate and friction coefficient.At 220 ? ? 260 ?,the wear rate and friction coefficient of CADI decreased.In the single abrasive scratch test,the lower the hardness of the structure,the more obvious the plowing degree of the abrasive particles to the CADI structure,the more the removal volume,and the wider the scratch produced by the abrasive particles.The corrosion mechanism of CADI is electrochemical corrosion.The corrosion of CADI in acid solution is hydrogen evolution corrosion,and the corrosion in neutral and alkaline solution is oxygen consumption corrosion.The higher the isothermal temperature is,the greater the corrosion rate is.The corrosion rate of CADI sample after impact wear is lower than that before impact wear.The corrosion rate is the highest in acid solution,the middle in alkaline solution and the lowest in neutral solution.The impact stress reduces the grain spacing and the rate of intergranular corrosion,while the formation of intergranular chromium poor zone promotes the intergranular corrosion.