Research On Heat Treatment Process Of High Chromium Cast Iron And Impact Abrasive Wear

Wear will cause the loss of surface material and it is the main cause of failure ofcomponents, so wear problem arouses people’s extensive attention and the research onabrasive wear is of great significance to the national economy development. As a kindof excellent wear-resistant material, high chromium cast iron has been widely used inindustrial field. The heat treatment of high chromium cast iron can make its hardnessand toughness good cooperate, which is an important research topic for a long time. Inaddition, the actual working conditions of high chromium cast iron are also verydifferent. The study on the wear mechanism of high chromium cast iron underdifferent working conditions will play a vital role for the full play of wear resistanceof high chromium cast iron.The heat treatment process for the two groups of high chromium cast iron withdifferent composition was studied in this paper. By analyzing the effects of quenchingtemperature, quenching agent and tempering temperature on microstructure andproperties of high chromium cast iron, the heat treatment process parameters of highchromium cast iron were optimized. The effects of different conditions on theabrasion resistance of high chromium cast iron after optimum heat treatment werestudied by impact abrasive wear tests, and the abrasive wear mechanism of highchromium cast iron in different conditions were discussed. The main conclusions ofthe thesis were as follows:(1) When the quenching temperature was lower, the amount and the size ofcarbide was larger, and it was reticulate distribution; when the quenching temperaturewas higher, the amount of residual austenite after quenching increased, and thecarbide began to be coarsen. Tempering at low temperature (≤400℃), could reduceand eliminate quenching stress, and the structure basically had no change; temperingat450℃～500℃, part of the martensite started to decompose, and there was also apart of residual austenite beginning to go on the secondary quenching, precipitatingcarbide; Tempering at high temperature (≥500℃), a large number of martensite andretained austenite both began to decompose, and the carbide started to be aggregatedand coarsened.(2) In this experiment, the as-cast Rockwell hardness of1#sample was49.4HRC,and the impact toughness was6.95J/cm2; the2#samples’ as-cast Rockwell hardness was51.8HRC, the impact toughness was6.74J/cm2. The optimum heat treatmentprocess of1#samples was970℃wind cooling+spray quenching+460℃tempering,and that of2#sample was990℃wind cooling+spray quenching+460℃tempering.Under the condition of this process, the structure of high chromium cast iron wassecondary quenching martensite+tempering martensite+residual austenite+eutectic carbide+secondary carbide. Hardness of1#sample is62HRC, and theimpact toughness is6.29J/cm2; Hardness of2#sample is65.2HRC, and the impacttoughness is5.94J/cm2.(3) By performing impact abrasive wear tests on two groups of high chromiumcast iron samples under the effect of1J、2J、3J impact energy and measuring the wearweightlessness, the wear resistance of high chromium cast iron under differentloading conditions was studied. With the increase of load, the wear weightlessness ofhigh chromium cast iron increased. When the load was small, wear weightlessnesswas small, then the wear resistance was good; with the increase of load, the wearweightlessness was increasing; when the load exceeded a certain value, hard andbrittle high chromium cast iron was easy brittle fracture, leading to wear failure. Withthe extension of time, the wear weightlessness of high chromium cast iron increasedgradually.(4) When the impact energy was low, the abrasive wear mechanism of highchromium cast iron was mainly cutting wear mechanism, supplemented by plasticdeformation wear mechanism and crack propagation mechanism. With the increase ofimpact energy, the role of cutting wear mechanism was significantly strengthened, andgouging abrasion mechanism and crack propagation mechanism began to play animportant role as well, meanwhile there existed fatigue wear mechanism. When theimpact energy was high, the main wear mechanism of high chromium cast iron wasgouging abrasion, crack propagation and cutting wear together, supplemented byplastic deformation wear mechanism and fatigue wear mechanism.