Study On Solidification Microstructure Control Of High Chromium White Cast Iron

High chromium white cast iron widely used in mining and metallurgy, buildingmaterials, aerospace and other fields owing to high hardness and high wear resistance. Itplays an important role in the field of wear resistance. However, the characteristic ofhigh hardness and low toughness had been existed in the application of high chromiumcast iron for many years, Which not only limits widely use，but also accelerated thedamage of materials. The toughness of high chromium cast iron mainly depends on themorphology, size, distribution and microstructure of the carbide.15Cr and28Cr alloyswere selected for the present study. Variable-temperature body had attempted tochanging the distribution of temperature field during solidification. Finally, it wouldbe expected to desirable microstructure. The microstructure and elements distributionafter temperature change was studied. The formation mechanism，structure changecharacteristic and alloy elements distribution were investigated in detail. The effect oftemperature field on microstructure during solidification was studied, the followingresults were obtained:The temperature field during solidification was influenced by the insertvariable-temperature body in the center of high chromium cast iron melt. Carbides wereobviously refined and homogeneously distributed in the area of interface ofvariable-temperature body and high chromium cast iron melt. Carbides were obviouslycoarse and exhibited the directionality in high temperature field. The carbides showedthe strongly directionality and became relatively coarseness near casting mould.The temperature field of28Cr alloy was changed by the insertion ofvariable-temperature body. The block carbides were refined at the interface of highchromium cast iron and variable-temperature body. With the increasing distance of variable-temperature body，the melt temperature raised and carbides size became coarse,the carbides distribution was not uniform. The microstructure near casting mould wascoarse and had a obviously directionality. C and Cr atoms obviously diffused near theinterface of high chromium cast iron and variable-temperature body. The same methodwas applied to Cr15alloy. The microstructure was well refined and carbides had afinely dispersed form in matrix. Carbides with indistinct directionality mainly showedthe needle-like and rod-shaped morphology. With the increasing distance ofvariable-temperature body，It was observed that carbides in high temperature field had aweak change tendency, but had the presence of carbides bonding and weakdirectionality. Carbides near casting mould were coarse and directionalThe change range of temperature field of high chromium cast iron was different bychanging temperature body size, the difference directly influenced the size, morphologyand distribution of carbides. The variable-temperature body with large size had astrongly changing ability. Meanwhile, large temperature gradient was formed aroundvariable-temperature body. Which had beneficial effects of carbides growth, and madecarbides growth along temperature gradient simultaneously. Finally, carbides exhibitedthe obviously directionality.