Microsturcture Research Of The Bionic And Nonsmooth Brake Drum

Cast iron material's production technology is simple,the manufacturing cost is low,mechanical properties and the casting performance is good,in the car and train's braking system is widely used.In order to improve cast iron material's performance, I made the following:The HT250 and QT600 was laser bionic melting in aqueous media cooling and HT200 was laser bionic melting in air media cooling.The laser melting technology was used on the braking material to improve surface property. The structure and property variation regulation of the braking material were researched systematically in different cooling way and laser processing parameters. The microstructure defects in the laser processing were also analyzed in the particle.The results show that when the laser bionic melting in air media cooling, there is solidness phase in the structure with fine grain size. Both the melting depth and width increase with increasing laser power capacity and the dendritic crystal in the structure decrease. But the melting depth decreases with increasing laser defocusing distance. The microhardness of the melting zone is 2-3times harder than the original zone. The composition of the melting sample doesn't change, but the phase changes from the original graphite,Fe3C and ferrite to Fe3C,austenite and martensite. The fatigue resistance performance and the friction and wear property improve largely after laser melting.When the laser bionic melting in aqueous media cooling, the hardness is higher, the wearability is better, the thermal fatigue resistance is better and the microstructure is smaller than the sample cools in the air. In this condition, the width and depth of melting layer decrease and the hardness increases with the increasing laser scanning speed. But the sample hardness improved largely with the increasing laser current. The biomimetics element zone cooling in the water is small and the shape changes from semicircle(cooling in air) to inverted parabolic(cooling in water) type and the element surface is smooth. The biomimetics element cooling in water have smaller microstructure and better wearability, hardness and fatigue resistance property than the element cooled in air and some irregular net and needle dissolve.In the laser bionic melting processuse design theory,so we gthe regression equation about depth and width of the melting zone of laser processing parameters: QT600's regression equation: HT250's regression equation:HT250's regression equationWhen processed by laser,crack and pore often exist in the melting layer. the main reason of the crack is the fast heating and cooling, it caused the stress in the melting layer;about the pore is the gas in the laser melting process can't escape during the freeze process in the layer.