Research On Laseralloying With Nano-carbide Ceramics Processing Of Low-ni-cr Infinite Chilled Cast Iron Rolls

The laser alloying technique was applied to the low- Ni-Cr infinite chilled cast iron rolls coated with nano-carbide ceramics in this paper. It has carried on a series of experiments which include increasing high temperature wear-resistance of the roller surface and suppressing the surface crack and enhancing the roller life. Powdered alloy was configuration and technological parameter was optimized and the microstructure morphology of the alloyed coating was analyzed and the theory was studied.Firstly, the foundation power No.0 was configured different ratio through increasing many tough element which is formed powder alloys No.1and No.2. The processing results were that the two kinds of powder No.1and No.2 are effective in suppressing the surface crack and No.2 powder is better than No.1 in the crack sensitivity.Secondly, technological parameter was optimized by orthogonal test and the analytic method of milium, The effect of many factors such as laser power,scanning velocity,facular diameter and so on to the quality of the alloyed coating have been studied. The experiment result show, the scanning velocity is the biggest factor to the alloy layer coating quality; in the same condition, increasing the scanning velocity will improve the hardness to the alloy layer coating but increasing laser power will not. Changing one of laser power or scanning velocity or facular diameter will not do this in certain scope. The optimal scanning speed is 3.5 m/min when the laser power is 4.4KW, facula diameter is 2.0mm, powder thickness is 0.06mm, using No.2 powder and overlapping is 30%, at that moment, the average thickness of laser alloyed coating is near to 0.4mm while average micro hardness is 1162.4HV.Thirdly, the micro structural morphology,composition,the phases of the alloyed coating were analyzed by the optical microscope and the scanning electron microscope binding energy spectrometer and the X-ray diffract meter. The alloy layer resistance to wear has been tested by MM-200 attrition machine. The installing equipment experiment has been carried in the steel mill.Analysis results show that after laser surface alloying, the section region on cast roller is divided into three distinctive zones .The laser melted zone was composed of cellular structure and dendrites crystals, microstructure is proeitectic carbide and demodified ledeburite Ld; heat-affected zone is mainly composed of marten site,residual austenite and carbide. In senmimolten the microstructure is demodified ledeburite Ld. Hardness of the roller after laser surface melting has a gradient distribution along the depth of melted zone. The laser melted micro-hardness is 1000HV, the senmimolten is 900HV and the heat-affected zone is 700HV. Degree of hardness maximum value is apart from superficial ?about 0.2mm.The wear resistantance experiment indicated that extremely thin microstructure of laser melted and plenty of proeitectic carbide and demodified ledeburite Ld are the most reason for resistance to better wear. The microstructure in senmimolten is though zone which cushions stress concentration and hinders the crack penetration link. From the wearing capacity appraisal, the alloy layer resistance to wear is above substrate 6 times.The production practice proved finishing roll is the best in production application; its service life enhances one time than before and increases the benefit for the good line factory 95,000, 0000 Yuan one year.