Study On Laser Surface Alloying Process Of Cast Iron Roll

Rolls are the important consumable parts in the metallurgical process. The surfacewear is one of major failures of roller. Therefore, using some methods to strengthen theroll surface is of great economic benefits.Some companies adopt surfacing, thermal spraying, spray welding and inductionheating to strengthen the roll surface. But all the alloy coating gained by these methods hassome defects. The laser surface alloying is a new surface modification technique, whichcan strengthen the roll surface and obtain dense coating with metallurgical bonding withsubstrate. On the point of energy inputting, the energy distribution of hollow circular laseris more rational than circle solid laser, which make hollow circular laser has a goodapplication prospect in the field of laser alloying. The aim of this paper is to get densecoating on the surface of roller by using hollow circular laser alloying, and this dense musthave good abrasion resistance. It can offer theoretical guidance for the application of thehollow circular laser alloying in the field of roll repairing.In this paper, the finite element model of the laser alloying process by using hollowcircular laser is established by the finite element analysis software ANSYS. And thepictures of the temperature field under the different parameters are obtained and thetemperature curve of five nodes which is changing with time is also obtained at the sametime. And compared with the pictures by using solid light, the energy distribution ofhollow circular laser is more rational. All these pictures can provide the theoretical help forthe experiment analysis in the latter.Pre-coat the Molybdenum-based on the surface of cast iron roller and conduct thelaser alloying by using hollow circular laser. Then carry out a systemic research to analyzethe microstructure, hardness and abrasion resistance. The effects of scanning speed, powerdensity and overlap rate on the quality of alloying coating were analyzed.The results show that after laser alloying the grain of coating is dense and fine. Thecoating can be divided the fused zone and phase transformation hardening zone. Thegrainof fused zone is in the shape of dendritic crystal+columnar crystal and the main components are eutectic carbides+Martensite. The main components of phasetransformation hardening zone are Residual Austenite+Martensite+Carbide.In this experiment parameter range, the results are as follows.(1) With the increase ofscanning speed, the thickness of coating decreases and the number of cracks increases.Also the scanning speed increasing makes the grain be more and more fine and thehardness and abrasion resistance of coating are gradually enhanced.(2) The power densityincreasing leads to the decrease of undercooling. So that the grain becomes more and morebulky and the hardness and abrasion resistance of coating is better and better, which causedby the increasing of Carbide.(3) Lap has great effects on the quality of coating. The grainof overlapping area is in the shape of cellular crystal and the original direction wasdamaged. The hardness of overlapping area is lower than the lap section, which caused bythe secondary remelting and tempering. The result of wear test shows when overlap rate is50%, the abrasion resistance is best.Finally, the optimal parameters are obtained. They are: the laser power of1800W,overlap rate of50%, scanning speed of40mm/s and the laser spot diameter0f1.71mm. Inthese parameters, the alloy coating of good wear resistance and dense microstructure isobtained.The reasons for the improvement of the micro-hardness and abrasion resistance of thealloy coating were as follows: the dense and small grain, the strengthening effect ofMartensite and a certain amount of Carbide, solid solution strengthening effect of alloyelements.