Research On High Temperature Thermal Fatigue Damage Mechanism Of Bimetal Specimen For Copper Plated With Nickel Plating

With the development of steel smelting technology,rolling becomes the main production process for strip production.It includes cold-rolled,hot-rolled and twin roll strip continuous casting.The process refines the crystalline structure,and the products have good structure and performance.The production way of continuous casting and rolling has become the most advanced mode in the field of iron and steel production.Roll is the main core components of Mill.In the process of rolling,the working conditions of roll are complex,especially in the production process of twin roll strip continuous casting.Roll must carry the complex condition of large alternating stress load and alternating high temperature.The main failure way of roll is fatigue crack failure on roll surface in addition to the normal friction and wear failure.It occupies a larger proportion in the production.It is important that extend the fatigue invalidation cycle of the roll and predicting its fatigue life accurately,because of the price of the roll cost is too high.It is good for improving quality and performance of the product.It is very important for reducing production cost.On the basis of the analysis of the domestic and foreign academics research,Summed up the important influence factors of initial fatigue crack and propagation behavior of the roll.According to the actual problems occurred in the production process of twin roll strip continuous casting of thermal fatigue failure,we designed the experiment device of thermal fatigue failure.It was investigated that the influence of different temperature on the thermal fatigue crack propagation under certain loading conditions;thermal fatigue crack propagation under the influence of different heating cooling frequency;thermal fatigue crack propagation under the influence of nickel coating;the matrix fatigue initiation and expansion mechanism in the high temperature cycle heating conditions.They were obtained by tests that the thermal fatigue crack propagation of the copper matrix accelerates with the increase of the temperature under the action of a certain load.As the heating temperature increases,the internal alternating thermal stress increases;the thermal fatigue crack propagation is accelerated when the heating frequency increases;the nickel coating has a certain heat resistance,the thermal fatigue crack growth rate of the sample with nickel coating is lower than that of the copper matrix;Under high temperature conditions,a large number of metal oxides at the crack tip accelerate the expansion of fatigue crack.