Study On Reversing Interface Heat Flux For Strip Casting By Dendrite Arm Spacing

In recent years, twin-roll strip casting, as a new technique, it not only consumes less energy, but also lowers the cost with short process during production. So, it is welcomed by many iron and steel industry all over the world and has made remarkable achievement in the field. Strip casting processes produce thin strips directly from liquid metal, thereby eliminating rolling steps and associated annealing operations. Freezing rate of metal depend on the condition of heat transfer between thin casting and casting roller. Thus, it will influence the structure property and surface quality of material. In addition, it is a decisive factor that is used to make the process planning. it is necessary to study heat transfer in the interface.A mathematic model for determination of the surface heat flux was built based on one of the inverse heat transfer methods. According to heat-conduction differential equation, the mathematical expression of the growth rate, solidification velocity, the temperature field of solidified shell, the temperature gradient field of solidified shell and interfacial heat flux during twin-roll strip casting can be calculated based on secondary dendrite spacing. The numerical calculation was carried out, taking1Cr18Ni9Ti stainless steel as an object. The relationship between these variables and the coagulation time were studied. The schematic model of heat flux before Kiss point for two-roll strip casting was established.The results showed that interfacial heat flux will become weaker and weaker with increasing of solidification time. In addition to the very short time of liquid steel contacting with crystal roll, the heat flux was in the same magnitude of106W·m-2with existing research. The two stages of interface heat flux were given:First, contact solidification stage, the declining rate of interfacial heat flux is very fast near meniscus; Second, it is slower in the position from nearer Kiss point. In addition, the further calculation indicated that twin-roll strip cast is a sub-rapid solidification process, which conforms to the actual situation. In addition, the further calculation indicated that the cooling rate is at10～103K/s magnitude and twin-roll strip cast is a sub-rapid solidification process, which conforms to the actual situation.