Dendritic Growth And Peritectic Solidification Of Steel

It is well known that steel is one of the most versatile metal materials due to its good combined properties and low price.Although the technology for producing steel and continuous casting are very mature at present,steel and iron materials are still affected by defects such as cracks and segregation in the production process.In the current study,although we have been able to observe the growth of the branches and phase changes process in solidification process of the small-size sample through X-ray in-situ observation techniques,continuous casting solidification is the continuous solidification process of high temperature steel fluid,and its operating space is small and opaque,so the evolution of the growth of the branches in situ observation in the process of continuous casting blank solidification has not yet been achieved.As a kind of steel with excellent performance,peritectic steel can be seen in all aspects of life.The characteristic of peritectic steel is that peritectic reaction occurs during solidification,and it is bound to be accompanied by volume shrinkage,which easily leads to cracks and other defects between continuous casting slab and continuous casting slab shell.Although many scholars have studied the peritectic reaction,but there is still great controversy about the mechanism of it.Due to the rise of computer technology in recent years,more and more attention has been paid to the method of numerical simulation.The rise of simulation methods such as phase field(PF)method and cellular automata(CA)method makes the description of dendrite growth and peritectic phase transformation process in the solidification process of continuous casting slab closer to reality.By comparison,the phase field method is adopted to couple the phase field,solute field and temperature field,and a phase field model for dendritic growth of binary,multicomponent alloy and a multiphase field model for inclusion reaction are established.The dendritic growth of binary alloy of peritectic steel under isothermal and non-isothermal conditions,dendritic growth during solidification of ternary alloy and peritectic phase transformation during solidification are simulated respectively,and the effects of different parameters on the growth reaction process are discussed.The main research contents and results are as follows:(1)In the process of simulating solidification of Fe-C binary alloy,the results calculated by the established model and LGK analytical model are compared.The results show that the model can well simulate the process of dendritic growth in solidification of binary alloy.When the umdercooling degree increases in the range of 15-25 K,the growth rate of dendrite tip increases from 3.59×10-3 m/s to 5.34×10-3/s,the number and growth rate of secondary dendrites increase,the enrichment phenomenon becomes more serious,and solute will be more enriched around the dendrite trunk.In the binary alloy solidification process of isothermal and non-isothermal,when the perturbation intensity increases in the range of 0 to 0.03,the growth of dendrite trunk does not change,but the number of secondary dendrites obviously increases.However,when the anisotropic increases from 0 to 0.05,the growth rate of dendrites increases obviously,but the number of secondary dendrites does not increase.(2)In the simulation of dendritic growth during solidification of Fe-C-P ternary alloy,LGK analysis model is firstly used to verify that this model can simulate dendritic growth process well.When the undercooling degree increases from 20 K to 30 K,the growth rate of dendrites increases obviously,and solute will be more concentrated near dendrites.However,with the decrease of the initial contents of the solute of carbon and phosphorus,the dendrite growth is obviously accelerated,and the concentration of solute accumulated near the dendrite also increases,but the increase is very small and will not exceed the decrease of its initial solute.(3)A high temperature confocal experiment was carried out on the selected peritectic steel samples.The growth rate of L/?/? triple point was measured to be 1.36 mm/s,and the advancing rates of L/? interface and ?/? interface were 12.4 ?m/s and 52.2?m/s respectively.(4)The phase diagram of peritectic steel samples was calculated by Factsage software.A multiphase field model of peritectic reaction is established.Through verification of one-dimensional simulation,this model can well simulate the peritectic reaction process during dendritic growth.The peritectic reaction of dendrite and the growth process of L/?/?triple point are simulated.Through calculation,the growth rate of L/?/? triple point is 1.09 mm/s,and the advancing rates of L/? interface and ?/? interface are 11.1 ?m/s and 44.4 ?m/s,respectively,which are consistent with the experimental results.When the undercooling degree and undercooling rate increase,the peritectic reaction is promoted.It was found that the peritectic phase change and the packet crystal reaction occurred simultaneously and were controlled by carbon diffusion.