Initiation And Propagation Of Intermediate Cracks And Surface Cracks In Continuous Casting Bloom

With the rapid development of science and technology,social productivity and economic markets,the demand for large sections and high-quality steel materials is increasing.However,quality defects such as segregation,porosity,and shrinkage are easily formed in the production process of large-section continuous casting billets,especially wide-thick slabs and blooms.Among various quality control technologies,soft reduction technology and heavy reduction technology have obvious effects on the improvement of defects such as segregation,center porosity and shrinkage.However,the application of soft reduction technology and heavy reduction technology has increased the risk of cracks to a certain extent.Unreasonable reduction positions and excessive reduction amount can easily cause crack defects.Therefore,while continuous casting soft reduction and heavy reduction technologies can effectively improve segregation,porosity and shrinkage,if crack defects can be effectively controlled,the quality of continuous casting billets with wide-large sections will be further improved,and the production of high-quality steel will be continuously promoted.In this paper,the critical criteria for the initiation of intermediate cracks and the critical criteria for surface crack propagation are determined experimentally.Then,the thermalmechanical coupling model of the full continuous casting process is established to simulate and analyze the thermal and mechanical behavior of the billets during continuous casting.A crack risk prediction model was established based on the crack criticality criterion and the thermalmechanical coupling model of the continuous casting process,and analyzed the risk of crack defects under different operating conditions,and then proposes a process optimization route for on-site production.The main contents and results are as follows:(1)The critical crack criterion was determined by the high-temperature tensile test,which provides the basis for crack risk analysis.The critical strain for the initiation of intermediate cracks in bearing steel is 0.05,the critical strain for initiating intermediate cracks in microalloyed steel is 0.04,and the critical strains of corner crack propagation of high titanium at 750℃,800℃,and 850℃ are 0.143,0.149,and 0.158,respectively.(2)Based on the actual caster roll train,a full-process thermal-mechanical coupling finite element model for continuous casting of blooms and wide-thick slabs was established.The heat transfer and deformation behavior of bearing steel bloom and microalloyed steel wide-thick slab in full continuous casting process were simulated and analyzed.The simulation results show that the stress and strain of the slab begin to increase in the bending section,the stress and strain of the slab in the curved section remain basically unchanged,the stress and strain in the straightening section increase,the stress and strain in the pressing section increase significantly,and the center strain of the slab in the pressing section Larger,reduced deformation can be better transmitted to the center of the slab to improve the internal quality efficiently.(3)Based on the critical criteria for crack initiation and propagation,and the thermomechanical coupling model of the continuous casting process,the risk prediction model for intermediate crack initiation and surface crack propagation was established.The risk of intermediate crack initiation of bearing steel bloom and microalloyed steel wide-thick slab,and the surface crack propagation risk of high titanium steel wide-thick slab were analyzed.