Study On The Temperature And Stress State Of Thin Slab In Continuous Casting

The thin-slab casting is a major and new technology that is developing in iron and steel production in the world. The study on the temperature and stress stale of thin slab in continuous casting has possessed of great significance. In this paper on the basis of comments on the published documents, author establishes the temperature model and the stress model of thin slab during the solidifying course and calculates the temperature field, the stress as well as strain distribution. Also, author obtains the secondary cooling software of thin slab and predicts the cracking possibility of the slab on various conditions. The gained results can be used to conduct the production and research of thin-slab casting.The temperature model for the heat transfer of thin slab in continuous casting belongs to a two-dimension model. In this model the method of the corrected equivalent specific heat is introduced and the changing time step is adopted. For the first time the cooling differences are considered between the surface of inner radius and that of outer radius of thin slab, and in the transverse direction of the strand. As the result, the temperature model has higher accuracy. And the conception for the effective coefficient of spraying water and the effective specific water flowrate in continuous casting is put forward for the first time. By simulating and optimizing calculation, we gain the results of the reasonable secondary cooling software of thin slab, the varying patterns of the temperature field and the solidified shell. The temperature of thin slab after shearing is high and the temperature in section is well-distributed. These results above are very important in the realization for continuous casting—continuous rolling (CC-CR).Then, author establishes a thermal elasto-plastic and creep (TEPC) stress model for thin slab under two dimensional plane strain condition for the first lime. The equations between stress and strain are given on thermal creep condition for elastic area, plastic area and transitional area of thin-slab section and the new formula of equivalent plasto-strain increment is first obtained by deduction. According to the solidifying features of thin slab, author develops and perfects the finite element method solving the TEPC stress question, and accomplishes the research on the automatic numbering of mesh points and triangular units at various solidifying stages of the strand. The results point out that when adopting changing belt-width storage for stiffness matrix of whole body [K] and using a corresponding solving method [L] I [L()][L| for the equilibrium linear equations, the calculating speed is fast and the occupied memory capacity is small, thus making calculating for stress question using microcomputer possible. For the first time, a weighted coefficient is introduced and used for the disposing of thermal load in the transition area of solidified shell so that there is higher calculating accuracy.Calculating using the TEPC stress model, we obtain the varying patterns of cracking index, equivalent stress, the first main stress, the first main strain and surface displacement (or bulging) during different solidifying stages of thin slab. And author makes first the systematic study at home and abroad on the influence of the factors on stress and strain distribution as well as internal crack formation of thin slab, which include the roller displacement to outside or deformation, the withdrawing and straightening of rollers. Also, author analyses the influence of the surface reheat on the cracking index near the solidifying forward position at the initial stage and the final stage of solidification, comparing the calculation results of TEPC model with those of TEP (thermal elasto-plastic) stress model.The research results point out that the creep has marked influence on stress and strain distribution of solidified shell. In the creep action, the influence of temperature on the stress is very remarkable, whereas the influence of creep time is slightly small. At the initial stage of thin-slab continuous casting, when the casting speed is high, the possibility yielding crack is fairly high;when (he casting speed is lower, the possibility is smaller. In the zone from the middle stage to the final stage , the cracking index is small. The roller displacement or deformation at the initial stage of secondary cooling, the excessive withdrawing force in the zone from the initial stage to the middle stage and the excessivestraightening force in the whole of' secondary cooling zone have remarkable influence on the stress and strain distribution and arc major reasons cracking in thin slab.The laboratory and manufacturing experiments verify that the temperature Held from experiments is better in keeping with that from calculations. The internal crack of the thin slab from laboratory tests do not appear. The manufacturing experiment results state clearly that the surface quality of thin slab is better. The internal quality of some heats is also better, and the internal crack do not exist. The conclusions above conform to the calculating results that arc basically without internal crack using the TEPC model on the conditions of some better machine and proccsR parameters. The some internal cracks come into being from the thin slab of exceptional heats and the crack is mainly transverse crack. The reasons yielding crack maybe are roller displacement or deformation, excessive withdrawing and straightening force, some unreasonable process parameters etc.. The calculating results of the temperature field is also consistent with the relevant results from references on the whole.