| In high-saving constructional steel, H-beam is popular for its weight-saving, loading capacity and the stability of cross-section. It has become one of the fastest developing and most using economic section steel. As a near net shape continuous casting product, beam blank is the idealist strand for H-beam. Rolling H-beam by beam blank has some significant advantages, such as low energy consumption, less process, high finished product rate and low cost. However, to date, the research about beam blank continuous casting technology is still hard to meet modern needs, and the control level of this technology is far below expectation. On the other hand, because of its complex cross-section shape, beam blank has more quality defects than other common strand. Therefore, studying on the key factors causing the defects during cooling and discussing on the influence of cooling condition on casting beam blank have great significance to the economy and science.In this paper, the main idea is to find the way of improving the quality of large continuous casting beam blank in Masteel. Firstly, the characteristics of beam blank continuous casting and distribution of quality defects were acquainted by field investigation. And then morphological characteristics of quality defects were analyzed. The conclusion is that cooling condition is the major factor causing crack defect. Attention was focus on studying the heat transfer of beam mold, thermal stress couple of mold/shell and secondary cooling scheme of beam blank by mathematical simulation. Moreover, the cause for crack during cooling was explored and cooling parameters in mold and the secondary cooling zone were optimized. The main work is listed in the followings:Based on the field investigation, the main defects of beam blank are crack, chap, pore and inclusion, which the crack even can cause the scrap rate high as 7 kg·t-1 . The typical beam blank cracks include web longitudinal crack, fillet longitudinal crack, narrow central longitudinal crack, web central internal crack and flange internal crack, and they can been analogy analyzed with common geometry blank crack. The result shows that web longitudinal crack, mainly from the same position in beam blank, have the greatest number. Chaps, appearing on the top of flange, are presumably caused by the flange internal crack. Through analysis, the author believe that the most effective and feasible method to induce existing quality defects of beam blank is to optimize the cooling condition in continuous casting.Two-dimensional finite element models of steady heat conduction below the meniscus region of beam blank molds were developed by using ABAQUS software. Moreover, the influence of grinding thickness of copper plate, cooling water velocity, cooling water temperature, the distribution ratio of cooling water between wide face and narrow face and the diameter and shape of restrictor rods on mold's temperature distribution were explored, and the mold's temperature distribution was evaluated by the peak temperature and the temperature difference between fillet and flange corner( T fillet - Tcorner). Furthermore, the simulation analysis and comparison discussion about the feasibility of part water channel optimization and the overall design for beam blank was completed after analyzing the design basis and probable methods of mold water channel optimization. The water channels design of type A can greatly decrease peak temperature and thermal gradient of mold hot face. Comparing to the conventional water channels, the peak temperature and T fillet - Tcorner of type A water channels decreases 32.5℃and 83.8℃. Meanwhile, three-dimensional model was used to describe the mold's heat transfer and to analysis the influence of vertical temperature variation and casting speed on the mold temperature. In addition, the formula about heat transfer coefficient of beam blank annular channel was discussed and compared with instance. Besides, the effect of copper plate angle and the diameter of chamfer on mold temperature was studied, which put forward the reference to the design of beam blank mold. Most of the above contents fill the gap of the investigation of beam blank mold copper which was reported by literatures.A beam blank mold/shell coupling thermal stress model was established to study the distribution of air gap between the molds, the temperature and thickness variation and the stress distribution. It has found that air gap appears in the flange and fillet with the maximum thickness of 0.45 mm. The thinnest part which is about 12.0 mm lies on the off-corner of the flange. The following thin part which is about 13.5 mm lies on the fillet. During different stages of solidification, the impact of excessive tensile appears in fillet, web and flange tip, which supplies a good explanation for the formation of crack.Beam blank solidification models from mold to cutter were constructed and regulated by nail method and infrared temperature measurement. Meanwhile, relating to its characteristic, the beam blank width temperature distribution is evaluated by the temperature standard deviation in wide face and traditional cold metallurgical norms in secondary zone. It is found that, under the existing secondary cooling condition , the regeneration in fillet was too large in section B of area One. And then the temperature is higher than normal, narrow temperature drops too fast and the overall temperature uniformity is poor. After optimization layout and water quantity of spray nozzle, all the problems have been resolved. The temperature standard deviation at the area two exit was reduced from original 78.24℃to 64.28℃, which shows an improved temperature uniformity. The idea of lateral temperature standard deviation of beam blank and the study about the layout and water quantity of spray nozzle in this part can be considered one of the innovations in this paper.Small hole mold which meet the optimization and original mold were implied in the field. The results show that the two mold's service life reduced by about 50 heats, and small hole mold's life is higher than that of original mold by 200 heats. After casting 500 and 100 heats, the cracking rate of beam blank casted by small hole mold reduced by 89.7% and 79.5% than that of original mold, respectively. And the surface microstructure of beam blank in different location is more uniform. The scene application before and after the optimization of secondary cooling scheme shows that the ration of rolled material quantity, which is causing by quality defects, decreased from 93.08 kg·t-1 to 18.61 kg·t-1, falling by 80%. The transverse temperature uniformity and internal microstructure are more uniform, and the center crack and the shrinkage pore on the flange are also significantly improved. In a word, the optimization of continuous casting cooling condition for beam blank causes the improved quality. It meets with the expectation of the research.
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