Study On The Control Of The Surface Cracks And The Cleanliness For H-Beam Blank

In the steel products, there are some kinds of special section steel. As an economic section material, H-beam has been used in many fields of national economy development. Beam blank is the idealist strand for H-beam production. In our country, there are only three beam blank production lines. Moreover, there are more defects on /in beam blank than other common strand. Therefore, studying on the H-beam blank quality assurance system, finding the key factors causing the defects and optimizing the casting technic has great significance to the economy and science.Based on the actual production process, the paper is aimed to find the key factors causing the surface cracks and the cleanness defects of beam blank and to optimize the casting technic. There are two research methods, the one is experiment analysis, and the other is numerical simulation. The former is to test and analyze the cracks, the inclusions and the flux in the mould, and to find the preliminary factor causing defects of beam blank. The latter is to simulate the flow field, temperature field and the inclusion movement, to find the key factor causing defects and the optimum the casting technic. The main work is listed in the followings:(1)The cracks on the H-beam web were analyzed under the metalloscope, the stereoscan and the energy spectrometer. Based on the pattern and the component of the surface cracks, the cracks characteristics were analyzed and the preliminary factor causing cracks were found.(2)By the tracers tracking, sampling taking and micro analyzing the steel cleanness, the source of inclusions were analyzed from steelmaking to continuous casting. T[O] in the steel was analyzed by infra-red absorption, the large-scale inclusions were analyzed by sample-electrolyzing method and the micro inclusions were analyzed by the metalloscope and the stereoscan. The methods increasing the cleanness and decreasing the defects were brought forward based on the above analysis.(3)The physicochemical property of the flux in the mould, such as the alkalipenia, the melting speed, the melting temperature and the viscosity was measured or calculated. The weakness of the flux was find, which may cause the surface defects of beam blank. The suggestion was put forward to modify the flux based on the above analysis and actual production.(4)The 3D coupled flow field and temperature field in the tundish was simulated used the finite element method. Then, the inclusions movement, the collection rate from the outlets and removal rate of the inclusions were calculated. The shortcomings of the fluid flow in the tundish were analyzed. Moreover, to increase the cleanness of the steel, the physical dimension of turbulence inhibitor was optimized.(5)The 3D flow field and the meniscus fluctuation in the mould were simulated used the finite element method. The influences of processing parameters (such as casting speed and the nozzle parameters) on the molten steel flow (such as the location of the vortex, the steel impact depth, the velocity and fluctuation of the liquid at free surface) were analyzed. In order to increase the cleanness of the steel, the optimum spans of the processing parameters were brought forward based on the calculation.(6)A coupled 2D thermo-mechanical finite element model was developed to compute the temperature and stress/strain profile in beam blank. By comparing the calculated data with the metallurgical constraints, the key factors causing the cracks on the beam blank can be found out. In order to optimize the processing parameters, a new optimization method was developed combined MOGA and FEM based on the MATLAB toolbox functions. The heat flow density was modified in each secondary cooling zone used this optimization method.In order to increase the cleanness of beam blank and decrease the cracks on the web, a series of corresponding methods are put forward in this paper. Now, online verifying of those optimization projects have been put in practice, which can prove that those are very useful and efficient to control the actual production.