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According to the mechanism of crack formation of blooming, blooming process control method. By controlling the surface crack of slab to reduce the amount of finished steel crack scrap. Needs to be pointed out is the first step to control the composition of molten steel, which is the premise of quality control of blooming, especially n, Nb content control, Nb and carbonitride precipitation caused by grain boundary embrittlement and the brittle zone to the high temperature expansion, when the Nb content can reach 0.01% crack on a sharp increase in the.
1 Optimization of heating process
Heating is one of the key process of bloom production. More than 1000 DEG C high temperature plasticity is good, section shrinkage rate was above 70%; less than 1000 Deg. C section shrinkage rate declined sharply and 750 DEG C appeared the lowest value, is about 30%, this is related to the original austenite grain boundary precipitation of coarse carbides of the temperature; after with further decrease of temperature, the high temperature plastic rose gradually, when the temperature in between 400-600 DEG C tends to be relatively stable. Through the high temperature of the steel plastic characteristics analysis, below 1000 DEG C, with the temperature change of the grains in the important phase transition in billet plastic changes violently, select the right into the furnace temperature, can effectively reduce the effect of stress on the quality of billet in the process of shipment, prevent stress cracks, so pack furnace ingot temperature to control in 550 DEG C.
At the same time, according to the heating process of the optimized steel grade. Control of low-temperature heating speed, to avoid low temperature rapid heating caused by crack expansion, to ensure uniform heating, to reduce the temperature gradient, to prevent rolling process in inhomogeneous deformation, and strictly control the heating temperature, prevent the melting of Cr2O3-MnO-SiO2 inclusions and avoid the crack of the first kind.
2 improved rolling process
Bloomer commercial timber is generally based on the rolling under high pressure, studies have shown that, rolling the same thickness of the steel plate, high pressure rolled with beneficial to the bubble, shrinkage and other casting billet internal defect of the welding. However, repeated trial show that subsurface crack when a bear larger rolling force, will be further extended, focuses on the steel bloom blooming, it should adopt the light pressure rolling, that is, to control the single reduction amount, appropriate to increase the rolling passes.
3 improved finishing surface cleaning method
For the surface quality of the finished product plate and slab surface finish is eliminate cracks produced in the process of heating and rolling are the most effective means. The blooming by manual flame cleaning surface defects, the steel for the clearing temperature more sensitive, low temperature clean easily induced delayed crack. Therefore, it is necessary to control cleaning slab temperature lower limit. Due to the subcutaneous crack can not be visual, can not be in accordance with the normal mode of local defects in the cleaning mode, to modify the model, using the whole peeling flame cleaning mode. According to the production of the characteristics of crack defects and multiple regions, the upper and lower surface width to both sides of the 350mm within the depth of cleaning up at least 7mm, and the rest of the depth of the cleaning depth can be around 5mm. Can be adjusted according to the actual situation of defects, clean up the road marks the transition smooth transition, clean up the width of the depth ratio and the length of the depth of more than 10, and smooth without edges and corners.