Research And Control On Transverse Corner Crack In Continuous Casting Of Rectangular Bloom Of Low Alloy Steel With Large Cross-section

Q345E steel grade is the highest level of the medium products of product line in Laiwu Steel, using vanadium, titanium, niobium, boron, micro alloying process, the carbon content of steel in 0.08 to 0.10%, belong to the peritectic steel, slab corner transverse cracks lead to a large number of slab surface defects and scrap metal rolling crack edge, seriously affected the slab percent of pass and rolling yield improvement. So the big cross section of the rectangular low alloy steel slab corner crack formation is analyzed, to study and formulate the corresponding control measures.This paper reviews the research status quo of the transverse corner crack of low alloy rectangular steel slab of major section, for the transverse crack problems of peritectic steel bloom by vanadium, niobium, boron, titanium micro alloyed in the continuous casting production process, by means of optical microscope and scanning electron microscopy(SEM) analysis and research on slab corner transverse crack morphology characteristics, microstructure precipitation, that the causes of the bloom corner transverse cracks of the peritectic steel with vanadium, niobium, boron, titanium micro alloyed elements is presented as follows: the solidification precipitation of MnS in the molten steel along the austenite grain boundary at higher temperature in the continuous casting process, and its slowly grew up with the temperature falling, and promoted the vanadium, niobium, boron, titanium, aluminum carbonatite precipitation under low temperature. As effective ferrite nucleation particles of MnS, and the precipitation of the carbon and nitrogen compounds of vanadium, niobium, boron and titanium, aluminum promoted the membrane formation of proeutectoid ferrite along austenite grain boundary, when subjected to mechanical stress or straightening stress in the two phase interface of ferrite and austenite, because of different intensity, the two phase stress is non-uniform, thus the stress concentration in the relatively soft membrane ferritic phase, and some pores generate around the precipitates, and the micropores aggregation leads to the formation of cracks.For the corner transverse cracks problem of the low alloy steel bloom in Laiwu Steel, that the technical measures of the improving slab surface temperature and its uniformity and reduce vibration mark depth and the measures of reducing the nitrogen content in steel is proposed, to control the slab corner transverse cracks. and, a promoved process is presented as follows: reduce the primary and secondary cooling intensity, improve the cooling uniformity, degrade the slab corner surface temperature from 800? to 900?; develop the "Slow cooling type" mold powder; optimize the vibration parameters; improve the protection effect of pouring to reduce the nitrogen content in steel. Industrial production results show that the slab corner crack defects basically eliminated by used the improved process.