Analysis and improvement of slab cracking in development stage of 980 MPa grade DH steel
The increasing complexity of automobile structures requires advanced high-strength steel materials with high strength and high elongation.DH steel is developed on the basis of traditional DP steel,which has better form-ability while maintaining strength,but slab cracking has become a key problem restricting the development of varie-ties.The causes of slab cracking of DH steel were studied by means of macroscopic examination,composition detec-tion and metallographic analysis.The results show that the internal quality problems such as coarse columnar crys-tals,serious central segregation and central cracks are the direct causes of cracking.The cracks will expand rapidly during the cooling process of the slab with internal cracks after heating.The thermal simulation test shows that the serious decarburization of the micro-cracks on the surface of the slab will not cause the slab to crack.By developing special mold powder,optimizing the accuracy of casting machine and reducing the temperature drop of slab process,the continuous casting of more than 1 500 t was realized,the slab retreat ratio was reduced from 7.0％to 0.2％,and the slab cracking rate was reduced from 1.74％to below 0.11％.The research results can provide reference for solving the problems of slab cracking and slab breaking in this kind of composition system.
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