Study On A Novel Approach For Evaluating The Contraction Of Hypo-Peritectic Steels During Initial Solidification By Surface Roughness

The surface quality of hypo-peritectic steel has been a long-term research topic in continuous casting technology.Early research on slabs showed that hypo-peritectic steel with a carbon content of 0.09–0.17% was prone to longitudinal cracks.To discover the reasons behind the longitudinal cracks,researchers have focused their attention on the ? ?? phase transformation of these steels.Noticing the cooling rate is an important factor affecting the degree of shrinkage of the peritectic phase transition.However,no matter the calculation models based on the actual production data in the factory or the experimental methods developed by predecessor,it is hard to characterize the degree of shrinkage of the peritectic phase transition under large cooling rate.And with the change of casting speed,the cooling rate of the shell surface also change.Therefore,the realization of characterizing the degree of shrinkage of the peritectic phase transition at a large cooling rate can not only clarify the fuzzy area of the influence of cooling rate on the degree of shrinkage,but also provide guidance for crack control of hypo-peritectic steel.In this paper,the surface roughness value was used to characterize the contraction degree of ? ? ? transformation of the hypo-Peritectic steel during the initial solidification process.And the melting,solidification,in-situ observation and surface roughness measurement process of the steel sample were realized by using the high-temperature confocal laser scanning microscope.Based on the results of previous studies on the cooling conditions in continuous casting,the cooling strength of continuous casting is taken as the cooling condition in the initial solidification process of steel sample.The surface roughness of ultra low carbon steel,peritectic steel and high carbon steel was measured.Combined with the phase diagram,the effects of different phase transition behaviors on the surface roughness are analyzed.It is found that the surface roughness of hypo-Peritectic steel with ??? transformation is obviously larger than that of ultra-low carbon steel and high carbon steel.To explore the effect of carbon content on the phase change shrinkage of peritectic steel under large cooling conditions,and to verify the correctness of the method for characterizing the contraction degree of ? ? ? transformation.The surface roughness Ra(?/?)of hypo-Peritectic steel with different carbon content were measuredThe main research results summarized below:(1)The degree of shrinkage of ??? transformation during the initial solidification determined the value of surface roughness.The larger the degree of shrinkage of the peritectic phase transition,the larger the value of surface roughness.(2)The values of surface roughness Ra(?/?)can be used to characterize the shrinkage degree of the peritectic phase transition under a large cooling rate.(3)Under the cooling rate of 20?/s,the Ra(? / ?)value of 0.10C% peritectic steel was 31.5 ?m,the Ra(? / ?)value of 0.14C% peritectic steel was 25.4 ?m,and the Ra(? / ?)value of 0.16C% peritectic steel was 17.2?m.As the carbon content increased from 0.10C% to 0.16C%,the degree of peritectic ??? transformation shrinkage gradually decreased.