In the continuous casting,the features of the high-temperature microstructure ( HTM),namely,the prior austenite grain size,the film-like ferrite and the distribution of the second phase participates,are the key factors to affect the slab corner transverse cracking susceptibility during bending and straightening.However,it is difficult to observe the features of HTM during the continuous casting.The features of HTM can be represented indirectly by the features of as cast microstructure ( ACM) at room temperature,thus the quantitative relationship between the slab corner transverse cracking and the features of ACM could be established.In this paper,the relationship between the features of ACM and the slab corner transverse cracking susceptibility of four micro alloyed steel grades under different cooling patterns was investigated and the criterion based on the features of ACM for the slab corner transverse cracking susceptibility was established.The results shows that : 1 ) The features of HTM can be demonstrated by five parameters of ACM,namely,prior austenite size ( DΥ),average size of ferrite ( DF),ferrite mixed index ( △E),film-like ferrite precipitation fraction (fMF) and the second phase distribution;2) The prior austenite grain size is a major factor to affect the features of ACM.The fMF,DF and AE increased with the increase in DΥ.And the second phase precipitates tend to be chain-like distribution along the austenite grain boundaries;3 ) The slab corner transverse cracking index has positive correlation with the five parameters of ACM and the coarse prior austenite grain size is a key factor.Transverse cracking could be prevented by the process optimization and prior austenitic grain refinement.