Abstract The paper reports on the physical metallurgy parameters influencing the transverse crack formation during the continuous casting of steels. The critical temperature region of the transverse crack formation is 700-1150°C. The generally accepted model of this crack initiation, based on the interaction of precipitates and/or non-metallic inclusions and localised plastic deformation in soft zones found on the grain boundaries of prior austenite, was discussed. On the contrary to this mechanism, the conditions leading to transverse cracking in case of very narrow intergranular ferrite films (volume faction lower than 10%) are described. The microcracks can be initiated in these films without the detected additional effect of precipitates and/or non-metallic inclusions. The microcraks are not found, when the volume fraction of ferrite is higher (30% approximately) and the thicker ferrite bands are formed around the grain boundary of primary austenite.