Synopsis In order to redllce the occurrellce oj suiftlCe difects oj a cOlltillUOUS castillg slab, the most suitable secolldary coolillg pattern was de filled all the basis oj the results oj a theoretical calCillalioll allri a laboratory scale exIlerimellt all the thermal hysteresis similar to those oj cOlltilluous castillg slabs. M oreover, i t has been considered ill this study that the trallsverse corner cracks could be relaled to the p resellce oj precipitates appeared ill the austenite grain boundaries. (1) T rallsverse corner cracks are formed by the precipitates oj AI N ap/leared all the grain boundary in the austenite region at the temperatures in the rallge oj 700 to 950°C. Especially , the AIN Jormatioll is accelerated by reheatillg it at the temperature above 700 e Jrom Ihp. lower temperature. (2) From tlIP experimelltal results all the roles oj secondary coolillg pattern and oj temperature nt the unbending roll in slnbs continuously cnst, it is nscertained that the occurrence oj transverse corner crack is SllCcessflll~l' prevellted ~y the secolldary cooling pattern, that is, a suitable coolillg rate is less thall 83 e lm ill the upper part oj continuolls casting machille. (3) T he lI<w~)'-devleoped slnay coolillg I,nttern is also eflective Jar the redllctioll oj 10llgitudillal slIr/ace cracks.