Abstract: On account of current status quo of S355J2 steel’s cracks in the production process, surface transverse cracks were analyzed by SEM and EDS, and low temperature brittle zone was detected by Gleeble-1500 test. The morphology and size of precipitates were analyzed by using TEM, and thermo dynamical calculations of precipitates were counted. The results indicated that the sulphur segregation at the grain boundary formed sulfides and increased the brittleness of grain boundary when γ→α transformation occurred which lead to rise the susceptibility of transverse cracks in steel. The low temperature brittle zone was 750—910 ℃, and the temperature of transverse crack susceptibility range was 745—903 ℃, which was in correspondence with the former. The ductility of steel decreased while the size of precipitates decreased, so did the thickness of ferrite film increased.

Key words: low temperature brittle zone, temperature range of transverse crack susceptibility, precipitates, ferrite