Abstract: The hot cracking tests and hot ductility tests verified that there are two types of hot cracks in low-carbon steel weld bead:the solidification cracks and the ductility-dip cracks.Their brittleness temperature ranges are 1480-1450℃ and 1100-850℃ respectively.The morphology feature of ductility-dip cracking is intergranular fracture with dimples and smooth facets,and there are (Mn,Fe)S precipitates on the cracking surfece.This type of cracking can the prevented by increasing the manganese content in the weld metal.The formation conditions and possible cause of the cracking were discussed.The authors noted that microcracks due to sulfur segregation aud(Mn,Fe)S precipitation at the austenitic grain boundaries may propagate and link up to form a low ductility fractuare.