Causes of unqualified elongation after fracture of ZG230—450 cast steel keel block

During the tensile test after normalizing of ZG230－450 cast steel keel block poured in a melting furnace, the elongation after fracture was unqualified. The causes of unqualified elongation after fracture were analyzed by means of macroscopic observation, chemical composition analysis, scanning electron microscopy and energy spectrum analysis, metallographic examination and so on. The results show that there were punctate MnS inclusions precipitated along the grain boundary of primary austenite in the tensile sample, which weakened the grain boundary bonding force. Under the action of tensile load, the crack propagated along the grain boundary of primary austenite, forming a mixed stone fracture of transgranular dimple and intergranular dimple, resulting in unqualified elongation after fracture of the material.