Research on Temper Brittleness of a High-strength Low Carbon Constructional Steel

Effects of tempering temperuture on the impact toughness of an high strength low carbon constructional steel was studied by charpy impact test,and the mechanism of the temper brittleness was analysed by SEM and TEM. The results showed that temper brittleness of the low carbon constructional steel appeared when the higher tempering temperatures were 580℃ and 610℃,the charpy impact energy at- 20℃ was reduced from 238 J (tempered at 550℃) to 19 J(tempered at 580℃) and the impact fracture was changed from ductile to brittle. The temper brittleness was mainly due to the many large sized brittle precipitation of M²³C⁶ phase containing Mo at the grain boundary,which was the source of the crack.