| Abstract: | To investigate the structure of quenched and tempered large section die, the cooling rate simulating that of central part for 300×300mm section has been used during quenching. As a comparision, ordinary quenching process has also been carried out. TEM observation shows that the structure of the latter is mainly lath martensite, and that of the former is B_I -bainite, which possesses higher temper stability than those found in low carbon low alloy steels. Transforming of great quantity of retain austenite and creating of chain-like distributed M_3C are considered as the main reason of the embrittement for the large section dies. |
