(1) high speed steel using loop cryogenic treatment process, axial ratio of martensite and carbon content decreases, the loop repeatedly after cryogenic treatment, further reducing the austenite content. Little influence extended cryogenic time on the austenite content.
(2) high speed steel loop repeatedly after cryogenic treatment, the average particle size of carbides decreased significantly, a large number of New Superfine carbides particles along the martensite twins and dislocation line precipitation. With the increase of cryogenic times, amount of carbide precipitation increased, size and spacing becomes small.
(3) high speed steel multiple loop cryogenic treatment result is better than 1 long cryogenic, compared with 1 long deep cryogenic treatment, many short time loop after cryogenic treatment on mechanical properties of high. In order to optimize the cryogenic treatment process in the actual production, should be appropriate to increase the number of cryogenic treatment.