Cryogenic treatment is not all retained austenite transforms into martensite, even if repeated cryogenic treatment, 5%-10% still retained austenite, cryogenic treatment will be retained austenite block breaking into film. And distribution in the martensite edge, can reduce the stress concentration at the edge, is beneficial to increase the strength of steel. But between martensite stable residual austenite microstructure composite tissue membrane and dispersed Markov body in different orientation of carbide. Have strong toughness, best.
(1) LD steel after cryogenic treatment is not complete transformation of retained austenite, repeat after cryogenic treatment still has residual austenite.
(2) LD steel after quenching and cryogenic treatment, quenching and tempering, cryogenic treatment with strong toughness, strength and composite cryogenic treatment has better strength and toughness and wear resistance, repeated cryogenic treatment effect is better.