Structure of αγ phase in alloys of the YuNDK and YuNDKT type
In alloys YuNDK and YuNDKT cooled from the two-phase region at rates of 50–100 deg/min the αγ has a martensitic structure. This confirms the assumption of a diffusionless mechanism of the γ→αγ transformation. At cooling rates considerably lower than 50–100 deg/min and during isothermal holding in a temperature range near the lower limit of the two-phase region the diffusional γ→α transformation is possible.
In alloy YuNDK24 the rate of the diffusional transformation is highest at 740°C; in this case it is completed in 3 h. In alloys YuNDK35T5 and YuNDK40T7 only the partial diffusional γ→α transformation occurs. The rate of the transformation is highest at 780°C.
KeywordsCool Rate Lower Limit Isothermal Holding Martensitic Structure Diffusional Transformation
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