Multiple or duplex heat treatment

[nasarali]

I heard some times with some kinds of steels, the double normalizing or hardening were used, so my question is:
What is the main function of multiple or duplex heat treatment, and when is more useful

 

[arunmrao]

Please be more specific about the heat treatment process ,description of part and the grade of steel to get a good response. Else,to me it smells of homework question.

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