Quote:
Originally Posted by theHIGHLANDER
This is interesting. Usually to anneal (soften) you heat at a specific temp for a specific time and slow cool. Stainless is that different?
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That process works for aluminum. I don't think it applies to stainless steel.
All martensitic and most ferritic stainless steels can be subcritical annealed (process annealed) by heating into the upper part of the ferrite temperature range, or full annealed by heating above the critical temperature into the austenite range, followed by slow cooling. Usual temperatures are 760 to 830°C for sub-critical annealing. When material has been previously heated above the critical temperature, such as in hot working, at least some martensite is present even in ferritic stainless steels such as grade 430. Relatively slow cooling at about 25°C/hour from full annealing temperature, or holding for one hour or more at subcritical annealing temperature, is required to produce the desired soft structure of ferrite and spheroidised carbides. However, parts that have undergone only cold working after full annealing can be sub-critically annealed satisfactorily in less than 30 minutes.
The ferritic types that retain predominantly single-phase structures throughout the working temperature range (grades 409, 442, 446 and 26Cr-1Mo) require only short recrystallisation annealing in the range 760 to 955°C.