Soak time

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Feb 10, 2013
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For AEB-L the heat treat info calls for a 5 minute soak at 1995F. What would happen to the steel if it was soaked for 10 minutes?
 
For AEB-L the heat treat info calls for a 5 minute soak at 1995F. What would happen to the steel if it was soaked for 10 minutes?

As a general rule, you're continuing to dissolve carbides, putting more carbon into solution. AEB-L has such little carbide that I think you run the risk of dissolving the carbides pinning the grain. You'll get grain growth and a lower Mf. The question is, at what point do these issues become objectionable? I think it has a lot to do with the condition of the steel going into HT? The AEB-L I have used was highly spheroidized and needed the longer soak.
 
IME - for high Cr+Mo steels aust temperature determines phase equilibrium. Once sufficient soak time to reach equilibrium, excessive soak time = waste of time and electricity.

Quoted from http://www.calphad.com/

In the temperature range of 1144-1379 °C (2091-2515 °F) the microstructure of Uddeholm AEB-L stainless steel consists of just one single phase: austenite. Thus, if AEB-L steel is hardened from an austenitization temperature that is higher than 1144 °C (2091°F) the resulting martensitic microstructure will contain no primary carbides.

Below the temperature of 1144 °C (2091 °F) the chromium-rich M7C3 primary carbides start to precipitate from the austenitic matrix. At the austenitization temperature of, say, 1052 °C (1925 °F) the equilibrium amount of chromium-rich M7C3 primary carbides is 3.3 molar percent (2.6 volume percent). The equilibrium amount of carbon and chromium in the austenitic matrix at 1052 °C (1925 °F) is 0.44 wt. % and 11.4 wt. %, respectively. (The amount of carbon and chromium in the matrix is a good indicator of the steel's hardenability and corrosion resistance, respectively.)
 
My take is that ( within reason) a longer soak than recommended does little harm, but no good. 5 minutes or 15 would make no difference that you could detect in AEB-L if all other things were done right.
 
Thanks for the info. On my oven when it reaches the 1995F target temp it clicks off (and drops a bit) and takes about 4-5 minutes to get back to 1995F and hold at that temp. That is where I start my 5 minute soak time from. I was wondering if I was doing some harm to the steel.
 
Stacy is right, temperature has more to do with grain growth than time.

No crazy heat treatments needed here. People smaerter than we are came up with these numbers.

Hoss
 

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Thanks for the post Devin. Do you happen to have a larger resolution pic? I'm having trouble reading that one.
 
Hoss, are those precipitated carbides the desirable small ones that you shoot for with AEB-L?
 
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