Soak time

[Lo/Rez]

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?

 

[Nathan the Machinist]

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.

 

[BluntCut MetalWorks]

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.)

 

[Stacy E. Apelt - Bladesmith]

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.

 

[Lo/Rez]

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.

 

[DevinT]

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

 

[Lo/Rez]

Thanks for the post Devin. Do you happen to have a larger resolution pic? I'm having trouble reading that one.

 

[jdm61]

Hoss, are those precipitated carbides the desirable small ones that you shoot for with AEB-L?