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Vijay B. Pawar
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Join Date: Jun 2011
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Isothermal Annealing of EN355 Forging

06/08/2011 8:53 AM

I have tried Isoannealing EN355 forging with soaking at 970°C for 3 Hrs. slow cooling to 700°C then soak at 660°C for six hours. But the microstructure observed was spheroidised cementite with bands of bainite. We are aiming for Ferrite + Pearlite. What cycle we should give?
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Milo
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#1

Re: Isothermal Annealing of EN355 Forging

06/08/2011 10:14 AM

Here is chemistry for this material:

Chemical composition in weight %: 0.20% C, 0.23% Si, 0.61% Mn, 0.011% S, 0.015% P, 2.0% Ni,
1.65% Cr, 0.19% Mo

This is a Case hardening steel.


.. The Isothermal process is what creates the bainite, if you don't want the bainite, why are you holding at high temperature to promote its formation?

I'm presuming that you don't want bainite, which is an acicular structur of Ferrite with Carbide; since you said you want ferrite and pearlite, my suggestion would be to take to LP anneal. Ask your supplier for the Time/ Temperature cycle for this grade. This should result in Ferrite / Pearlite.

http://pmpaspeakingofprecision.com/2010/06/29/5-reasons-to-anneal-steel/

http://en.wikipedia.org/wiki/Annealing_(metallurgy)

You might also want to look at Normalizing on future work directly after forging ( not on this batch of mixed structure forgings!!!)

Here's Dan Herring's explanation on this topic:

http://www.vacaero.com/News-Info-From-Industrial-Heating-Magazine/News-Info-From-Industrial-Heating-Magazine/The-Importance-of-Normalizing.html

Also see : http://info.lu.farmingdale.edu/depts/met/met205/normalizing.html

Milo

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Vijay B. Pawar
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Join Date: Jun 2011
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#2
In reply to #1

Re: Isothermal Annealing of EN355 Forging

06/16/2011 2:22 AM

Sir, heating at 970°C was done to completely austenitise the steel & dissolve as forge structure completely.

After soaking at 970°C, it was hold at 660°C for sufficient time for isothermal transformation into ferrite & pearlite. I didn't understand why bainite is formed after following this cycle.

Our existing furnace set up is for such type of H.T. cycle only. We have one austenitisation furnace (four trays are loaded at a time) with hydraulic pusher & isothermal transformation furnace (five trays are loaded at a time) with hydraulic pusher.

For LP normalising of EN355 forgings, what should be cycle followed?

Our previous trials have shown that with even still air cooling after normalising, it gives completley bainitic structure in EN353 & EN355 forgings.

For direct normalising from hot forging, what should be the type of set-up?
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