Can we reduce the time holding in heat treament before quenching ? 2

[stanislasdz]

In order to reduce the cost of our heazt treatment we look for reducing the time holding of heat treatment espacialy in the holding in austenitic area before the quenching.

For a standard alloy steel like 20Mn6 or 25CD4 when the temperature imposed have reach the right value we hold the furnace a this temperature for 2 hours + 1 hour par inch of thickness.

Question :

1- Can we reduce the time holding of 2 hours, since there is no chemical diffusion like in homogeneising ?

Thanks in advance for all if you have a answer !!

Stan

 

[Yallapragada1022]

You can apply "one hour per inch" soak after the furnace reaches the temperature. I am not sure why you are holding for 2:00 hours after furnace reaches the temperature.

Hope this helps.

Rao Yallapragada

 

[stanislasdz]

Perhaps only a "rule of thumbs" used by the people who are in heat treatment before. may be also to be sure that the temperature had reach the heart of the part !!

Me too i'm so surprised to soak for 2 hours ?

But in other hand, i have look for indications in Volume 4 of ASM handbboks and i have not found any things for time soking for steel casting...

May be i don't look for well !

 

[swall]

The proper way to do this is to drill a hole to the center of your heaviest section (use a scrap part as to not ruin a good one)and insert a thermocouple and monitor the core temperature of the part.

 

[Yallapragada1022]

I agree with swall on proper way to figure out the soak time. We employ this method in our vacuum furnaces (carburizing) and other atmosphere furnaces (Carburizing & hardening).

I also think that you won't go wrong with "One hour per inch" rule.

Rao Yallapragada

 

[stanislasdz]

thanks all !

But my question what are the soaking time best time from your experiences ?

2 hous like us ?
1:2 like have sujected to me a friend ?

i dont have any clear answer !! is there any good paper on this ?

Thanks gain

 

[metengr]

For austenitizing carbon and low alloy steels, the established hold time to assure no thermal gradients is 1 hour per inch of material thickness at temperature. The actual rate of austenitizing is less than this hold time. However, given the lag time to avoid temperature mismatch 1 hour per inch was established.

There is an excellent paper on this very subject. It deals with suggested austenitizing temperatures for various grades of steels, transformation of austenite as a function of time at temperature, etc;


"Heat Treatment Procedure Qualification, Final Technical Report" by The Pennsylvania State University

 

[stanislasdz]

I have just the paper, it 's a wonderful paper !!!!


metenger : you are an ANGEL,

 

[CdotS]

I use less than 1 h/inch for 0.30C steels up to 3 inches. It seems to be working.

Metengr, can you please give the full reference for the Penn state uni paper so that I can get a copy? Any pdf version available on the Internet?

 

[stanislasdz]

Hi cdots

here the link :

http://www.osti.gov/bridge/servlets/purl/836878-AegKFa/836878.PDF

 

[stanislasdz]

in our facory we use 2 hours + 1 hour by inch

when i ask why 2 hoours the Heat treatment departement say me that 2 hours to be sure that all the transformation to the austenite is done ?

May be it's wrong , are you agree Cdots ?

 

[EdStainless]

Thi initial hold time (2 hour in your case) is to assure that the entire load has reached temperature. The 1 hr per inch thickness is enough time to assure that the part heats through and fully transforms.
Trust us, you can reduce the time. You will need to run some tests to figure out how much.

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[stanislasdz]

Sorry EdStainless !!!!!!

I trust the experts of this forum.... my questions were just to be sure.

Thanks !

 

[redpicker]

Just to chime in, yes, you should be able to reduce this time. The hour per inch rule is to insure adequate time with "normal" furnace loading and furnace heating rates. Depending on furnace design, your part configuration, and loading, you can significantly reduce this time.

We are processing 9.5 inch bar with a austenitizing furnace resident time of just over 1.5 hours, or less than 10 minutes per inch. You have to be careful (the PSU report seems to be an excellent reference), but there is no reason to hold to the 1 Hour per Inch rule if you know you can control the process.

rp