more about stainless steel heat treat

A few weeks ago I've asked in this forum (with the nick name "sillar" that now I changed with part of my name: "Bruno Cris") how to heat treat in the best way stainless steel. You gave me three way to proceed:
- fill with Argon the oven
- coate blades with Turco compound
- put blades into a stainless steel envelope

In these last weeks, trying to find the easiest way for me, I discovered that:

Talking with the builder of my oven he told me that is not possible modify it to use with argon inside for various reasons (heating elements are not made to work with argon atmpsphere and the equipement to store argon is very expensive and so on). So I must excude this way.
Regarding Turco compuund I've discovered that Italy division of Turco do not produce it anymore in Italy because the market is low (now heat treat process in controlled atmosphere is diffuse) and there is no way to purchase Turco Pretreat compound in Italy.
So I've decided to use the third way: wrap the blade in a stainless steel envelope.

Yesterday I've seen in a big hardware store a small bottle (not rechargeable) of compressed Argon (1 lt at 60 bar) for less than 15 Euro (I think around 15 $?) and I remember what Gene Osborn as written in another post on this forum about his method to fill with argon the stainless steel envelope.
Can someone (Gene Osborn may be) explain me in detail more about how to fill the envelope?

I'm sorry for the length of this post, I'm trying tho hexplaine what I mean in a language that is not mine; I hope that you understand my poor English.

Thank you.
Ciao a tutti, Bruno

Bruno, if I remember the argon is heaver than air. I've had good luck without the argon but it wouldn't hurt. I would think if you make your envelope and leave one small end open to insert your blade first then just add the argon and close up the stainless foil. I'd just try it without anything first and see if your happy with the results. Are you able to get the foil? Ray

Thank you Ray for your answer.
I'm sorry but with my bad English I don't understand if you are asking me if I'm able to make the stainless envelope (when you say : ."Are you able to get the foil?"); if this is the question I answer you that I have not try to make an envelope using foil at the moment so if you can explain me I'll be happy.
I think that during the next week end I'll try to heat treat one blade only with the envelope and without argon. The stainless steel I use (ma5m stainless steel by UNGINE) is for air quenching, you think I can blow on the envelope with a fan to increase cooling (ma5m data sheet say that cooling must be rapid (1050?c to 20?c in less than 60 sec)?
Thanks, Bruno.

The foil is specially made for heat treating, and is capable of very high temperatures (2000 deg. F). It can be purchased from industrial suppliers in 50-foot rolls.

My experience has been, with air quenching stainless steels, that nothing is needed inside the foil envelope. Most literature on the subject also advises to quench in STILL AIR (no fan).

Don, are you removing the blade from the foil or are you leaving it in? I've got five blades (ATS 34) in my oven at this very time. Do you let your blades soak at 1400 for a few minutes before they go to critical?

Bruno, thats a really fast change in temperture, almost sounds to sudden. I've never heard of the steel your using so I don't know what to suggest in quenching it. Maybe the fan will do it OK. There are some stainless steels in the US that suggest using a fan. Hope you understand, Ray

This may be a steel like S3V that Jerry Hossom say needs to be placed between two steel plates to get it down to temp fast enough.

Good Luck

Bob Sigmon

Ray, I put ATS34 in a cold furnace. It takes an hour to ramp up to full austenizing temperature, which is plenty of time for the steel to become acclimated.

When they're done, I pull the rack of blades in wrappers out and put it on the concrete floor. When the visible red heat is gone, I pick them up one at a time with tongs in one hand, and a metal snip in the other, and get them out of the envelopes; then back into the rack until they are about 150 deg. F. Then, right into the tempering oven.

Thank you everybody.
Reading the last post of Don Cowles I've one more question: the tempering procedure must be immediatly after the cooling phase or I can wait? My idea is to pull the blade off from the oven and let it cooling in the foil (helping that with a fan). When it is at the room temperature get it out of the envelopes and put it in a freezer for around 12 h and after that proceed with the thempering phase. My idea is to do heat treat in this way, what do you think about that?
Here following I write an extract of the Ugine stainless steel data sheet:

MA5M chemical composition:

C 0.50
Si 0.20
Mn 0.20
Cr 13.5
Mo 0.50
V 0.10

"…austenitizing at 1050? - 1060? C must be followed by a rapid cooling (1050 to 20?C in less than 60 sec.) in a stream of cracked ammonia (I don't know what it is!) or pulsed air, or preferably, by quenching in an oil bath. Cooling can be continued to sub-ambient temperatures (-40 ?C). A tempering treatment is performed at 250?C to relieve stresses".

Ciao, Bruno.

Bruno, see my post here about the sequence of events:
pub42.ezboard.com/fcustom...D=57.topic

Bruno,

I am not familiar with the steel that you are using but it resembles 420C in it's components. I would guess that they are recommending the fast quench because of the low carbon content (.5%) in order to get the quenched steel as hard as possible. If this is the case, you might try pulling the steel out of the stainless foil immediately after removing from the oven and use an interupted oil quench to cool as quickly as you have stated. (I would recommend that you heat the oil to 120-130 degrees farenheit)

Another method to eliminate the oxygen from the envelope of stainless foil is to burn it off. I add either a small amount of sawdust or some paper to the inside of the envelope. This burns off at approximately 450 degrees farenheit and will eliminate what oxygen is inside of the envelope which is what you are after.

Gary

Gary, I've found that you don't need to put anything in the foil. I used to do the same thing but alway had to clean it off the blade. It works fine empty. Sometimes I even remember to put the blade in. How's your vac system turn out? Did Bob get his line out to you yet? Ray

Hi everybody, I've turn on the oven few minutes ago!!
During this week end I'll try to heat treat myself my blade. Now I've made the stainless steel envelope and i've put inside my blade and now I'm waiting that the oven reach the right temperature. Tomorrow or monday I'll inform you about the result.
Thanks, Bruno.

Ciao,
saturday I've heat treated my blade using the way to wrap it in a stainless steel envelope and quench in air … it seems ok; now I'm looking for someone that can test the hardness and in the next week end I'll try with another blade but quenching it in oil.
Thanks for you help.
Ciao, Bruno.