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heat treating question

Joe Miranda

Titanium
Joined
Oct 19, 2004
Location
Elyria Ohio
I have several heat treating related questions.

1) Can I use the same oil for quenching for O-1, 4140, and SS440C?

2) When tempering, once the required temperature is reached, then what? In other words, do you quench it once again in oil or do you air cool or what? I have never been able to find any info on this.

3) What kind of oil is best to use for quenching?

Thanks,

Joe
 
440C, like D-2, is an air hardening steel. You don't have to quench it, just bring it to tempering temp., soak, and take out and air cool.
Paul
 
>"1) Can I use the same oil for quenching for O-1, 4140, and SS440C?"<

O1 and 440C are deep hardening steels, so almost any oil is OK. Various heats of 4140 behave differently, but none of them harden as deeply as the other 2. It also depends very much on how thick it is. Thin stuff, up to ~3/4", no problem. Thicker stuff may need a faster quench-colder oil, vigorus moving in the oil. Special high-quench-rate oils will help.


>"2) When tempering, once the required temperature is reached, then what? In other words, do you quench it once again in oil or do you air cool or what? I have never been able to find any info on this."<

You can safely oil quench from the temper, and it's actually preferred. Just remember to allow O1 and 440C to get all the way down to room temp. before you temper. 440C may benefit from a double temper, with subzero exposure after the 1st temper.
 
I assume your not after the state of the art of heat treatment or you wouldnt have asked.... so


I temper my o-1 in a toaster oven. I toast it on high untill it turns the appropriate straw or blue color for your application and pull it out to air cool afterword.

it should not realy matter much either way.
 
I've not worked with 4140 , but 440 is heated to 1900-1950 deg. 20 min. plus 5 min. per in. of thickness , air quench in still air [thin flat pieces quench well between alum. plates] cool to room temp. I then follow with a 300 deg snap quench .5 hr. and a 24 hr. soak in liquid nitrogen, temper at 450 2 times for 2 hrs. 0-1 is much easier to h.t. 1450 deg. until heated through , or until it becomes nonmagnetic , quench in oil ,temper at 400deg. Many of the steel suppliers list heat treat info on their sites .
 
A toaster oven with one of the long shank high temp. thermometers stuck into it via a hole drilled through the cabinet makes a pretty good tempering oven under abt. 450 degrees. You should get the oven up to tempering temp. ahead of time,and temper the hardened steel when it is just cool enough to hold in your hand. Letting it get fully down to room temp. is bad for the longevity of the tool.Brownell's Gunsmithing sells high temp. thermometers with a long stainless steel shank.I think one goes to 800 deg.,but they can be had to go a lot hotter. Kitchen ovens are not very accurate,and you need to be within abt. 25 deg. for best results. Kitchen ovens can be 75 deg. off.
 
Correct me if I'm wrong, but we used to call it solution treating SS,Heat and quench to get it soft, then run up to a lower temp to harden, Its been a long time. Same with coppers and alum.
 
Thanks gentlemen.

Jimmy D, yeah I heated to @1900F and oil quenched. I haven't Brinell tested it yet but using the old file test the file skated over the surface. So far so good.

dsergison, yeah I am after state of the art. Why wouldn't a person ask questions if they are after state of the art? Everyone has to start somewhere.

bene, ok - so I quench after tempering. That's what I needed to know.

gwilson, I have a heat treat oven at my disposal so I am able to get accurate temps. But I will sure keep your method in mind for my home shop.

pgfaini, yes I know I can air cool the stainless but I don't have a good safe place to leave steel that is 1900F setting around. I am concerned that once it is not glowing red someone will want to touch it when I am not there to scold them.

Thanks again to everyone for your help. It is much appreciated.

Joe
 
Joe, You might also want to think about, if air hardening, using a stainless steel foil to wrap your workpiece in, to prevent decarburization @ hardening temperatures.Polished steel comes out with a nice "satin chrome" finish, unless wrapped in brown paper to burn up the air under the foil.

Paul
 
A very nice quenching oil for carbon steels is soy bean oil. Available from Sam's club at about $15 for 5 gal. High flash point and no stink. Scale settles to bottom and oil remains clean.

A candy thermometer can determine if your kitchen oven is accurate.

Hot items left on a bench can be labeled "hot" with writing next to them with soapstone and an arrow pointing to the item. Never saw any dolt pick up an item so labeled, but I guess it could happen...Joe
 
Hi Joe
We heat treat tonnes of 4140 every year.
You can buy quenching oil (called quenching oil)I know various brand names of what it is called in Australia but not sure if these will cross over to US
4140 can also be quenched in polymer quenching medium. In certain sizes we have also quenched in water. 4140 has a temper brittlenes zone between approx 220degC to 450degC so it is wise to stay out of this temp range when tempering.
No need to quench after tempering as it is not the sudden drop in temperature that is changing the steel but rather the taking of the steel up to a certain temp to allow the atomic structure to "re aquaint" its self with its neighbours as such. Quenching after tempering will not normally do any harm, depending on the size of the job but really is not neccessary. We normally just allow to air cool (unless the customer is waiting to pick the job up).
Dsegison's method is not recommended as the oxide colour method of tempering is really only good for between 210degC and 370/400deg C which for 4140 puts you right in the temper brittleness zone. The colour method also tends to only give a skin temper as normally you can not soak the piece for the correct time. Better to set your heating equipment using a accurate instrument EG thermocouple, pyrometer, etc. We normally work on a soaking time to temper of 1 hour per 1" of thickness
Cheers
 
forgemaster,

Thanks. That is a great help. I will print off your post and keep it on file. I have heat treated 4140 many times but I love your explanation. Also, the oil I use for quenching is at least 14 years old (that's how long I have been here). It is the property of a different department that has had rapid turnover. Consequently, it has been a neglected area. We are a R&D lab and I am currently the only one who does any heat treating. The oil level in the tanks is getting low due to smoking off during the quench and I need to replenish it. Thanks for the good info from down under.

Joe

Joe
 
Joe D,

Writing in soap stone that something is "hot" around here would be a sure invitation to touch it to make sure it really is. I'll check into the soy bean oil. I like that idea. Even when it smokes some off it will just smell like someone's cooking.

Joe
 
When you do a double draw as was mentioned before (450 twice) aren't you supposed to use a slightly lower temp for the second draw ?? IE 450 then say 425 ?

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
I then follow with a 300 deg snap quench .5 hr. and a 24 hr. soak in liquid nitrogen,
temper at 450 2 times for 2 hrs
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>


Bill
 
No. The main purpose of the cold soak is to try to force any retained austenite [RA][the normal high-temp. phase of steels] to transform to martensite. If any RA does transform when cold, it should be tempered high enough to provide the toughness required, without softening it too much. If 425 deg. F is OK, that's what the 1st temper should be.

I think you are referring to a simple stress relief [SR], which is usually done slightly lower than the temper. But post cold-soak heat treatment is another temper, not a SR.

Some "sources" of info on this subject have it wrong.
 
The 300 deg. draw is actually a stress relief , the actual temper is after the subzero treatment. I mistyped in my first post , I've heard it referred to as a" snap temper " not a snap quench.
 








 
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