Recommendations for Small Heat Treating Oven

SobtzakTech · Jul 12, 2020

Hello All!
I'm looking at making some parts out of 4130 that is annealed. I'd like to heat treat it and get it to a hardness of around 30-35 Rockwell-C. The parts I'm making around 4in x 1.5in x 2in but I'd like to heat treat around 6-10 pieces at a time. I've been snooping on the web but was wondering what is a popular oven for a small shop. I'm thinking a something that can run off 220V single phase Any suggestions?! I'd appreciate the feedback!

Tom

DDoug · Jul 12, 2020

SobtzakTech said:
Hello All!
I'm looking at making some parts out of 4130 that is annealed. I'd like to heat treat it and get it to a hardness of around 30-35 Rockwell-C. The parts I'm making around 4in x 1.5in x 2in but I'd like to heat treat around 6-10 pieces at a time. I've been snooping on the web but was wondering what is a popular oven for a small shop. I'm thinking a something that can run off 220V single phase Any suggestions?! I'd appreciate the feedback!

Tom

That might be large enough to send out, should get better results.

Gordon Heaton · Jul 12, 2020

We use a Paragon. It is quite compact but has enough room for what you describe, runs on 230V 1P and is equipped for inert atmosphere. The programming is very flexible and temp control is very accurate.

BuffDan · Jul 12, 2020

Bar z Industrial Development Products | Hotshot Ovens

cstrickland · Jul 13, 2020

We use a Vulcan box benchtop furnace with programmable controls. It is a 3-1750 I believe. The oven is about 18" square inside. I know they also make slightly bigger ones. we use it all the time for one off and small batches as you described.

ChipSplitter · Jul 13, 2020

>>OP, if you're close to Saginaw check out Hi-tech Steel Treating. Most shops around here (including us) use them and get great results.

They have a separate oven going for all the common stuff every night, 4140, 4130, A2, 12L14, D2, S7, CPM, etc., etc.

SobtzakTech · Jul 13, 2020

Thanks for the recommendation. I'll check them out.

SobtzakTech · Jul 13, 2020

Oh really! I'm not too far from Saginaw. I'll see what they can do.

gbent · Jul 13, 2020

If doing it yourself you will have to protect against decarburization. Stainless steel bags are the easiest method. For no harder than you specify, consider making from pre-heat treated materiel. Or you could make them from a PH stainless such as 15-5 or 17-4, they only need a high temperature soak. Quench and temper is not used.

KMoffett · Jul 13, 2020

What's your price limit? There are muffle furnaces on eBay. I've converted a couple of older ones from mechanical thermostats to digital PID controllers. If you go for more that the cheap PID controllers you can get ramp and soak ones.

Doug W · Jul 15, 2020

4140 PH is usually 28-32Rc, and typically at the 28 end. But you can find it harder or have the material heat treated prior to machining.
30-35Rc is still fairly easy to saw and machine, no warpage, scale, heat treat mishaps and better finishes than annealed.

SobtzakTech · Jul 15, 2020

gbent - I'v thought about getting pre-hardened but I'm always trying to expand my knowledge and abilities. Heat treating has always been something I've shunned away but now want to try. I see a couple books that this site recommends. Might have to check them out.
With that being said, I've never seen steel bags before (shows you how ignorant I am here). You say to use this to keep from de-carburizing. By chance can you use the to carburize something, say mild steel? I talked to a machinist who was at a class I was at. He noted that he carburizes parts by packing in organic material and then putting it in the oven. Have you done this?

KMoffet - I've looked around. I was hoping for something around $1,000-$2,000 range.

Thanks for the info!

machinistrrt · Jul 15, 2020

You might try HGR, their #0720-001-0017, Lindberg/BlueM. Like most of their stuff, it has some rough spots. I have one similar, had to add the controller. Works.
While never done on "real" parts, I've taken mild steel, heated it up, dunk in sugar, repeat a few times, heat & quench. You'll bake enough carbon into it to be useful. Don't use leftover sugar in your shop coffee.

jspivey · Jul 15, 2020

Look at what EvenHeat has to offer. I have one of their ovens at home and use one at work on a weekly basis. They seem to be reliable and the programmable controller is really nice, if you get that option.

Gordon Heaton · Jul 16, 2020

SobtzakTech said:
. . .can you use the [bags] to carburize something, say mild steel?. . ./QUOTE]

You can use them to 'case harden' lower carbon steels. It isn't required, though, because you can bury the part in your carbon source which helps keep oxygen away.

SobtzakTech · Aug 23, 2020

All,
Its been a while since I responded but thanks to your feedback, I went with Gordon Heaton's recommendation and got a Paragon oven. I got some case-hardening compound from McMaster-Carr just to try some parts. They're in the oven now. I have some follow-up questions since I'm new to this. As an engineer they talk about the processes and metallurgy but never how to actually do it!! :rolleyes5:

So I'm looking for some guidance on the following:

1. Based on a YouTube video on pack hardening, I'm at 1700F and was going to go for 8hrs. Is that in the ballpark for mild steel? If so, how deep of a hardening should I expect?
2. Do I have to harden and temper afterwards or will I get a hardened part just from this?
3. Assuming I have to harden and temper afterwards, any recommendations on time and temps? The parts I'm doing are about 4in long, 1.25in thick, and 2in high.
4. Since I'm just a small side shop, I'm always looking for cheaper means!

The hardening compound is not cheap. I've seen hardening done with charcoal and then I've met a guy who uses bone char. Has anyone done this? Any recommendations on where to get the bone char?? Might try it.

Again, thanks all for the info. This is good stuff!

1953chevB · Aug 24, 2020

SobtzakTech said:
Hello All!
I'm looking at making some parts out of 4130 that is annealed. I'd like to heat treat it and get it to a hardness of around 30-35 Rockwell-C. The parts I'm making around 4in x 1.5in x 2in but I'd like to heat treat around 6-10 pieces at a time. I've been snooping on the web but was wondering what is a popular oven for a small shop. I'm thinking a something that can run off 220V single phase Any suggestions?! I'd appreciate the feedback!

Tom

you may need two ovens

In case not aware , FYI low alloy steel heat treating
to hold hardness 30-35 HRC has to austenitize , quench & temper, temper must be with in one hour or it will crack
austenitize temp = 1650-1700 deg. F
quench in oil or water (I recommend oil less distortion)
then temper at oil -1050 +/- 25 Deg. F , water = 1100 +/- 25 Deg. F
see ref link : AISI 4130 Alloy Steel (UNS G41300)

to anneal = 1515 +/- 25 Deg F then air cool

1953chevB · Aug 24, 2020

SobtzakTech said:
All,
Its been a while since I responded but thanks to your feedback, I went with Gordon Heaton's recommendation and got a Paragon oven. I got some case-hardening compound from McMaster-Carr just to try some parts. They're in the oven now. I have some follow-up questions since I'm new to this. As an engineer they talk about the processes and metallurgy but never how to actually do it!! So I'm looking for some guidance on the following:

1. Based on a YouTube video on pack hardening, I'm at 1700F and was going to go for 8hrs. Is that in the ballpark for mild steel? If so, how deep of a hardening should I expect?
2. Do I have to harden and temper afterwards or will I get a hardened part just from this?
3. Assuming I have to harden and temper afterwards, any recommendations on time and temps? The parts I'm doing are about 4in long, 1.25in thick, and 2in high.
4. Since I'm just a small side shop, I'm always looking for cheaper means! The hardening compound is not cheap. I've seen hardening done with charcoal and then I've met a guy who uses bone char. Has anyone done this? Any recommendations on where to get the bone char?? Might try it.

Again, thanks all for the info. This is good stuff!

this is called pack case hardening
this is a little off than what I am use to, I work with gas carburizing case harden parts.
there is a lot of information out there on this subject.
Brain is not working, but the higher the temp the faster and more carbon is absorbed into the parent material.
for pack case hardening more like 1750 Deg F , then throw into the carbon. if I remember right I need to research this because memory loss
Normal gas carburizing is 1750 Deg F in a carburizing oven in methane. It is longer the time more case depth received, what case depth
will you be trying to achieve.

edit : here ya go
Pack Carburizing
In pack carburizing, the work is surrounded by a carburizing compound in a closed container. The container is heated to the proper temperature for the required amount of time and then cooled slowly.
Commercial carburizing compounds usually consist of hardwood charcoal, coke and about 20 percent of barium carbonate. Barium carbonate promotes the formation of carbon dioxide (CO2). This gas in turn reacts with the excess carbon in the charcoal to produce carbon monoxide, CO. Carbon monoxide reacts with the low-carbon steel surface to form atomic carbon which diffuses into the steel. The carburizing compound is in the form of coarse particles or lumps so that when the cover of the container is sealed, sufficient air is trapped inside to form carbon monoxide. The carburizing process does not harden the steel. It only increases the carbon content to some predetermined depth below the surface to a sufficient level to allow subsequent quench hardening.
It is difficult to quench the part immediately, as the sealed pack has to be opened and the part removed from the pack. Due to this, the entire pack is cooled slowly and the part is subsequently hardened and tempered.
This method is efficient and economical for individual processing of small lots of parts or of large, massive parts. However it is not well suited to the production of thin carburized cases that must be controlled to close tolerances. Because of inherent variation in case depth, the method is not used on work requiring a case depth of less than 0.030 in. and tolerances are at least 0.010 in.

john.k · Aug 24, 2020

The home gun makers use bone char ,there is someone on (IIRC) Home Shop Machinist ,who has made a number of olde world guns ,like 73 Winchester copies,from common mild steelplate,and carburized them in bone char for a reasonable degree of case colour+hardness .......however ,if colour+ hardness is your goal ,you must quench directly as possible from the pack .........if you allow to cool and then reheat ,which is preferable from a metal quality aspect,all colour will have disappeared......Incidentally ,4 hrs in bone char at 850-900C is what most seem to use........,if guns are the object ,I suggest you start anew in the gunsmithing forum on PM.

1953chevB · Aug 24, 2020

best steels for pack carb. or gas carburizing is 8620, 9310 steels
core hardness ~ 30-43 HRc
case hardness ~ 58 Min HrC

austenitize at 1550 Deg F
quench in oil
Temper at 300 Deg F

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