Questions on heat treating

[L1A1Rocker]

I've never done any heat treating (hardening) but I know it needs to be done on the muzzle brake that I'll be making soon. I have some Kasenit but don't know if it's really worth using it or not. Plus the Kasenit instructions say to quench in water. I always thought that quenching in oil was better.

Can anyone give a bit of advice (with a nod toward this being for a muzzle brake) or maybe point me to some online tutorials?

Thanks folks

[doubloon]

From what little I've read (toying around with blade making) about quenching water cools metal faster than oil, some knife makers prefer oil because it's slower than water and has less a chance to crack or warp the piece but water tends to produce maximum hardness because it's faster.

And ... it all depends on the type of steel you're using vs what hardness you're trying to achieve.

http://www.hocktools.com/diyht.htm

ETA: I've never read up on Kasenit before but it appears to be all about case hardening for low carbon steels. I'd definitely use water as instructed and it's probably going to matter what kind of steel you have. I don't think it will do anything "bad" to a high carbon steel since the purpose it to add carbon to the surface being treated but it doesn't sound like it would be necessary or add any value to treating a high carbon steel.

[L1A1Rocker]

Thanks for responding. The first brakes are going to be from 4140. Later I may be doing some 416.

[Fulmen]

I haven't used Kasenit, nor am I an expert on heat treatment but I'll give it a shot anyways: Kasenit and Cherry Red are intended for case hardening of low carbon steels by increasing carbon/nitrogen content. Simple carbon steels require a pretty aggressive quench, so water would probably be the best choice. Remember that the case hardening will be quite thin, so for it to have any real effect you need it to be pretty hard. I've done a bit of case hardening with charcoal, 2-4 hours soak time, water quench and a 2 hour anneal at 500F produces a good case perhaps 0,005-0,01" deep.

But if you're using 4140 there is no need for kasenit. Here's a couple of pages with info:
http://www.metalravne.com/selector/steels/42crmos4.html
http://www.anvilfire.com/FAQs/heat-treating-4140.php


Don't know what kind of setup you have, but heating to non-magnetic, oil quench and a 500°C temper should be doable without a furnace.

[Capt. Link.]

Fulmen pointing out that the case would be thin is very important unless you plan on making this piece over and over.If this is part of a QD mount the necessity of a through hardened piece is even more important.
The choice of quench mediums depends on many factors other than just hardness.A fast quench with fresh cold water can cause distortion warpage because it cools very fast.Oil and brine are often chosen because of heat load carrying ability and slower cooling with less warpage.You might try O1 tool steel if you don't have enough heat plus time to reach the curie point in a medium carbon steel for transformation to take place.You must take pains when machining this material as it will harden with very little heat without using a quench to many peoples dismay.

[L1A1Rocker]

Well, I really appreciate everyone replying but I'm more confused than before. So let me try asking this way. . .

I have a QA/QD muzzle brake machined from 4140 steel. What would be a good procedure for someone without a furnace (just a oxygen acetylene rig) to heat treat it for hardness and durability?

[Rich V]

Well, I really appreciate everyone replying but I'm more confused than before. So let me try asking this way. . .

I have a QA/QD muzzle brake machined from 4140 steel. What would be a good procedure for someone without a furnace (just a oxygen acetylene rig) to heat treat it for hardness and durability?

Here are a couple of references for 4140 heat treatment.
http://www.houstonheattreat.com/news/June11/08.html
http://www.csus.edu/wac/journal/2012/Be ... _Draft.pdf

I think trying this with a torch will be difficult at best. Look for someone in your area that has a pottery kiln that you could use. I have a small one just for heat treating.

My favorite steel for tough use is 17-4 SS. Not bad to machine in the annealed condition and heat treating is very simple. Heat the part to 900 F for 1 hour then air cool. This will get you into the low R40 range with ~180,000 psi yield strength. There is essentially no warping from heat treating 17-4 and it is very corrosion resistant.

I wish there was a source of 17-4 seamless tubing, would be great for cans.

[cal50]

You can flame harden smaller parts fine with an oxygen / acetylene torch. Use a neutral flame to evenly heat the part then quench. You should know the hardening temp, quench, then you will anneal or normalize the part.

The temp needed depends on your material (tool steel, alloy steel, etc.) and quench. Kasenit works decent for surface hardening but leaves a fugly finish sometimes.

Pre-heatreat 4140 is prehardened around 28-32 Rc and cuts well and has good durability. 17-4 stainless is great to work with also.

[curtistactical]

4140 will get very brittle if you don't do it right, 4140 is designed to be a strong material but not a real hard one. If you get it above 48-50 Rc hardness it will be brittle. I also really like 17-4ss it a great material to machine and holds up real well in suppressors. My advice would be to not try heat treating 4140 on your own there are plenty of companies out there that do heat treating. Honestly for a personal brake on a form 1 I wouldn't bother heat treating it since its 4140, at worst you might eventually wear the threads out but it is plenty strong the way it is. Kasenit is not designed for 4140, it is designed for 1018/1020 steel. 4140 is hardened throughout not just case hardened. If you want a good material you can harden yourself use O-1 as stated above, it is an oil hardening steel.

[L1A1Rocker]

Alright. I'll just park it and call it done.

[Tony M.]

I have a fair bit of experience in this. For the application you're working on, the specific hardness isn't critical, you're hardening to reduce wear.

4140 isn't as complex as some steels, but isn't as simple as the 10 series steel either. Heat treat is fairly simple for your application.

Heat to cherry red using as large a neutral flame as possible (rosebud torch tips are great for this) and hold at that temperature for approximately 60 seconds. Allow to slowly cool back to black (air cooling is fine for this step, no need for vermiculite or similar insulators) and repeat that process 2 more times. This is a simple 'normalization' process. It essentially relieves the stresses imparted through machining.

One normalized, heat again to cherry red, hold for 90-120 seconds, quench in plain water (no need for superquench or any surfactant). Immediately place the part into an oven that is preheated to 400-435 degrees Fahrenheit, and leave in the oven for no less than 1 hour.

The scale produced can be removed with various methods ranging from wire wheel to a dilution of muriatic acid.

That should yield a part in the low to mid 40's on the rockwell scale with excellent durability and impact resistance.

This method (visual) should only be used on parts that are 'non critical'. Muzzle devices would be fine for instance, but receivers should be heat treated in properly temperature controlled ovens.

[L1A1Rocker]

I have a fair bit of experience in this. For the application you're working on, the specific hardness isn't critical, you're hardening to reduce wear.

4140 isn't as complex as some steels, but isn't as simple as the 10 series steel either. Heat treat is fairly simple for your application.

Heat to cherry red using as large a neutral flame as possible (rosebud torch tips are great for this) and hold at that temperature for approximately 60 seconds. Allow to slowly cool back to black (air cooling is fine for this step, no need for vermiculite or similar insulators) and repeat that process 2 more times. This is a simple 'normalization' process. It essentially relieves the stresses imparted through machining.

One normalized, heat again to cherry red, hold for 90-120 seconds, quench in plain water (no need for superquench or any surfactant). Immediately place the part into an oven that is preheated to 400-435 degrees Fahrenheit, and leave in the oven for no less than 1 hour.

The scale produced can be removed with various methods ranging from wire wheel to a dilution of muriatic acid.

That should yield a part in the low to mid 40's on the rockwell scale with excellent durability and impact resistance.

This method (visual) should only be used on parts that are 'non critical'. Muzzle devices would be fine for instance, but receivers should be heat treated in properly temperature controlled ovens.

Excellent. I think I can do that. Thank you for posting that writeup.

[Fulmen]

According to this: http://www.nhml.com/embrittlement-of-steels.cfm tempering in the 200-400°C range should be avoided. Unless you need it very hard (in that case 4140 isn't really the best material) a 500°C temper seems safest.

[Tony M.]

According to this: http://www.nhml.com/embrittlement-of-steels.cfm tempering in the 200-400°C range should be avoided. Unless you need it very hard (in that case 4140 isn't really the best material) a 500°C temper seems safest.

I've read some of those material studies before, and I will admit it's been a while, but my personal experience has been very different, and I found 4140 to be very tough when tempered at 400-450°F. Based on those studies though, a higher temper shouldn't cause any issues, and would indeed ensure more notch strength.

[Fulmen]

I'm not one to argue against actual experience, but it does at least seem prudent to do a few tests before choosing the temper. A brake will be subjected to shock loads, so a brittle material would be less than ideal.

[Tony M.]

A brake will be subjected to shock loads, so a brittle material would be less than ideal.

Agreed.

I would amend my recommendation on tempering temperature to be above 700 F. I doubt you'd have any issue with a lower temperature temper, but you're not loosing enough hardness to make much difference in wear, and might be increasing the toughness enough to matter.

If you don't have a HT oven (or can't borrow one) your handy kitchen oven on 'self cleaning' mode will do a pretty reasonable job of giving a higher temperature temper, and the cycle will have the handy benefit of providing a pretty decent soaking time.

[Fulmen]

I agree, a 500°C temper should give 40HRC which is pretty decent. According to my charts that's 1200MPa UTS, and the impact toughness will be 2-3 times that of a low temperature temper.

[Kuraki]

Quench medium is determined by the steel or process. For example, 4140 is an oil quench hardening steel, but if you were to surface harden it with Kasenit or other product, you would be best served following the instructions and quenching in water, because the Kasenit is altering the makeup of the steel at the surface level and rules for 4140 no longer apply.

Quenching is the easiest part for the home heat treater, as it's generally air, oil, or water, and brines or other methods aren't even discussed except for some rare examples of some knifemakers using austempering methods involving molten salt baths (you don't even want to consider this).

4140 is a perfectly suitable choice for material of a muzzle brake, it's strong, it blues well, it is readily machinable, and is generally available in 2 forms - annealed and pre-hardened. Prehard 4140 is generally 35 RC, which is a perfectly acceptable hardness for what a brake does, while still being machinable at reduced speeds with HSS or carbide tools.

The hardest part for a home heat treater is hitting the correct temperature to enable austenite formation, then cooled at the correct rate to allow austenite to martensite transformation. Or, for 4140, heated to 1500 F and quenched in oil. Variations in that critical temperature will increase or decrease austenite creation, variations in the rate of cooling will increase or decrease martensite transformation. In otherwords, too hot, too fast, brittle part. Too cool, too slow, no transformation. Too hot, too slow, annealing, etc, etc. The problem for the home heat treater, along with the Springfield Armory producing 1903 rifles for WW2, is the lack of accurate thermocouples, ie the inability to control that critical temperature. Resulting in poor heat treatment results of brittle receivers. Additionally, soak time vs cross section of the part, variation in temperature of the parts, all lead to inadequate heat treatment.

Home treaters are generally limited by lack of temperature sensing and lack of soak environment, and the use of a torch therefore limits them to small parts easily kept at a relatively even temperature across the entire part, and a knowledge of what color means what temperature. It is a wildly subjective process.

Kasenit is a product designed to give surface hardness in places where through hardening is not possible (1018 base metal, lack of HT equipment, etc). Case hardening has a minimal impact on strength of a part but can greatly increase wear resistance. It's also much harder to screw up.

If I were to make muzzle devices that I thought needed to be hardened for wear resistance do to on/off of the suppressor, and didn't have access to the equipment to do it properly, the order of methods I'd choose would be:
1- machine from prehard materal
2- machine and send out for nitride or other surface treatment
3- machine and case harden
4- machine and attempt through hardening


All that said, I've finished my QD TI can and brakes, which were made from 4140 in the annealed state, and I have zero intention of hardening them at all, though I have all the equipment necessary to do it.