DIY case hardening ?

[fishnbeer]

so i polished the living snot out of the sear surfaces on my AR. my factory trigger was horrible. i could actually see a groove where the hammer makes contact. so basically i stoned it down until that groove was gone, then took it to a wire wheel, then a cloth polishing wheel.

i most likely went past the surface hardening. so i looked into doing it myself. i have a torch to heat it up, and i was thinking of quenching it in used motor oil for the higher carbon content (and price) . i have heard of people heat treating AK receivers in oil so why not an AR trigger?

[G-forceJunkie]

Google Kasinite. Brownells sells a version of it.

[kcstott]

Stop and buy a new trigger. What you are doing is putting the rifle in a potentially unsafe condition.
If you went past the case the you removed way too much material

[fishnbeer]

i already planned on buying a giessle (sp?) but wanted to try this first. i dont think it would cause an immediate problem, im sure it would after a few hundred rounds tho.

trigger feels like butta now!

[Mikeb]

Is the part mild steel? If is high carbon or alloy it wont like case hardening.
Mike

[Sunday]

From years of experience,,,, Buy a geissel trigger [the one that costs around $180.00] and you will not ever look back. I have found that if a custom trigger is available that is the best choice. Been there and done that many times 40 years ago.

[kcstott]

i already planned on buying a giessle (sp?) but wanted to try this first. i dont think it would cause an immediate problem, im sure it would after a few hundred rounds tho.

trigger feels like butta now!

It will if you took to much off the front of the trigger or changed the angle any.
I didn't care for the

then took it to a wire wheel, then a cloth polishing wheel

that has the potential to change angle and round corners bad.

Triggers should only be dressed by experienced hands with hone stones or on a surface grinder. A polishing wheel has no support and will do what it wants to the surface regardless of your influence.

[69powerwagon]

You probably took off too much for safe operation if you took off the groove marks, you only need to smooth the high spots to lower friction not eliminate the lowest spots. A polisher will also round the corner on the sear when a sharp corner is most important. A stone is the only thing that should be used. Also, you need to have heat treating explained to you. you cannot case harden with a torch. Case hardening is done only to low carbon steels with a compound like kasinite in a furnace using long soak times. Torch hardening using quenching only works on higher carbon steels, like 4130 that ak receivers etc are made out of. With a low carbon steel the case hardening compound imparts carbon into the outside of the steel but all else remains soft. With better steels, heating and quenching hardens the part all through. Im guessing that your part is not case hardened, but a better steel that is hardened all through since now adays better steel is cheaper than case hardening. You should research how to do trigger jobs as well as the different hardening techniques and applications before delving into that territory.

[echo884]

I too am interested in kasenit/cherry red. I agree that with parts available, just to get a new part. But if something is hard to get, maybe it's better to repair. I saw a video on midwayusa http://www.midwayusa.com/General.mvc...n-_-1_ydyatyb8 that shows him using a torch. At about the 7min mark, it shows him using something called Cherry red to case harden. Might be something better to practice with before trying the real thing. I was thinking about doing something like this if I ever get a deal on a "broken" gun.

[kendog4570]

Ol Larry used mild steel for the sear. This material will respond to applications of carbonaceous compounds like Kasenite. Notice he didnt attemt to re-harden the tumbler?
Who knows what material M16 fire control parts are made of.

[kcstott]

Off topic but if you want to make parts from solid that can be heat treated with a torch in the garage you need to look at O-1 and A-2 tool steels. Both can be heat treated in the garage with great success. The are also very forgiving in terms of heat input and hardness.

O-1 and A-2 are also readily available at the big machine tool supply houses MSC, McMaster, etc. That would be what I would make a part out of that required heat treat but only a torch being available.

And don't compare AK heat treating with a torch to a proper oven heat and time controlled environment. What we do to a AK is a very crude form of heat treat an it only works due the the properties of the metal.

4130/4140 should be soaked in an oven at 1600 degrees for two hours then quenched in either brine or oil then drawn back (tempered) to what ever hardness you want within a given range. And when we draw these parts back we are only attaining an approximate hardness of about 35 Rc. A trigger sear surface should be in the upper 50's

As foe the material that a AR15 M16 trigger is made from All i know is it is a precision casting or metal injection molding. After market stuff of the boutique variety could be anything under the sun that works well.