Metal hardening question

[fox fire]

I'm curious about the best way to harden a sear (or anything else), I've read post about heating in a certain manner to soften the metal so they could drill& tap to manufacture a adjustable sear, then they went thru a heating with a torch then cooled it in oil then repeat the process again, supossedly to retemper the metal.
 
 Just wunder'n what ya'll mite have to say about this.
 
 

[tacklebury]

Hardening has to do with the quench temperature and what you quench it in.  Typically, to simply harden something a little, get it a dull red and quench in oil.  To really harden, (note gets more brittle too) you heat more to red or yellow and quench in water/oil depending on the desired result. 

[Frank46]

I would think that any work done to make an adjustable trigger such as adding a screw to remove the 1st stage would be done without any annealing of the metal. But could be wrong on this. However properly hardening metal could be done using a torch heating to red heat and dumping it in motor oil. The tempering would be at a much lesser degree of heat and again in the oil. Casehardening only leaves a hardened shell, once you get through that it should be fairly easy to drill and tap. You can use kasenit from brownells and following the instructions should work also. Hope this helps, and someone else will surely be along to help. Frank

[mechanic]

Hardening for most carbon steels is as already described to you.  If you wish to temper, place the parts in a 400 degree oven, (don't let the wife catch you), for about an hour, then just turn the oven off and leave it until it cools to the touch.
 
To anneal, you need to bring the metal to red, then cool very slowly.  I usually use a bucket of sand on the forge heated until the bucket won't take any more heat, then plunge the heated part into the sand, kill the forge and let it cool slowly.
 
Bear in mind there are now hundreds of alloys out there, some are air hardening, etc.  What works for most won't work for all.
 
Ben

[ironglow]

  Forging knife blades we  forge them at regular heat, then thrust them in  ashes, kitty litter or vermeculite and let gradually cool overnight..that anneals or normalizes the steel for grinding/sanding.  When we want to harden carbon steel we heat it to what I call "tangerine' color..the austenetic state.
  Test it with a magnet, if the steel is NOT attracted to the magnet, you're at the right temp... so plunge it in oil until it has come well down in temperature (do it outdoors, could be smoky).
  There is such a thing as hardening oil but you may not have access to some.  So, but for your purposes I would suggest ATF (automatic transmission fluid)

[fox fire]

WOW, idnt expect a reply this quik, The powder you can buy from Brownells, would it do as good of a job as quenching  
 
 I need to dig around about this to see if I can learn something here, I have to fab a sear for a old .22 rifle & it needs to be heardened for best results in the long run, dont like the idea of half do'n a job.
 
 Thanx for the info gents, thats what I love about this forum, no matter what I ask thers sevral experienced hands that give good useable info.
 
  Thanx again. 

[gunnut69]

The heating and qwenching then drawing the part (tempering) will only work on steel with a certain amount of carbon, high carbon steel. Carberizing or casehardening only works on mild steel (either cold rolled or hot rolled). The 'mild' steel hasn't enough carbon to take a temper. If case hardening mild steel the metal is heated to a high red heat and plunged into the 'CaseNit' material (it's a granular powdery material) and that precess is repeated, usually at least a couple of times. The part with its coating of casenit is then reheated to a bright red heat and plunged in water.. This will cause the surface of the mild steel to absorb free carbon from the case hardening material and then that surface hardening is brought to a brittle hard state. The core of the part will stay fairly soft and provides the toughness require of the part.. The case hardening process can be repeated if the skin was too thin or not hard enough. If high carbon steel is used the final heat treat will cause the part to be brittle hard,,,all the way through.  Some parts are made from each material. S&W revolver parts (blued steel models) are made from mild steel that's case hardened for wear resistance.  Other revolver parts such as some Colt parts are carbon steel. Other parts may be made from alloys that require additional steps to harden and temper, such as super cold soaks.. Most 22 rifle parts (at least the older models) are made with case hardened parts.. More modern components such as sears for ruger 10/22's are cast, usually from an airhardening material and only get a surface grind at the contact areas.. The are other processes such the remington trigger in current production that use fused metal techknowledgy that can't be hardened by heateing and cooling, they are hardened by plating them with hard chrome alloys that are hard enough to resist wear with no tempering at all. If making parts such as a sear I use muld steel (usually hot rolled as it's easier to machine) and case harden it with several applications of casenit. I even in a fit of respect for the old ways once or twice hardened some muzzle loader parts by heating in a fire with leather char and sumping the resulting mess into cool water.. The skin that formed was fairly deep and quite hard..and the frizen didn't shatter..

[Frank46]

If you wish to just harden the .22 trigger then first do any work that needs to be done. I would expect that whatever hardening that was done at the factory would be case hardening. That is hard on the outside and softer towards the middle. The kasenit powder would do very well for what you are wanting. On the .22 trigger, if it has seen a lot of use then its a good chance that it has worn down the factory case hardening and could stand to be redone. I made a boring bar for my lathe out of a compressed air cylinder shaft after removing the piston. I found it was easy to cut the slot for the boring tool and drill the set screw. Followed the directions on the can and
now a file just slides off where I had done the work. So at least in my case it worked as I wanted. Frank

[too phister]

Ive done some case hardening on a bunch of small parts out of a action for a guy, the hardest part is not to overheat and melt sharp edges. easy to tell when you get it right, a standard file glides right over leaving a line on the file.