O1 Heat Treating Technique Recommendations

[JMD82]

Looking for some guidance and recommendations on how I should go about heat treating a trigger that has the sear on it. The trigger was machined using O1 tool steel that started out as 1/4” thick flat stock. The trigger tang and sear itself remains at 1/4” thick. The trigger is 1-3/4” long x 1” tall. A good portion of the middle section had to have 1/8” of material removed to accommodate other parts that work with the trigger assembly. The trigger also has a 1/4” hole drilled in it to accommodate the pivot pin for the trigger. There is also a section of the trigger that had to be machined and measures 1/4” thick x 1/4” L x 1/8” Tall. This small section acts like a shelf. I had to drill a very small hole in this shelf to install a pin to hold a spring in place.

I’ve been reading up on heat treating for the past week to figure out the best method to eliminate warping, cracking, or deformation. My main concern is warping in the thin areas in the middle part of the trigger that has majority of the material removed. Another concern is cracking around the pivot pin and spring retaining pin hole. On the pivot pin hole I did a very light chamfer on the ID to remove the sharp edge as I read that will help reduce cracking. I also plan on packing this 1/4” hole with steel wool as well. Can’t do much to the small pin hole as it’s very small.

After reading for days and discussing it with coworkers, I’m trying to find out if I should go with an oil quench or let it air cool since this part is rather small. I feel that a water quench would be too aggressive and would do the most harm.

If it is recommended to oil quench, I plan on using some type of vegetable oil, peanut oil, etc.

I’m also considering an air cooled method as I have read that it can work on smaller parts made with O1 and warping, cracking will be some what non existent. Just need to make sure it’s hardened in the end.

If doing one of the two above methods, I plan on tempering afterwards to draw it back just a tad if either method passes the file test.

A coworker and I discussed just heat treating the sear portion if warping and cracking was a concern, but I feel that the area behind the sear would be brittle and eventually break. We also discussed just heating the part up the a cherry red and case hardening it.

Any thoughts or recommendations? I’m very new to this so excuse my long drawn out first post…lol.

JMD82

Thanks in advance for your help.

 

[technocrat]

Even though it is not very thick you would be best to agitate it in the oil. This keeps exposing the trigger to fresh cool oil.

 

[???]

Fasten to wire so long section is vertical, rotate while heating so it's evenly heated. Get someone to stir the oil till you have a vortex in the centre. Place under oil in center of vortex and stir.

If you drop it in with the longest edge contacting first it will warp.

If you have a local toolroom ask them to send the parts together with their O1 for hardening and buy them some beers. Hardening without the proper facilities is hit and miss and it sounds like you've put a lot of work in the parts.

 

[technocrat]

When you hit the hardening temp the material will become non magnetic. Use a strong magnet at a safe distance to induce a bit of deflection. As soon as it relaxes you are ready to quench.

 

[gbent]

When heating use a carburizing flame. Make a couple of test pieces and harden them first. O1 is an oil hardening steel, you probably can't get a desired, even hardness relying on air quench. There are air hardening steels, you might consider one of them for your next project. If you are going to temper the piece with a torch, you must remove the part from the flame to see the color that indicates your temperature. Your kitchen oven may provide better control of the tempering temperature if it will reach the desired temperature. Tempering should be done immediately, when the part temperature cools to about 150F.

 

[John MacArthur]

First wrap it in a cocoon of small wire; this technique is used in clock and watchmaking to keep small parts more evenly heated. Soak the cocoon in borax paste, heat to cherry red, plunge in oil and as mentioned, agitate aggressively. You don't mention if you have any sharp inside corners, but these are places that cracks can start. O1 should be fairly forgiving; I use it for many small parts, even some with sharp inside corners, and you can see in the pics that I didn't even wrap them.
Good luck,
Johnny

 

[Rickyb]

A2 may be a better option than O1

 

[John MacArthur]

Sounds like it is already made from O1. Thought I'd point out that the blue temper is spring temper, a sear might need to be a little harder, like heated to a straw brown. Might check with a gunsmith. The spring temper is darn tough though.