Receiver heat treating

[radkins]

I have mentioned my single shot build project here several times and I am making some progress with it, 45-90 caliber falling block type action. A friend was over yesterday and tells me that even though my receiver is being machined from 4140 pre-hard I will still have to have it hardened and tempered before it will be strong enough. I was under the impression that 4140 pre-hard could be used as is without further heat treating? :confused:

Just a couple of questions, if the pre-hard material does need to be hardened and tempered would it be ok to have 4140 Color Case hardened?

Would I have been better off to just have started with annealed 4140 and then had it heat treated?

How much (most important question here) will the dimensions change, if any, during the heat treat?

I have come a long way with this thing and put a lot of work into it so I would really be disappointed to find out I have made a mistake with the material I am using.

[Bob Ford]

Radkins,

Can not give you a answer as I have not seen your action. If it is a copy of older designs the steel used for the most part was not as good as what you are using. If you have it heat treated expect warp/ dimension changes. If you are going to fire the action less than 2,000 times I doubt you will have a problem. Before firing record the measurements and head space then every ten shots check it again, you will soon know if there is a problem. As a general rule soft weak actions stretch before failure. Overly hard actions fail like a grenade. Being only R C 30-32 it will wear if not kept clean. If this is a problem look into Electroless nickle on the wear surfaces.

Bob

[JCHannum]

Without seeing the action, it is difficult to make a call as to its strength. With adequate wall thickness and shoulder area, 4140 prehard should be more than strong enough.

The Frank deHaas single shot books are very good references on single shot action and include dimensions of most actions. The thickwall high wall was a very strong action, and almost indestructable. If your action approaches the dimensions of that I would see no reason for concern.

Another very good reference is the Walter Meuller book on building a falling block action available through Village Press. The introductory chapter consists of strength and engineering calculations, and as I recall information on heat treating and use of prehard.

Additional heat treating of 4140 will not appreciably increase the strength of the action, and I don't see a need to have that done as it will probably result in the same hardeness when done. Heat treating probably will result in some dimensional changes and final fitting will have to be done.

I do know that you definitely do not want to case harden 4140, it will result in a dangerously hard action as the process will make the action very brittle. Lower carbon steels are used for casehardening, 8620 is probably the first choice.

Now in return for our free advice, how about a couple of photos of your action. Inquiring minds want to know.

[radkins]

The thickwall high wall was a very strong action, and almost indestructable. If your action approaches the dimensions of that I would see no reason for concern.

This action very closely approaches the dimensions of the High wall in critical areas and is in fact a fairly close copy of it. I originally set out to build a close copy of the Sharps but after handling and shooting a High Wall in 45-70 I went with that general design instead. Actually I was more asking about the idea of using 4140 pre-hard "as is" for a rifle action without any further treatment, I was assuming it was ok but this fella was telling me that without hardening it would be too soft and would loosen up after only a few shots. I was under the impression that annealed 4140 would be too soft "as is" but that the pre-hard was ok, looks like he had me worried over nothing.




Now in return for our free advice, how about a couple of photos of your action. Inquiring minds want to know.


I am close to reaching the point where I am sure everything is going to workout ok and as soon as I get the action internal parts finished and functioning I will get some pics up.

Much thanks to both of you I feel better about it now.

[38_Cal]

Through hardening steels, like 4140, should not be case hardened...they'll be brittle all the way through, and you don't want a grenade eight inches from your nose! :eek:

David

[ulav8r]

Most likely the person that told you it would be too soft knew not what he was talking about. Unless the design uses very minimal locking areas, your pre-hardened material should be good. It all depends on the area of the receiver supporting the block and the area of the sidewalls connecting the rear of the receiver to the front of the receiver. Refer again to Bob Fords reply.

[fishfrnzy]

Your 4140 HT should be 28-32 RC or 287-320BHN. Tensile should be in the 140,000 psi and yeild in the 105,000 psi range. Basicly the material as a grade 8 bolt. Pretty stong but still machinable. This material is used on a lot of high torque shafts as in comes without further heat treat.

You can make it stronger by heat treating again but you probably would not want to go over 40-45 RC as you will start to get brittle for this alloy. On page 15 and 16 of the link you can see the data if you harden it more. Typical practice is to add .30-40 to your fisnish dimensions and machine that off after heat treat.

Also note the end quench hardenability data, as the farther you get from the quenced edge ( the OD in your case ) the less the quench will harden the steel. 4340 is better in this regard. Hope this helps.

http://www.emjmetals.com/pdf/bluebook-r.pdf