SMAW Process on 4140 Low-Alloy Steel - Appropriate Electrode?

MrEquivocal · Sep 30, 2005

Hello,
I have been welding for about a year now, started out with the 6011 then graduated to the 7018 until I figured out actually how to weld

I feel I've reached a point where I can move on to welding more exotic metals. I am currently in the middle of a rifle build that requires me to weld the receiver to the front trunion. However, the trunion is made of a rather unusual metal in this case. 4140. The weld is extremely crucial, if it fails it may cause serious bodily injury (but no pressure here :laugh: )

I'm willing to risk it, I have complete confidence in my abilities as a welder but I do not have enough experience right now to make this important decision as to electrode selection so I bow to your wisdom.

The receiver is made out of 4130 carbon steel and is 1.05mm (.041") thick. The trunion itself is 4140 Chromium-molybdenum steel and is no thinner than 3.15mm (0.124"). My personal belief is that I can bore down into the trunion about 2-2.5mm with say a 11/64" drill and back fill it with 1/8" (smaller diameter if it's available) Jetweld LH-90 MR electrode.
I did a little homework before posting this and came to the conclusion 7018 does not offer enough tensile strength. From what I gather I can expect about 50,000-60,000 psi in this application but I would like at least 80,000 psi as it is a somewhat high shock application (picture the bolt slamming to the rear of the rifle after each cycle) and these welds are what holds essentially the front of the gun to everything else.

Most likely I will have to heat treat the holes in the receiver and anneal them before I weld so the weld does not rely soley on the softened natural state 4130 carbon steel.

Am I on the right track or do I need a serious education? :help:

Thank you for taking the time to read this,
Rob Windham

EDIT: Should also probably state that I have a Hobart Stickmate 235 (capable of 235A) This model is AC only.

Sandy · Sep 30, 2005

Welding .041 to .124 in itself doesn't really pose any problems untill you start to add them up. Possibility of repeated impact is one. Neither 4130 or 4140 or 'low' carbon by any means so that's problem number two. Chrome-moly is number three. Perhaps more research if you haven't already done it. Could very well be you have done tons plus some tho. Many of these things are riveted in place aren't they? Sounds like what you are proposing is about like a tiny plug weld?? Maybe verify that welding is an acceptable method then back to a welding board for the correct process.

I believe there will be some controlled heating involved. 7018 has some good impact qualities. 10018 might be good too.

Type in "reciever trunions" and some quite interesting informational sites appear.

Hammack_Welding · Oct 1, 2005

I do a fair amount of gunsmithing in my spare time as a hobby. Installing barrels, and building rifles etc... I personally would recomend only TIG welding these pieces. To start with welding those thicknesses together with SMAW you are going to have to deal with warpage and deflection issues. Another thing to consider is that an AC welder is not going to pull a true Low hydrogen rod like a 8018 or a 11018 satisfactorily not to mention that you will have to deal with slag getting in the way. You will need to heat treat the pieces when finished to gain full strength which means that you need a filler metal that contains the same heat treatable properties as well.if you are determined to stick weld the pieces I have used esab atom arc 4140 rods before but it was on thicker pieces. remember preheat and controlled cooling are very important. Hope some of that helps you. ~Jackson

SMAW Process on 4140 Low-Alloy Steel - Appropriate Electrode?

Top Contributors this Month

Recommended Communities