Welding question

[deepcreekdale]

I am an amateur welder using an acetylene/O2 set up and have a question for any experienced welders out there. I can run a decent bead and make good strong joints. However, recently, I was doing a quick repair on a mild steel trigger guard I was making and ran into a little problem which has happened occasionally in the past when I weld to effect a repair, which is not that often obviously. The joint was fine, no pinholes or anything but when I went to finish it, at the point of the weld, the metal was glass hard, no file would touch it. Is there something I am doing wrong or am I using the wrong welding rod? I am not sure what the exact composition of my rods are, I bought them as a bundle in the 1970's at the recommendation of the dealer when I bought the set up. If the rod is or could be the problem, what would you experienced journeymen welders recommend I use since my 40 year old supply is about gone? Most of my welding is making items like jigs or fixtures etc, so this is has never been a big issue before but it would be nice to be able to use it on mild steel parts on occasion that I want to finish.

[FDR]

Most modern gunsmiths use this:
https://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/welding/3-1-2-nickel-steel-welding-rod-prod594.aspx

Fred

[David R. Pennington]

Did you quinch it to cool it after the weld? If so it is possible your part or your filler had enough carbon in it to harden. You might try bringing the part up to a dull red and burying it in a bucket of warm wood ashes overnight to see if it will aneal. If not you will have to finish with grinding or abrasives.
I have bought mild steel rod by pound from welding supply house. I try to use same material as the repair if I can. I have used scrap thin pieces of wrought iron when repairing a wrought iron part.

[B.Barker]

If your guard was a cast one from a dealer it may not be mild steel. One of the dealers told me they never knew what there parts were cast from even though they ask for a certain steel. Sometimes they would get axe heads that wouldn't heat treat and sometimes there parts that should have been mild steel were high carbon. I would try annealing it like already mentioned.

[Goo]

First off you must do a spark test on what you need to weld to find out if its mild steel or if its carbon content is high this something you cannot take it for granted, the steel can not be welded without consequences. If there is a high carbon content you are going to have problems regardless which rod you choose the steel crystal structure will alloy and reorient itself to the “ hard as glass “ condition you describe.  It doesnt matter how slowly the weld cools, you do not need to quench for the part for the welded area to harden. There is mild steel welding rod available for gas welding steel but you need to talk to the guys behind the counter at the welding supply and tell them what you want to do so they can sell you the right rod.    As a guidline steel from water pipe welds ok some of the cold rold flat stock from big box mega home store welds really well, hot roll steel wil not, galvanized will make you sick from zinc fumes. Using borax (20 mule team ) as a flux will improve results on gas welds. Also almost no one gas torch welds steel any more, most people dont even think its possible , 40years ago it was standard practice and required learning at trade school, but not anymore.

[jerrywh]

 There ar better welders on this forum than me but I have done a lot of gun repair and run into this problem many time in the past. I think you will find that this hardness is only a thousands or so deep. If you take a dermal tool  with a small stone or sander and grind off the top few thousands it will then file OK. But it is hard on files. You might try welding with plain iron wire from the hardware store.

[45-110]

i cant remember all the details......but having a carburizing flame or a neutral flame affects the weld. one of these actually puts carbon into the weld and therefore makes a hard spot even in mild steel. need a pro welder to weigh in on this.
kw

[dogcreek]

Did the part that you welded have a case on it? If so, carbon is drawn to the spot you weld and makes it very hard.

[deepcreekdale]

Appreciate all the responses and advice as always. The piece I recently was working on was mild steel, (weldable steel from Lowes after shaping in a coal forge) and the hardness is deep into the weld. I thought it might be the filler rod I am using but sometimes it doesn't seem to harden the same. I have done some welds over the years on the same type metal that didn't seem to develop a hard spot at all. I guess it only happens on gun parts that need to look good, never on fixtures, or jigs! If memory serves and it may not, when I bought the filler rod long ago, I asked for nickel steel rod as that what was recommend  by Roy Dunlop in his book on gunsmithing. I always let my welds air cool, never put them in water I heard once that can cause cracks. I have tried annealing these hard spots before, but have never been able to do so with any success.  I sort of agree with 45-110, I am wondering if I am putting too much carbon deep into the weld but I always try for a neutral flame although I am not that good a welder to be the perfect judge all the time. However I will also take FDR's advice and order from Brownells, plus you can always ask them for tech advice and explain the application.

[Clint]

It seems to me that the longer you stay in the puddle, the harder the weld deposite becomes. Since you are putting intense heat into a very local area while most of the parent metal is "cool" it will pay to normalize or anneal the whole piece and that should help to make the welded area behave.

[Goo]

I asked for nickel steel rod as that what was recommend  by Roy Dunlop in his book on gunsmithing. .

Nickel rod might be the cause, nickel rod reduces sparks flying while welding carbon steel but it can make the welded area hard to file.  Maybe Roy had a specific goal in mind for using nickel steel rod. I used to use stainless rod which has a lot of nickel to reduce the sparkler effect while tig welding regular steel but you would have to use a grinder instead of a file to smoth or blend the bead