How to weld 1/2"armour plate?

[Joe Lorenzino]

I have been working in a welding repair shop for a few years, so this is what I would suggest.

Although I haven't welded armour plate, we do have to repair cutting edges on loader buckets and such. The normal procedure is to "V" it out properly, then fill it in with narrow "stringer" beads using 1/8" dia. low hydrogen ( _ _18 series, i.e.: 7018, 8018, 11018 ) electrodes at around 125 amps.. If you have a DC machine, they are always run DC Reverse. If you have an AC machine, and it has sufficient open circuit voltage to start and run an _ _18 series rod (many of the lighter ones do NOT) then use a 7018AC rod which has ionisers in the flux to allow it to run properly on an AC machine. On plate that thin, preheat is not essential, but would help prevent possible cracking. A preheat of 200°-250°F is ample, and mostly used to dry out any moisture that my contribute to hydrogen embrittlement.

A better choice is a more "forgiving" low hydrogen rod (higher percentage-of-elongation) such as an ArcTec 223 from ArcTec Alloys. This allows the weld to stretch more than an _ _18 series rod, and so puts less stress in the base metal. We use this rod for the long welds when attaching cutting edges to buckets as it causes less warpage and has higher impact resistance.

Stainless rods ARE nickel/chromium, and the 18-8 they speak of would be a standard 304 grade. All of the "300" grades of stainless are "austenitic" meaning nonmagnetic and nonhardenable. Higher nickel (first number) makes it tougher, higher chromium makes it harder. If using this type of rod, a 304L, or 309L would be good choices as the "L" signifies "Low Carbon", and it will not pick up as much hardness from the base material. The drawback is the price, and that they do not weld very well out of position. A better choice in this category would be ArcTec 265 Unichrome, which has a much higher strength rating, and welds some what better out of position.

If wanting to use a MIG, I would lean towards a Flux core, Dual Shield, or Metal core type of wire, for added weld ductility. If using solid wire, a type ending with S2 or S3 would be preferable to an S6 wire because of a higher elongation value. If Mig welding, I would definitely use a preheat to prevent the weld from cooling to fast and causing hardness/brittleness problems.

A high nickel rod designed for use on cast iron, like an ArcTec Supercast 90, would likely give very good results as well.

[cletrac (RIP)]

Well, there we have it from an expert on the subject! Joe, I was by your shop the other day but you weren't around.

[colin jones]

Hey guy's! Darrin, quite simply, prepare, as in grind clean, V out about least half the thickness you're welding to both pieces and leave a little gap for penetration, High amps on your welder, set gas to 18-20. Solid wire welding with mig is already low hydrogen. If you're going to war then preheat if you're not "don't bother" inert mig gas prevents hydrogen from affecting your welds. watch your welding while you're doing it, you can see if it's flowing or sitting on top. if it's not a flowing a flatish weld then you need more heat or you're dragging instead of pushing. If you welder is on high amps it will put plenty of heat into the material anyway. Don't try and weld an oxy cut that still has slagg on it as it won't work.
"My 2 bobs worth""
Colin.

[eddy8men]

great thread fella's and thanks to all those that have given advice, i'll be needing it soon

cheers

rick

[cletrac (RIP)]

It looks like you have your work "cut out" for you!

[eddy8men]

very true

[Lynn Eades]

Thanks for your very useful posts. For those of us not so skilled, it is great to be able to pull up this thread in the future, as a reference.

[Darrin Wright]

thanks guys for all your input.
I am picking up a heavy duty mig today from a friend and will look at preparing the steel this weekend and commence welding next week.

I think (and this thread has confirmed) preparation is a very important factor, so will grind a vee on both sections of the hull & panel, and ensure any slag is removed.
Weld in some braces to support the new panel, some minor tacks to get it in the right spot, adjust with a hammer, then weld away alternating from side to side so that heat expansion does not affect the new panel.
When finished grind and tidy up the welds, then run over it with a flapper sanding disc to get the surfaces right. When the hull is blasted get them to concentrate on the welded area to get the surface texture the same.

Thanks again