building up rails

I have never done it- Years ago I saw the results on two different machines and it was a mess- whether it was done improperly or more likely a poor system I do not know for sure.
I suspect the weight of the machine is to much for thickness of material, as it becomes thinner it mushrooms and breaks

I don't believe anyone makes those weld-on rail repair plates nowadays. People hardly even build up rails any more with weld. Those videos you saw are likely to be WW2 vintage .. when salvage and rebuild of scrap components was critical and widely encouraged by Cat. It's a whole lot different story nowadays, unfortunately, in our throw-away society.

I'm with OneWelder as to its success rate and viability. On a D2 it might work O.K. .. but the action of a track roller on the rail is a heavy rolling, squeezing action, that keeps flattening and squeezing out the rail metal. This means you need a metal in the rail that is hard as well as tough, to resist wear as well as the rolling, squeezing action.

Accordingly, low alloy, high strength steels .. with good hardenability .. containing manganese, boron, molybdenum, vanadium, and nickel .. are used for links. They are then deep induction hardened, resulting in high Rockwell hardness, and a depth of around 1/4" - 3/8" (depending on machine size) to ensure satisfactory life.

You would be hard-pressed to find any plate material containing the same steel alloys as Cat track links .. and if you did find some that were close, it would be expensive plate.
Add in profile cutting the sections, and you are running into more $$$. Then you have to weld them on - more $$'s again. Finally, you end up with a rebuilt product that is only 3/4 as good as the original factory item.

In the old days, factory undercarriage was expensive, and labor was relatively cheap. Nowadays, new undercarriage has got cheaper compared to what it used to cost, while labor costs have gone up. As a result, rebuilds of many things are rarely economic.

Now, I know that D2 undercarriage is NLA, so this isn't helping you a great deal. However, what I'm pointing out is that it wouldn't be economic for anyone to produce those repair plates in the 21st Century .. and even if you could get them, there would still be a lot of time involved in rail rebuild.
The simplest and cheapest option is to source good used track chains from a parted out tractor .. or if you wanna go the whole hog, convert to D3 undercarriage.

When I was working yet at the dealer we had a track shop just for welding up tracks and it was a submerged type system where the welding wire was submerged in a black sand type material as it ran along the links. It was big business then but don,t know how much is done today as OZ said.Rollers and idlers were also built up in the same manner but they had to be taken apart completely to do it.I was over to the shop the other day and they said shop labor now id $91.00 hour and road service was $99.00 I believe they said but I can,t remember if track welding was a flat rate or not back then but I kind of believe it was.

If you have plenty of time and want to rebuild the chains, I'd suggest an E-12018 low hydrogen rod. You could use E-7018 but it wouldn't last as well as the higher tensile strength stuff. As far as using plates, that was pretty well covered but if you want to try it, I'd go with a T-1 alloy, beveled on the edges and a slotted hole in the middle.

SJ -
It is submerged Arc the the local Massey Ferguson dealer did for a few yrs in the S- when they moved they stopped as far as I know.
They looked excellent- the but is quite often the eyes were stretched - or broke before you got sufficient wear to pay for the welding.
Mike
A lot depends on your ;
link condition
pins and bushings
your welding equipment
the amount of time you can devout to this

One Welder, it,s been probably 20 or 25 years ago or more when they had the shop but they moved the equip. to another branch so don,t know what they did then. Most our track work was big tracks as we had lots of coal strippings going on here and road building so it did pay them and they didn,t wear them out beyond fix before they had them built up.

SJ
Different location - same time frame, maybe a Little further back
They were going from farm equipment to construction equipment,
All dozers they took in trade received the build up treatment- but some should have been passed over
At the time I priced them out on a machine and it came close to replacement costs so I did not have it done

OL' Grump--if you build up rollers. idlers and chains should the weld material be the same? if you have a rockwell hardness greater on one component won't all the wear be on the softer weld buildup??

I'm doing this process right now. I just finished the idlers. I used hard surface rod on the leading edge and mixed 7018 on the sides with the hardsurface to wind up in between. On the chain surface i'll use 7018 for the bulk and a thin hardsurface on the edges to stop it from mushrooming over. 11018 is twice the cost of 7018 and how many hours a year must a person expect to get out of a toy. I need a few hundred hours work right now to build a lane and landscape but it should be pretty much retirement at 100hrs or so a year after that.
Chris