Hey fellas, thought I'd chime in about landing gear repair too.
I didn't think welding across the leg would be a good idea either, so I didn't do mine. Sorry it hasn't flown to say good or bad, but you all know the leg inside is really the part that matters. If it's considered to be a beam in bending, then welds along the neutral axis would be better suited than those across material with higher stress. Some of the testimonies here verify T-18's have flown with soft gear or repaired gear without repeating the heat-treatment. I'm not the expert at metallurgy, but if I'd like to help if I can explain what I know to those who might not know.
To do it right, weld on steel that's been totally annealed (softened). Internal stresses can cause it to crack after welding if it's already 'hard'. Afterward, for heat treating to get the 180,000 psi strength and 'spring' in the material it first has to be heated above transition temperature, which may be roughly 1400F (above cherry-red) and then quenched. Then it's tempered by raising it back up to a different temperature (several hundred F) and cooling slowly. This potentially softens it, slightly, but with the great advantage of being less brittle and reduces built-up internal stresses. It has to remain below the transition temp or you ruin the initial treatment. Unfortunately, welding does just that.
By definition, welding is a process where materials are fused together by melting them (~3800F). It really ruins the original heat treatment. To get it back you need to repeat the whole treatment over again. Simply re-heating it actually only softens it more because it cools relatively slowly. The quenching process is the trick that 'freezes' steel in it's austenitic state. Don't do this at home unless you're an expert and have all the facilities. I sent mine to Hinterliner(sp?) in Utah. Yes, at the edge of machinability at 180,000 psi steel can still be machined, but you'll notice it may be a little harder to do than when it's soft. I reamed my steel spar fittings only after heat-treating because the process can distort things a little. Lot's of guys use a file on the edge of a part to feel and compare hardnesses. Welding on 'hard' steel can often lead to more cracking, due to internal stresses and uneven conditions within the material. Professional heat-treaters give it time to 'soak' in the oven and get it all even.
Nevertheless, there are T-18's flying without pristine heat-treatments on their gear, and evidently they seem to work. Maybe it's a matter of use or how good your landings are, but that's not the design. If the actual leg inside hasn't been affected by heat that would help. I surely hope not to have to repair my gear. If I did it would be a hard choice to remove it and sent it out again for treatment, and perhaps I wouldn't either. Thought you guys might need to know. Hope it helps.
Les Krumel, Albuquerque
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