I got Step down transformer which reduces voltage from 230 VAC to 40 VAC ~ 100 amp. I can weld with it while having no problems. Also I got another one step down transformer which is three phase, but has one single phase input, where it's now powered. Outputs about 600 amps 6 VAC. I've picked up 4.2 mm welding stick and it doesn't create arc it just melts down in seconds. How do I weld with this thing ?
As 6VAC is too low an open-circuit voltage for an arc welder, you could make a spot welder.
Spot welding works well with steel and stainless steel, less well with highly thermally and electrically conductive materials.