We have had a large sampling of gears and shafts analyzed form the 020, 02a and 02j VW transaxles at a local heat treat plant here in Portland, Oregon. It turns out to be a proprietary blend of materials. It has very similar characteristics to 8620. When tested for hardness most samples are running right at 62Rc. Or simply VERY hard. Great for street gears. The down side of being super hard is being brittle. They don't hold up to shock very well and have no plasticity. In other words they have no give. Once the gears are tempered they are indeed softer and have added plasticity. They can literally absorb more shock load and will allow the tooth to bend then reform rather than shattering. Our first set of heat treated gear were done around 1995. Lots of guys were turboing their 16Vs and popping trannies to no end. Once we dialed in the correct hardness we have had nothing but success with this method. The main reason for pursuing this avenue was to mimic real race gears that we had been handling. We have installed VW motor sport, Hor and other race gears and noted how much softer they were than stock gears. Please call 503-735-5532 or email with questions.
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vw race gears
Before and after. Dark gears have just been heat treated. Lighter gears are after they have been cleaned, bead blasted, and polished.

vw race gears
Heat treated VW gearstack ready for install