All I've got is what I already said here:
viewtopic.php?f=1&t=180598&hilit=make+stake
Medium carbon is good if you're sure you've got a piece of it -- buy new steel or spark-test your candidate pieces. Low carbon of course welds easier, though you should also build about a quarter again as massive, up to a certain point: thick and heavy roundstock for a T stake doesn't need to be anything elaborate, mild roundstock being about all you'd need, and your weld-fabricating method would be to fill in a bevel: here's your round - O and here's your beveled piece of square or heavy bar stock at its end -
/===. You can use two bevels if you like so they will come together like this: O<=== and you weld on both sides, filling in completely with multiple passes of weld.
Of the mediums, 4130 or 5160 are probably the easiest to come by. 1050 or 1060 simple steels are still around. Steel gets more delicate to work with as its carbon increases -- it is become less chemically stable and thus inclined to start burning instead of melting, at lower and lower temperature with increasing carbon content until finally only a few tens of degrees separate welding temperature from burning temperature. So, keep the carbon way low as in 1016 or such steel, and you can readily weld it up all the livelong day. Just fine for the shafts of the stakes as a rule.
Mild steel will ding up easier, but also just as easily can be filed smooth again. Med-carbon is just an optimized solution, for when you're actually ready and really need your stakes to be harder. Bending sheet metal, it's not so big of a deal.
This too may be relevant to your interest:
viewtopic.php?f=1&t=180257&hilit=make+stake
viewtopic.php?f=1&t=180011&hilit=make+stake
We have a Search button here onsite, J. Hillard, and that button is your friend as much as it is mine.