700° would be too hot. Try rubbing boiled linseed oil on it around 500°. Dunking doesn't work as good as rubbing. Might have to reheat and apply a few coats to get it where you want it.I tried the black finish on a small metal bracket that hold a reflector. Low carbon steel.
I set up a propane torch on the grill. Tuna can and olive oil. Using a Fluke 568 IR Thermometer, heated it up to about 500-600°F. Placed in the oil.
It didn't take. I sanded and cleaned it fairly well. It took a smokey looking patina. The darkest part was the side that made first contact with the oil. I tried twice and the same results both times.
I'm guessing it needs to be hotter. Pushing at least 700° before it go's to the oil.
Ill try it again on something else. I gave up and painted the bracket.
boiled linseed oil is often used by blacksmiths... They are pretty experienced with thisA different oil might take better, too. In his vise video he used rapeseed oil.