nail header

This is my nail header. It is forged from an old piece of steel that was in a sewer. (I didn't steal it, it was replaced by a new one) The hole on the left is for hanging. There is a tapered hole under the nail header made by drilling and punching. I then filed to a square. I quenched it in water a red cherry heat and after making a few nails, there is absolutely no damages on the hole. I it probably mild steel but I'm not sure.