My shop in NY was literly in the service yard for the Rail Road. There was a pile of spikes the size of a truck the I could use. The northeast was a mix of dozens of spur lines that dated back to the 1800's, many had been abandoned and torn up. We had great piles of wood, rails, plates and spikes. Much was scrapped. The spikes come in many variaties, from pig steel to high carbon quality.
Look for WHC or HC. These tested out in the 1050-1065 range, made fair knives. The real value being the artistic nature of the spike itself, way cool, made a bunch.
Step one is to sand blast of get all scale off and then check for cracks. A cracked spike will result in a cracked knife. We use ferric chloride to check.
Twist the handle area at the head, then fuller out. There is a lot of steel there.