Despite the many claims that railroad spikes make for great knives, the carbon content of a rail road spike knife is not generally high enough to provide good edge retention. Even the more modern HC rail road spikes fall far short of being considered a quality knife despite the HC or “High Carbon” content. What that HC really means is that it is high carbon for a rail road spike. The carbon content still does not approach what is needed to take a good hardening.
To address this challenge a wee bit, I like to quench rail road spikes in something generally called super quench. I believe the person who originated the term was Robb Gunter. The recipe I use is:
Five gallons water
Five pounds salt
32 Ounces Dawn blue dishwashing liquid.
Seven ounces Jet-Dry (unscented)
The rail road spike is brought to a non-magnetic state and then quenched. There is no tempering because at best this will bring a rail road spike to 50 on the rockwell c scale. For mild steel, it is more like 45 RC. Any effort at bluing with heat or tempering will defeat the purpose of the super quench.
The quench will last for some time. You can tell when the mixture is loosing effectiveness when when it drifts from the original blue color (like windex) to more of a green.
So why, if they do not produce a quality knife, do I forge knives out of rail road spikes? Well, the edge retention is often a great deal better than some of the utter crap that comes into the United States from Pakistan and folk seem happy with that. Besides, they are a fun way to illustrate the trans-formative nature of forging a knife rather than simply removing stock.