Depends on how often you use it, and what you use it on. You can harden it if you want. Black pipe is carbon steel. Remember, the harder you make it, the harder it is to resharpen when needed.
A machinist built a post for me that was part of a mechanical accounting machine many years ago, and case hardened it with potassium cyanide. He had made it a little too thick where the slide was supposed to fit over it. Tried to stone it down, but couldn't even touch it. Took it back to the machinist, and he said how am I supposed to do anything with that now? I asked about heating it back up to soften it? He said, yes that would do it. So he fixed it and case hardened it again. Was interesting to see the chemical reaction as he dropped the red hot post into a little pile of potassium cyanide. Really sputters! Don't try this inside or you'll poison yourself. Deadly stuff.
Tom