Slag is glass like stuff that was floating around on molten steel at the steel mill. It is placed there to keep the air away from the steel so it does not literally burn up like a sparkler and this slag stuff (also molten during the firing and pouring of the steel) scavenges impurities out of the steel and provides a way to separate the impurities from the steel. This big lump is a chunk of solidified slag. Actually this is a relatively tiny piece. I lived in a steel town as a kid and used to go to the mill with my dad some times. This stuff was eeeeevvvverrrrrywhere. Some of it is kind of pretty in its own way. Most of it was gray green with some lighter streaks in it. I put the black thing in the photo as a “color” reference . . . also the white paper. You can just see that the slag is green not black.
. . . annnnyway the heated and hammered end of this square steel rod . . .
. . . this is how a blacksmith makes a tongue depressor . . .
. . . this square steel rod has what you were talking about on it. It is “fire scale” or “mill scale”. Note that it did not rust but the bare cold rolled surface of the steel rod did rust right next to the heated and hammered fire scale area. In the second photo I was attempting to show the surface of the cold rolled square rod. Cold rolled means the surface will be as most expect steel to look shiny and reflective not black or blue and scaly. Hot rolled is the latter (blue / black and non reflective).
PS: the black stuff you are seeing may be buffing compound from polishing the blade. (?)
c
Wowbagger
. Thanks! I suspect you're right about the black stuff, but this is interesting info. Would love to know the answer to @Dadpool question about Hammer Tested, etc..
