Yeah, there's the big question, just how good does a firing pin need to be anyway? In Dunlap's book he tells of making firing pins out of several steels when replacements were unavailable after WWII. They pretty much all worked though he recommended going with a factory replacement when you could. I've seen factory pins break in O/Us, don't know if it was a design/tolerance problem or just that heavy hammer strike on the little pin with not much to absorb energy before it bottoms out in the hole. Thinking the latter, I want to err on the side of impact resistance just because I don't really know.
Blue embrittlement in plain carbon steel is a bit controversial. In fact the cause of the phenomena was and may still be not precisely known though there are a lot of theories. One article related it to impurities in the steel (plain carbon) which varies by melt which may be why sometimes you see it and other times not so much. Like I said, read the articles and get confused.
