4130 & 4140

[G.T.]

Hi to all, just a general steel question that some of our more experienced gunsmiths might be able to answer?? How does 4130 & 4140 take salt blue?? I think just about any part on a luger, with the exception of the trigger lever, and maybe hold-open could be made from those two steels? Wha'd'ya think guys.. .. best to all, til..lat'r...GT...