S & P in Steel

Actually the spec limit on most steels is 0.04 weight percent.

Sulfur and phos are an undesired impurity, but it is very expensive to remove these elements though it can be done.

However, With todays analytical technologies, we are almost counting atoms, so "zero" is not acheivable.

Manganese is added to steel to tie up the sulfur as manganese sulfide, preventing it from forming Iron Pyrite, which is brittle at rolling temperatuires.

See my Blog post here.

For machining applications, boith Sulfur and Phosphorous contribute to machinability. Sulfur alone inSAE/AISI 11XX steels, and both Sulfur and Phos in 12XX.

Milo