For nearly three quarters of a century, metallurgists have added elements such as lead, sulfur, and selenium to enhance the machinability of stainless steels. The eternal challenge has been to keep the levels of such additions low enough that they do not seriously compromise other vital properties.The world's first free-machining stainless steel, invented by Carpenter's Frank Palmer in 1928, was a straight chromium grade with sulfur added. It was the forerunner of today's Type 416 stainless. Sulfur and phosphorus were both added to make Carpenter Type 303 stainless, the first free-machining chrome-nickel stainless, in the early thirties.
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