Free Cutting Steel Square 11SMnPb30+C
11SMnPb30 is a free-machining steel with low carbon content. The term free-machining implies that the analysis is tailored to promote machinability at the expense of other properties. The material can be machined at high speeds and it is short-chipping, which expediates processing in unmanned machines. The principal additions promoting machinability are sulphur and lead, both of which are present in an amount 0.3%, but a high phosphorous content can also contribute. The positive influence of lead for machinability derives from its low melting point whereby the particles of lead in the steel melt in the vicinity of the cutting edge thereby contributing locally to lubrication. The high level of machinability is further enhanced by cold drawing.
11SMnPb30 +C is standardised in SS-EN 10077 - 3. The (discontinued) SS-designation is 1914. The base steel 11SMnPb30 does not have very high strength but yield and tensile strengths are enhanced somewhat via cold drawing. The minimum prescribed level of yield strength varies depending on edge length over the range 440 - 245 MPa. The interval for tensile strength decreases and the minimum allowed elongation in a tensile test increases somewhat as the edge length of the bar increases. There is no guarantee for impact toughness.
The edge-length tolerance for 11SMnPb30 +C as cold-drawn squares is quite good, h11 as defined in ISO 286 - 2 or better. Furthermore, straightness is considerably better than what is typical for hot-rolled square bars and the maximum height of arc is 0.001 times bar length. Straightness as a property is important for processing in bar-feed machines.
The weldability of 11SMnPb30 is limited as a consequence of the high levels of sulphur and lead. However, should the application require that the part has a wear-resistant surface, 11SMnPb30 +C can be case hardened.