SF-Alloys In Cutting Conditions chart

Hey All,
I'm looking at benchmark Carbide's machining data chart while setting stuff up for an Invar job. They have a data column called "SF-Alloys" with <32, >32, and >42 as values to judge speeds/feeds by. Can anybody clue me in on what that means? Depending on the value it changes the recommended SFM and IPT.

Thanks