Maxel 400 FM is a corrosion resistant pre-hardened, free machining steel intended for use as a holder or backing in plastic molding. Maxel 400 FM is similar to conventional 420 mold steel, but sulfur has been added to enhance its machining properties. This datasheet provides information on composition. It also includes information on corrosion resistance as well as heat treating, machining, and joining. Filing Code: SS-637. Producer or source: Crucible Service Centers.