Rapid solidification of specially controlled molten metal produces numerous tiny graphite flakes that can be one-tenth the size of those in green sand castings. Increase fatigue durability Enhance flame and induction hardening Tensile strength is related to graphite flake size in gray iron - smaller flakes give higher strength. Chemical composition and matrix structure are two significant factors affecting strength and hardness. Geometry, presence of cores, and heat treatment influence graphite and matrix structure and therefore strength and hardness. Normally, machining is done in the soft ferritic condition minimizing machining cost.
Excellent heat treat response facilitates hardening.
Green Sand Molding Sand molds made with a moist sand, in which the moisture is present at the time metal is poured into the mold, are called green sand molds. Green sand molds, which are used more extensively than any other mold material, may be used for making small, medium, and large castings. These molds are relatively inexpensive to produce, since the basic material is readily available. Simple, even some complex, changes may be made in the pattern design, and thus in the mold design, at very little cost. Green sand is adapted easily and quickly to mechanical and automated production methods.