Gray iron, or grey cast iron, is a type of cast iron that has a graphitic microstructure. It is named after the gray color of the fracture it forms, which is due to the presence of graphite. It is the most common cast iron and the most widely used cast material based on weight
Grey iron is an iron alloy which includes carbon and silicon in addition to the iron, in various concentrations, depending on the needs of the manufacturer producing the alloy. This substance is sometimes referred to as “cast iron,” although cast iron actually includes other iron alloys. Grey iron is very easy and cost effective to make, making it a highly popular iron alloy. Its properties make it highly suitable for a wide range of uses, and examples of this iron alloy can be seen in many locations around the world, including museums which maintain products of historic interest.
Gray iron is by far the oldest and most common form of cast iron. The fluidity of liquid gray iron, and its expansion during solidification due to the formation of graphite, have made this metal ideal for the economical production of castings in a variety of industries. Many engineers design castings using gray iron due to its excellent machinability, dampening characteristics and self-lubricating properties.
The tensile strength of grey cast iron, plastic and toughness are much lower than cast steel, but it has a considerable compressive strength as same as cast steel, cast iron is also commonly used in the worst mechanical properties. Meanwhile, the matrix of grey cast iron mechanical properties also have some effect, the ferrite matrix of grey cast iron graphite sheets thick, strength and hardness of the minimum, it is commonly used for the stove parts and some low requirements to tensile strength. Pearlite matrix of grey cast iron has small graphite, have a higher strength and hardness, the main castings used to manufacture the more important. Ferrite pearlite matrix of a graphite cast iron pieces is thicker than pearlitic grey cast iron, so has worse performance than pearlitic grey cast iron. So there are many demand in industry for pearlite matrix of grey cast iron.
Good casting properties, good vibration damping, good wear resistance, good machinability and low notch sensitivity.
In China, we classified the grey cast iron degree by HT100, HT150, HT200, HT250, HT300 and HT350. For ASTM A48, DIN 1691, ISO 185, JIS G5501 and BS1452 standards
? G100: For small loads, the friction and wear no special requirements for important castings, such as protective cover, cover, oil pan, hand wheels, frame, floor, hammer, small handle, etc.
? G150: Under moderate load of castings, such as the base, frame, box, knife, bed, bearing seat, table, wheels, cover, pump, valve, pipe, flywheel, motor blocks and other.
? G200 and G250: Requirements withstand greater load and a certain degree of tightness or corrosion resistance of the more important castings such as cylinder, gear, base, flywheels, bed, cylinder block, cylinder liner, piston, gear box, brake wheel, coupling Plate, medium pressure valve, etc.
? G300 and G350: Under high load, wear and high air tightness important castings, such as heavy machine tools, shears, presses, automatic lathe bed, frame, frame, high-pressure hydraulic parts, piston rings, force larger gear, Cams, bushings, large engine crankshaft, cylinder block, cylinder liner, cylinder head, etc.