Views: 71 Author: Site Editor Publish Time: 2018-05-30 Origin: www.fuchun-casting.com
Cast irons are a family of iron-carbon alloys. Their high carbon content (usually 2–4%) gives cast iron its characteristic hardness. To facilitate a better understanding of these materials, they can be divided into five groups, based on composition and metallurgical structure: white cast iron, malleable cast iron, grey cast iron, ductile cast iron and alloy cast iron.
The carbon in white cast iron exists in the form of cementite and its section is gray. It is a good anti-wear material and works under abrasive wear conditions.
White cast iron includes ordinary white cast iron, low alloy white cast iron, medium alloy white cast iron, and high alloy white cast iron. China has a national standard (G.B8263-87).
White cast iron is hard and brittle, and it is not easy to cut. It is seldom used directly in casting parts.It is used in applications where abrasion resistance is important and ductility not required, such as liners for cement mixers, ball mills, certain types of drawing dies and extrusion nozzles.
Malleable cast iron is a kind of cast iron with high toughness which is treated by graphitization or oxidative decarburization annealing.As graphite is floc like, the fracture and tip effect of the matrix are reduced, the strength and toughness of malleable iron are much higher than that of gray iron.It should be pointed out that malleable iron can not be processed by forging, but it is only a name.
Malleable iron is divided into Ferritic Malleable Iron, pearlite malleable iron and white core malleable iron, in which pearlite malleable iron has relatively high performance, and can be used to make crankshaft, gear and other wear-resistant parts instead of some steel.
Ferritic Malleable iron is usually used for making pipe fittings, pipe fittings and low and medium pressure valves.
White heart malleable iron is mostly used for thin-walled shell parts with good weldability and toughness.
Grey cast iron is one of the most widely used casting alloys and typically contains between 2,5% and 4% carbon and between 1% and 3% silicon. It has excellent casting property, machinability, abrasion resistance and shock absorption. The compressive strength and hardness are close to that of carbon steel, but the tensile strength and plasticity are low and brittleness is large. Grey cast iron is simple in production process and low in price. It is widely used in mechanical engineering and is mainly used for wear resistant components under moderate load.
Ductile cast iron is the best mechanical property. As graphite is spherical, it greatly reduces the separation and tip effect on the matrix. The mechanical properties are much higher than that of gray iron, and the strength is close to the steel, and there are some advantages of gray cast iron.
Such as better damping, friction reducing, low notch sensitivity, excellent casting and excellent machinability. The disadvantages are large shrinkage, large white chowing and poor fluidity. The requirements for raw materials and smelting and casting process are higher than those of gray cast iron.
Typical applications are agricultural (tractor and implement parts); automotive and diesel (crankshafts, pistons and cylinder heads); electrical fittings, switch boxes, motor frames and circuit breaker parts; mining (hoist drums, drive pulleys, fly wheels and elevator buckets); steel mill (work rolls, furnace doors, table rolls and bearings); and tool and die (wrenches, levers, clamp frames, chuck bodies and dies for shaping steel, aluminium, brass, bronze and titanium).