used for a wide range of applica- tions, from table legs and bases to large fountains and building fa- cades. Gray iron is particularly good for applications in which vibration damp- ing is required, such as engine blocks and frames for manufactur- ing equipment. For higher strength applica- tions, ductile iron can be used. Ductile iron, because


Table 2. Composition Range for Un-Alloyed Cast Irons (in %) Iron Family Carbon Gray


Ductile CGI


Malleable White


2.5-4.2 3-4


2.5-4


2.2-2.8 1.8-3.6


1.8-3 1.5-3


0.15-1 0.1-1


0.10-1


1.2-1.9 0.15-1.2 0.5-2 0.15-0.8


Silicon Manganese Sulfur 1-3


0.02-0.25


Phosphorus 0.02-1


0.01-0.03 0.01-0.1 0.01-0.03 0.01-0.1 0.02-0.2 0.02-0.2


0.02-0.2 0.02-0.2


marily controlled by the carbon and silicon content of the metal and the cooling rate of the casting. Te desired proper-


ties should be specified rather than the factors that influence them. Te most significant


of its strength and duc- tility, often is specified in severe applications. Like gray iron castings, ductile iron is used in a wide range of appli- cations, from pumps, compressors valves and fittings to diesel engine parts and oil field machinery. Table 1 shows specifications,


Gray iron is characterized by the graphite flakes in its microstructure that resist wear and galling while damping vibration.


markets for gray iron include powertrain parts for transportation equipment, farm and construction equip- ment, diesel engine components, pumps, compressors, and valves and fittings. Centrifu- gally cast pipe is also a major application for gray iron alloys. Te mechanical


properties of gray iron are determined by its


characteristics and applications for both gray and ductile iron. Table 2 shows the ranges for elements in gray and ductile iron.


Gray Iron Gray iron derives its properties


from flake graphite in its microstruc- ture. Its unique attributes include excellent machinability at hardness levels that produce superior wear- resistant characteristics, the ability to


“


resist galling and excellent vibration damping. When the composition of the molten iron and its cooling rate are suitable, the carbon in the iron separates during solidification and forms interconnected graphite flakes. Te graphite grows edgewise into the liquid and forms the characteris- tic flake shape. Te properties of gray iron also


are influenced by the relative hard- ness of the metal matrix, which is the iron that surrounds the graphite. Microstructural properties are pri-


The most significant


markets for gray iron include powertrain parts for


transportation equipment, farm and construction equipment, diesel engine components, pumps, compressors, and valves and fittings.”


40 | METAL CASTING DESIGN & PURCHASING | Sept/Oct 2014


chemical composition, processing technique in the metalcasting facility and solidification and cooling rates. Te amount of graphite present, the length of the flakes and its distribu- tion in the matrix directly influence the properties of iron. Basic strength and hardness are determined by the metallic structure in which the graphite occurs. Graphite has little strength


or hardness, so it decreases these properties of the metallic matrix. However, graphite provides several valuable characteristics to cast iron, including: • Te ability to produce cast- ings in complex shapes, such as water-cooled engine blocks.


• Good machinability, even at wear-resisting hardness levels and without burring.


• Dimensional stability under differential heating.


• High vibration damping as in power transmission cases.


• Interface lubrication reten- tion as in internal combustion engine cylinders.


Te lower strength grades of gray


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