Steve Manik asked: Iron casting
Cast iron generally means grey cast iron, but is identifies a group of ferrous alloys which solidify with a eutectic.
Overview:
Iron accounts for more than 95% the alloy material, while the main alloying elements are carbon and silicon. The amount of carbon in cast iron is 2.1-4% while ferrous alloys with less carbon are called carbon steel by definition. Cast iron has appreciable amount of silicon normally 1.3%. Therefore, these alloys should be considered ternary Fe-C-Si alloys.
In spite of this, the principles of cast iron solidification are understood from the binary iron carbon phase diagram, where the eutectic point lies at 1154 °C and 4.3 wt% carbon. Because cast iron has this composition, its melting temperature of 1150 to 1200 °C is about 300 degrees less than the melting point of pure iron. Cast iron tends to be brittle, though the name of particular alloy may suggest opposite. The color of a fracture surface may be utilized to identify an alloy; carbide impurities allow cracks to pass straight through resulting in a smooth “white” surface, while graphic flakes deflect a passing crack and initiate countless new cracks as the material breaks, leading to a rough surface that looks grey with its low melting point, good fluidity, castability, excellent machinability and wear rising resistance, cast irons have become an engineering material with a wide range of uses like pipes, machine and auto parts.
Products:
Cast iron is produced by remelting pig iron, normally with large quantities of scrap iron and steel and initiating steps to remove unwanted contaminants like phosphorus and sulfur. Depending on use carbon and silicon content are lessened to the required levels which may be anywhere from 2% to 3.5% and 1% 3% respectively. Other elements are then added to the melt prior to the final form being made by casting.
Iron is generally melted in a small blast furnace called cupola. After melting is over the melted iron is ladled from the forehearth of blast furnace. This system was developed by the Chinese whose innovative ideas brought revolution in field of metallurgy. Before that iron was melted in an air furnace, which is a type of reverberatory furnace.
Some advantages of cast iron in engineering uses:
a) A family of metals having capacity of being used for engineering and production needs.
b) You can have it in a wide range of mechanical and physical properties.
c) Good strength to weight ratio.
d) Generally cheaper than other competing metals and lower financial cost per unit of strength compared to other metals.
e) Lesser density and higher thermal conductivity then steels at comparable tensile strength levels.
f) Easily mechniable, allows high speeds and feeds and less energy due to free graphite being presence.
g) Many iron castings may be utilized without heat treatment (as cast) but when required may be heat treated to increase overall properties or local property like surface hardness.
h) Very good damping capability especially in grey irons.
i) Chemical analysis may be changed to give improved special properties like corrosion resistance, oxidation and wear resistance.
j) Quickly changes from design to finished goods.
k) Capable of having highly complex sizes from ounces to 100 tons.
l) Of flexible pattern and capacity to improve appearance for sales appeal.
m) You can make intricate shapes as well as very thin to very thick sections.
n) Capable of redesigning and combining two or more parts from metals into a single casting thereby lessening assembly cost and time.
o) Capable of being cast with inserts of other metals.
p) Many casting systems for low, medium or high production.
q) Less tendency toward residual stress and warpage than other competing metals.
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