10292010- Ch. 13 - Easy to machine good vibration damping 1...

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10/29/2010- Ch. 13 Thursday, November 04, 2010 11:25 AM 13.11 Cast Irons 2-4.5% Carbon, lower pouring temp then steel. Liquid iron is very fluid so you can make complex castings. Five general types of Iron. 4 Common. Difference is structure formed during the eutectic reaction. 1. White Iron Most of the eutectic carbon is in the form of Fe 3 C. L->gamma+ Fe 3 C Room temperature is pearlite + Fe 3 C. It can be almost 50% Fe 3 C and is hard and brittle. Used for wear plates and any application where resistance is critical. 1. Grey Iron Fe 3 C is not stable (but it might as well be) it usually does not break down. Graphite is very stable. Grey Iron eutectic carbon forms as graphite rose-shaped form. Graphite is interconnected and looks like flakes in cross sections. Graphite is very low strength and can act as a stress con centration. Low ductility (approximately 1%. Intermediate strength.
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Unformatted text preview: Easy to machine, good vibration damping. 1. Malleable Iron- old alloy. Cast as white iron (carbides)contains silicon. Destabilizes the Fe 3 C. Heat to high T, hold for a long time. Fe 3 C breaks down to from graphite clumps. Graphite then has much higher strength and ductility. 1. Ductile Iron-Molten metals are treated with Mg (magnesium) and then form Mg 2 Si particles and graphite forms on the Mg 2 Si and surface tension changes to form graphite modulus. Grey- good thermal conductivity but low strength Ductile- high strength but poor thermal conductivity. Need something in between. 1. Compacted Graphite Iron-Not a main group and isn't discussed often. The graphite is a mixture of blunt interconnected flakes (some spheres) the strength is close to ductile conductivity close to gray Iron. For all of the properties of Iron see Table 13.5...
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