ENGR 240 - 11.14.07

ENGR 240 - 11.14.07 - ENGR 240 November 14, 2007...

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ENGR 240 – November 14, 2007 Microstructure and Properties of Iron-Carbon Alloys o Iron-iron carbide eutectoid γ(.76wt%C)  α(0.022wt%C) + Fe 3 C ferrite cementite T E = 727°C Pearlite alternating ferrite + cementite layers (lamellae) Typically formed from 540-700°C Thickness ration of α to Fe 3 C is 8:1 o Absolute thickness depends on T Close to T E thick layers (coarse pearlite) o Diffusion of carbon is high resulting in thick lamellae Bainite forms as needles or plates (depending on Temperature) T is between 215-540°C Fine microstructure of ferrite matrix with cementite needles Bainite and pearlite are competitive o Once one of these are formed, you have to austenitize to get the other (ie. You have to heat about T E forming austenite) Spheroidite Take pearlite or Bainite and heat between 700°C-T E for (~1 day) Get sphere-like particles of Fe 3 C embedded in a continuous matrix of ferrite o Wants to have a lower boundary area so that it is more stable
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This note was uploaded on 04/07/2008 for the course ENGR 240 taught by Professor Gross during the Fall '07 term at Bucknell.

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ENGR 240 - 11.14.07 - ENGR 240 November 14, 2007...

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