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Materials Question - Calculating Percent Carbon ?

  1. Apr 18, 2009 #1
    1. The problem statement, all variables and given/known data
    Calculate the percent carbon in an iron-carbon alloy that will give no volume change when liquid transforms to austenite plus graphite during solidification.

    2. Relevant equations
    Density of liquid = 7.0 g/cc
    Density of austenite = 7.69 g/cc
    Density of graphite = 1.5 g/cc

    3. The attempt at a solution

    For constant volume, lets say the area is 1 cubic centimeter

    x*(1.5 g/cc)+y*(7.69 g/cc) = (1 cc)*(7.0 g/cc)

    Since the volume is constant, x+y = 1 cc, and thus
    y = 1-x

    Putting it into the original equation yields:
    x*(1.5 g/cc) + (1-x)*(7.69 g/cc) = (1 cc)*(7.0 g/cc)

    Thus, x=0.111 cc, y=0.889 cc

    Now at this point I am confused. Since the graphite is 100% carbon, there will be 1*.111 % carbon, but what will it be for the austenite as we are not given what temperature this occurs at so that we may not see the iron-cementite phase diagram

    Any ideas?
  2. jcsd
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