### Lever Rule

• Given a binary phase diagram, the composition of an alloy, its temperature, and assuming that the alloy is at equilibrium, determine:

• what phase(s) is (are) present,

• the composition(s) of the phase(s), and

• the mass fraction(s) of the phase(s)

The Lever Rule is a way in which to calculate the proportions of each phase present on a phase diagram in a two phase field at a given temperature and composition.
The lever rule is a mechanical analogy to the mass balance calculation. The tie line in the two-phase region is analogous to a lever balanced on a fulcrum. Finding the amounts of phases in a two phase region:

1. Locate composition and temperature in diagram

2. In two phase region draw the tie line or isotherm

3. Fraction of a phase is determined by taking the length of the tie line to the phase boundary for the other phase, and dividing by the total length of tie line

### Solved Example:

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Refer the following Cu-Ag phase diagram. At 900$^\circ$C, the approximate composition of the solution at 20% Ag is:

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Pure iron is the structure of: (UKPSC JE Mech 2013)

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The lower critical temperature for all steels, in Deg Celsius, is: (RRB JE ME CBT 2 Aug 2019)

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In grey cast iron, carbon is present in the form of:

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In nodular iron, graphite is in the form of:

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What cast iron has modular or spheroidal graphite?

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The temperature at which ferromagnetic alpha iron transforms to para-magnetic alpha iron is:

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Ferromagnetic $\alpha$-iron exists in temperature range of:

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Paramagnetic $\alpha$-iron changes to $\gamma$-iron at:

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Pearlite is a combination of: (Vizag MT Mech 2013- Re-exam)