Give the approximate temperature at which it is desirable to heat each of the following iron–carbon alloys during a full anneal heat treatment: (a) 0.20 wt% C (b) 0.60 wt% C (c) 0.76 wt% C (d) 0.95 wt% C.

The first step is to find the eutectoid temperature (also known as the critical temperature) for each alloy. The eutectoid temperature in the iron-carbon phase diagram is 723°C, which corresponds to a carbon content of approximately 0.76 wt%. This is the point at which the equilibrium phases of austenite and ferrite transform to pearlite upon cooling. Alloys with a carbon content lower than 0.76 wt% C will have a critical temperature below 723°C and alloys with a carbon content higher than 0.76 wt% C will have a critical temperature above 723°C.

Using the iron-carbon phase diagram and considering an appropriate annealing temperature range (generally from 25 to 50°C above the critical temperature) for each alloy, we can determine the approximate temperatures as follows: (a) 0.20 wt% C: This alloy has a lower carbon content than the eutectoid composition, thus we can assume the critical temperature is below the eutectoid temperature of 723°C. Taking the temperature range 25 to 50°C above the critical temperature, we can estimate the annealing temperature to be around 700°C to 725°C. (b) 0.60 wt% C: The carbon content of this alloy is also below the eutectoid composition, so the critical temperature is expected to be below 723°C. Considering a temperature range 25 to 50°C above the critical temperature, we can estimate the annealing temperature to be around 715°C to 740°C. (c) 0.76 wt% C: Since the carbon content of this alloy corresponds to the eutectoid composition of 723°C, the critical temperature will be exactly the eutectoid temperature. Taking the annealing temperature range 25 to 50°C above the critical temperature, we can estimate the annealing temperature to be around 748°C to 773°C. (d) 0.95 wt% C: This alloy has a higher carbon content than the eutectoid composition, thus we can assume the critical temperature is above the eutectoid temperature of 723°C. Taking the temperature range 25 to 50°C above the critical temperature, we can estimate the annealing temperature to be around 765°C to 790°C. In summary, the approximate annealing temperatures for each alloy are: (a) 0.20 wt% C: 700°C - 725°C (b) 0.60 wt% C: 715°C - 740°C (c) 0.76 wt% C: 748°C - 773°C (d) 0.95 wt% C: 765°C - 790°C