Mechanical Engineering - Engineering Materials - Discussion

The correct answer is there are two critical points.

Steel containing 0.8% carbon is hypereutectoid steel, which means it has a carbon content above the eutectoid point (0.77% C). In this case, there are two critical points:

1. A1 : The temperature at which austenite starts to form during heating (around 723°C /1333°F for 0.8% C steel).
2. A3 : The temperature at which austenite is fully formed during heating (around 845°C /1553°F for 0.8% C steel).

These critical points are important because they mark the beginning and end of the austenitization process, which is crucial for heat treatment processes like hardening and tempering.

The other options are not correct because:
- There is no single critical point for steel with 0.8% carbon.
- There are only two critical points (A1 and A3) for hypereutectoid steels like this.
- The number of critical points is fixed for a given steel composition, not variable.

What is the critical point in carbon?

How we find out no.of critical point?