Question

what happens when this eutectoid steel is first quenched to the 50% line at m s 10 4 sec, followed by rapid reheating to t n>t>m s and held there shortly and then quenched to t

Answer 1

Quenching eutectoid steel to
`\(M_s > T > M_f\)` forms martensite. Isothermal holding at elevated temperature allows pearlite or bainite. Rapid reheating and quenching below
`\(M_f\)` retains martensite at room temperature.

The described heat treatment process for eutectoid steel involves a series of steps, including quenching, isothermal holding, rapid reheating, and subsequent quenching. The terms mentioned refer to specific transformation temperatures for eutectoid steel, and the phases present at room temperature depend on the details of the heat treatment. Let's break down the steps and discuss the potential phases:

1. Quenching to the 50% line at
`\(M_s > T > M_f\)` (martensite start to martensite finish):

- Quenching to a temperature between the martensite start
`(\(M_s\))` and martensite finish
`(\(M_f\))` temperatures typically results in the formation of martensite. Martensite is a hard and brittle phase with a fine lath-like microstructure.

2. Isothermal holding for
`\(t > 10^4\)` sec:

- Isothermal holding at an elevated temperature for a significant duration allows for the transformation of austenite into various phases. The specific phases formed depend on the temperature and time. Common phases include pearlite and bainite, both of which are composed of ferrite and cementite.

3. Rapid reheating to
`\(T_N > T > M_f\)`:

- Rapid reheating to a temperature range between the nose temperature
`(\(T_N\))` and martensite finish
`(\(M_f\))` may result in the dissolution of some of the phases formed during the isothermal holding step.

4. Holding at the elevated temperature:

- Holding at the elevated temperature for a short duration allows for further transformation or stabilization of the microstructure.

5. Subsequent quenching to
`\(T < M_F\)`:

- Quenching to a temperature below the martensite finish temperature
`(\(M_f\))` favors the retention of the martensitic phase.

The phases present at room temperature depend on the specific temperatures and times involved in each step. If the quenching and reheating steps are designed to avoid the formation of pearlite or bainite, and if the final quenching is rapid enough, martensite may be the dominant phase at room temperature.

Keep in mind that the actual phases and their proportions will be influenced by the specific details of the heat treatment, including temperature values, holding times, and cooling rates. For a more precise analysis, it's recommended to consult phase diagrams for the specific eutectoid steel composition in question.

The complete question is:

What happens when this eutectoid steel is first quenched to the 50% line at Ms > T > Mfat a rate faster than the CCR, and then isothermally held for t>104 sec, followed by rapid reheating to TN>T>Mf?, and held there shortly and then quenched to T<MF? What phases are present at room temperature?