Steel becomes soft and pliable by

Options

A. Annealing
B. Nitriding
C. Tempering
D. Case hardening

Explanation

**Step-by-Step Solution:**

1. **Understanding Steel Composition**: Steel is primarily an alloy of iron and carbon. The properties of steel can be altered through various heat treatment processes.

2. **Identifying the Processes**: The question lists several processes: annealing, nitriding, tempering, and gas hardening. Each of these processes affects the properties of steel differently.

3. **Defining Annealing**: Annealing is a heat treatment process where steel is heated to a high temperature and then allowed to cool slowly. This process helps to relieve internal stresses, reduce hardness, and improve ductility.

4. **Heating and Cooling**: During annealing, the steel is heated until it becomes red hot (approximately 700-800°C). Once it reaches this temperature, it is held for a period to allow for uniform heating. Afterward, it is slowly cooled, often in a furnace.

5. **Result of Annealing**: The slow cooling process allows the microstructure of the steel to change, which results in a softer and more pliable material. This makes the steel easier to work with and shape.

6. **Conclusion**: Among the options provided, annealing is the process that makes steel soft and pliable.

**Final Answer**: Steel becomes soft and pliable by **annealing**.

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