Q1: __________ is not a case hardening process.

ANS:A - Carburising

Carburizing is a case-hardening process used to increase the surface hardness of low-carbon steels or iron-based alloys. The process involves introducing carbon into the surface layer of the material to create a hardened outer shell while maintaining a relatively softer and more ductile core. This is achieved by exposing the material to a carbon-rich environment at elevated temperatures. The typical steps involved in carburizing are as follows:

1. Preparation: The surface of the steel or iron-based component is cleaned thoroughly to remove any contaminants such as oxides, oils, or scale.
2. Heating: The component is heated to temperatures typically ranging from 850°C to 950°C (1562°F to 1742°F) in a furnace or sealed chamber. This temperature is sufficient to allow carbon atoms to diffuse into the surface layer of the material.
3. Carburizing Atmosphere: The component is placed in an environment rich in carbon, such as a mixture of hydrocarbons (e.g., methane, propane) or carbon monoxide. This atmosphere facilitates the absorption of carbon atoms into the surface of the material.
4. Diffusion: Carbon atoms diffuse into the surface layer of the material, typically to a depth of a few thousandths of an inch (or a few tenths of a millimeter), depending on the process parameters and the desired case depth.
5. Quenching: Once the desired case depth is achieved, the component is rapidly cooled (quenched) to room temperature to harden the surface layer. This rapid cooling helps to trap the carbon atoms in a solid solution, resulting in a martensitic structure with increased hardness.
6. Tempering: In some cases, the hardened component may undergo a tempering process to reduce internal stresses and improve toughness. Tempering involves reheating the component to a lower temperature and then allowing it to cool gradually.

The result of carburizing is a hardened surface layer with increased wear resistance, while the core remains relatively soft and tough. This allows the component to withstand abrasion, fatigue, and other forms of wear, making it suitable for applications such as gears, shafts, bearings, and other mechanical components subjected to high loads and abrasive conditions.