__________ are normally subjected to sub-zero treatment.

ANS:B - Gauges or precision parts

Gauges or precision parts are commonly subjected to sub-zero treatment. Sub-zero treatment, also known as cryogenic treatment, involves exposing materials to very low temperatures, typically below -100°C (-148°F) for an extended period. This process is often used to improve the mechanical properties of materials, particularly those used in precision applications such as gauges or precision parts. Precision parts, such as gauges, cutting tools, molds, and other components used in precision engineering, require high dimensional stability, wear resistance, and durability to maintain accuracy and performance over time. Sub-zero treatment can provide several benefits for precision parts:

1. Stress Relief: Sub-zero treatment can help relieve residual stresses introduced during machining or fabrication processes, reducing the risk of distortion or dimensional changes.
2. Increased Hardness and Wear Resistance: Cryogenic treatment can enhance the material's hardness and wear resistance by transforming retained austenite into martensite and precipitating fine carbides or other strengthening phases.
3. Improved Dimensional Stability: Sub-zero treatment helps to stabilize the material's microstructure, reducing the risk of dimensional changes due to thermal cycling or mechanical stress.
4. Enhanced Performance: Precision parts treated with sub-zero treatment often exhibit improved performance, longevity, and reliability in demanding applications.