---
title: "Purposes of heat treatment"
subject: "Civil Engineering Materials"
chapter: 8
key: "semester_3/civil_engineering_materials:heat-treatment-objectives"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/heat-treatment-objectives
site: BCT Engineering
---

# Purposes of heat treatment

Civil Engineering Materials · Chapter 8: Metals and Alloys

- Asked in: 2074 Chaitra, 2 marks; 2078 Kartik, 2 marks; 2076 Chaitra, 2 marks; 2071 Chaitra, 2 marks; 2059 Poush (old course), 2 marks (asked 5 times)
- Video: [Heat Treatment -The Science of Forging (feat. Alec Steele)](https://www.youtube.com/watch?v=6jQ4y0LK1kY) — Real Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/heat-treatment-objectives
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-8

## Question

What are the purposes (objectives) of heat treatment of metal?

## Short answer

Heat treatment aims to alter mechanical properties: it can increase hardness, soften metal, improve strength and toughness, relieve stresses, refine grain, and enhance ductility. It also enables surface hardening and improves electrical or magnetic characteristics.

## Answer

The main purposes of heat treatment of metals (steel) are:

1. **To increase hardness** and wear resistance (for example cutting tools and bearing surfaces) by quenching.
2. **To soften the metal** and improve machinability and cold working (annealing).
3. **To improve strength and toughness**, and to obtain a good combination of them (normalizing, tempering).
4. **To relieve internal stresses** caused by welding, casting, forging or cold working, preventing cracking and distortion.
5. **To refine the grain size** and make the structure uniform (homogeneous).
6. **To increase ductility** and malleability.
7. **To harden only the surface** and keep a tough core (case hardening).
8. **To improve electrical and magnetic properties**, and corrosion/heat resistance.
9. **To remove gases** and improve the structure of castings.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Hardness is increased by
   A. Quenching
   B. Annealing
   C. Slow cooling
   D. Normalizing
   Answer: A. Quenching hardens. (Key point: Hardness)

2. Heat treatment relieves
   A. External loads
   B. Internal stresses from welding, casting or forging
   C. Corrosion
   D. Rust
   Answer: B. Stress relief. (Key point: Stress relief)

3. Case hardening gives
   A. Soft surface
   B. Uniform hardness
   C. Hard surface with tough core
   D. Brittle core
   Answer: C. Surface only. (Key point: Case hardening)

## Related in Civil Engineering Materials

- [Principle of heat treatment of metal](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aheat-treatment-principle) — Civil Engineering Materials, chapter 8, asked 5×
- [Heat treatment, objectives, isothermal annealing](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aheat-treatment-isothermal-annealing-s) — Civil Engineering Materials, chapter 8
- [Mechanical vs heat treatment; red shortness](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Amechanical-vs-heat-treatment-red-shortness) — Civil Engineering Materials, chapter 8
- [Mechanical vs heat treatment, tempering](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Amech-heat-treatment-isothermal-tempering) — Civil Engineering Materials, chapter 8
- [Heat treatment, tempering and quenching](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aheat-treatment-tempering-quenching) — Civil Engineering Materials, chapter 8
- [Heat treatment and three methods](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aheat-treatment-three-methods) — Civil Engineering Materials, chapter 8

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- [Heat treatment processes of steel](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Aheat-treatment-of-steels) — Material Science, chapter 6
- [Notes on powder metallurgy and heat treatment](https://www.bctengineer.com/question.md?key=semester_7%2Fmachine_design_ii%3Apowder-metallurgy-heat-treatment-notes) — Machine Design II, chapter 3