---
title: "Annealing, normalizing and tempering of steel"
subject: "Workshop Technology"
chapter: 7
key: "semester_2/workshop_technology:heat-treatment-annealing-normalizing-tempering"
source: https://www.bctengineer.com/q/semester_2/workshop_technology/heat-treatment-annealing-normalizing-tempering
site: BCT Engineering
---

# Annealing, normalizing and tempering of steel

Workshop Technology · Chapter 7: Material Properties

- Asked in: year not given, 8 marks
- Video: [Heat Treatment Process ~ Annealing ~ Normalising ~ Hardening ~ Tempering](https://www.youtube.com/watch?v=CsFJGF3oCyc) — Study Central
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/workshop_technology/heat-treatment-annealing-normalizing-tempering
- Whole chapter: https://www.bctengineer.com/md/semester_2/workshop_technology/chapter-7

## Question

Explain annealing, normalizing and tempering of steel. State the purpose, heating temperature and cooling method for each, and differentiate between annealing and normalizing.

## Short answer

Annealing: heat 30–50°C above upper critical, furnace cool; softens, refines grain. Normalizing: 40–50°C above upper critical, air cool; refines grain, uniform structure, stronger. Tempering: reheat hardened steel below A1 (150–650°C), air cool; reduce brittleness, improve toughness. Annealing differs from normalizing by slower furnace cooling, giving softer, coarser pearlite vs fine pearlite.

## Answer

Heat treatment is controlled heating and cooling of a metal in the solid state to change its properties such as hardness, strength, ductility and grain size.

#### Annealing
- Heat the steel to 30 to 50 °C above the upper critical temperature (A3 for hypoeutectoid; above A1 for hypereutectoid), soak, then cool very slowly in the furnace.
- Purpose: soften the steel, improve machinability and ductility, relieve internal stress, refine grain, and make it ready for further working.
- Structure: coarse pearlite (and ferrite), which is soft.
- Types: full annealing, process (sub-critical) annealing for cold-worked low carbon steel, spheroidising for high carbon steel, stress-relief annealing.

#### Normalizing
- Heat to 40 to 50 °C above the upper critical temperature, hold briefly, then cool in still air.
- Purpose: refine grain, remove stress left by forging, rolling or casting, give uniform structure and better strength than annealed steel.
- Structure: fine pearlite.

#### Tempering
- Done after hardening (quenching), which makes steel hard but brittle with residual stress. The steel is reheated below A1 (150 to 650 °C), held and cooled in air.
- Purpose: reduce brittleness and internal stress, improve toughness, with some loss of hardness.
- Higher temper temperature gives lower hardness and greater toughness (150 to 250 °C for cutting tools, 350 to 450 °C for springs, 500 to 650 °C for shafts and gears). Colour changes (straw to blue) indicate temperature on a polished surface.

#### Annealing versus normalizing
| Annealing | Normalizing |
|---|---|
| Cooling slowly in the furnace | Cooling in still air |
| Softest condition | Harder and stronger |
| Coarse pearlite | Fine pearlite, small grains |
| Better machinability and ductility | Better strength; moderate machinability |
| Longer, more costly cycle | Shorter, cheaper |

## Check yourself

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

1. How is steel cooled in annealing?
   A. Quenched in water
   B. Cooled in still air
   C. Cooled very slowly in the furnace
   D. Cooled in oil
   Answer: C. Slow furnace cooling gives the softest, coarse pearlite structure. (Key point: Annealing cooling)

2. Compared with annealed steel, normalized steel is
   A. Softer with coarser grains
   B. Harder and stronger with fine pearlite
   C. Identical
   D. Brittle and hardened
   Answer: B. Air cooling is faster, giving fine pearlite and higher strength than annealed steel. (Key point: Normalizing vs annealing)

3. Tempering is done after hardening to
   A. Increase hardness further
   B. Reduce brittleness and internal stress, with some loss of hardness
   C. Soften fully
   D. Melt the grains
   Answer: B. Quenched steel is hard but brittle; reheating below A1 improves toughness. (Key point: Tempering purpose)

4. A higher tempering temperature gives
   A. Higher hardness, less toughness
   B. Lower hardness, greater toughness
   C. No change
   D. Higher hardness and toughness
   Answer: B. More tempering lowers hardness and increases toughness, e.g. 500-650 °C for shafts and gears. (Key point: Tempering temperature effect)

## Related in Workshop Technology

- [Jigs and fixtures: purpose and differences](https://www.bctengineer.com/question.md?key=semester_2%2Fworkshop_technology%3Ajigs-and-fixtures-purpose-differences) — Workshop Technology, chapter 12
- [Reaming, honing and lapping compared](https://www.bctengineer.com/question.md?key=semester_2%2Fworkshop_technology%3Areaming-honing-lapping-differences) — Workshop Technology, chapter 5

## Related in other subjects

- [Transformer heating and cooling time constants (25°C/37.5°C)](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Atransformer-heating-cooling-constants) — Electric Machine Design, chapter 2, asked 3×
- [Transformer heating and cooling time constants (25°C/40°C)](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Atransformer-cooling-constant-45c) — Electric Machine Design, chapter 2, asked 3×
- [Heating and cooling time constants](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Aheating-cooling-time-constants) — Electric Machine Design, chapter 2, asked 3×
- [Slow cooling of 0.4% C steel](https://www.bctengineer.com/question.md?key=semester_3%2Fmaterial_science%3Aslow-cooling-04-carbon-steel) — Material Science, chapter 6