Skip to content

Tempering

What is Tempering?

Tempering is a heat treatment process carried out after hardening, mainly on steel, to reduce brittleness and increase toughness while maintaining some hardness.

In Product Design, tempering is essential because hardened steel on its own is often too brittle for safe or practical use.

Why Tempering is Used

After hardening, steel becomes: - Very hard ✅ - Very brittle ❌

Tempering is used to: - Reduce brittleness - Increase toughness - Improve impact resistance - Make the material safer and more reliable in use

Most hardened steel components are always tempered before use.

How Tempering Works

Tempering involves reheating hardened steel to a lower temperature and then allowing it to cool naturally.

Basic Steps:

  1. Steel is first hardened (heated and quenched)
  2. The hardened steel is reheated to a moderate temperature
  3. It is held at this temperature for a period of time
  4. The steel is allowed to cool slowly in air

This controlled heating allows internal stresses to be relieved.

Tempering Temperatures

  • Tempering temperatures are much lower than hardening temperatures
  • Typically between 150°C and 650°C

The higher the tempering temperature: - The lower the hardness - The higher the toughness

Designers choose the tempering temperature based on required performance.

Effects of Tempering

After tempering: - ✅ Toughness increases - ✅ Brittleness decreases - ✅ Impact resistance improves - ❌ Hardness slightly decreases

Tempering creates a balance between hardness and toughness.

Hardening vs Tempering

Process Purpose Effect
Hardening Increase hardness Makes steel hard but brittle
Tempering Reduce brittleness Improves toughness and safety

Hardening and tempering are used together, not separately.

Types of Tempering

Low‑Temperature Tempering

  • Retains high hardness
  • Slight increase in toughness
  • Used for:
  • Cutting tools
  • Knives

High‑Temperature Tempering

  • Lower hardness
  • Much higher toughness
  • Used for:
  • Springs
  • Structural components

Key Properties Affected by Tempering

Property Effect
Hardness Slightly reduced
Toughness Increased
Brittleness Reduced
Impact Resistance Increased
Durability Improved

Advantages of Tempering

  • Makes hardened steel usable
  • Reduces risk of cracking
  • Improves safety
  • Increases service life
  • Allows properties to be tailored

Disadvantages of Tempering

  • Slight loss of hardness
  • Requires careful temperature control
  • Additional manufacturing step
  • Energy use

Typical Uses in Product Design

Tempered steel is used in: - Cutting tools - Springs - Gears - Shafts - Knives - Automotive components - Machine parts

Almost all hardened steel products are tempered.

Materials Suitable for Tempering

  • Carbon steel ✅
  • Alloy steel ✅
  • Some stainless steels ✅
  • Aluminium ❌ (heat treated differently)
  • Copper ❌
  • Polymers ❌

Health and Safety Considerations

  • High temperatures involved
  • Risk of burns
  • Industrial process only
  • Requires temperature‑controlled ovens
  • Not suitable for school workshop manufacture

Tempering Compared to Other Heat Treatments

Process Main Purpose
Hardening Increase hardness
Tempering Reduce brittleness
Annealing Soften metal
Normalising Improve grain structure

Suitability for Product Design

Tempering is suitable when: - Hardened steel is too brittle - Impact resistance is required - Safety is critical - Long service life is needed

Tempering is not suitable when: - Maximum hardness is the only priority - Very soft materials are required - Non‑ferrous metals are used

Exam Tips (A Level)

  • Define tempering as reheating after hardening
  • State it reduces brittleness and increases toughness
  • Mention it is used on steel
  • Compare with hardening
  • Use examples such as springs or tools
  • Explain why tempering is necessary

Key Keywords

  • Tempering
  • Heat treatment
  • Toughness
  • Brittleness
  • Hardened steel
  • Reheating
  • Impact resistance

Overall Summary

Tempering is a heat treatment process used after hardening to reduce brittleness and improve toughness in steel. By reheating hardened steel to a controlled lower temperature, internal stresses are relieved and the material becomes safer, tougher, and more suitable for real‑world use. Although tempering slightly reduces hardness, it creates a vital balance between hardness and toughness, which is essential for tools, springs, gears, and structural components. In A Level Product Design, tempering should be understood as a necessary follow‑up to hardening, ensuring materials meet performance, safety, and durability requirements.