Tech Team · Kintek Solution

Tempering steel does not increase its hardness; instead, it reduces hardness while improving toughness and ductility. This process involves reheating hardened steel to specific temperatures, which transforms its microstructure. At lower tempering temperatures (300–750°F), the hardened martensite becomes troostite, a softer and tougher structure. At higher temperatures (750–1290°F), sorbite forms, which is even softer but more ductile. Tempering is essential for balancing hardness with toughness, especially in highly stressed components, but it is not a method to increase hardness.

Key Points Explained:

1. What is Tempering?

   • Tempering is a heat treatment process that follows hardening. It involves reheating hardened steel to specific temperatures to modify its microstructure and mechanical properties.
   • The primary goal of tempering is to reduce brittleness and improve toughness, ductility, and dimensional stability, rather than increasing hardness.

2. Effect of Tempering on Hardness

   • Tempering reduces the hardness of steel. When hardened steel (martensite) is tempered, it transforms into softer structures like troostite or sorbite, depending on the temperature.
   • At lower tempering temperatures (300–750°F), troostite forms, which is softer than martensite but tougher.
   • At higher tempering temperatures (750–1290°F), sorbite forms, which is even softer but more ductile than troostite.

3. Purpose of Tempering

   • Tempering is used to balance hardness with toughness. While hardening increases hardness, it also makes steel brittle. Tempering alleviates this brittleness, making the steel more suitable for applications requiring both strength and durability.
   • It is particularly important for components subjected to high stress, such as gears, springs, and tools, where a balance of hardness and toughness is critical.

4. Comparison with Hardening

   • Hardening involves heating steel above its upper critical temperature (over 900°C) and rapidly cooling it (quenching) to form martensite, which is very hard but brittle.
   • Tempering follows hardening to reduce brittleness and improve toughness. It does not increase hardness but instead optimizes the steel's overall mechanical properties.

5. Practical Implications for Equipment and Consumable Purchasers

   • When selecting steel for applications requiring high hardness, tempering should not be considered a method to increase hardness. Instead, hardening processes like quenching are used.
   • For applications requiring a balance of hardness, toughness, and ductility, tempering is essential. Purchasers should consider the intended use of the steel and specify the appropriate heat treatment process (hardening and tempering) to achieve the desired properties.

In summary, tempering steel does not increase hardness but is crucial for improving toughness and ductility. It is a complementary process to hardening, ensuring that steel components can withstand stress without being overly brittle.

Summary Table:

Aspect	Details
What is Tempering?	Heat treatment process that reduces brittleness and improves toughness.
Effect on Hardness	Reduces hardness; transforms martensite into softer troostite or sorbite.
Purpose	Balances hardness with toughness for high-stress applications.
Comparison to Hardening	Hardening increases hardness; tempering reduces brittleness post-hardening.
Practical Implications	Essential for components like gears, springs, and tools requiring durability.

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