Lesson 6: HEAT TREATMENT II – equipment and auxiliary materials for heat treatment

In this lesson, we’ll explore the equipment and auxiliary materials essential for the heat treatment process.

  1. Types of Heat-Treating Furnaces
  • The heart of heat treatment lies in the furnaces, responsible for heating, holding, and sometimes cooling workpieces per specific programs.
  • Furnaces used in heat treatment fall into two main categories: batch furnaces and continuous furnaces.

1.1. Batch Furnaces

  • Basic batch furnaces consist of insulated chambers with reinforced steel shells, heating systems, and access doors.
  • Batch furnaces like box, bell, elevator, car-bottom, and pit types are used for various heat-hold-cool cycles.
  • Ideal for low-volume parts, specialized components, small batches, and diverse heat-treat cycles.


1.2. Continuous Furnaces

  • Continuous furnaces share components with batch furnaces but operate in uninterrupted cycles.
  • Suitable for high-volume production, they enable automation and precise repetition of time-temperature cycles.
  • Types include rotary-hearth and straight-chamber continuous furnaces, with various subcategories.

1.3. Heating of Furnaces

  • Furnaces can be direct-fired or electrically heated.
  • Direct-fired furnaces expose workpieces to combustion products, with options for different gases and oils.
  • Electrically heated furnaces cover a wide temperature range, with open or indirect heating elements chosen based on temperature and atmosphere.
  1. Media Used for Heat Treatment
  • The choice of heat treatment medium significantly influences the process outcome, whether gaseous or liquid, and neutral or active in chemical action.

2.1. Gaseous Heat Treatment Media

  • Heat treatment in air is simple but can lead to oxidation and decarburization of steel.
  • Neutral protective gases, like endogas and nitrogen, shield against harmful air effects.
  • Active gases, such as hydrogen, participate in thermochemical reactions.
  • Vacuum technology provides a clean, impurity-free environment for heating, although precautions are needed for low-melting-point alloys.

2.2. Liquid Heat Treatment Media

  • Liquid media include salt baths, metal baths, water, emulsions, and oils.
  • Salt baths offer excellent heat transfer and quick heating but are less used due to hazardous waste.
  • Metal baths are being phased out due to emitted metal vapors.
  • Water is highly effective but has varying cooling rates during different phases.
  • Fluid technologies use suspended ceramic powders in gas to achieve precise temperature control and consistent results.


  • Understanding the equipment and auxiliary materials used in heat treatment is crucial for achieving desired material properties.
  • Whether using batch or continuous furnaces, selecting the right heating method, or choosing the appropriate heat treatment medium, each decision impacts the final outcome.
  • Heat treatment remains a vital process for enhancing material characteristics and ensuring product quality across various industries.

In this lesson, you’ve gained insights into the equipment and auxiliary materials that play pivotal roles in the heat treatment process. Understanding how to utilize different furnace types and media options enables you to make informed decisions for achieving specific material properties and product quality.

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