Heat Treatment

Heat treating (or heat treatment) is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve the desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, carburizing, normalizing and quenching. Although the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.

LCN / Tufftride

Salt bath soft nitriding treatment has many brand names, such as  LCN, Tenifer, Tufftride , Melonite and ARCOR. Although there are many brands, the same nitriding treatment process can be seen. It belongs to the low-temperature salt bath surface hardening method, which is suitable for surface hardening of precision parts such as various carbon steel, low alloy steel, stainless steel, high-speed steel and various cast iron.

  • Improve surface hardness and wear resistance
  • Improve fatigue resistance
  • Preservative
  • Minimal size change
  • Self-lubricating and anti-seize surface characteristics

GSN / Gas Soft Nitriding

GSN (Gas Soft Nitriding) is a thermochemical treatment

  • Improve wear resistance and fatigue resistance
  • Improve corrosion resistance and thermal performance
  • Minimal size change


QPQ (Quench-Polish-Quench) is a special type of carbonitriding surface hardening treatment. The original intention is quenching-polishing-quenching, which can improve corrosion resistance. Sometimes it is known as Tufftride, Tenifer or Melonite. Through the salt bath compound treatment, a compound infiltration layer is formed, so as to achieve the purpose of surface modification of the part. It has not been quenched, but has achieved the effect of surface quenching. Due to the minimal dimensional change, it is suitable for machining parts that need to be combined. In order to reduce the surface roughness of the workpiece, the surface of the workpiece can be polished once, and then oxidized in the salt bath.

  • Improve surface hardness
  • Increase wear resistance and corrosion resistance
  • Improve fatigue strength and heat resistance


Carburizing is the heat treatment of iron and steel. The iron or steel is heated in a carbon-rich material (such as charcoal or carbon monoxide) to absorb the carbon into the metal. The main features are

  • Increase surface hardness
  • Increase wear resistance
  • Increase fatigue strength and tensile strength
  • Remedy undesirable decarburization during previous processing

High frequency

It mainly uses induction current to heat the necessary surface parts of the workpiece, and performs necessary heat treatment procedures such as quenching and tempering to obtain the surface characteristics of high surface hardness and good toughness of the core of the workpiece. Its main features are

  • Partial work hardening is possible. With high hardness and original softness and toughness
  • Uniform hardening quality
  • Increase fatigue strength
  • Surface hardening effect
  • Minimal size change


Annealing is a kind of heat treatment that changes the microstructure of the material and thereby changes the mechanical properties such as hardness and strength.

  • Increase flexibility
  • Ductility and toughness
  • Release internal residual stress
  • Produce specific microstructure


Normalization is an annealing process that uses heating to refine grains and release stress. The main application of this treatment method is

  • Improve the ductility and flexibility of hardened steel
  • Pre-process of hardened steel subsequent heat treatment
  • Restore the ductility and flexibility of the material after cold working

Thermal Refining

Quenching and tempering is a heat treatment method to adjust the performance of medium carbon structural steel. Important parts such as gears, shafts and other manufacturing materials are usually subjected to quenching and tempering.

  • Homogenize the material structure
  • Increase material strength and toughness while maintaining machinability
  • Increase wear resistance
  • Nitriding hardening or surface heat treatment can be carried out later

Gas carburizing

The workpiece is placed in a sealed heating furnace and heated, and a carbon-containing gas or a carbon-containing liquid is introduced. The process of carburizing the workpiece at this temperature becomes gas carburizing. Its characteristics are:

  • Fast processing speed
  • Can control the thickness of carburized layer
  • Can be quenched directly


Carburizing and nitriding is a surface modification technology in metal processing. It is commonly used in low-carbon and medium-carbon steels that are cheap and easy to process. Its characteristics are:

  • Improve surface hardness and reduce corrosion
  • Increase fatigue strength and impact strength
  • Especially suitable for steels with low surface hardening, such as valve seats


Also known as nitrocarburizing, it is a nitriding process that can form a layer of nitride compound on the surface of the nitride object in a short time. Its characteristics are:

  • Enhances surface hardness
  • High wear resistance
  • Excellent fatigue strength
  • Improved corrosion resistance
  • Zero to minimal distortion


Quenching can enhance the strength and hardness of steel and cast iron. The rate of rapid cooling also affects the surface hardness and core hardness of the material. After quenching, the material becomes brittle, so it is usually tempered to reduce the brittleness of the material. Items such as screws, gears, rotating shafts, and metal blocks are often quenched.

  • Strengthen the strength and hardness of the workpiece
  • Need to be tempered again


Tempering is to heat the quenched steel to an appropriate temperature below the austenite transformation temperature, keep it at a high temperature for 1 to 2 hours and then cool it down. After tempering, the structure of steel tends to be stable, its brittleness decreases, and its toughness and plasticity increase. Tempering is often accompanied by quenching and is the last process of heat treatment, which can eliminate or reduce quenching stress, stabilize the shape and size of steel, and prevent deformation and cracking of quenched parts. High temperature tempering can also improve cutting performance.

  • Reduce brittleness
  • Improve toughness and plasticity
  • Reduce or eliminate stress
  • Prevent deformation and cracking
  • Improve processing performance

Metallographic analysis

Metallographic analysis is the study of the physical structure and composition of metals using a microscope. Inferring the composition/structure/quantity/mechanical properties of the three-dimensional structure through the two-dimensional visualization image plays a key role in understanding the development and manufacturing of materials.

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