Metal vacuum hardening is a heat treatment process that increases hardness, strength and wear resistance by heating metals in a vacuum and then rapidly cooling them. This process differs from normal hardening, which heats metals in the presence of air or other gases. In this blog post, we will explain the benefits, applications and methods of metal vacuum hardening.
Benefits of Metal Vacuum Hardening
Vacuum hardening of metal has several advantages over normal hardening, e.g:
- It preserves the surface chemistry of the metal, preventing oxidation, decarburisation or contamination by air or gases.
- It produces bright and clean metal surfaces that do not require further polishing or finishing.
- Allows precise control and homogeneity of temperature and atmosphere during heating and cooling, ensuring consistent and repeatable quality and properties of the metal.
- Reduces metal distortion and cracking due to lower thermal stresses and more uniform cooling rates.
- It enables faster and more efficient processing of metals as it eliminates the need for protective coatings or cleaning steps before or after hardening.
Metal Vacuum Hardening Applications
Metal vacuum hardening is suitable for a wide range of metals and alloys, especially those that are highly alloyed, stainless or sensitive to oxidation or contamination. Some examples of metals that can be vacuum hardened are:
- Spring steels
- Cold worked steels
- Quenched and tempered steels
- Anti-friction bearing steels
- Hot finished steels
- Tool steels
- Cast iron alloys
Metal vacuum hardening is used for various industries and applications that require strong, durable and wear-resistant metal parts, for example:
- Engineering industry
- Aerospace industry
- Tool manufacturing industry
- Automotive industry
Metal Vacuum Hardening Methods
Metal vacuum hardening is carried out in special furnaces that can create a high vacuum (low pressure) environment by using a vacuum pump to remove air from a closed chamber. The metal parts are placed inside the chamber and heated by convection or radiation to a high temperature (up to 1,300°C) depending on the type and composition of the metal. The heating time also depends on the desired hardening depth and the size and shape of the metal parts.
After reaching the required temperature, the metal parts are rapidly cooled by a stream of inert gas (usually nitrogen) flowing through the chamber. The cooling rate determines the final hardness and microstructure of the metal. Cooling can be done in different ways as follows:
- Gas quenching: The gas flows uniformly around the metal parts at high pressure (up to 20 bar) and speed (up to 100 m/s), creating a strong cooling effect.
- Oil quenching: The gas flows through a heat exchanger that transfers heat to an oil bath outside the chamber. The oil bath then cools the metal parts by conduction.
- Gas-oil quenching: Gas flows through a heat exchanger that transfers heat to an oil spray outside the chamber. The oil spray then cools the metal parts by convection.
In most cases, metal vacuum hardening is followed by tempering, a reheating process that reduces the metal's brittleness and increases its toughness. Tempering can also be done in a vacuum furnace or in a conventional furnace with an inert gas atmosphere.
Conclusion
Metal vacuum hardening is a heat treatment process that increases hardness, strength and wear resistance by heating metals in vacuum and then rapidly cooling them. This process has many advantages over normal hardening, such as preserving surface chemistry, producing bright and clean surfaces, allowing precise control and uniformity of temperature and atmosphere, reducing distortion and cracking, and allowing faster and more efficient machining. Metal vacuum hardening is suitable for a variety of metals and alloys that are highly alloyed, stainless or sensitive to oxidation or contamination. Metal vacuum hardening is used for various industries and applications that require strong, durable and wear-resistant metal parts.
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