vacuum hardening
what is vacuum hardening?
Vacuum hardening is a heat treatment process used to increase the hardness and wear resistance of components.
In this process, the components are hardened under a controlled vacuum, enabling high temperatures of up to 1,300 °C to be reached. The aim of this process variant is the creation of bright metallic workpiece surfaces which render further mechanical processing unnecessary.
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vacuum hardening – key facts at a glance
- Vacuum hardening is a heat treatment process in which components are hardened under a controlled vacuum. It increases hardness and wear resistance.
- The vacuum hardening process consists of four steps: annealing, normalising, quenching and tempering. Temperatures of up to 1,300 °C can be achieved in a vacuum furnace.
- Quenching is usually carried out using nitrogen. The subsequent tempering process balances toughness and hardness.
- The advantages of vacuum hardening include: no oxidation, minimal distortion and a bright metallic finish without the need for further machining.
- Suitable materials are primarily high-alloy steels, such as tool steels and stainless steels. Unalloyed and low-alloy steels are not suitable.
- The depth of hardening indicates how deeply a component is hardened. It depends on the material composition and the cooling rate.
vacuum hardening process
Hardening is the heating and subsequent cooling of steel at such a speed that there is a considerable increase in hardness, either on the surface or throughout.
In the case of vacuum hardening, this process is done in vacuum furnaces in which temperatures of up to 1,300 °C can be reached. The quenching methods will differ with regards to the material treated but gas quenching using nitrogen is most common.
In most cases hardening takes place in conjunction with subsequent reheating, the tempering. Depending on the material, hardening improves the hardness and wear resistance or regulates the ratio of toughness to hardness.
advantages & characteristics of vacuum hardening
- Avoidance of oxidation: The vacuumed environment prevents the formation of oxide layers on the surface of the workpiece. This keeps the surface clean and free of impurities, resulting in better surface quality.
- Prevention of deformation: Uneven thermal stresses are minimized, resulting in less deformation of the workpiece. This is particularly important for precision-manufactured parts, where dimensional accuracy and shape precision are crucial.
- Reduced processing times: Since vacuum hardening takes place in an environment without reaction gases, no costly cleaning or finishing steps are required. This results in reduced processing times and higher productivity.
- Improved material properties: Vacuum hardening results in improved material properties, including higher hardness and wear resistance. Precise control of the hardening process allows tailored properties to be achieved for specific applications.
- Environmentally friendly: Vacuum hardening does not require the use of harmful reaction gases, resulting in an environmentally friendly hardening option. It reduces the emission of harmful emissions and waste that can occur with conventional hardening processes.
which materials are suitable for the vacuum hardening process?
Practically all technically interesting steel alloys, such as spring steels, cold-worked steels, quenched and tempered steels, anti-friction bearing steels, hot-worked steels and tool steels, as well as a large number of high-alloy stainless steels and cast-iron alloys, can be hardened.
Vacuum hardening however, is mostly used for high-alloy steels and steels that require a bright metallic workpiece surface.
- Tool steels: Tool steels are commonly used for cutting tools, molds and other tools that require high hardness and wear resistance. Examples of tool steels suitable for vacuum hardening are AISI D2 (material number 1.2379), AISI O1 (material number 1.2510) and AISI M2 (material number 1.3343).
- Stainless steel: Stainless steel, also known as high-grade steel, is used in various industries due to its corrosion resistance and mechanical properties. Stainless steels such as AISI 440C (material number 1.4125) and AISI 304 (material number 1.4301) are suitable for vacuum hardening.
how is vacuum hardening used, and in which industries?
In which industries and for which components is vacuum hardening used? – Vacuum hardening offers numerous advantages and is used in various industries.
- In the automotive industry, it improves the wear resistance, hardness and fatigue resistance of components such as transmission parts, crankshafts and piston rings.
- Similarly, in the aerospace industry, vacuum hardening provides high strength and improved fatigue properties for components such as turbine blades and engine parts.
- In toolmaking, it increases the service life and wear resistance of tools such as stamping and bending dies.
- In addition, vacuum hardening in medical technology ensures high precision, hardness and corrosion resistance in surgical instruments and implants.
- General metalworking also benefits from the advantages of vacuum hardening, especially for precision components for the electronics industry and mechanical engineering.
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frequently asked questions – vacuum hardening
What advantages does vacuum hardening offer compared to other hardening methods?
It minimizes workpiece distortion since there is no direct contact cooling. The process control is precise and reproducible, leading to consistent results. The vacuum prevents oxidation or discoloration on the surface of the workpiece.
What is the hardening depth in vacuum hardening?
The hardening depth in vacuum hardening refers to the depth to which the workpiece is hardened. It measures how deeply hardening processes, such as martensite formation, penetrate into the material. The hardening depth depends on various factors, such as material composition and cooling rate.
Are there limitations to vacuum hardening?
Yes, there are some limitations to vacuum hardening. The process is not suitable for all materials, especially mild and low-alloy steels. In addition, vacuum hardening can be more expensive than other hardening processes due to the equipment required and the longer process cycle. There are also limits to the size of the workpieces, as they must fit inside the vacuum chamber.
What Temperatures Are Used in Vacuum Hardening?
The temperatures used in vacuum hardening vary depending on the material and desired properties. Typically, temperatures range between 800 °C and 1200 °C. The exact temperature is carefully selected to achieve sufficient hardening without damaging the workpiece.
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