Vacuum heat treatment of precision turned parts

Vacuum heat treating precision machined parts is a controlled heating and cooling process that alters the physical properties of a metal to meet specific requirements. In many cases, vacuum heat treatment is used to increase strength, hardness and wear resistance. However, depending on the materials and processes involved, it can also be used to relieve internal stress, improve machinability, improve electrical or magnetic properties, or increase ductility and softness.
The vacuum heat treatment process consists of 3 basic steps:
1. Heating: When the metal is heated to a specific temperature, the structural properties will change.
2. Soaking: Keep the metal at the specified temperature until the whole part is heated evenly.
3. Cooling: The metal is cooled to room temperature at a specified rate.
Vacuum heat treatment is mainly used on steel and steel alloys, but can also be used on some grades of aluminum.
There are 4 basic types of vacuum heat treatment of steel:
1. Vacuum Hardening: As the name suggests, this process is used to harden the material, making it stronger. However, during this process, the material also becomes less ductile (i.e. becomes more brittle) and, depending on the application, requires vacuum tempering after vacuum hardening.
For parts that require vacuum hardening, materials are slowly heated to high temperatures, soaked at a specific temperature for a specific time, and then rapidly cooled by immersing them in water or oil. This rapid cooling in liquid is called quenching.
For carbon steel, the steel must be cooled to below 1000 degrees Fahrenheit in less than 1 second. For alloy steels, the cooling rate is reduced.
2. Vacuum Tempering: Hardening the material will increase internal stresses and vacuum tempering will relieve these stresses. The material will go through a similar 3-step process as it hardens, albeit at a lower temperature. The cooling process for vacuum tempering is almost always carried out in air rather than liquid.
3. Vacuum Annealing: Vacuum annealing is often used to increase the ductility of the material (making the metal less likely to crack), to relieve stress, or to soften the metal. It is generally considered the opposite of hardening. In this process, the metal is heated very slowly to a specified temperature, held there for a specified time (soak), and then slowly air-cooled—usually by leaving the part in the furnace during normal cooling. For low carbon steel, the vacuum annealing temperature is higher, and the annealing temperature decreases as the carbon content increases.
4. Normalization: This process is used to relieve the internal stress generated during processing. For vacuum normalizing, parts are removed from the furnace for air cooling after the heating and soaking stages. Removing from the furnace will cause the part to cool faster – although the mass of the part will affect that rate (smaller and thinner parts cool faster than larger and thicker parts). Vacuum normalized steel is stronger than vacuum annealed steel.
While there are many metal properties that can be improved by vacuum heat treatment, the process can have some detrimental effects on the surface of the part.
1) Oxide scale on the surface of the component – affects the surface finish
2) Part deformation – some slender parts will bend or deform during heat treatment
3) Part tinting – the heat treatment process will darken the material and no longer be as shiny as it would be after machining.

Equipment selection: The RVT series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.