Vacuum heat treatment

1. Definition: Heat treatment that places the heating and cooling processes of heat treatment in a vacuum.

2.Vacuum degree: The degree of negative pressure in a vacuum state.

3. Classification of vacuum: According to the degree of vacuum, it is divided into four categories:

Low vacuum: (10-10^-2) ×133. 3Pa

Medium vacuum：(10-3-10^-4) ×133. 3Pa

High vacuum: (10^-5-10^-7) ×133.3Pa

Ultra high vacuum：10^-8×133.3Pa

4. Characteristics of vacuum heat treatment：

High quality: no oxidation, no decarburization, and small deformation on the surface of the parts;

Improve mechanical properties and extend service life: The obvious improvement in plasticity and toughness is due to the degassing effect of vacuum heat treatment;

Low energy consumption: The use of insulating materials with good thermal insulation performance and small heat capacity makes the heat storage and heat dissipation losses of the furnace very small, and the thermal efficiency is high；

Reduced pollution and no pollution: Vacuum electric heating has no furnace gas or combustion exhaust gas, so it does not pollute the atmosphere;

High cost.

5. Special effects and associated phenomena of vacuum heat treatment:

Surface protection;

Surface purification: while preventing oxidation, it will decompose oxidized substances;

Degreasing effect: The oil dirt brought in during machine processing is decomposed into oxygen, water vapor, carbon dioxide, etc. after being heated;

Degassing: The gas in the metal diffuses to the surface, the gas escapes from the metal surface, and the gas is discharged from the vacuum furnace.

Evaporation (evaporation) phenomenon of elements: Alloy elements with high vapor pressure evaporate from the surface of the workpiece, resulting in a reduction in material properties; at the same time, vacuum evaporation may occur, affecting the quality of vacuum heat treatment.

Vacuum heating oil quenching causes carburization of steel parts: For example, for 30CrMnSiA and 30CrMnSiNi, steel A was oil quenched at a vacuum of 10^-2×133.3Pa and a heating temperature of 900°C, and carburization was found.

6. Applications of vacuum heat treatment:

Vacuum heat treatment process

1. Vacuum annealing

2. Vacuum quenching (divided into vacuum gas quenching and vacuum oil quenching)

3. Vacuum heat treatment of alloy steel

4. Vacuum chemical heat treatment (divided into vacuum carburizing, vacuum ion carburizing and vacuum carbonitriding)