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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

The role and purpose of vacuum heat treatment

Metal heat treatment is to heat metal or alloy workpieces in a certain medium to a suitable temperature, maintain it at this temperature for a certain period of time, and then cool it in different media at different speeds. By changing the surface or internal appearance of the metal material, A process that uses microstructure to control its performance. Compared with other processing techniques, vacuum heat treatment generally does not change the shape and overall chemical composition of the workpiece, but gives or improves the performance of the workpiece by changing the microstructure inside the workpiece or changing the chemical composition of the workpiece surface.

Vacuum tempering

The structure obtained by high temperature tempering is tempered sorbite. Vacuum tempering is generally not used alone. Vacuum tempering is performed after the vacuum hardening treatment of the parts. The main purpose is to eliminate the hardening stress and obtain the required structure. Vacuum tempering is divided into low temperature, medium and high temperature tempering according to the different tempering temperatures. Tempered martensite, troostite and sorbite were obtained respectively. Among them, the heat treatment combined with high-temperature tempering after vacuum hardening is called hardening and tempering treatment, which has better strength, hardness, plasticity and toughness. Therefore, it is widely used in important structural parts of automobiles, tractors, machine tools, etc., such as connecting rods, bolts, gears and shafts. The hardness after vacuum tempering is generally HB200-330.

Vacuum annealing

Pearlite transformation occurs during vacuum annealing. The main purpose of vacuum annealing is to make the internal structure of the metal reach or approach an equilibrium state to prepare for subsequent processing and final heat treatment. Stress relief annealing is a vacuum annealing process performed to eliminate residual stress caused by plastic deformation processing, welding, etc. and existing in castings. There are internal stresses inside the workpiece after forging, casting, welding and cutting. If not eliminated in time, the workpiece will be deformed during processing and use, affecting the accuracy of the workpiece. It is very important to use stress relief annealing to eliminate the internal stress generated during the processing. The heating temperature of stress relief annealing is lower than the phase transformation temperature, so no structural transformation occurs during the entire heat treatment process. Internal stress is mainly eliminated naturally through the process of heat preservation and slow cooling of the workpiece. In order to eliminate the internal stress of the workpiece more completely, the heating temperature should be controlled during heating.

Generally, it is put into the furnace at low temperature, and then heated to the specified temperature at a heating speed of about 100°C/h. The heating temperature of the welded parts should be slightly higher than 600℃. The holding time depends on the situation, usually 2 to 4 hours. The holding time for stress relief annealing of castings is set to an upper limit, the cooling rate is controlled at (20~50)℃/h, and the casting can be air-cooled only when it is cooled to below 300℃. Aging treatment can be divided into two types: natural aging and artificial aging. Natural aging is to place the casting in an open field for more than half a year, so that it can occur slowly, thereby eliminating or reducing the residual stress. Artificial aging is to heat the casting to 550~650℃. Perform stress relief annealing, which saves time than natural aging and removes residual stress more thoroughly.

The purpose of vacuum tempering

Vacuum tempering is a heat treatment process that heats vacuum hardened metal products or parts to a certain temperature, holds them for a certain period of time, and then cools them in a certain way. Vacuum tempering is an operation performed immediately after vacuum hardening, and is usually also a workpiece. It is the last process of heat treatment, so the combined process of vacuum hardening and vacuum tempering is called final heat treatment. The main purposes of vacuum hardening and vacuum tempering are:

1) Reduce internal stress and brittleness. hardened parts have great stress and brittleness. If they are not vacuum tempered in time, they will often deform or even crack.

2) Adjust the mechanical properties of the workpiece. After hardening, the workpiece has high hardness and brittleness. In order to meet the different performance requirements of various workpieces, the hardness, strength, plasticity and toughness can be adjusted through tempering.

3) Stable workpiece size. Vacuum tempering can stabilize the metallographic structure to ensure that it will no longer deform during subsequent use.

4) Improve the cutting performance of certain alloy steels.

The purpose of vacuum hardening

1) Improve the mechanical properties of metal products or parts. For example: improving the hardness and wear resistance of tools, bearings, etc., increasing the elastic limit of springs, improving the comprehensive mechanical properties of shaft parts, etc.

2) Improve the material properties or chemical properties of some special steels. Such as improving the corrosion resistance of stainless steel and increasing the permanent magnetism of magnetic steel. When hardening and cooling, in addition to the reasonable selection of hardening media, the correct hardening method is also required. Commonly used hardening methods mainly include single-liquid hardening, double-liquid hardening, graded hardening, isothermal hardening, partial hardening, etc.