Vacuum brazing of stainless steel

Stainless steel is a kind of steel which is mainly composed of chromium and other alloying elements and has corrosion resistance in general corrosive medium. In order to improve the electrode potential and maintain good corrosion resistance, the content of chromium in stainless steel should be above 12.5%.Stainless steel has good corrosion resistance, also should have excellent mechanical properties, process performance and large working temperature, temperature range (650 – – 250 – c), and is suitable for manufacturing requirements corrosion resistance, resistance level, resistance to high temperature and cryogenic parts and equipment, widely used in petroleum, chemical, electrical, instrumentation, food, medical, aerospace and atomic energy industries.

Stainless steel according to its main into I can be divided into high chromium stainless steel and chromium nickel stainless steel two categories.According to its structure can be divided into austenitic stainless steel, ferritic stainless steel, martensite stainless steel, precipitation hardening stainless steel four categories.

Chromium-nickel stainless steel is formed by adding an appropriate amount of nickel to high chromium (>Cr16%).Cr-ni stainless steel generally has austenitic structure, according to the impact of alloy elements on the structure and properties, can be divided into austenitic stainless steel, austenitic – ferritic stainless steel and precipitation hardening stainless steel.Because austenitic stainless steel has good cold deformation performance, room temperature, especially at low temperature of high plasticity and toughness, corrosion resistance and good welding and other advantages, it is the most widely used in stainless steel, accounting for about 70%.

vacuum braze furnace
There are two types of SIMUWU vacuum brazing furnace. The first kind of heating element is molybdenum sheet, and the heat insulation screen is all-metal screen furnace with molybdenum sheet and stainless steel. This kind of furnace is characterized by high vacuum and suitable for vacuum brazing of aluminium alloy, heat-resistant material and stainless steel. The heating elements and insulation materials of the other type of furnace are graphite elements. This kind of furnace is suitable for copper brazing of carbon steel with low vacuum requirement.

Vacuum Brazing Technology of Stainless Steel
The process of vacuum brazing of stainless steel is preparation before brazing, assembling and filling filler metal, and inspection of brazing out of furnace.

Stainless steel preparation before welding
Usually, after removing oxide skin by sand blasting or shot blasting, the workpiece is put in acetone, alcohol, gasoline or distilled water and cleaned by ultrasonic for about 30 minutes. Batch production of degreasing in trichloroethylene vapor degreasing tank was carried out.

Selection of solder:
Correct selection of filler metal is an important factor to ensure the quality of brazed joints.
Basic requirements for solders:
(1) The filler metal should have a suitable melting point. Low melting point: low strength of brazed joint. The melting point is too high: the grains of matrix metals are easy to grow up: the mechanical properties are easy to deteriorate, and even cause the danger of over-burning and corrosion.
(2) The filler metal should have good wettability, diffusivity and filling gap ability.
(3) The linear expansion coefficient of the solder should be close to that of the base metal. Otherwise, it is easy to bow up a larger internal stress and even produce cracks in the brazing seam.
(4) All brazed joints should meet the technological requirements of the products, such as adequate mechanical properties, corrosion resistance, conductivity and thermal conductivity.
(5) The filler metal itself should have good plasticity as far as possible and can be processed into various shapes, such as wire, strip, foil, etc.
(6) The filler metal should not contain toxic and other elements harmful to human body, and use precious and rare elements as little as possible.