PRODUCT CATEGORIES

Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

What are the advantages of vacuum heat treatment?

Compared with conventional heat treatment, the mechanical properties (especially plasticity and toughness) of metal material workpieces after vacuum heat treatment have been significantly increased. The reason is that the vacuum heat treatment has a good degassing effect. Surface purification and degreasing heat the workpiece in a vacuum state. The oxide film, slight rust, nitrides, hydrides, etc. on the surface are reduced, decomposed or volatilized and disappear, leaving the metal with a smooth surface. This is vacuum A characteristic of heat treatment.
The oxidation reaction of metal is a reversible reaction. When the metal is heated, whether an oxidation reaction or a decomposition reaction of the oxide occurs depends on the relationship between the partial pressure of oxygen in the heating atmosphere and the decomposition pressure of the oxide.

The decomposition pressure of oxygen is the partial pressure of oxygen produced after the decomposition of the oxide reaches equilibrium. If the decomposition pressure of oxygen is greater than the partial pressure of oxygen, the oxide decomposes, the oxygen produced is released, and what remains is the clean surface of the metal. Metal surface purification effect. There is very little residual oxygen in the vacuum, and the partial pressure of oxygen is very low. The higher the vacuum, the lower the partial pressure of oxygen, which is lower than the decomposition pressure of the oxide. The reaction proceeds to the right, so the vacuum provides the metal oxide with a heating decomposition conditions.

In addition, under the premise that the oxygen partial pressure in the furnace is very low, metal oxides can be decomposed into suboxides, which are easily sublimated and volatilized during vacuum heating. The substances adhered to the surface of the workpiece are mainly oil stains, etc., which are carbon, hydrogen, and oxygen compounds with high vapor pressure. They are easy to volatilize or decompose during the vacuum heating process, and are removed by the vacuum pump, which has the effect of purifying the surface of the workpiece.

It should be noted that when the oxide on the metal surface is heated in a vacuum, it may also react with H2 and C diffusing outward from the inside of the metal material, thereby reducing the oxide on the metal surface. During the decomposition process of oxides, it is also accompanied by the removal of organic substances such as grease. Even without special cleaning to remove organic substances on the surface, the surface of the workpiece can still have a bright surface. The reason is that these greases and lubricants are all It is aliphatic and is a compound of carbon, hydrogen and oxygen. It has a high decomposition pressure, so it is easily decomposed into gases such as hydrogen, water vapor and carbon dioxide when heated in a vacuum, and is then pumped away by the vacuum pump to prevent it from contacting parts at high temperatures. If any reaction occurs on the surface, a clean surface without oxidation or corrosion can still be obtained. The purification effect of the vacuum enhances the metal surface activity, which is conducive to the absorption of C, N, Cr, Si and other atoms, making carburizing, nitriding and nitrogen-carbon The speed of co-penetration is accelerated, and the penetration layer is more uniform.

Another characteristic of vacuum heat treatment is the evaporation of metal surface elements, which is reflected in the mutual bonding between parts after heat treatment of high-chromium cold work mold steel or chromium stainless steel, or between parts and material baskets (tooling), and the surface appears. Orange peel shape, very rough, and the corrosion resistance is significantly reduced. This is the shortcoming of vacuum heat treatment – the evaporation of metal. Regarding the evaporation of metal, it is derived from the theory of phase balance. The equilibrium pressure of steam acting on the metal surface (steam (pressure) is different. When the temperature is high, the vapor pressure is high, and the evaporation amount of solid metal is large; when the temperature is low, the vapor pressure is low. If the temperature is constant, the vapor pressure will have a certain value. When the external pressure is less than the When the vapor pressure reaches a certain temperature, the metal will evaporate (sublimate). The smaller the external pressure, that is, the higher the degree of vacuum, the easier it is to evaporate. Similarly, metals with higher vapor pressure are easier to evaporate.

It can be seen that the vapor pressure of different metals is different. Full attention should be paid to the evaporation problem according to the material of the workpiece, that is, according to the vapor pressure and heating temperature of the alloy elements of the workpiece being processed during heat treatment, the appropriate vacuum degree should be reasonably selected to prevent the surface from evaporating. Evaporation of alloying elements.

Commonly used elements in steel such as Mn, Ni, Co and Cr, as well as elements such as Zn, Pb and Cu, which are the main components of non-ferrous metals, have high vapor pressures and can easily produce vacuum evaporation during vacuum heating and cause workpieces ( Or adhere to each other with tooling). In fact, there is a certain correspondence between vapor pressure and heating temperature. As long as the vacuum degree is appropriately selected, the evaporation of alloy elements can be prevented.

In addition, during vacuum heating, the type of metal material can be considered, and high-purity inert gas (i.e., reverse gas filling such as high-purity nitrogen, high-purity argon, etc.) can be introduced at a certain temperature to adjust the vacuum in the furnace. degree, using low vacuum heating method to prevent the evaporation of alloy elements on the surface of the workpiece. This measure is more effective for workpieces such as high-speed tool steel and high-alloy steel.