The prospect of the state of heat treatment and thermochemical treatment technology

1. State of heat treatment technology

(1) to promote the use of high-pressure gas quenching

Foreign heat treatment manufacturers attach great importance to the cooling of the heat treatment process. In accordance with the technical and technological requirements of the product, it can be slow, but oil quenching, single-gas quenching, and so on. Fast atmosphere recirculation is used to spray high-pressure gas into the cooling chamber, which regulates the flow rate and flow rate changes to achieve the cooling rate at a certain time to achieve the cooling curve required during heat treatment to ensure the quality of the heat treatment of parts. Before quenching the quenching gas with gas quenching, nitrogen, helium, etc., and now with strong air spraying, so that the workpiece is very quickly cooled, the surface quenching is only a very thin oxide film, gray, the color of the parts is still beautiful, saving a lot of nitrogen and inert gas to further reduce the cost of heat treatment.

Low-pressure vacuum carburizing and high-pressure gas quenching is an advanced carburizing process; it carburizes quickly, has a good carbide structure, small quenching cracking and deformation, energy saving, and carburizing raw materials. The surface quality of the cemented parts is good, and it contributes to environmental protection and other characteristics.

(2) Heat treatment equipment using oil cooling

Fan cooling, heat exchanger cooling, cooling tank cooling, and all necessary cooling devices, all with oil seals from the cold, complete replacement of the water-cooled cooling system, the entire heat treatment furnace without any cooling water. For example, hot air circulation cooling: the original water in the water pipe to the water pipe to the oil pipe leads to a small fuel tank with a diameter of 102 mm installed next to the fan, the oil cooling system is completely closed, when the heat carrier of the fan increases, the proportion of heated oil naturally floats upwards, causing natural oil circulation. In the case of a small fuel tank and natural heat dissipation, the hot oil is cooled and then added to the cycle so that there is no water and no power in the condition of a complete replacement of water cooling. The oil in the heat exchanger with the filled oil tank is replaced with cooling oil; the cooling oil is heated by heat exchange of hot oil; the change in the proportion of oil causes the circulation of the cooling oil, the radiator outside the tank, the effect to achieve the effect of complete oil cooling, saving a lot of cooling water.

(3) Nitriding furnace using a hydrogen probe

The German company Ipsen uses a hydrogen probe and the corresponding technology to measure the nitrogen potential in the nitriding furnace to control and regulate the atmosphere of the nitriding furnace to modernize the nitriding furnace.

(4) Gas tube

Currently, most European heat treatment equipment uses gas radiant tubes, using natural gas heating. Gas heating technology and equipment in Europe have been very mature; the gas burner has a standard series manufactured by a professional burner manufacturer, and the inner tube of the gas tube is made of stainless steel in ceramics to extend the service life and improve the power. Natural gas heating to improve energy efficiency and reduce production costs.

2. Methods of deformation and prevention of heat treatment

There are two forms of heat treatment deformation: one is a change in size, and the other is a change in the geometric shape of the part. The heat treatment technology is different; the size of the part and the geometry of the deformation and anti-deformation method do not coincide.

Heat treatment. The process of austenitizing heating, the longer the insulation time, the higher the temperature, the more austenite melting, the greater the martensite expansion. During cooling, the greatest expansion of martensite followed by a change in the volume of bainite, bainite, and bainite is very small. In low-temperature quenching, martensite shrinks; shrinkage is proportional to the supersaturated carbon content. At room temperature -200 ℃ heating, part of the residual austenite will be converted into martensite, expansion. But the expansion due to 200 ℃ near the martensitic decomposition, so the performance changes little.

In conventional heat treatment, the main reason for the change in the shape of the part is the thermal stress and phase transition stress that occurs during the heating and quenching of heat treatment. Heating too quickly, relatively large parts in the furnace, parts of different parts of the temperature, will lead to thermal deformation. Insulation, residual stress processing will be released and deformation, parts of the weight will lead to deformation. Cooling due to different parts of the cooling rate of different parts will lead to thermal stress deformation, leaving parts. Even if the cooling rate is the same, cooling is always fast and the heart is slow. Thus, the surface of the first phase changes the plastic deformation of the unstable core. If there is material in the segregation of the material or decarburization of the material, the phase transition stress is more uneven, more easily lead to deformation of parts. In addition, if the uneven thickness of the parts will also lead to different cooling rates.

In the heat treatment of forgings, in order to reduce the deformation of the placed parts, the maximum is vertically hung, the second is vertically located at the bottom of the furnace, the third is with two levels, the support position over the entire length of one-third, and four between one-fourth is flat on the heat-resistant steel fixture.

In the process of cooling parts, the type of quenching medium, cooling characteristics, hardening, etc., and related deformations. The change in cooling characteristics can be adjusted by changing the viscosity, temperature, and pressure of the liquid at the medium level, using additives, mixing, and the like. The higher the viscosity of the quenching oil, the higher the temperature, the less oval deformation. In a static state, the deformation is small.

The following methods can effectively reduce deformation: ① salt bath quenching, ② high-temperature oil quenching, ③ QSQ method, ④ decompression quenching, ⑤ three-tank quenching. Salt bath quenching and high-temperature oil quenching are similar, quenched at the martensitic transformation temperature, increasing the homogeneity of martensitic transformation. QSQ is a two-fluid quenching. Decompression quenching is achieved by reducing the surface pressure of the quenching medium, thereby extending the vapor film stage, reducing the cooling rate of the high-temperature zone, and making the cooling rate of the parts uniform. The first three parts of the quenching structure are simple: the first part is cooled by oil from the quenching temperature to slightly above the Ms temperature point, then baked in the atmosphere to maintain the uniformity of the entire temperature part, and then cooled by oil, so that the uniformity of martensitic transformation significantly improves the unevenness of deformation.