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Core tip: the surface of spring can be generally treated, such as blackening (blue), phosphating, electroplating, spray molding, etc. In recent years, the zinc chromium film dacroa DACROMET dacroa protective layer has excellent corrosion resistance, which is 710 times the corrosion resistance of the traditional electroplating layer, and there is no hydrogen embrittlement in the electroplating process. Generally, the surface of springs can be treated, such as blackening (blue), phosphating, electroplating, spray molding, etc. In recent years, the zinc chromium film "dacrom DACROMET da...
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In the actual work, we often encounter that the spring cannot push the moving object to the set position, that is to say, the length of the spring's computational freedom becomes shorter.The main reason is that there is no initial compression, that is, a spring is made into a spring, which is compressed to its compression height or to its compression height (if necessary) with a greater force, and cannot be restored to its original free length upon release.Its shortened quantity is called "initial compression quantity".After repeating 3-6 times of compression, the length is no lo...
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Analysis of deformation prevention measures for heat treatment of metal spring

日期: 2018-09-04
浏览次数: 26
nelson

Analysis of deformation prevention measures for heat treatment of metal spring


There are two types of heat treatment deformation: one is the size change, the other two is the change of part geometry. Different methods of heat treatment, deformation and deformation prevention of parts size and geometry are also different.

The longer the holding time and the higher the temperature are, the more carbon is dissolved into austenite and the larger the expansion of martensite is. The expansion of martensite is the largest, followed by upper bainite, and the volume change of lower bainite and troostite is very small. At low temperature tempering, martensite shrinks and the amount of shrinkage is directly proportional to the supersaturated carbon content. When heated at room temperature of -200, part of austenite is transformed into martensite and expanded. However, the expansion of the martensite due to decomposition near 200 c has little change.

In conventional heat treatment, the main reason for the shape change of parts is the thermal stress and phase transformation stress during heat treatment and quenching. Excessive heating speed, relative to heating furnace parts are too large, parts of the temperature is different, will lead to thermal deformation. During heat preservation, the residual stress will be released and deformed, and the weight of the parts will also lead to deformation. When cooling, due to different parts of the cooling rate of different parts, will form thermal stress and deformation of parts. Even if the cooling speed is the same, the cooling surface is always fast and the heart is slow. Therefore, the surface of phase transformation causes plastic deformation of the core without phase transformation. If there is segregation of alloy composition or surface decarbonization in the material, the phase change stress is more inhomogeneous and the deformation of parts is more easily caused. In addition, if the thickness of the parts is uneven, the cooling rate will also be different.

In the heat treatment of forgings, the way of placing parts to reduce deformation is to hang them vertically as far as possible, to place them vertically at the bottom of the furnace, to support them horizontally with two points, to place the fulcrum between one-third and one-fourth of the full length, and to place them flat on the heat-resistant steel tooling.

In the cooling process of parts, the types, cooling properties and hardenability of quenching medium are related to deformation. The change of cooling performance can be adjusted by changing the viscosity, temperature, liquid pressure, additives and stirring of the medium. The higher the viscosity of quenching oil, the higher the temperature, the smaller the elliptical deformation. In static state, the deformation is small.

The following ways can effectively reduce deformation: 1. salt bath quenching; 2. high temperature oil quenching; 3. QSQ method; 4. vacuum quenching; 5. one trough three-stage quenching. Salt bath quenching is similar to high temperature oil quenching in that both quenching occurs at martensitic transformation temperature, which increases the homogeneity of martensitic transformation. QSQ is double liquid quenching. Vacuum quenching is to extend the steam film stage by lowering the liquid pressure of quenching medium, and the cooling rate in high temperature zone decreases, so that the cooling rate of parts is uniform. The structure of one trough and three-stage quenching is simple. Firstly, the part is cooled by oil to the temperature slightly higher than MS. Then it is discharged and kept in the atmosphere, so that the whole temperature of the part is uniform, and then cooled by oil, so that the martensite transformation is uniform and the deformation irregularity is greatly improved.


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