1. The quenching Ms point decreases with the increase of C%.
When the quenching is too cold, the austenitic body begins to turn into the temperature of the ashedra, which is called the Ms point, and the completion temperature is called the Mf point. The higher the content of %C, the lower the temperature of Ms point. The Ms temperature of 0.4%C carbon steel is about 350.
℃ or so, and 0.8% C steel was reduced to about 200 ℃ or so.
The quenching liquid can be added with appropriate additives.
1) adding salt to water can double the cooling rate: the cooling rate of brine quenching is fast, and there is no phenomenon of quenching and quenching, which can be described as the ideal quenching agent. The proportion of salt added is appropriate for 10% of the weight.
2) the water impurities than pure water for quenching liquid, water with solid particles, helps the wash effect of workpiece surface, vapor membrane effect, makes the cooling speed increases, can prevent quenching spots. Therefore, it is very important to quench the quenching process without using pure water.
3) polymer can allocate water-soluble quenching liquid with water: polymer quenching liquid modulate different performance in accordance with the degree of water quenching liquid, convenient and no fire, pollution and other public hazards, and forward-thinking.
4) add dry ice ethanol can be used in cryogenic treatment fluid: add dry ice to ethanol can be produced in - the uniform temperature of 76 ℃, is very practical cryogenic cooling fluid.
The relationship between hardness and quenching speed.
As long as the steel quenching cooling rate is changed, different hardness values will be obtained. The main reason is that the internal structure of the steel is different. When the cooling speed is slow and sometimes after steel of Ps curve, the austenitic temperature is higher, austenitic experience generated wave to the body, the starting point for Ps, endpoints for Pf, the hardness of small wave to body. If the cooling speed is accelerated and the cooling curve does not cut through the Ps curve, the austenitic experience becomes a higher hardness of the field. MaTian medium hardness is associated with the carbon content of solid solution, thus MaTian medium hardness will increase with the % of C content and larger, but after more than 0.77% C, martensitic carbon solid solution has no significant increase in the body, the hardness change are easing.
The difference between quenching and tempering cooling method of high frequency machine.
There are three common cooling modes for quenching:
1) continuous cooling;
2) constant temperature cooling;
3) stage cooling.
In order to reduce the occurrence of quenching in quenching process, the critical area temperature above is suitable for the rapid cooling of high frequency machine above the critical cooling rate. Slow cooling is an extremely important key technique when entering hazardous areas. Therefore, when this type of cooling is carried out, it is best to use stage cooling or constant temperature cooling (flax). The common cooling methods of tempering treatment include quenching and cooling, which are cold and cold. Tool steel is suitable for cooling. When the tempering temperature of tool steel is hot and cold, it is easy to produce a crack due to the remnant of the vosfield body, which is called a tempering crack. However, if the alloy steel adopts the cooling method of cooling, it can easily lead to temper brittleness. After quenching MaTian often exist in medium and residual austenitic, placed in a room temperature for a long time may cause the occurrence of cracks, which is caused by residual austenitic body formation, expansion as a result, this phenomenon is especially the most susceptible to the cold climate in winter. In addition, the other big weakness of the residual vostfield body is that the hardness is too low, which makes the tool's cutting deterioration. The use of cryogenic treatment has led to the formation of the astigma, leaving the residual waseda body unable to produce even further cooling. Or in the form of external force processing, the residue of the unsteady remains of the voss field is made up of the flaxen, reducing the influence of the residual austenitic body on the steel characteristics.
5. Reasons for insufficient hardness after quenching.
The purpose of quenching is to make the steel surface satisfactory hardness, if the hardness value is not ideal, it may be caused by the following factors:
1) the quenching temperature or the austenitic temperature is not enough;
2) may be caused by insufficient cooling rate;
3) if a decarbonization occurs before the surface of the workpiece is heated, the effect of the surface hardening of the workpiece will be greatly reduced;
4) when the surface of the workpiece is rusted or black, the hardness of the workpiece is obviously insufficient. Therefore, it is advisable to use the bead hammer method to remove the surface of the workpiece before applying the quenching process.
The causes of the quenching.
The main reasons for high frequency quenching are: size and shape of workpiece, low carbon content, cooling mode and pretreatment method. Steel heat treatment can produce quenching crack, the resulting quenching process can produce stress, the stress and MaTian repose of production process, steel is not usually a start producing MaTian repose of the fracture, but in MaTian repose of transformed by about 50% (the temperature about 150 ℃ or so), i.e. before quenching is coming to an end. To rapid cooling quenching process, therefore, in the high temperature, and low temperature slowly cooling, cooling "after the first fast slow" will grasp the key links, the situation of the quenching cracks can be to a minimum.
7. Overheating is easy to produce quenching cracks.
Heating more than appropriate quenching temperature above 100 ℃, call it overheated. Overheating, austenitic crystallization of particles becomes overgrowth of body, lead to generate massive MaTian after quenching medium and brittle, easy to appear symmetrical dispersed the backbone of acicular MaTian transverse cracks (this is called MaTian repose of crack), the cracks easily developed into the quenching cracks. So when your artifacts in austenitic body temperature to produce overheating, subsequent quenching and cooling are unable to prevent the generation of quenching crack, so someone called "overheating" in quenching cracks of fire.
8. The tissue before quenching will affect the quenching crack.
The pre-quenching of the high frequency machine will certainly affect the success or failure of the quenching. The most normal precursors should be normal tissue or anneal (wave body structure). If the pre-quenching tissue is an overheated tissue, the spheroidized tissue will have different results. Quenching cracks caused by overheating organization, glomeration organization can even hardened and avoid quenching crack and quenching, so the tool steel or high carbon steel before quenching, can execute glomeration processing is one of the important technology of quenching. Spheroidized annealing or spheroidization can be applied to obtain spherical carbide. If the carbide is in the network, it is easy to quench the fracture.
9. Quenching parts caused by room temperature.
After quenching the high frequency machine parts, if it is placed at room temperature for a long time, there may be two kinds of defects, such as the use of cracks and deformation. It is also known as the aging crack, especially in the cold winter night, as the temperature drop leads to the remains of the vosfield body, which causes the rifts to occur, which is also called the night weeping crack. The deformation is also known as the aging deformation, which is the phenomenon that the workpiece is placed at room temperature to cause the change of size shape, mostly due to incomplete tempering treatment. In order to prevent deformation, the steel structure needs to be stabilized, so it is necessary to remove the residual water from the unsteady state (deep cold treatment). Then the implementation of 200 ℃ ~ 250 ℃ tempering processing make MaTian repose of stabilization.