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How to quench the die steel
Dec 05, 2017

How to quench the die steel

Different die steel has different quenching methods, quenching the workpiece is heated and incubated in water, oil or other inorganic salts, organic aqueous quenching medium rapid cooling. After quenching the steel hardens, but at the same time becomes brittle. In order to reduce the brittleness of the steel, the quenched steel is insulated for a long time at an appropriate temperature higher than room temperature and lower than 650 ° C, and then cooled. This process is called tempering. Annealing, normalizing, quenching, tempering is the overall heat treatment in the "four fire", of which quenching and tempering are closely related, often with the use of indispensable.

Heat treatment process generally includes heating, insulation, cooling three processes, and sometimes only heating and cooling of the two processes. These processes are interconnected and can not be interrupted. Heating is one of the important processes of heat treatment. Metal heat treatment of many heating methods, the earliest use of charcoal and coal as a heat source, and then the application of liquid and gaseous fuels. Electric applications make heating easy to control, and without environmental pollution. These heat sources allow direct heating, as well as indirect heating of the floating particles by molten salt or metal. The company is located in:

Metal heating, the workpiece exposed to the air, oxidation, decarburization often occur (that is, the carbon content of steel parts surface), which has a negative impact on the surface properties of parts after heat treatment. Therefore, the metal should usually be heated in a controlled atmosphere or in a protective atmosphere, in a molten salt and in a vacuum, or by a protective coating or a packaging method. The company is located in:

Heating temperature is one of the important process parameters of heat treatment process, select and control the heating temperature is to ensure the quality of heat treatment the main problem. The heating temperature varies with the metal material being treated and the purpose of the heat treatment but is generally heated above the phase transition temperature to achieve high temperature microstructure. In addition, the transformation takes a certain amount of time. Therefore, when the metal workpiece surface reaches the required heating temperature, it must be kept at this temperature for a certain period of time to make the temperature both inside and outside consistent so that the microstructure changes completely. This time is called holding time. When using high-energy density heating and surface heat treatment, the heating rate is very fast, generally there is no holding time, while the holding time of chemical heat treatment tends to be longer. The company is located in:

Cooling is also an indispensable step in the heat treatment process, the cooling method is different due to different processes, mainly to control the cooling rate. General annealing the slowest cooling, normalizing cooling faster quenching cooling faster. However, it also has different requirements due to different types of steel. For example, an empty hard steel can be hardened with a normal cooling rate.


Quenching purposes

The purpose of quenching is to make martensite or bainite transformation of undercooled austenite to obtain martensite or lower bainite structure, and then cooperate with tempering at different temperatures to greatly improve the strength, hardness and resistance of the steel Grinding, fatigue strength and toughness, to meet the different requirements of various mechanical parts and tools. Can also be quenched to meet the special ferromagnetic steel, corrosion resistance and other special physical and chemical properties.

Quenching process

The metal workpiece is heated to an appropriate temperature and maintained for a period of time, then immersed in the quenching medium rapid cooling metal heat treatment process. Quenching medium commonly used brine, water, mineral oil, air and so on. Quenching can improve the hardness and wear resistance of metal parts, which are widely used in a variety of industrial, mold, measuring tools and wear-resistant parts (such as gears, rollers, carburized parts) that require surface wear. By quenching and tempering at different temperatures, the strength, toughness and fatigue strength of the metal can be greatly improved, and the cooperation between these properties (comprehensive mechanical properties) can be obtained to meet the different requirements of use. In addition to quenching can also make some special performance of the steel to obtain a certain physical and chemical properties, such as quenching so that the permanent magnet to enhance its ferromagnetic, stainless steel to improve its corrosion resistance. Quenching process is mainly used for steel. Commonly used steel heated above the critical temperature, the original at room temperature will be all or most of the organization into austenite. Then the steel immersed in water or oil rapid cooling, austenite that is transformed into martensite. Compared with other organizations in steel, martensite has the highest hardness. Quenching rapid cooling will cause internal stress within the workpiece, when it is large to a certain extent, the workpiece will be distorted or even cracked. To do this, you must choose the appropriate cooling method. According to the cooling method, quenching process is divided into single-liquid quenching, dual-media quenching, martensite graded quenching and bainite austempering 4 categories. The company is located in:

Quenching effect of an important factor in quenching the workpiece hardness requirements and testing methods:

Hardened workpiece hardness

Quenching the hardness of the workpiece affected the quenching effect. Quenching the workpiece is generally Rockwell hardness tester, test HRC hardness. Hard quenched hard steel and surface hardening of the workpiece can test the hardness of HRA. Thickness of less than 0.8mm hardened steel, superficial surface hardening of the workpiece and hardened steel rod diameter less than 5mm, you can use the surface Rockwell hardness tester, test HRN hardness. The company is located in:

In the welding of carbon steel and some alloy steels, the HAZ may quench in the phenomenon of hardening and easy to form a cold crack, which is to be avoided in the welding process. The company is located in:

Due to the hard and brittle metal after quenching, the resulting surface residual stress can cause cold cracking and tempering can be used as one of the means to eliminate cold cracking without affecting the hardness. The company is located in:

Quenching on the thickness, smaller diameter parts more appropriate to use, for parts too large, quenching depth is not enough, carburizing the same problem exists, this time should be considered in the steel by adding chromium and other alloys to increase strength. The company is located in:

Quenching is one of the basic means of strengthening steel materials. Martensite in steel is the hardest phase in Fe-based solid solution (Table 1), so quenching of steel can achieve high hardness and high strength. However, the great brittleness of martensite, combined with quenching after quenching steel internal larger quenching stress, and therefore not suitable for direct application, must be tempered. The company is located in:

Table 1 steel iron-based solid solution microhardness value

Application of quenching process

Quenching process in the modern machinery manufacturing industry has been widely used. Important parts of machinery, especially in the automotive, aircraft, rocket application of steel almost all quenched. In order to meet the technical requirements of various parts of the dry, developed a variety of quenching process. For example, according to the accepted treatment of the site, there are overall, partial quenching and surface hardening; phase change by heating is complete, complete quenching and incomplete quenching (for sub-eutectoid steel, the law also known as subcritical quenching); by cooling When the phase change content, there are graded quenching, isothermal quenching and under-speed quenching.


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