High frequency and medium frequency hardening the surface of induction heat treatment is the use of induced current on the surface of the workpiece quenching treatment, after cooling/heating surface to obtain high hardness martensite structure, and the internal organization still has good toughness, plasticity, and high strength, etc., in order to meet the parts under the action of the alternating load has a high service life. As we know, induction heating and heat treatment furnace have completely different heating modes. Induction heating of workpiece does not rely on external heat source, but alternating current is generated on the workpiece surface when alternating current passes through the inductor. A closed loop is formed on the workpiece surface, and heating is achieved by the resistance of metal to passing current. The heat required for induction heating comes from two sources: the eddy current thermal effect, which is the main source of heat; Hysteresis heat effect – this heat is much less than eddy current heat effect. In modern production, the parts surface hardening technology has been widely applied, medium truck, light vehicles and cars of 200 ~ 300 parts need, such as surface hardening, information on induction hardening technology is the most economic, most effective and most direct means of heat treatment, it is a good parts surface strengthening method, can obviously improve the fatigue strength and service life of parts.
The purpose of the surface quenching of the parts is to improve the surface hardness of the parts, the heart still has enough strength and toughness to meet the needs of fatigue resistance of mechanical parts.Hardening of parts by surface quenching can significantly improve wear resistance. If carbon content of parts is increased, wear resistance will be better.And carburizing and quenching, such as 20 cr after carburizing surface carbon content reached 0.9% ~ 1.2%) than that of high frequency quenching (carbon content in 0.45% of the 45 steel) wear resistance significantly increased, so the different using conditions and work requirements, general high frequency quenching is used to request more good comprehensive mechanical properties, high fatigue strength of structural components, in most parts of the carbon content is 0.37% ~ 0.47%, before the process carried out for the quenched and tempered treatment, for the final heat treatment prepared for the organization.The common defects in high-frequency quenching are as follows: unqualified depth of hardened layer, low surface hardness, soft spot and soft belt, unqualified structure of hardened layer, large deformation, cracking, large residual stress, sharp Angle overheating, etc.Compared with the general quenching process, induction heating quenching process has its own characteristics, equipment performance, sensor quality and shape, the material and shape of parts, cooling methods, as well as heating speed and temperature, will directly affect the quenching quality, so the production process should be carefully controlled.
Generally, for the workpiece that is not required to be treated as a whole, the workpiece should be heated by induction heating at high frequency and intermediate frequency as far as possible. This method has the advantages of high efficiency, stable quality and energy saving, which cannot be replaced by other processes.The formulation of high-frequency and intermediate frequency induction heating quenching process is basically consistent with the common heat treatment, which should take into account the characteristics, performance (power and frequency) of the equipment, the quality of the inductor, the material and shape of the workpiece, cooling mode, heating temperature and heating speed, etc., all of which affect the quenching quality of the parts.The carbon content and original structure of the workpiece are the key and important basis for determining the process parameters, which must be taken seriously. The best induction quenching heat treatment process parameters of the parts should be determined through experiments to achieve the purpose of high-frequency quenching.It should be noted that the original structure of high-frequency and intermediate frequency quenched workpiece should be tempered Soxhlet after quenching and tempering treatment. The structure has fine grain, good toughness and plasticity, and high comprehensive mechanical properties.
Induction hardening material divided into two types of steel and cast iron, steel and divided into high quality carbon structural steel such as 35 and 40, 45, 50, alloy structural steel, such as cr, 30 to 35 40 cr, cr, cr, 40 MNB 45, 45 MNB, 30 crmo, 35 crmo, 40 crmo,
35 CrNiMo, 40 CrNiMo, 45 CrNiMo and cast steel ZG270-500, ZG310-570, etc.The relationship between the surface hardness of the steel after quenching and the carbon content in the steel is hardness (HRC) =20 + 60(2C-1.3C2), where C is the carbon content of the steel and the quenching medium is water.Application of high frequency and medium frequency quenching has a variety of parts, such as all kinds of gear, shaft, crankshaft, camshaft, cylinder liner, piston pin, adapter, caterpillar pin, machine tools guide, worm gear and worm, valve lifter, a variety of tools, etc., so its cost is low, the efficiency high, and the characteristics of small deformation has been very widely promotion and application.
There are three types of cast iron that can be quenched by induction;Common nodular cast iron such as QT600 — 3, QT700 — 2, QT800 — 2, QT900 — 2 is commonly used for automobile parts, such as crankshaft, camshaft, brake shoes, bearing blocks, etc.Common malleable iron KTH350 — 10, KTH270 — 12, KTZ450 — 06, KTZ550 — 04, etc., used for making rocker arm and brake shoe, etc.;Common grey cast iron such as HT200 — 40, HT250 — 47, HT300 — 54, HT350 — 61, etc., used for making cylinder jacket and cylinder cover, etc.
In the actual heat treatment process of parts, all kinds of materials to be treated, the shape and size of parts, technical requirements are different, each professional heat treatment plant used by the induction treatment equipment has its own characteristics, common high-frequency equipment models are KQG-30, KQG-60, KQG-80, KQD-40, KQD-60, etc.Intermediate frequency equipment models are KGPS-300, KGPS-500, KGPS-750, KGPS-2000, etc.
Intermediate frequency quenching consists of heating quenching and continuous heating quenching. The frequency of intermediate frequency induction heating is generally 8000Hz and 2500Hz. Compared with high-frequency induction heating, its heating frequency is characterized by low frequency, high efficiency and large penetration depth of current, so the wall thickness of the inducer increases. Medium frequency induction power supply device of electric parameters have generator no-load voltage, load voltage generator, generator current, effective power, power factor, the transformer turns ratio, the electric capacity, etc., the electric parameters and the shape and size of workpiece, technical requirements, heating method and sensor structure has a close relationship, the thermal parameters, including heating time, quenching cooling fluid pressure and cooling time, etc.
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