Induction heating surface quenching has the advantages of good surface quality, small brittleness, hard oxidative decarburization and small deformation of quenched surface, so induction heating equipment has been widely used in metal surface heat treatment. Definition Induction heating: The workpiece is placed in the inductor. The inductor is usually a hollow copper tube with input IF or high frequency AC (300-300000 Hz or higher). The alternating magnetic field generates an induced current of the same frequency in the workpiece. The induced current is uneven in the distribution of the workpiece, strong on the surface, and weak inside, to the core close to 0, using this skin effect The surface of the workpiece can be heated rapidly, and the surface temperature rises to 800-1000oC in a few seconds, while the core temperature rises little.
Frequency selection Induction heating frequency selection: The frequency is selected according to the requirements of heat treatment and heating depth. The higher the frequency, the shallower the heating depth.
High-frequency (10KHZ or more) heating depth of 0.5-2.5mm, generally used for heating small and medium-sized parts, such as small modulus gears and small and medium-sized shaft parts.
The intermediate frequency (1~10KHZ) has a heating depth of 2-10mm, and is generally used for shaft heating with large diameter and gear heating with large and medium modulus. Well-known domestic manufacturer Hebei Hengyuan Electric Furnace Manufacturing Co., Ltd.
Power frequency (50HZ) heating hardened layer depth of 10-20mm, generally used for heat transfer of larger size parts, surface quenching of large diameter parts (diameter? 300mm or more, such as rolls).
The empirical formula induces the depth of the hardened layer of the hardened surface layer, depending on the frequency of the alternating current, generally the frequency is high and the heating depth is shallow, and the depth of the hardened layer is shallow. The relationship between the frequency f and the heating depth δ has the following empirical formula: δ = 20 / √ f (20 ° C); δ = 500 / √ f (800 ° C).
Where: f is the frequency, the unit is Hz; δ is the heating depth, the unit is millimeter (mm).
The specific application of induction heating surface quenching has the advantages of good surface quality, small brittleness, hard to oxidize and decarburize the quenched surface, and small deformation. Therefore, induction heating equipment has been widely used in metal surface heat treatment.
The induction heating device is a device that generates a specific frequency induced current, performs induction heating and surface hardening treatment.
Quenching application of induction heating surface quenching
I. Application: The workpiece subjected to alternating load such as torsion and bending requires the surface layer to withstand higher stress or wear resistance than the core. It is necessary to strengthen the surface of the workpiece and is suitable for carbon content We=0.40～0.50. % steel.
Second, the process: rapid heating combined with immediate quenching and cooling. By rapid heating, the surface of the steel to be processed reaches the quenching temperature, and the heat is transferred to the center without cooling. The surface layer is hardened to martensite, and the center is still unquenched. The original plasticity and toughness are better (or positive). Fire and tempering) organization.
Third, the main methods: induction heating surface quenching (high frequency, intermediate frequency, power frequency), flame heating surface quenching, electrical contact heating surface quenching, electrolyte heating surface quenching, laser heating surface quenching, electron beam heating surface quenching.
Fourth, induction heating surface quenching
(1) Basic principle: The workpiece is placed in an inductor wound with a hollow copper tube. After passing through an intermediate frequency or high frequency alternating current, an induced current of the same frequency is formed on the surface of the workpiece to rapidly heat the surface of the part (a few seconds). The temperature can be raised from 800 to 1000 degrees, and the core is still close to room temperature. Immediately after spraying water to cool (or oil-immersed), the surface layer of the workpiece is hardened.
(2) Selection of heating frequency: The relationship between the depth δ (mm) of the induced current flowing into the surface layer of the workpiece and the current frequency f(HZ) at room temperature is such that the frequency increases, the current penetration depth decreases, and the hardened layer decreases.
Commonly used current frequencies are:
1. High-frequency heating: 100～500KHZ, commonly used 200～300KHZ, is the high-frequency heating of electron tube type, the hardened layer depth is 0.5～2.5mm, suitable for small and medium-sized parts.
2, medium frequency heating: current frequency is 500 ~ 10000HZ, commonly used 2500 ~ 8000HZ, the power supply equipment is mechanical medium frequency heating device or thyristor intermediate frequency generator. Hardened layer depth ~ 10 mm. Suitable for shafts with large diameters, medium and large gears, etc.
3. Power frequency heating: The current frequency is 50HZ. It adopts mechanical power frequency heating power supply equipment, and the hardened layer depth can reach 10~20mm, which is suitable for surface quenching of large diameter workpieces.
(3) Application of induction heating surface quenching:
Compared with ordinary heating and quenching, it has:
1. The heating speed is extremely fast, which can expand the A-body transition temperature range and shorten the transition time.
2. After quenching, the surface of the workpiece can be obtained with very fine cryptocrystalline martensite, and the hardness is slightly higher (2~3HRC). Low brittleness and high fatigue strength.
3. The workpiece processed by the process is not easy to be oxidized and decarburized, and even some workpieces can be directly assembled after being processed.
4, hardened layer depth, easy to control operation, easy to achieve mechanization, automation.
V. Flame surface heating and quenching: suitable for flame surface quenching of medium carbon steel 35, 45 steel and medium carbon alloy structural steel 40Cr and 65Mn, gray cast iron and alloy cast iron. The workpiece is rapidly heated by flame spraying with an acetylene-oxygen or gas-oxygen mixture. Immediately after the surface of the workpiece reaches the quenching temperature, it is sprayed with water to cool. The depth of the hardened layer is 2 to 6 mm, otherwise it will cause severe overheating and deformation cracking of the workpiece surface.
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