What is high frequency quenching of steel pipes?

What is high frequency quenching of steel pipes?

High-frequency quenching is mostly used for surface quenching of steel pipes (seamless pipes and welded pipes). It is a metal heat treatment method that generates a certain induced current on the surface of the steel pipe, rapidly heats the surface of the steel pipe, and then quickly quenches it. Induction heating equipment, that is, equipment for induction heating and surface quenching of steel pipes.

Induction heating principle: The steel pipe is placed in an inductor, which is generally a hollow copper pipe, and medium-frequency or high-frequency alternating current (1000-300000Hz or higher) is input. The alternating magnetic field generates induced currents of the same frequency in the steel pipe. The distribution of this induced current in the steel pipe is uneven. Strong on the surface, weak on the inside, and close to zero in the center. Utilizing this skin effect, the surface of the steel pipe can be rapidly heated, and the surface temperature rises to 800-1000°C within a few seconds, while the core temperature rises very little.

High frequency quenching process
Rapid heating combined with immediate quench cooling. The surface of the steel being processed reaches the quenching temperature through rapid heating. It cools quickly without waiting for heat to reach the center. Only the surface layer hardens to martensite, and the center is still the original unquenched annealed (or normalized or tempered) structure, with good plasticity and toughness.

Main methods of high frequency quenching
Induction heating surface quenching (high frequency, medium 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.

Application of high frequency quenching
For steel pipes that are subjected to alternating loads such as torsion and bending, the surface layer is required to bear higher stress or wear resistance than the core. The surface of the steel pipe needs to be strengthened. It is suitable for steel with higher carbon content We=0.40~0.50%.

Compared with ordinary heating quenching
1. The heating speed is extremely fast, which can expand the transformation temperature range of body A and shorten the transformation time.
2. After quenching, extremely fine cryptocrystalline martensite can be obtained on the surface of the steel pipe, with a slightly higher hardness (2~3HRC). Less brittle and higher fatigue strength.
3. The workpieces treated by this process are not easy to oxidize and decarburize, and some steel pipes can even be assembled and used directly after treatment.
4. The hardened layer is deep, easy to control and operate, and easy to realize mechanization and automation.
5. Flame surface heating and quenching

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