1 , application

　　A workpiece subjected to alternating loads such as torsion and bending requires the surface layer to withstand higher stress or wear resistance than the core. It is required to strengthen the surface of the workpiece, and is suitable for steel with a carbon content of We = 0.40 to 0.50% .

2 , process methods

Rapid heating combined with immediate quenching.

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.

3 , the main method

　　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.

Surface hardening principle

( 3.1 ) Basic principles:

　　The workpiece is placed with a hollow copper tube wound inductors, into the intermediate frequency or high frequency alternating current, are formed of the same frequency induced current in the workpiece surface, the part surface is heated rapidly (within a few seconds can be heated 800 ~ 1000 degrees, the heart is still close to room temperature) Immediately after spraying water to cool (or oil quenching ) , the surface layer of the workpiece is hardened.

( 3.2 ) Selection of heating frequency

The relationship between the depth δ ( mm ) of the induced current flowing into the surface of the workpiece at room temperature and the current frequency f ( HZ ) is as follows: 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 , for electronic tube high-frequency heating, hardened layer depth of 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. The depth of the hardened layer is 2 to 10 mm . Suitable for shafts with large diameters, medium and large gears, etc.　　

3 , power frequency heating: 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.