For workpieces subjected to alternating loads such as torsion and bending, the surface layer is required to bear higher stress or wear resistance than the core, and the surface of the workpiece needs to be strengthened. It is suitable for steel with a carbon content of We=0.40-0.50%.
Second, the process method
Rapid heating combined with immediate quench cooling.
Through rapid heating, the surface of the steel to be processed reaches the quenching temperature, and it cools rapidly without waiting for the heat to reach the center, only the surface layer is quenched into martensite, and the center is still annealed (or positive) with good plasticity and toughness. Fire and tempering) organization.
3. Main methods:
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.
Fourth, induction heating surface quenching
(1) Basic principle:
Put the workpiece in the inductor made of hollow copper tube, and after passing the intermediate frequency or high frequency alternating current, an induced current of the same frequency is formed on the surface of the workpiece, and the surface of the part is rapidly heated (the temperature can be increased by 800～ 1000 degrees, the core is still close to room temperature), and then spray water to cool (or oil immersion quenching) immediately to harden the surface layer of the workpiece. (as shown in the animation below)
(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:
The frequency increases, the current penetration depth decreases, and the hardening layer decreases.
Commonly used current frequencies are:
1. High frequency heating: 100～500KHZ, commonly used 200～300KHZ, it is electronic tube type high frequency heating, hardened layer depth is 0.5～2.5mm, suitable for small and medium-sized parts.
2. Intermediate frequency heating: The current frequency is 500~10000HZ, commonly used 2500~8000HZ, and the power supply equipment is a mechanical intermediate frequency heating device or a thyristor intermediate frequency generator. Hardened layer depth ~ 10 mm. Suitable for larger diameter shafts, medium and large gears, etc.
3. Power frequency heating: the current frequency is 50HZ. Using mechanical power frequency heating power supply equipment, the depth of the hardened layer 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 transformation temperature range of A body and shorten the transformation time.
2. After quenching, the surface layer of the workpiece can obtain extremely fine cryptocrystalline martensite, and the hardness is slightly higher (2-3HRC). Lower brittleness and higher fatigue strength.
3. The workpieces treated by this process are not easy to be oxidized and decarburized, and even some workpieces can be directly assembled and used after treatment.
4. The hardened layer is deep, easy to control and operate, easy to realize mechanization and automation.
Five, flame surface heating and quenching
It is suitable for flame surface quenching of medium carbon steel 35, 45 steel, medium carbon alloy structural steel 40Cr and 65Mn, gray cast iron and alloy cast iron. It is to rapidly heat the workpiece with a flame jet burned by acetylene-oxygen or gas-oxygen mixture. After the surface of the workpiece reaches the quenching temperature, spray water to cool it immediately. The depth of the hardened layer is 2 to 6 mm, otherwise the surface of the workpiece will be seriously overheated and deformed and cracked.