Torsion and bending under alternating load function of artifacts, requirements of surface layer is higher than the core under stress or wear resistance, the workpiece surface is put forward to strengthen requirements, suitable for We = 0.40 ~ 0.50% carbon steel.
2. Process method.
Rapid heating is combined with immediate quenching and cooling.
By rapid heating to treat processing on the surface of the steel quenching temperature, ranging from heat to center the rapid cooling, only make the surface hardening of martensite, center is still not quenching of original plasticity, toughness good annealing or normalizing and tempering.
Iii. Main methods:
Induction heating surface quenching (high frequency, intermediate frequency and power frequency), flame heating surface quenching, electric contact heating surface quenching, electrolyte heating surface hardening, laser heating surface quenching, electron beam heating surface hardening.
4. Induction heating surface quenching.
(I) basic principles:
The workpiece is put in the wind with the hollow copper pipe in sensor, after access to intermediate frequency or high frequency alternating current (ac), formed in the surface with the frequency of the induced current, rapid heating of parts surface (a few seconds to temperatures of 800 ~ 1000 degrees, heart is still close to room temperature) immediately after the water spray cooling (or oiled quenching), the workpiece surface hardening.
(2) selection of heating frequency.
Common current frequencies are:
1. High frequency heating: 100 ~ 500KHZ, commonly used 200 ~ 300KHZ, for electronic tube type high frequency heating, the hardened layer is 0.5 ~ 2.5mm deep, suitable for small and medium sized parts.
2. Medium frequency heating: the current frequency is 500 ~ 10000HZ, and it is commonly used for 2500 ~ 8000HZ. The power supply device is a mechanical medium frequency heating device or a silicon controlled intermediate frequency generator. Hardened layer depth ~ 10mm. Suitable for large diameter shafts, cogs, etc.
3. Working frequency heating: the current frequency is 50HZ. The hardened layer can reach up to 10 ~ 20mm, which is suitable for the surface quenching of large diameter workpiece.
(iii) application of induction heating surface quenching:
Compared with ordinary heating quenching,
1. The heating speed is extremely fast, which can expand the temperature range of A body and shorten the transition time.
2. After quenching, the surface of the workpiece can be obtained with a very fine cryptocrystalline martensite, with a slightly higher hardness (2 ~ 3HRC). Low brittleness and high fatigue strength.
3. The workpiece processed by this process is not easy to oxidize and decarbonize, and even some workpieces can be directly assembled and used after processing.
4. The hardened layer is deep, easy to control operation, easy to realize mechanization and automation.
5. The flame surface is heated and quenched.
It is suitable for the surface quenching of 40Cr and 65Mn, gray cast iron and alloy cast iron of medium carbon steel. The workpiece is rapidly heated by a flame jet of acetylene - oxygen or gas - oxygen mixture. When the surface of the workpiece reaches the quenching temperature, the water spray is cooled immediately. The depth of the hardened layer is 2 ~ 6mm, otherwise the surface of the workpiece can be seriously overheated and deformed.