Wed, 24 Oct 2018 03:30:57 +0000
Induction heating surface hardening application
Workpieces subjected to alternating loads such as torsion and bending require that the surface layer withstand higher stress or wear resistance than the center, and require strengthening of the workpiece surface, which is suitable for steel with carbon content of 0.40-0.50%.
Two. Process method
Rapid heating is combined with immediate quenching.
The surface of the steel to be processed reaches quenching temperature by rapid heating, and quenches rapidly without equal heat transfer to the center. The surface hardens only as martensite, and the center is still annealed (or normalized and tempered) structure with good plasticity and toughness.
Three, main methods:
Induction heating surface quenching (high frequency, medium frequency, power frequency), flame heating surface quenching, electric contact heating surface quenching, electrolyte heating surface quenching, laser heating surface quenching, electron beam heating surface quenching.
Four. Induction heating surface quenching
(1) basic principles:
The workpiece is placed in an inductor winded by a hollow copper tube, and the inductive current of the same frequency is formed on the surface of the workpiece after the medium frequency or high frequency alternating current is applied. The surface of the workpiece is heated rapidly (within a few seconds it can be heated up to 800-1000 degrees, and the center is still close to room temperature) and then cooled by water spraying (or oil immersion quenching) immediately to harden the surface layer of the workpiece. (shown below in animation)
(two) selection of heating frequency
At room temperature, the relationship between the depth of induction current flowing into the surface of the workpiece and the current frequency f (HZ) is mm.
With the increase of frequency, the penetration depth of the current decreases and the hardenability layer decreases.
The commonly used current frequencies are:
1. High-frequency heating: 100-500KHZ, commonly used 200-300KHZ, high-frequency heating for electronic tubes, hardening depth of 0.5-2.5mm, suitable for small and medium-sized parts.
2. Intermediate frequency heating: current frequency is 500-10000HZ, commonly used 2500-8000HZ, power equipment for mechanical intermediate frequency heating device or silicon controlled intermediate frequency generator. The depth of hardened layer is 10 mm. Suitable for larger diameter shaft, medium and large gears, etc.
3, power frequency heating: the current frequency is 50HZ. The hardening depth can reach 10-20 mm by using mechanical power supply, which is suitable for surface hardening of large diameter workpiece.
(three) application of induction heating surface hardening:
Compared with conventional heating quenching,
1, the heating speed is very fast, which can expand the range of A bulk transition temperature and shorten the transformation time.
2. After quenching, extremely fine hidden martensite can be obtained on the surface of the workpiece, and the hardness is slightly higher (2 ~ 3HRC). Low brittleness and high fatigue strength.
3. The workpiece treated by this process is not easy to oxidize and decarbonize, and even some workpieces can be directly assembled and used after treatment.
4, hardened layer is deep, easy to control operation, easy to realize mechanization and automation.
Five, flame surface hardening
It is suitable for flame surface quenching of medium carbon steel 35, 45 and medium carbon alloy structural steel 40Cr and 65Mn, gray cast iron and alloy cast iron. It is a rapid flame heating process using acetylene oxygen or gas oxygen mixture. When the surface of the workpiece reaches quenching temperature, spray water is cooled immediately. The depth of hardened layer is 2 ~ 6mm, otherwise it will cause serious overheating and deformation of workpiece surface.