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Gear shaft heat treatment
Gear shaft heat treatment

Steel ball surface heat treatment

Steel ball surface heat treatment

It is a heat treatment operation method that uses a certain method to generate a certain frequency of induction current on the surface of the workpiece, to heat the surface of the part rapidly, and then quench and cool it rapidly.
Principle: As shown in the figure, electromagnetic induction produces an induced current of the same frequency, i.e. eddy current. The distribution of eddy currents in the cross-section of the workpiece is not uniform, the heart is almost equal to zero, while the surface current density is very large, called the “skin effect”, the higher the frequency, the current density of the surface layer is very thin. Relying on this current and the resistance of the workpiece itself, the surface of the workpiece is rapidly heated to quenching temperature, while the heart temperature is still close to room temperature, and then immediately cooled by water spray, so that the surface of the workpiece hardened.

Steel ball surface heat treatment

Classification: Induction heating can be divided into three categories:

 (1)High frequency heating
Commonly used frequency is (200 ~ 300) KHZ, the depth of the hardened layer is (0.5 ~ 2.5) mm.
(2) Medium frequency heating
The common frequency is (2500~8000) HZ, the depth of hardened layer is (2~10) mm.
(3) Industrial frequency heating
Current frequency of 50HZ, no frequency equipment, the city with alternating current can be, hard layer depth of (10 ~ 20) mm or more, the city with alternating current that.
Advantages and disadvantages: induction heating surface quenching heating speed, high productivity, heating temperature and hardened layer depth is easy to control, the steel ball surface oxidation and decarburization less, the steel ball deformation is small, you can make all the quenching process to achieve mechanization, automation.

2 Properties after induction surface quenching

  1.  Surface hardness: by high and medium frequency induction heating surface quenching of the workpiece, its surface hardness is often 2 to 3 units higher than ordinary quenching (HRC).
  2. Wear resistance: high-frequency quenching of the workpiece wear resistance than ordinary quenching to high. This is mainly due to the hardened layer of martensite grain size, carbide dispersion, as well as relatively high hardness, high surface compressive stress and other comprehensive results.
  3.  Fatigue strength: high, medium frequency surface quenching so that the fatigue strength is greatly improved, notch sensitivity decreases. For the same material workpiece, hardening layer depth in a certain range, with the hardening layer depth increases and fatigue strength, but the hardening layer depth is too deep when the surface is compressive stress, and thus the hardening layer depth increase hit fatigue strength instead of decreasing, and make the workpiece brittle increase. General hardening layer depth δ = (10 ~ 20) % D. More appropriate, where D is the effective diameter of the workpiece.

Factors affecting the quality of steel balls

  1. Material density: steel balls, cast iron balls, alloy steel balls, etc., the density of different materials are different, steel density than cast iron, alloy steel is different depending on the density and content of the main alloy elements.
  2. steel ball manufacturing method: rolling and forging of steel balls with dense organization, so the density is large, casting of cast steel balls, cast iron balls or casting alloy balls, such as the organization is not very dense, and even the pores, so the density is smaller.
  3. steel ball metallographic organization: martensite, austenite, bainite, ferrite and other different crystal structure density is not the same, the crystalline fineness also has an impact.
  4. Chemical composition element influence: the finished steel ball due to the chemical composition contained in the composition of iron, carbon, chromium, manganese, sulfur, phosphorus and other components are different, then the hardness of the steel ball, impact abrasion has different degrees of impact, in general, the amount of chromium, the steel ball wear resistance is high. Good quality!
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