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What are the types of surface quenching heat treatment processes

What are the types of surface quenching heat treatment processes


This article introduces you to the knowledge of surface quenching heat treatment. If you want to learn steel casting and processing, you can first learn about the theoretical knowledge related to quenching. Let's learn about heat treatment quenching process type and surface quenching heat treatment.Get more news about Multi-heads Laser Texturing,you can vist our website!

Surface hardening heat treatment introduction:
The workpiece is rapidly heated by different heat sources, and when the surface temperature of the part reaches above the critical point (when the core temperature of the workpiece is below the critical point), it is rapidly cooled, so that the surface of the workpiece is hardened and the core remains intact. organization. Industrial applications are more inductive heating and flame heating surface quenching.

Quenching heating temperature:
The quenching heating temperature is mainly determined by the phase transition point of the steel. For the sub-eutectic steel, the quenching heating temperature is generally Ac3+ (30-50 C), and the hypereutectoid steel is Ac1+ (30-50 C). The reason for this is that, for the hypoeutectic steel, if the heating temperature is lower than Ac3, the heating state is composed of austenite and ferrite two phases, and the ferrite is preserved after quenching and cooling, so that the hardness of the parts after quenching Uneven, reduced strength and hardness. The purpose of 30-50 C higher than the Ac3 point is to ensure that the core of the workpiece can reach the temperature above Ac3 in the specified heating time. The ferrite can be completely dissolved in the austenite, and the austenite composition is relatively uniform. The body grains are not coarse. For hypereutectoid steel, when the quenching heating temperature is between Ac1 and Ac3, the heating state is fine austenite grains and undissolved carbides, and after quenching, cryptocrystalline martensite and uniformly distributed spherical carbon are obtained. This kind of tissue not only has high strength and hardness, high wear resistance, but also good toughness. If the quenching heating temperature is too high, the carbides are dissolved, the austenite grains grow, and after the quenching, flake martensite (crystallized martensite) is obtained, the microcracks increase, the brittleness increases, and the quenching cracking tendency increases. Big. Due to the dissolution of the carbide, the carbon content in the austenite increases, the amount of retained austenite increases after quenching, and the hardness and wear resistance of the steel decrease. The purpose of higher than Ac1 point 30-50 C is similar to that of hypoeutectoid steel, in order to ensure that the temperature of each part in the workpiece is higher than Ac1.
(1) Liquid quenching

Haituo electromechanical single-liquid quenching is a quenching operation method in which an austenitic workpiece is rapidly immersed in a quenching medium and cooled to room temperature. The selection of the single-liquid quenching cooling medium is based on the fact that the cooling rate of the workpiece in the medium must be greater than the critical cooling rate of the steel of the workpiece, and the workpiece should not be quenched. Single-liquid quenching medium is water, brine, alkaline water, oil and some specially formulated water-based quenching agents.

(2) Two-liquid quenching

In order to overcome the shortcomings of single-liquid quenching, the quenching and cooling of the workpiece is as close as possible to the ideal situation, and two media with different cooling capacities can be used together, that is, the heated workpiece is first quenched into the first medium with high cooling capacity. Allow it to cool slightly above the Ms temperature (about 300 C), then immediately transfer to a second medium with less cooling capacity and cool to room temperature. This quenching cooling method is called two-liquid quenching.

For some workpieces, in order to further slow down the cooling rate below Ms, Haituo Electromechanical can also use water quenching air cooling or oil quenching air cooling, and air can also be treated as a cooling medium.

(3) Classification quenching (martensitic quenching)

The cooling method is characterized in that the workpiece is first immersed in a bath having a temperature slightly higher than Ms, and is kept in the bath until the surface of the workpiece and the center are cooled to the bath temperature, and then the air cooling is taken out. The bath temperature is generally Ms + (10 ~ 20) C. The components of the medium in the bath are a salt bath, an alkali bath, and a neutral salt bath.

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