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Use of normalizing

Use of normalizing

The use of normal fire?

Normalizing is a heat treatment that improves the toughness of a steel sheet. After heating the steel structure to 30~50 °C above the Ac3 temperature, the steel is cooled for a while. The main feature is that the cooling rate is faster than annealing and less than quenching. During normalizing, the crystal grains of the steel can be refined in a slightly faster cooling, which not only can obtain satisfactory strength, but also can significantly improve the toughness (AKV value) and reduce The tendency of the member to crack. After normalized treatment of some low-alloy hot-rolled steel sheets, low-alloy steel forgings and castings, the comprehensive mechanical properties of the materials can be greatly improved, and the cutting performance is also improved.

Normalizing has the following purposes and uses:

1. For the sub-eutectic steel, normalizing is used to eliminate the superheated coarse-grained structure and Wei's structure of the cast, forged and welded parts, the banded structure in the rolled material; refine the grain; and can be used as pre-heat treatment before quenching .

2. For hypereutectoid steel, normalizing can eliminate the reticulated secondary cementite and refine the pearlite, which not only improves the mechanical properties, but also facilitates the subsequent spheroidizing annealing.

3. For low carbon deep-drawn thin steel sheets, normalizing can eliminate free cementite at the grain boundary to improve its deep drawing performance.

4. For low-carbon steel and low-carbon low-alloy, normalized, more fine-grained pearlite structure can be obtained, so that the hardness is increased to HB140-190, avoiding the "sticking knife" phenomenon during cutting and improving the machinability. . For medium carbon steel, it is more economical and convenient to use normalizing fire in the case where both normalizing and annealing can be used.

5. For ordinary medium carbon structural steel, in the case where the mechanical properties are not high, normalizing can be used instead of quenching and high temperature tempering. It is not easy to operate, and the structure and size of the steel are stable.

6, high temperature normalizing (Ac3 above 150 ~ 200 ° C) due to high diffusion rate at high temperatures, can reduce the composition analysis of castings and forgings, high temperature normalized after the coarse grains can pass the second lower temperature positive The fire is refined.

7. For some low and medium carbon alloy steels used in steam turbines and boilers, normalizing to obtain the structure of the back body, and then tempering at high temperature, it has good creep resistance at 400~550 °C. .

8. In addition to steel and steel, normalizing is also widely used in the heat treatment of ductile iron to obtain a pearlite matrix and improve the strength of ductile iron.

Since normalizing is characterized by air cooling, ambient air temperature, stacking mode, airflow, and workpiece size all have an impact on the organization and performance after normalizing. Normalizing tissue can also be used as a classification method for alloy steel. Usually, after the sample is heated to 900 ° C according to a diameter of 25 mm, the obtained structure is air-cooled into pearlitic steel, bainitic steel, martensitic steel and austenitic steel.

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