Normalizing is a heat treatment that improves the toughness of steel. After heating the steel components to a temperature of 30-50 ℃ above the Ac3 temperature, hold them for a period of time and air cool them out of the furnace. The main characteristic is that the cooling rate is faster than annealing but lower than quenching. During normalizing, the crystalline grains of the steel can be refined in a slightly faster cooling process, which not only achieves satisfactory strength, but also significantly improves toughness (AKV value) and reduces the tendency of components to crack After normalizing, the comprehensive mechanical properties of some low alloy hot rolled steel plates, low alloy steel forgings, and castings can be greatly improved, and the cutting performance can also be improved.
Normalizing is mainly used for steel workpieces. Normalizing and annealing of general steel are similar, but the cooling rate is slightly higher and the microstructure is finer. Some steels with a very low critical cooling rate can transform austenite into martensite by cooling in air. This treatment is not normalized and is called air cooling quenching. On the contrary, some large cross-section workpieces made of steel with a higher critical cooling rate cannot obtain martensite even after quenching in water, and the quenching effect is close to normalizing. The hardness of steel after normalizing is higher than that after annealing. When normalizing, it is not necessary to cool the workpiece in the furnace like annealing, which occupies a short furnace time and has high production efficiency. Therefore, in production, normalizing is generally used instead of annealing as much as possible. For low-carbon steel with a carbon content lower than 0.25%, the hardness achieved after normalizing is moderate and more convenient for cutting than annealing. Normalizing is generally used for cutting and work preparation. For medium carbon steel with a carbon content of 0.25-0.5%, normalizing can also meet the requirements of cutting processing. For lightweight parts made of this type of steel, normalizing can also be used as the final heat treatment. Normalizing high carbon tool steel and bearing steel is to eliminate network carbides in the structure and prepare the structure for periodization annealing.
The final heat treatment of ordinary structural parts, due to the better comprehensive mechanical properties of the workpiece after normalizing compared to the annealed state, can be used as the final heat treatment for some ordinary structural parts with low stress and performance requirements, to reduce processes, save energy, and improve production efficiency. In addition, for certain large or complex shaped parts, when there is a risk of cracking during quenching, normalizing can often replace quenching and tempering treatment as the final heat treatment.
Email: oiltools14@welongpost.com
Grace Ma
Post time: Oct-23-2023
