Heat treatment normalizing process

The normalizing process is a heat treatment process in which the steel is heated to 30-50°C above Ac3 (or Acm), and then cooled in still air after a suitable heat preservation time. The normalizing that heats the steel to 100-150 ℃ above Ac3 is called high-temperature normalizing.

The main purpose of normalizing for medium and low carbon steel castings and forgings is to refine the structure. Compared with annealing, the pearlite lamellae and ferrite grains after normalizing are finer, so the strength and hardness are higher.

Due to the low hardness of low carbon steel after annealing, the phenomenon of sticking to the knife occurs during cutting, and the cutting performance is poor. By increasing the hardness by normalizing, the cutting performance can be improved. Some medium carbon structural steel parts can be replaced by normalizing and tempering to simplify heat treatment. craft.

The hypereutectoid steel is normalized and heated by a knife above Acm, so that the cementite that was originally mesh is completely dissolved into the austenite, and then cooled at a faster rate to inhibit the precipitation of cementite at the austenite grain boundary, thereby It can eliminate network carbide and improve the structure of hypereutectoid steel.

Welded parts that require weld strength are normalized to improve the weld structure and ensure weld strength.

During the heat treatment process, the repaired parts must be normalized, and the structural parts that require mechanical performance indicators must be normalized and then quenched and tempered to meet the mechanical performance requirements. After normalizing, medium and high alloy steel and large forgings must be tempered at high temperature to eliminate the internal stress generated during normalizing.

Some alloy steels undergo partial martensitic transformation during forging to form hard structures. In order to eliminate this kind of bad organization, when normalizing is adopted, the normalizing temperature is about 20℃ higher than normal normalizing temperature by heating and heat preservation.

The normalizing process is relatively simple, which is conducive to normalizing with forging waste heat, which can save energy and shorten the production cycle.

Improper normalizing process and operation also produce tissue defects. Similar to annealing, the remedy method is basically the same.