Differences between annealing and normalizing of seamless steel pipes

The main difference between annealing and normalizing:

1. The cooling rate of normalizing is slightly faster than that of annealing, and the degree of supercooling is larger
2. The structure obtained after normalizing is relatively fine, and the strength and hardness are higher than that of annealing.

The choice of annealing and normalizing:

1. For low carbon seamless steel pipes with carbon content less than 0.25%, normalizing is usually used instead of annealing. Because the faster cooling rate can prevent the low carbon seamless steel pipe from precipitation of free tertiary cementite along the grain boundary, thereby improving the cold deformation performance of the stamping parts; normalizing can improve the hardness of the steel and the cutting performance of the low carbon seamless steel pipe. ; When there is no other heat treatment process, normalizing can refine grains and improve the strength of low carbon seamless steel pipes.

2. The medium carbon cold-drawn seamless steel pipe with carbon content between 0.25% and 0.5% can also be normalized instead of annealing. Although the medium-carbon steel cold-drawn seamless steel pipe with carbon content close to the upper limit has high hardness after normalizing, it is still It can be cut, and the normalizing cost is low and the productivity is high.

3. Cold-drawn seamless steel pipes with a carbon content between 0.5 and 0.75%, due to the high carbon content, the hardness after normalizing is significantly higher than that of annealing, and it is difficult to perform cutting processing, so complete annealing is generally used to reduce Hardness and improved machinability.

4. High carbon or tool steel with carbon content > 0.75% of cold drawn seamless steel pipe generally adopts spheroidizing annealing as a preliminary heat treatment. If there is a meshed secondary cementite, it should be normalized first. Annealing is a heat treatment process in which the cold drawn seamless steel pipe is heated to an appropriate temperature, kept for a certain period of time, and then slowly cooled. Slow cooling is the main feature of annealing. Annealed cold-drawn seamless steel pipes are generally cooled to below 550 ℃ with the furnace and air-cooled. Annealing is a widely used heat treatment. In the manufacturing process of tools, molds or mechanical parts, etc., it is often arranged as a preliminary heat treatment after casting, forging and welding, and before cutting (rough) processing to eliminate some of the problems caused by the previous process. defects, and prepare for subsequent operations.

Annealing Purpose:

①Improve or eliminate various structural defects and residual stress caused by steel in the process of casting, forging, rolling and welding, and prevent deformation and cracking of the workpiece;
② soften the workpiece for cutting;
③ Refine the grain and improve the structure to improve the mechanical properties of the workpiece;
④ Prepare the organization for final heat treatment (quenching, tempering).