Key Differences Between Normalizing and Annealing
- Cooling Rate
Compared with annealing, normalizing has a faster cooling rate, resulting in a finer pearlite structure and higher strength and hardness.
2.Purpose
For low and medium carbon hypoeutectoid steels, normalizing and annealing serve the same purpose: both are intended
to improve machinability.
However, for hypereutectoid steels, a normalizing process should be performed before spheroidizing annealing. This
step eliminates the network-like secondary cementite, ensuring that all cementite is spheroidized during the subsequent
spheroidizing annealing.
3.Selection of Normalizing vs. Annealing
1） During normalizing, there is no need to cool the workpiece along with the furnace (as required for annealing). This
shortens the furnace occupancy time and improves production efficiency, so normalizing is generally used instead of
annealing whenever possible in production.
2）For low-carbon steels with a carbon content below 0.25%, normalizing results in moderate hardness—this makes
machining easier compared to annealing. Therefore, normalizing is typically adopted to prepare for machining.
3）For medium-carbon steels with a carbon content of 0.25–0.5%, normalizing can also meet the requirements for
machining. Additionally, for light-load parts made of such steels, normalizing can also be used as the final heat
treatment.
4）Generally, annealing is often adopted for alloy steel billets. If normalizing is used instead, the faster cooling rate will
result in higher hardness after normalizing, which is unfavorable for machining.
Processing Route for General Mechanical Parts
Blank parts formed by casting or forging undergo preparatory heat treatment first, followed by mechanical machining processes such as turning and milling, and finally final heat treatment to complete the processing of mechanical parts.
Annealing and normalizing are mainly used as preparatory heat treatments for steel. They eliminate and improve certain microstructural defects and internal stresses caused by the previous process, laying the foundation for subsequent machining and heat treatment in terms of structure and properties. Only when the required properties of the workpiece (such as strength and hardness) are not high, they are used as the final heat treatment.
Your message must be between 20-3,000 characters!