What is the difference between annealing and normalizing? Today we will explain the difference between the two in an easy-to-understand way.
Commonly used heat treatment methods all require the word "fire", which means heating, and the word before fire represents the purpose to be achieved. From the perspective of Chinese word structure, annealing should actually be called "fire retreat" and normalizing is called "fire normal".
Annealing
Annealing, that is, fire retreat, means that the material is "regressed" or "returned" to a certain state by heating. Annealing also means "heating and reorganization". The state to which it retreats depends on the temperature. Annealing at high temperatures is thorough, and annealing at low temperatures is just so-so. Therefore, there are many classifications of annealing, and from low to high temperatures, they are: stress relief annealing, recrystallization annealing, spheroidizing annealing, complete annealing and diffusion annealing (homogenization annealing).
We can use the human body's feelings as an analogy to explain these types of annealing, so it is easy to understand. First of all, we imagine the material to be heat treated as a person who has experienced all kinds of ravages and is physically and mentally exhausted.
Then stress relief annealing is like stretching your body when you are tired, which makes you feel more comfortable, but the cells of your body are still tired.
Recrystallization annealing is like you have a good sleep, and your body cells are finally stretched.
Spheroidizing annealing is to make adjustments, open up various veins and nodules (layered network carbides) in the body, and knead them.
Complete annealing requires recuperation, find a place with a good environment to relax your mind, abandon all pressure, and return to yourself.
But people may have some primary diseases (component segregation and tissue heterogeneity), and it is difficult to eliminate them by recuperation, so diffusion annealing is needed to completely eliminate the pathology.
But no matter what annealing, the cooling speed will not be very fast. The purpose is to eliminate tension and relax the body and mind so that you can take on the next work with a brand new body and mind. Back to our materials, it is to soften the metal, make it more suitable for cold processing and forming, and enhance the ductility and toughness of the metal.
Normalizing
Normalizing means "fire correction". The word "normal" can be understood as two meanings - normal and perfect. Normalization is to heat the metal material to make its structure normal and perfect.
Since it needs to be normalized, it means that the material is a bit "abnormal and imperfect" before normalization. The material before normalization has defects such as coarse grains, uncoordinated proportions, uneven composition and organization, various Widmanstatten structures, banded structures and network carbides, and high internal stress. Normalizing is to improve these conditions. The following figure is the material after normalization:
Seeing this, you may think that this looks no different from the material before annealing, and the role of heat treatment seems to be similar to annealing. In fact, the difference is quite large. From the difference in heat treatment, normalizing does not give you time to grow fat like annealing, it needs to control the body shape. From the ultimate goal, annealing is to make you softer and easier to handle to adapt to the next transformation. Normalizing allows you to improve your quality without reducing your ability to adapt to the next greater challenge. (文章来源：微信公众号- iMechanics机械)
