Annealing: Give metal a soothing SPA,Normalizing: Rapid cooling makes the metal full of vitality.

In the "magical world" of metal material processing and heat treatment, normalizing, annealing, quenching and tempering are like four magicians with different personalities but super powers. They can give metal materials completely different "super powers" by waving their magic wands. However, for those who have just entered this field or have only a superficial understanding of heat treatment processes, these four magicians are often difficult to distinguish. Don't worry, today we will unveil their mystery and make them clear!

Annealing: Give metal a soothing SPA

Annealing is simply a "gentle masseur" in the field of metal material heat treatment, giving metal a super soothing SPA. Its main task is to "relax" the metal, reduce the hardness, make cutting processing easy and enjoyable, and eliminate all the annoying internal stresses to prepare for the subsequent "trouble".

Imagine that the metal is like being severely "ravaged" during forging, the internal structure becomes a mess, the residual stress is as large as a blown-up balloon, and the hardness is frighteningly high. If it is processed directly at this time, the tool must be "crying in the toilet". At this time, annealing comes on the scene! It heats the metal to the appropriate temperature, allowing the atoms inside to have enough time to "wander" and re-arrange. Then it slowly cools down, just like loosening a tight spring a little bit, allowing the metal to return to a comfortable and stable state.

For example, we want to make a large gear blank. 

After forging, the hardness is high and the stress is large, and direct processing is impossible. At this time, annealing the blank is like giving this "irritable brother" a full body massage, making it docile, reducing the hardness, and eliminating the stress, and subsequent processing is much easier. The annealing temperature and cooling method of different metal materials may be different, but the goal is the same, that is, to make the metal have a more uniform structure and more suitable performance, just like arranging different relaxation methods for people with different personalities.

Normalizing: Rapid cooling makes the metal full of vitality

Normalizing and annealing are like a pair of "twin brothers", they look a bit similar, but their personalities are very different. Normalizing is also to heat the metal above the critical temperature first, let it "warm up" and keep it warm for a period of time, but the key difference lies in the cooling method. Normalizing uses the method of letting the metal cool naturally in the air, and the cooling speed is much faster than annealing, just like giving the metal a "sprint training". 

This fast cooling speed makes the metal structure after normalizing more dense, and the strength and hardness are higher than the annealed metal, and it also retains good toughness. Normalizing is often used as a "preparatory warm-up coach" for medium and low carbon steel to improve the cutting performance of the material and make organizational preparations for the subsequent "official competition"-the final heat treatment process.

Just like we want to build a house, steel is the building material. 

After normalizing, the steel is like a well-trained athlete, with improved uniformity of organization and fewer minor internal defects, laying a solid foundation for subsequent processing and meeting the mechanical performance requirements of the house. Moreover, the normalizing process is simple, low-cost, and has a short production cycle, just like an efficient and affordable fitness coach, which is very popular in actual production!

Quenching: Extreme cooling creates a "steel tough guy"

Quenching is definitely the "crazy racer" in the heat treatment process. Its style is "fast, accurate, and ruthless"! It can make metal materials instantly have extremely high hardness and strength, just like turning an ordinary person into a "steel tough guy". 

The quenching process is as follows:

First heat the metal above the critical temperature, let it fully "heat up", keep it warm for a period of time, and let the internal organization of the material become austenite, which is a "full of energy form". Then quickly throw it into a cooling medium, such as water, oil or other special coolants, just like a racer's foot on the accelerator to the bottom, so that it can cool quickly.

This rapid cooling has caused a radical change in the internal structure of the metal, with austenite turning into hard and brittle structures such as martensite. The appearance of martensite has greatly improved the hardness and strength of metal materials, as if it were wearing an indestructible armor. However, although this armor is hard, it also makes the metal very "fragile" and has poor toughness. There is also huge internal stress hidden inside, just like a tough guy with a bad temper, which may "explode" or even "crack" if you are not careful.

For example, when we make tools such as knives and molds that require extremely high hardness and strength, quenching is an indispensable link. Only after quenching can a sharp knife have enough hardness to cut various materials like a superhero. But the quenched tool is like a "beast" that has not been completely tamed. It still needs to be treated later to improve its toughness, otherwise it will easily "break down" during use.

Tempering: The perfect "peacemaker" with both hardness and softness

Tempering is a "peacemaker" who is specifically used to clean up the "mess" of quenching. Although the hardness and strength of quenched metal materials are frighteningly high, they are brittle and have high internal stress. Using them directly is like carrying a "time bomb", which is too risky. The task of tempering is to reheat the quenched metal to a temperature below the critical temperature, keep it warm for a period of time, and then slowly cool it down.

Through tempering treatment, the hard and brittle structures such as martensite formed by quenching will decompose and transform like magic, and the internal stress will be released. The toughness of the material has been significantly improved, while the hardness and strength can be maintained at a high level, achieving a perfect balance of rigidity and flexibility. Different tempering temperatures are like different "mediation plans" that can obtain different material properties.

Low-temperature tempering is like a "fine maintenance" for "tough guys" such as tools and measuring tools, mainly to maintain their high hardness and wear resistance; medium-temperature tempering is like a "special training" for "elastic guys" such as springs, which can maintain a certain elasticity while improving toughness; high-temperature tempering is like a "comprehensive physical examination and conditioning" for important structural parts, which can obtain better comprehensive mechanical properties, so that the material has both a certain strength and good toughness.

Take the crankshaft of a car engine as an example. 

After quenching, the crankshaft becomes very strong, but its toughness is insufficient, just like a reckless man with only brute force. Through high-temperature tempering treatment, the crankshaft is like being "trained" to be a master of both civil and military affairs. While maintaining high strength, its toughness is also improved, and it can better withstand various complex loads during the operation of the engine, ensuring the reliable operation of the "big heart" of the engine.

Normalizing, annealing, quenching and tempering, the four heat treatment process magicians, each have their own skills and application scenarios. They cooperate with each other, like a super powerful team, and together constitute a complete system for the performance regulation of metal materials. In actual production, Sinostar MACH has to reasonably select and combine these processes according to the types, uses and performance requirements of metal materials to give full play to the potential of metal materials and produce high-quality products that meet various needs. Now, do you have a clear understanding of them and will never confuse them again?