The difference between annealing, normalizing, tempering, and quenching of seamless steel tubes

1. Annealing

Heat the steel to a certain temperature and keep it warm at this temperature, and then slowly cool it to room temperature.

There are several kinds of annealing, spheroidizing annealing, stress annealing and so on.

A. steel is heated to a predetermined temperature for a period of time, and then slowly cooled with the furnace. It is called complete annealing. The purpose is to reduce the hardness of steel and eliminate the uneven microstructure and internal stress in steel.

B. heating the steel to 750 degrees, holding it for a period of time, slowly cooling to 500 degrees, and finally cooling it in the air, this is called spheroidizing annealing. The purpose is to reduce the hardness and improve the cutting performance of steel, mainly for high carbon steel.

C. stress relieving annealing is also called low temperature annealing, heating the steel to 500~600 degrees, holding it for a period of time, cooling slowly with the furnace below 300 degrees, and then cooling at room temperature. During the annealing process, the microstructure does not change, mainly eliminating the internal stress of the metal.

2. Normalizing

After heating the steel to 30-50 degrees centigrade above the critical temperature, the heat treatment process of cooling in the static air is called normalizing after the heat preservation is suitable for a proper time.

The main purpose of the normalizing is to refine the tissue, improve the performance of the steel, and obtain an organization near the equilibrium state.

The main difference between normalizing and annealing is that the cooling rate of normalizing is slightly faster, so the production cycle of the positive heat treatment is short. Therefore, when annealing and normalizing can meet the requirements of part performance, normalizing as much as possible.

3. Quenching

The steel is heated to a temperature above the critical point (No. 45 steel quenching temperature is 840-860 DEG C, quenching temperature of carbon tool steel is 760~780 DEG C), keep a certain time, and then at a proper speed in the water (oil) cooling for heat treatment process engineering martensite or bainite is called quenching.

The main difference between quenching and annealing and normalizing is the rapid cooling rate, in order to obtain martensitic structure. Martensitic structure is an unbalanced structure of steel after quenching. Its hardness is high, but its plasticity and toughness are poor. The hardness of martensite increases with the increase of the carbon content of the steel.

4. Tempering

When the steel is hardened, it is reheated to a certain temperature below the critical temperature, heat preservation for a certain time, and then cooling to room temperature, which is called tempering.

After quenching, the steel parts can not be used directly. They must be used after tempering. Because of the high hardness and brittleness of the hardened steel, brittle fracture often occurs in direct use. Tempering can eliminate or reduce internal stress, reduce brittleness and improve toughness. On the other hand, it can adjust the mechanical properties of hardened steel and achieve the performance of steel. According to the different tempering temperature, tempering can be divided into three kinds: low temperature tempering, middle temperature tempering and high temperature tempering.

A. Low temperature tempering 150 ~ 250. reduce internal stress, brittleness, high hardness and wear resistance after quenching.

B. Medium temperature tempering 350~500; improve the elasticity, strength.

C. Tempering 500~650 at high temperature; tempering at higher than 500 degrees centigrade quenched steel is called high temperature tempering. After high temperature quenching, quenched steel has good comprehensive mechanical properties (not only a certain strength, hardness, but also a certain plasticity and toughness). So ordinary medium carbon steel and medium carbon alloy steel are often treated with tempering after quenching. Shaft parts are most used.

Quenching + high temperature tempering is called quenching and tempering treatment.