What are the purposes and methods of annealing?

Quenching is a method of heat treatment of this metal material. It means that the metal material is slowly heated to the necessary temperature, maintained for a sufficient time, and then cooled by water at a suitable rate. The aim is to reduce strength and improve drilling process performance; eliminate internal stress, stabilize specifications, reduce deformation and crack tendency; optimize crystal, regulate mechanism, eliminate shortcomings of mechanism. To be precise, quenching is the thermal treatment of raw materials, including metal composite materials and polymer materials. Moreover, the quenching purpose of the new material is different from that of the traditional metal material.

Quenching purpose:

(1) Reducing strength and improving drilling performance.

(2) Remove internal stress, smooth specification, reduce deformation and crack tendency.

(3) Optimize the crystal, adjust the mechanism and remove the shortcomings of the mechanism.

(4) Equilibrium the structure and composition of raw materials, improve the characteristics of raw materials, or prepare the mechanism in advance for subsequent conditioning treatment.

Annealing process is widely used in production and manufacturing. According to the requirements of steel parts, quenching purposes are different. There are many kinds of quenching process standards, such as thorough quenching, spheroidizing annealing, and de-stress annealing.

If the isothermal temperature is too low or too high, the tensile strength will be higher after quenching and tempering treatment; if the isothermal temperature is too high, the isothermal maintenance time will be increased as far as possible. The purpose of isothermal annealing of steel is consistent with recrystallization and tempering treatment. However, the process flow and the necessary industrial equipment are very complicated for the manufacturers of medium-sized and large-scale pull-back equipment. Therefore, the key point is generally to apply low-temperature martensite to the carbon steel whose change in the metallographic transformation temperature path is equivalent to slow change. If the recrystallization heat treatment process is adopted, it will be uneconomical and social development if the recrystallization heat treatment process is used as far as possible for more than ten hours; if isothermal annealing is used, the production cycle can be greatly shortened, and the structure and characteristics of all cast iron castings can be more symmetrical. Isothermal annealing can also be reused in different stages of hot working of steel. For example, when air-cooled quenched rigid carbon steel is cooled from high temperature to indoor temperature, when the careful part changes to austenite, cracks will appear on the surface layer which has caused austenite transformation; if the hot ingot or billet of such steel is put into the isothermal furnace around 800 C in the whole process of cooling circulating water, the isothermal temperature will be maintained until the austenite transformation occurs. When the phase transformation of metallographic structure is carried out and air cooling is announced, the cracks can be avoided. 1. Recrystallization Heat Treatment-Complete Heat Treatment

It is applied to aluminium alloy profiles caused by solid disk phase transformation (recrystallization) during equilibrium heating and cooling water. The annealing temperature is a temperature above or below the phase transformation temperature of each aluminium alloy profile. Warming and cooling water are slow. Aluminum alloy profiles are recrystallized several times in the process of heating and cooling water, so it is called recrystallization heat treatment, which is often referred to as heat treatment.

This heat treatment method is equivalent to being widely used in steel. The recrystallization annealing process of steel is that the temperature rises slowly up to 50-65 C above and below Ac3 (hypoeutectoid steel) or Ac1 (eutectoid steel or hypereutectoid steel), keeps appropriate time, and then the cooling water goes out slowly. According to the transformation of metallographic structure (or pre-eutectoid metallographic structure or cementite) into austenite (first phase transformation recrystallization) and second phase transformation recrystallization (second phase transformation recrystallization) caused by cooling water, the metallographic structure with fine crystallization, thick lamella and uniform structure (or so on) is formed. Preeutectoid metallographic structure or cementite. The annealing temperature above and below Ac3 (hypoeutectoid steel) causes complete recrystallization of steel, which is called complete heat treatment. The annealing temperature between Ac1 and Ac3 (hypoeutectoid steel) or between Ac1 and Acm (hypereutectoid steel), which causes partial recrystallization of steel, is called incomplete heat treatment. Both of them are mainly used in hypoeutectoid steel castings, forgings and weldments to eliminate structural defects (such as widmanstatten structure, ring structure, etc.) and make the structure smaller and more uniform, so as to improve the plastic deformation and plasticity of iron castings. They are mainly used for forging and rolling of medium and high carbon steel and high alloy steel. If the cooling water speed after forging and rolling is high, the metallographic structure is fine and the compressive strength is high. If the forging and rolling temperature is too low, the welding stress in the cast iron is also large. At this time, incomplete heat treatment can be used instead of complete heat treatment, resulting in recrystallization of metallographic structure, crystallization becomes smaller, together with reducing compressive strength, eliminating welding stress and improving drillability. In addition, the spheroidizing annealing of hypereutectoid steel with the annealing temperature between Ac1 and Acm is not a complete heat treatment.