Why should slewing bearings be annealed? Annealing purpose and process type

Why should slewing bearings be annealed? In fact, slewing bearing slewing bearing annealing is a process of bearing heat treatment. Generally, the bearing metal is heated to a certain temperature and maintained for a period of time, and then the metal is cooled at a suitable speed. This method improves the toughness of bearing steel. , Reduce the bearing hardness and residual stress to reduce the probability of deformation and cracks, and enhance the stability of the bearing material.
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Why should slewing bearings be annealed?

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The purpose of slewing bearing annealing may be for three reasons:
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1. The annealing process can reduce the hardness of the bearing steel, improve the plasticity, and facilitate the later cutting and deformation processing.
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2. Annealing can refine the grains of the bearing material, eliminate the structural defects caused by the casting, forging and welding of the bearing, uniform the structure and composition of the steel, and improve the performance of the steel to prepare for the later heat treatment.
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3. The annealing process can eliminate the internal stress in the steel and prevent or reduce the possibility of deformation and cracking of the bearing. In one case, the annealing process is not only for the annealing of metallic materials but also for non-metallic materials. After understanding why slewing bearings should be annealed, the following editor will introduce the types of annealing processes for slewing bearings. In fact, there are many types of annealing processes, and the processes applicable to different steel structures are also different.

Type of annealing process for slewing bearing

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1. Recrystallization annealing

Recrystallization annealing, also called full annealing, is an annealing process in which the iron-carbon alloy is austenitized and then slowly cooled or stopped in a near-equilibrium state. The heating temperature of carbon steel is generally Ac3+ (30~50℃); alloy steel is Ac3+(500~70℃); the holding time depends on the type of steel, the size of the workpiece, the amount of furnace installed, the selected equipment model, etc. factors are determined. In order to ensure that the supercooled austenite undergoes pearlite transformation, the cooling of the recrystallization annealing must be slow, and the furnace is cooled to about 500 ℃ and air-cooled.

This annealing process is mainly used for hypoeutectoid steel, generally medium carbon steel and low and medium carbon alloy structural steel forgings, castings and hot-rolled profiles, and sometimes for their welded components; it is not suitable for hypereutectoid steel, Because the recrystallization annealing of hypereutectoid steel needs to be heated to above Acm, during slow cooling, cementite precipitates along the austenite grain boundaries and is distributed in a network, resulting in increased brittleness of the material, leaving hidden dangers for heat treatment.

2. Uniform annealing

Uniform annealing, also known as diffusion annealing, is to reduce the segregation of the chemical composition of the metal casting or forging billet and the inhomogeneity of the structure. It is heated to a high temperature, kept for a long time, and then slowly cooled to homogenize the chemical composition and structure. Purpose of the annealing process. The heating temperature of the homogenization annealing is generally Ac3+ (150-200 ℃), that is, 1050-1150 ℃, and the holding time is generally 10-15h, in order to ensure that the diffusion is fully carried out, and the purpose of eliminating or reducing the uneven composition or structure is large. Due to the high heating temperature, long time and coarse grains of diffusion annealing, recrystallization annealing or normalizing should be performed after diffusion annealing to re-refine the structure.

3. Incomplete annealing

Incomplete annealing is an annealing process in which the iron-carbon alloy is heated to a temperature between Ac1 and Ac3 to achieve incomplete austenitization, followed by slow cooling. Incomplete annealing is mainly suitable for medium and high carbon steel and low alloy steel forgings and rolling parts. Its purpose is to refine the structure and reduce the hardness.

4. Stress relief annealing

One of the key reasons why slewing bearings should be annealed is the annealing process to eliminate residual stress caused by plastic deformation processing, welding, etc. and existing in the casting. There is internal stress inside the workpiece after forging, casting, welding and cutting. If it is not eliminated in time, the workpiece will be deformed during processing and use, affecting the accuracy of the workpiece. It is very important to use stress relief annealing to eliminate the internal stress generated during processing.

5. Isothermal annealing

Isothermal annealing is to heat the steel or blank to a certain temperature and hold it for a period of time, then quickly cool it to a certain temperature in the pearlite temperature range and keep it isothermally, so that the austenite is transformed into a pearlite-type structure, and then in the air. Medium cooling annealing process.

This process is suitable for medium carbon alloy steel and low alloy steel, and its purpose is to refine the structure and reduce the hardness. The heating temperature of hypoeutectoid steel is Ac3+(30～50)℃, and the heating temperature of hypereutectoid steel is Ac3+(20～40)℃, keep it for a certain period of time, and carry out isothermal transformation with furnace cooling to slightly lower than Ar3 temperature, and then air-cooled. . The isothermal annealing structure and hardness are more uniform than the crystallization annealing.

6. Spheroidizing annealing

Spheroidizing annealing is an annealing process to spheroidize carbides in steel. It is heated to 20-30°C above Ac1, kept for a period of time, and then slowly cooled to obtain the structure of spherical or granular carbides uniformly distributed on the ferrite matrix.

Spheroidizing annealing is mainly used for hypereutectoid steel and alloy tool steel (such as cutting tools, measuring tools, molds and bearings, etc. all steel grades). Its purpose is mainly to reduce hardness, improve machinability, and prepare for subsequent quenching. There are many spheroidizing annealing process methods, and the two commonly used processes are ordinary spheroidizing annealing and isothermal spheroidizing annealing. Compared with ordinary annealing methods, spheroidizing annealing can not only shorten the cycle, but also make the spheroidized structure uniform, and can strictly control the hardness after annealing.

7. Recrystallization annealing

Recrystallization annealing is also called intermediate annealing. It is a heat treatment process in which the metal after cold deformation is heated to above the recrystallization temperature and maintained for an appropriate time to recrystallize the deformed grains into uniform equiaxed grains to eliminate deformation strengthening and residual stress.

The above is the introduction of the reasons why the slewing bearing needs to be annealed. It also includes the types of annealing processes and their respective characteristics and process introductions. I hope to help you have a clearer understanding of the annealing process. In addition, our company produces slewing bearings, slewing bearings, and slewing drives of various types and precisions. If you have any needs, please feel free to inquire.