Vacuum heat treatment process for bearing steel

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The full name of bearing steel is rolling bearing steel. It has high compressive strength and fatigue limit, high hardness, high wear resistance and certain toughness, good hardenability, and extremely strict control of sulfur and phosphorus. It is a high-quality steel. Most of the bearing steels used by our company are materials imported from Japan, and some of them are made of domestically developed bearing steels with the same composition and similar processing technology as Japanese steels, and the steel grade is SUJ2.

SUJ2 bearing steel production method: the steel plant adopts vacuum degassing smelting method, continuously casting into steel rods (or die casting), forging forming ratio of 6 or more, the steel is hot-rolled and then spheroidized and annealed, and then cold-drawn; then , Supply in accordance with various technical conditions specified (such as: non-metallic inclusions, depth of decarburization layer, dimensional tolerance, shape, appearance, hardness, organization and other indicators).

After the bearing steel bar is shaped once by turning, it enters the previous heat treatment process of our company. SIMUWU vacuum heat treatment furnace bearing steel hardening.

Before entering the vacuum heat treatment process, let us first understand what annealing is? What is quenching? What is tempering? Why do various different processes need to be carried out?

1. Annealing: Annealing is a commonly used preliminary heat treatment process in production. It is to heat steel to an appropriate temperature, hold it for a certain period of time, and then slowly cool it to obtain a heat treatment process close to the equilibrium structure. Its purpose is to eliminate or reduce the structural inhomogeneity of the internal stress and chemical composition of the casting, forging and welding parts; it can improve and adjust the mechanical properties and process performance of the steel, and prepare the structure for our turning process (simply put : Reduce the hardness, facilitate processing, and prepare for quenching). The steel we use is actually “spheroidized annealing” in the steel plant (heated to 750-770 degrees, kept for a certain period of time, and slowly cooled to below 600 degrees and air-cooled). There are many types of annealing processes for steel, including complete annealing, incomplete annealing, isothermal annealing, spheroidizing annealing and diffusion annealing, etc.; there are also recrystallization annealing, stress relief and dehydrogenation annealing, etc.; they are not introduced here.

2. Quenching and tempering: The quenching and tempering of bearing steel is a very important and widely used process in the heat treatment process. Quenching can significantly improve the strength and hardness of steel. If it is matched with tempering at different temperatures, the internal stress of quenching can be eliminated (or reduced), and the strength, hardness and toughness can be matched to meet different requirements. Therefore, quenching and tempering are two inseparable heat treatment processes.

(1) Quenching is a heat treatment process in which steel is heated above the critical point, and then cooled at a rate greater than the critical cooling rate (Vc) after holding to obtain martensite or lower bainite structure.

(2) Tempering is a heat treatment process in which the quenched steel is heated to a temperature below the A1 point for a certain period of time, and then cooled to room temperature in an appropriate manner. It is the next heat treatment process immediately after quenching, and at the same time determines the structure and performance of the steel in use, and is related to the service life of the workpiece, so it is a key process.

Vacuum Heat Treatment Furnace