Full name rolling bearing steel bearing steel with high compressive strength and fatigue limit, high hardness, high wear resistance and a certain toughness, good hardenability, sulfur and phosphorus very strict control, it is a high quality steel. Most of them are imported from Japan bearing steel material used, is also part of the use of a consistent development of domestic and Japanese steel components, similar to the process of bearing steel, steel is SUJ2.

SUJ2 bearing steel production methods: vacuum degassed steel smelting mode, continuous cast steel bar (or die casting), forging forming more than 6, after hot rolling steel ball annealing, further cold drawing; and various techniques available in accordance with the conditions (eg: non-metallic inclusions, decarburization depth, dimensional tolerances, shape, appearance, hardness, structure and other indicators).

Bearing steel bars after turning machining after forming, heat treatment step to enter our front channel.

Before entering the heat treatment step, let us first look at what is annealing? What is hardening? What is tempering? Why should different process?

1, annealing: annealing is used in the production of preliminary heat treatment process, the steel is heated to a suitable temperature, holding a certain time, and then slowly cooled, to get close to equilibrium tissue heat treatment process. Its purpose is to eliminate or reduce casting, forging and welding parts stress and chemical composition of tissue inhomogeneity; can improve and adjust the mechanical properties of the steel and process performance for our turning machining processes make the organization ready (simply say : reduce the hardness, ease of processing, in preparation for the quenching). And in fact we use steel in the steel mills on a "ball annealing" process (heated to 750-770 degrees, holding a certain time, slowly cooled to 600 degrees below air cooling). Annealing process a lot of types of steel, have full annealing, incomplete annealing, isothermal annealing, spheroidizing and diffusion annealing; there recrystallization annealing, stress relief annealing and dehydroepiandrosterone; there will not be introduced.

2, quenching and tempering: quenching and tempering bearing steel heat treatment process is a very important, very broad application processes. Quenching can significantly improve the strength and hardness of steel. If matched with different tempering temperature, to eliminate (or mitigate) quenching stress, but also get the strength, hardness and toughness with, meet different requirements. Therefore, quenching and tempering are inseparable two heat treatment process.

(1) quenching the steel is heated to above the critical point, after holding greater than the critical cooling rate (Vc) was cooled to obtain martensitic or bainitic heat treatment process.

(2) is hardened and tempered steel is heated to a certain temperature for A1 points below a certain time, in an appropriate manner to cool to room temperature heat treatment process. It was immediately before the next hardening heat treatment process, and determines the microstructure and properties in the use of state of the relationship between the life of the workpiece, it is a key step.

We learned some basic knowledge of aspects of the heat treatment process after rolling ball bearings to see if we heat treatment process:

Vacuum hardening: Its greatest feature is no oxidation, no distortion, no cracking, for my company's precision bearings, beginning on the use of vacuum heat treatment process. Whether Japan and domestic vacuum furnace vacuum furnace are cold, heat two vacuum chambers (degree of vacuum thermal chamber controlled 2.0Pa less, 9.3Pa less cold room), the heating process of bearing steel process according to a predetermined curve (temperature and time) were stepwise heating, the maximum rose to 840 ± 10 ℃; however, by a cooling medium or gas-cooled oil cooler, oil temperature control at 60-80 ℃, the maximum does not exceed 100-120 ℃.

Oil Tempering: According to the characteristics of the bearing rings, we have adopted a low oil tempering, temperature controlled at 180 ± 10 ℃. Internal stress and brittleness, dimensional stability and its main aim to reduce after quenching, can maintain high hardness and high wear resistance under the premise, in order to avoid cracking or premature failure when used. Hardness HRC: 60-64.

Similarly, for stainless steel bearing products, also must go through this heat treatment process, of course quench curve (temperature and time) is different, higher temperature (1040 ± 10 ℃), time is relatively long. And within half an hour after quenching but also for cryogenic treatment (in front of which it has already been discussed), whose main role is to reduce the residual austenite organization, organizational stability, improve the stability of the ferrule precision. However, when cryogenic treatment should control the austenite content can not be too small, because a certain amount of residual austenite help to improve bearing life.