Bearing steel is the steel used to make balls, rollers, and bearing rings. Bearing in the work is under great pressure and friction, it requires high and uniform hardness and wear resistance of bearing steel, as well as high elastic limit. The uniformity of chemical composition, the content and distribution of non-metallic inclusions, and the distribution of carbides in bearing steel are very strict. Bearing steel is also called High Carbon Carbon Carbon Carbon Steel, containing about 1% WC and 0.5%-1.65% WCR.

An annealing process in which the carbide in a steel is spheroidized. SPHEROIDIZING or softening annealing. The aim is to reduce the hardness, homogenize the structure, improve the machinability and prepare for quenching. Mainly applicable to carbon tool steel, alloy spring steel, rolling bearing steel and alloy tool steel eutectoid steel and hypereutectoid steel with carbon content greater than 0.77% .

In the conventional annealing process, high purity nitrogen is usually used to protect the steel. The purity of nitrogen is 99.999% and the dew point is-65 °C. High Purity Nitrogen in conventional production, there are two ways:

First, liquid nitrogen. Liquid nitrogen is obtained by fractional distillation of air. The air is first purified and then liquefied under pressure and cooling. The components in the air are separated according to their different boiling points. The purity of liquid nitrogen is about 99.99% .

Secondly, the hydrogenation gas is purified after the preparation of nitrogen by PSA. The general purity (99%-99.9%) of ordinary nitrogen is produced by PSA (pressure swing adsorption) , and the oxygen in ordinary nitrogen is reacted with hydrogen to form water, which is then absorbed, the purity of pure nitrogen is 99.9995% , which is higher than that of liquid nitrogen.

The nitrogen gas in the above way enters the spheroidizing annealing furnace for annealing protection.