Forging of bearing steel

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 strict control on sulfur and phosphorus. It is a kind of high-grade and high-quality steel that can be used as cold tool steel. Specific gravity: 7.81

（1） Forging temperature of bearing steel

(1) Initial forging temperature: 1150 (1120), final satin temperature: 850 (800) degrees.

(2) The surface defects shall be removed before forging, and it shall be heated rapidly after preheating as far as possible.

(3) During warm processing, the blue brittle zone of 200~400 degrees should be avoided. During hot working, avoid entering high temperature brittle zone (greater than 1250). Try to avoid entering the hot brittle zone (800~950 degrees).

（2） Post forging heat treatment

(1) After forging — pre heat treatment (spheroidizing annealing) — final heat treatment (quenching+low temperature tempering)

(2) Spheroidizing annealing purpose: reduce hardness, facilitate processing, and prepare for quenching.

Spheroidizing annealing process: heating to 750~770 ℃, holding for a certain period of time, and air cooling after slowly cooling to below 600 ℃.

(3) Quenching+low temperature tempering and hardness table of various bearing steels

Steel grade quenching temperature and low temperature tempering hardness of quenching medium HRC

GCr6 800~820 Water or oil 150~170 62~64

GCr9 800~830 Water or oil 150~170 62~64

GCr9SiMn 810~820 Water or oil 150~160 62~64

GCr15 820~846 oil 150~160 62~64

GCr15SiMn 800~840 oil 150~170 62~64

（3） Quenching and quenching medium

(1) Quenching color (experience): white is the hardest and brittle, yellow is hard and tough, and blue is soft and tough.

(2) Quenching medium

A. Water: Generally, the temperature shall not exceed 40 ℃, and there shall be no impurities such as oil and soap.

B. Aqueous solution of salt and alkali: add 5~10% salt or alkali to the water.

The cooling speed of salt solution is ten times that of water, and the hardness is high and uniform, but the organizational stress is large, which has a certain corrosion effect. The temperature is less than 60 degrees.

Alkali solution (caustic soda solution) is highly corrosive and has a small scope of application.

C. oil: including engine oil, spindle oil, transformer oil, diesel oil, etc. It can reduce deformation and cracking. Carbon steel is not applicable. Oil temperature: 60~80 ℃, and the maximum temperature shall not exceed 100~120 ℃.

（4） Tempering temperature

The bearing steel is tempered at low temperature. Temperature: 150~250 ℃. It can reduce internal stress and brittleness on the premise of maintaining high hardness and high wear resistance, so as to avoid cracking or premature damage during use. Hardness HRC: 58~64.