Forging of the 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 extremely strict control of sulfur and phosphorus. It is a type of high-grade high-quality steel. and can be used as cold-made mold steel. Proportion: 7.81

1 Forging temperature of the bearing steel （℃）

(1) Initial forging temperature: 1150℃ (1120) and final forging temperature: 850℃ (800℃).

(2) Remove surface defects before forging, try to preheat and then quickly heat.

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

2 Heat treatment after forging

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

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

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

(3) Various bearing steel quenching + low temperature tempering and hardness table

Steel grade  quenching temp. and quenching medium  low temp. tempering 　 hardness 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 does not exceed 40℃, and there should be no impurities such as oil and soap.

　　B Aqueous solution of salt and alkali: add 5-10% salt or alkali in water. 

　　 The cooling rate of the salt solution is ten times that of water, the hardness is high and uniform, but the structure stress is large, and there is a certain degree of corrosion. The temperature is less than 60 degrees. {HotTag}

　　Alkali solution (caustic sodium solution) is highly corrosive and has a small application range.

    　C Oil: including engine oil, spindle oil, transformer oil, diesel oil, etc. It can reduce deformation and cracking. Not suitable for carbon steel. Oil temperature: 60 to 80 degrees, the highest is not more than 100 to 120 degrees.

  4Tempering temperature

The bearing steel adopts low temperature tempering. Temperature: 150~250 degrees. Under the premise of maintaining high hardness and high wear resistance, the internal stress and brittleness can be reduced to avoid cracking or premature damage during use. Hardness HRC: 58~~64.