Five Common Heat Treatment Methods For Gear Forgings

When gear forgings are produced, they are generally treated by heat treatment, heating, heat preservation and cooling. The main heat treatment methods are the following five methods.

1. Surface quenching of gear forgings: commonly used for medium carbon steel and medium carbon alloy steel, such as 45, 40Cr steel, etc. After surface quenching, the tooth surface hardness is generally 40-55HRC. The characteristics are high fatigue pitting resistance, high anti-bonding ability and good wear resistance. Since the tooth core is not hardened, the gear forging still has enough toughness to withstand small impact loads.

2. Carburizing and quenching of gear forgings: commonly used for low carbon steel and low carbon alloy steel, such as 20, 20Cr steel, etc. After carburizing and quenching, the tooth surface hardness can reach 56-62HRC, while the tooth core still maintains a high toughness. The bending strength and tooth surface contact strength of the gear forging are high, and the wear resistance is good. It is often used in important gear transmissions subject to impact loads. After carburizing and quenching, the gear forgings have large deformation and should be ground.

3. Nitriding of gear forgings: Nitriding is a surface chemical heat treatment. No other heat treatment is required after nitriding, and the tooth surface hardness can reach 700-900HV. Since the gears after nitriding have high hardness, low process temperature and small deformation, they are suitable for internal gears and gears that are difficult to grind. They are often used for nitriding steel containing alloy elements such as chromium, copper and lead, such as 38CrMoAlA.

4. Tempering of gear forgings: Tempering is generally used for medium carbon steel and medium carbon alloy steel, such as 45, 40Cr, 35SiMn steel, etc. The tooth surface hardness after tempering is generally 220-280HBS. Because the hardness is not high, the finishing of gear forgings can be carried out after heat treatment.

5. Normalizing of gear forgings: Normalizing can eliminate internal stress, refine grains, and improve mechanical properties and cutting performance. Gear forgings with low mechanical strength requirements can be normalized with medium carbon steel, and large diameter gear forgings can be normalized with cast steel.