Compared with ordinary carbon steel and some low alloy steels, 39NiCrMo3 steel contains alloying elements such as nickel, chromium, and molybdenum, which makes it have excellent hardenability. During the quenching process, a uniform martensitic structure can be obtained on the cross section of a larger workpiece. For example, when processing large-sized 39NiCrMo3 shafts or gears, it can ensure a good hardening effect from the surface to the core. Ordinary carbon steel may only be hardened on the surface, and the core is still a soft structure.
The alloying elements in 39NiCrMo3 steel can increase the recrystallization temperature of the steel. When heated at high temperature, its grain growth tendency is small, so that it has good anti-overheating stability. In contrast, some ordinary steels are prone to coarse grains during high temperature heat treatment, resulting in reduced performance.
During the tempering process, 39NiCrMo3 steel can maintain good strength and hardness at higher temperatures and has good tempering stability. Compared with some carbon steels, 39NiCrMo3 steel can be tempered at a higher tempering temperature to eliminate quenching stress while still maintaining high strength and hardness, while carbon steel tempering temperature may significantly reduce hardness.
39NiCrMo3 steel is suitable for nitriding. After nitriding, a nitrided layer with high hardness, good wear resistance and corrosion resistance can be formed on the surface, further improving the surface performance of parts. It is suitable for occasions with extremely high requirements for surface performance, such as some key parts of aircraft engines, which is an advantage that many ordinary steels do not have.
Chemical composition % of steel 39NiCrMo3 (1.6510): EN 10277-5-2008
| C | Si | Mn | Ni | P | S | Cr | Mo |
| 0.35 - 0.43 | max 0.4 | 0.5 - 0.8 | 0.7 - 1 | max 0.025 | max 0.035 | 0.6 - 1 | 0.15 - 0.25 |
39NiCrMo3 Heat Treatment Process
- Softening annealing: Heat the steel to 650-690°C, then slowly cooling in the furnace to reduce the hardness of the steel, which is convenient for subsequent processing. The hardness is generally lower than 240HBW.
- Normalizing: Heating to 860-880°C and air cooling. It can improve the structure and cutting performance of the steel, refine the grains, and increase strength and toughness.
- Quenching: Heat the steel to 830-850°C, then quickly cool it in water or oil to obtain martensitic structure. It will improve hardness and strength, but reduce toughness.
- Tempering: After quenching, heat the steel to 540-630°C. According to different cooling methods and tempering temperatures, the hardness, toughness and other properties can be adjusted to eliminate quenching stress, stabilize the structure and size, and prevent deformation and cracking.
Hardness of 39NiCrMo3 Steel with Different Diameters After Quenching and Tempering
- Diameter ≤16mm, the Brinell hardness HB is between 331-380.
- Diameter between 16-40mm, the Brinell hardness HB is between 298-359.
- Diameter between 40-100mm, the Brinell hardness HB is between 271-331.
- Diameter between 100-160mm, the Brinell hardness HB is between 240-286.
- Diameter between 160-250mm, the Brinell hardness HB is between 225-271.
