The specific situation of the heat treatment process and hardness of 42CrMo steel pipe

42CrMo is a commonly used alloy structural steel with excellent mechanical properties and heat treatment plasticity and is widely used in the manufacture of mechanical parts and engineering machinery. Heat treatment is one of the important processes for 42CrMo to obtain excellent performance. 42CrMo is a high-strength alloy structural steel with good comprehensive mechanical properties. It is suitable for manufacturing high-strength, high-wear resistance, high corrosion resistance, and high-hardness parts and equipment. This material has a wide range of applications in many industrial fields due to its excellent mechanical properties and heat treatment plasticity, such as engineering machinery, automotive parts, petroleum machinery, and aerospace. The heat treatment process has a significant effect on the performance of 42CrMo. The heat treatment process of 42CrMo is a key factor in its performance. Different heat treatment processes will result in different hardness, strength, and toughness of the material.

The heat treatment process of 42CrMo refers to heating the steel to a certain temperature, and after the insulation and cooling process, the steel undergoes a phase change, thereby changing its organizational structure and performance. The heat treatment process of 42CrMo mainly includes four common processes: annealing, normalizing, quenching, and tempering.

The main heat treatment processes and effects of 42CrMo steel pipes:

① Annealing: used to eliminate internal stress and improve processing performance.

② Normalizing: Improve the strength and hardness of the material.

③ Quenching: Improve the strength, hardness, and wear resistance of the material.

④ Tempering: Reduce the brittleness of the material and improve toughness.

The delivery hardness of 42CrMo is generally 240-270HB. After normalizing, the hardness can be increased to 280-320HB. The hardness after quenching can reach 50-55HRC, while the hardness after tempering is about 50HRC. Different heat treatment processes will correspond to different hardness, strength, and toughness.

Hardness changes of 42CrMo steel pipes under heat treatment:

① The hardness of 42CrMo without any treatment is about 180→200HB.

② The hardness of 42CrMo after annealing can reach 220→230HB.

③ The hardness of 42CrMo after normalizing treatment can reach 250→300HB.

④ The hardness of 42CrMo after quenching + tempering treatment can reach about 280→340HB.

Quenching and tempering is to heat 42CrMo to 850-880 degrees Celsius, keep it warm for a period of time, and then cool it with water or oil. This heat treatment method enables 42CrMo to achieve a uniform martensitic structure, thereby improving its hardness and strength while maintaining high toughness. The quenched and tempered 42CrMo has high tensile strength and yield strength and is suitable for the manufacture of parts requiring high strength and fatigue resistance.

Quenching + tempering is to heat 42CrMo to 860-880 degrees Celsius, keep it warm for a period of time, and then cool it quickly (usually using water cooling). Then heat the steel to a temperature below the critical temperature of the steel for tempering. This heat treatment method enables 42CrMo to obtain a uniform and fine martensitic structure, improving its hardness and toughness. After quenching and tempering, 42CrMo has a higher hardness, and its wear resistance and impact resistance are also improved. It is suitable for manufacturing parts that require wear resistance and impact resistance.

After heat treatment, the hardness of 42CrMo is usually between 260-300HB. Depending on the different heat treatment processes and workpiece shapes, the hardness range may vary. The hardness of 42CrMo after quenching and tempering is higher, which can meet the use requirements of many mechanical parts. The hardness of 42CrMo after quenching and tempering is lower, but it has better toughness, which is suitable for manufacturing parts that require high strength and high toughness.

Due to its good mechanical properties and heat treatment plasticity, 42CrMo is widely used in engineering machinery, automotive parts, petroleum machinery, aerospace, and other fields. For example, when manufacturing heavy-duty parts such as engine crankshafts, transmission gears, and wind turbine main shafts, choosing 42CrMo can ensure the strength and life of the parts.

As a commonly used alloy structural steel, 42CrMo can obtain different hardness and properties through heat treatment processes. Quenching and tempering and quenching + tempering are two common heat treatment processes. Choosing the appropriate process according to different use requirements can meet the performance requirements of parts. The hardness of 42CrMo is usually between 260-300HB. It has excellent mechanical properties and heat treatment plasticity and is suitable for a wide range of applications. 42CrMo steel is an ultra-high-strength steel with high strength and toughness, good hardenability, no obvious tempering brittleness, high fatigue limit, multiple impact resistance after quenching and tempering, and good low-temperature impact toughness. This steel is suitable for manufacturing large and medium-sized plastic molds that require certain strength and toughness. It has high strength and hardenability, good toughness, small deformation during quenching, and high creep strength and lasting strength at high temperatures. It is used to manufacture forgings that require higher strength and larger quenched and tempered sections than 35CrMo steel, such as large gears for locomotive traction, supercharger transmission gears, pressure vessel gears, rear axles, connecting rods, and spring clips with extremely high loads. It can also be used for oil-deep well drill pipe joints and salvage tools below 2000m and can be used for bending machine molds, etc.

10 types of 42CrMo heat treatment methods and their corresponding hardness cases:

No.1 Annealing 760±10℃ annealing, furnace cooling to 400℃ air cooling, corresponding hardness: HB 220-230.

No.2 Normalizing 860±10℃ normalizing, air cooling after leaving the furnace, corresponding hardness: HB 250-300.

No.3 Quenching+tempering 840±10℃ quenching or oil (depending on the complexity of the product shape), 680-700℃ tempering, corresponding hardness: HB<217.

No.4 Quenching+tempering 840±10℃ quenching oil, then 470℃ tempering, corresponding hardness: HRC41-45.

No.5 Quenching and tempering 840±10℃ quenching oil, then 480℃ tempering treatment, corresponding hardness: HRC35-45.

No.6 Quenching and tempering 850℃ quenching oil, then 510℃ tempering treatment, corresponding hardness: HRC38-42.

No.7 Quenching and tempering 850℃ quenching oil, then 500℃ tempering treatment, corresponding hardness: HRC40-43.

No.8 Quenching and tempering 850℃ quenching oil, then 510℃ tempering treatment, corresponding hardness: HRC36-42.

No.9 Quenching and tempering 850℃ quenching oil, then 560℃ tempering treatment, corresponding hardness: HRC32-36.

No.10 Quenching+tempering 860℃ quenching oil, then 390℃ tempering treatment, corresponding hardness: HRC48-52.

42CrMo heat treatment process steps: 42CrMo alloy steel heat treatment usually includes preheating, austenitizing, cooling, and tempering steps.

① Preheating: Preheating is an important part of the heat treatment process. The main purpose is to make the workpiece reach a uniform temperature to avoid prestressing heat or temperature deformation during the austenitizing process. It is generally controlled between 700℃ and 800℃, and the time depends on the size of the workpiece and the amount of furnace loading. The temperature should be raised slowly during the preheating process to avoid cracks or deformation of the workpiece.

② Austenitizing: Austenitizing is an important part of the heat treatment process. The main purpose is to dissolve all or part of the ferrite in the steel so as to obtain good austenitizing mechanical properties during the cooling process. Generally controlled between 900℃～950℃, the holding time is determined according to the size of the workpiece and the size of the furnace. During the process, the temperature in the furnace should be kept uniform to avoid stress or deformation of the workpiece.

③ Cooling: Cooling is an important link in the heat treatment process, and its main purpose is to obtain the required mechanical properties. The cooling method generally adopts oil cooling or water cooling, and the cooling rate should be controlled within an appropriate range to avoid the occurrence of cracks or deformation of the workpiece. Different mechanical properties can be obtained.

④ Tempering: Tempering is the last link in the heat treatment process, and its main purpose is to eliminate the residual stress inside the workpiece and improve the toughness and stability of the workpiece. The tempering temperature is generally controlled between 500℃～650℃, and the holding time is determined according to the size of the workpiece and the amount of furnace loading. During the tempering process, the temperature should be slowly lowered to avoid cracks or deformation of the workpiece. After tempering, air cooling or furnace cooling should be carried out.