Details of 40Cr alloy steel pipes in industrial projects

40Cr alloy steel pipes are defined according to the production materials (that is, the material), which means alloy steel pipes; while seamless steel pipes are defined according to the production process (seamless or seamless), which is different from seamless steel pipes, including straight seam welded steel pipes and spiral steel pipes.

40Cr alloy steel pipes can obtain good comprehensive mechanical properties, low temperature impact resistance, good hardenability, oil quenching can improve fatigue strength, and complex shape parts are prone to cracking during water quenching. The cold bending plasticity is medium, the cutting performance is good after heat treatment, and the weldability is poor. It is generally used in the quenched and tempered state, and can also be carbonitrided and high-frequency quenched. It is one of the widely used alloy structural steels.

40Cr alloy steel pipes can be used to manufacture medium-speed and medium-load parts after quenching and tempering, such as machine tool gears, shafts, worms, spline shafts, thimble sleeves, etc.; quenching and high-frequency quenching are used to manufacture parts with high surface hardness and high wear resistance, such as gears, shafts, spindles, crankshafts, spindle sleeves, pins, connecting rods, intake valves, screws, etc. Quenching and medium-temperature tempering are used to manufacture heavy-load and medium-speed impact parts, such as oil pump rotors, sliders, gears, spindle sleeves, etc.; quenching and low-temperature tempering is used to manufacture heavy-load, low-impact, wear-resistant parts, such as worms, shafts, sleeves, etc.; carbon-nitrogen treatment is used to manufacture transmission parts with larger sizes and higher low-temperature toughness, such as shafts, gears, etc.

1. Supply status and hardness of 40Cr alloy steel pipes: Annealed, hardness ≤207HBS. Elastic modulus of 40Cr alloy steel pipe: elastic modulus E (20℃) /MPa 200000～211700, shear modulus G (20℃) 80800
2. Quenching process of 40Cr alloy steel pipe: 40Cr alloy steel pipe quenching 850℃, oil cooling; tempering 520℃, water cooling, oil cooling. The surface quenching hardness of 40Cr alloy steel pipe is HRC52-60 and flame quenching can reach HRC48-55.
3. Nitriding treatment of 40Cr alloy steel pipe: 40Cr alloy steel pipe belongs to nitridable steel, and the elements it contains are conducive to nitriding. After nitriding treatment, 40Cr alloy steel pipe can obtain higher surface hardness. The hardness of nitriding treatment after quenching and tempering is as high as HRA72~78, that is, HRC43~55.

The process route of nitriding workpieces: forging - annealing - rough machining - quenching and tempering - finishing - stress relief - rough grinding - nitriding - fine grinding or grinding. Since the nitriding layer is thin and brittle, a higher-strength core structure is required, so quenching and tempering heat treatment should be performed first to obtain tempered troostite and improve the core mechanical properties and nitriding layer quality. Soft nitriding is active nitriding, and gas nitriding is more commonly used.