40CR thick-walled seamless steel pipe is a hollow-section circular steel with no seams around the circumference. It is manufactured from solid billets by piercing to form a rough pipe, which is then processed through hot rolling, cold rolling, or cold drawing. Compared to solid steel products like round bars, the steel pipe is lighter in weight while maintaining the same bending and torsional strength, making it an economical cross-section material.

In accordance with standard GB/T 3077-2008: Chemical composition (mass fraction, %) C 0.37~0.44, Si 0.17~0.37, Mn 0.50~0.80, Cr 0.80~1.10, Ni ≤0.30.

40cr Thick-Walled Seamless Steel Pipe Mechanical Properties

Sample blank size (mm): 25

Heat treatment for 40CR thick-walled seamless steel pipe

Quenching Heating Temperature (°C): 850; Cooling Agent: Oil

Two, Quenching Heating Temperature (℃): -

Annealing heating temperature (°C): 520; Cooling medium: Water, Oil

Tensile Strength (σb/MPa): ≧980

Yield Point (σs/MPa): ≧785

Ultimate elongation (δ5/%)：≥9

Section Reduction Ratio (ψ/%): ≧45

Impact Absorption Work (Aku2/J): ≧47

Bainite hardness (HBS 100/3000) (annealed or high-temperature tempered condition): ≦207

Critical Point Temperature

(Approximate Value) Acm = 780℃

Active Heat Treatment Standard

Temperature: 850~870°C, Hardness: 179~229HBS.

Cold Compression Blanks Softening Treatment Specification

Temperature 740~760°C, insulation time 4~6h, then cool down at a rate of 5~10°C/h, to ≤600°C, and air cool after removal.

Before treatment hardness ≤ 217HBS, after softening hardness ≤ 163HBS.

Iron屑 Protection Swing Hardening Specification

(670±10)℃×2h, heat slowly in the furnace, (710±10)℃×2h, cool slowly in the furnace, (670±10)℃×2h, heat slowly in the furnace again, (710±10)℃×2h, cool slowly in the furnace once more, (670±10)℃×2h, heat slowly in the furnace once more, (710±10)℃×2h, cool slowly in the furnace again, total of 3 cycles, then cool down to 550℃, air cool after removal. The hardness after treatment is 153HBS.

Hardening and Tempering Standards

Quenching temperature: 850℃ ±10℃, oil cooled; tempering temperature: 520℃ ±10℃, water or oil air-cooled.

【Features】Medium carbon modified steel, cold heading die steel. The steel offers moderate pricing, ease of processing, and after appropriate heat treatment, it achieves certain toughness, ductility, and wear resistance. Normalizing promotes spheroidization of the structure, improving the machinability of blanks with hardness less than 160HBS. After tempering at 550~570°C, the steel exhibits strong comprehensive mechanical properties. The hardenability of this steel is higher than that of 45 steel, making it suitable for high-frequency quenching, flame hardening, and other surface hardening treatments.

　　【Application】This steel, after quenching and tempering, is used to manufacture mechanical parts subjected to moderate loads and speeds, such as car steering knuckles, rear axles, and gears, shafts, worm gears, splined shafts, and tips on machine tools. After quenching and medium-temperature tempering, it is suitable for parts that can withstand high loads, impacts, and moderate speeds, like gears, main shafts, oil pump rotors, sliders, and sleeve rings. After quenching and low-temperature tempering, it is used for parts that can bear heavy loads, low impacts, and have wear resistance with a solid thickness under 25mm, such as worm gears, main shafts, shafts, and sleeve rings. After quenching and high-frequency surface hardening, it is ideal for parts requiring high surface hardness and wear resistance without significant impact, such as gears, sleeves, shafts, main shafts, crankshafts, mandrels, pins, connecting rods, screws, bolts, and intake valves. Additionally, this steel is suitable for manufacturing various transmission parts that undergo carbonitriding treatment, such as large-diameter gears and shafts with good low-temperature toughness.

Availability and Hardness: Annealed condition, hardness ≤ 207HBS. Elastic Modulus of 40Cr: Elastic Modulus E (20℃) /MPa 200000-211700, Shear Modulus G (20℃) 80800

40CR thick-walled seamless steel tube quenching process

40Cr quenched at 850°C, oil cooled; tempered at 520°C, water and oil cooled. The surface hardness of 40Cr steel pipe after quenching is HRC 52-60, while flame quenching can reach HRC 48-55.

40Cr thick-walled seamless steel pipe nitriding treatment

40Cr is a nitriding steel, with elements that promote nitriding. After nitriding treatment, 40Cr achieves a high surface hardness, with the hardness after tempering treatment reaching HRA72~78, equivalent to HRC43~55. The process route for nitriding workpieces: forging - annealing - rough machining - tempering - finishing - stress relief - rough grinding - nitriding - fine grinding or polishing. Due to the thin and brittle nitriding layer, a high-strength core structure is required, necessitating a tempering heat treatment to obtain tempered sorbite, enhancing the core mechanical properties and the quality of the nitriding layer. Soft nitriding is an active nitriding process, with gas nitriding being the most commonly used.

40cr thick-walled seamless steel pipe welding

Preheat the 40Cr material before welding to prevent internal quenching and cracking of the weld due to matrix cooling. Perform a normalizing treatment once before tempering after welding.

Weldability of 40Cr: It is prone to segregation during crystallization and is sensitive to crystalline cracks (a type of thermal crack), which can easily lead to cracking in the pit and concave parts of the weld during welding. With a high carbon content, rapid cooling is likely to result in a quench-hardened structure (martensite) that is highly sensitive to cold cracks. In the overheated zone, with a high cooling rate, it is easy to form a brittle high-carbon martensite, leading to embrittlement of the overheated zone.

Key Welding Techniques for 40CR Thick-Walled Seamless Steel Pipe

Welding is typically performed in the annealing (normalizing) condition.

2. Welding methods are unrestricted.

3. Use higher line energy and adjust the preheat temperature appropriately; generally, the preheat temperature and interlayer temperature can be controlled between 250-300°C.

4. Welding materials should ensure that the composition of the deposited metal is essentially the same as the base material, such as J107-Cr

5. Post-weld heat treatment should be conducted promptly. If it's difficult to perform the tempering treatment immediately, intermediate annealing can be carried out or the part can be held at a temperature above the preheat for a period to expel diffused hydrogen and soften the tissue. For products with complex structures and multiple weld seams, an intermediate annealing can be performed after a certain number of welds have been completed.