First, a brief introduction to the material of 35CrMo seamless steel pipes
35CrMo seamless steel pipes are a type of medium-carbon alloy structural steel seamless pipe. Their core characteristics are as follows:
(1) Chemical composition of 35CrMo seamless steel pipes:
Carbon: 0.32%-0.40%, providing basic strength;
Chromium: 0.80%-1.10%, improving hardenability and tempering stability;
Molybdenum: 0.15%-0.25%, refining grains and enhancing high-temperature strength and toughness;
Silicon and Manganese: assisting in deoxidation and strengthening ferrite;
Phosphorus and Sulfur: ≤0.035%, reducing low-temperature brittleness. (2) Mechanical Properties of 35CrMo Seamless Steel Pipe:
Tensile Strength: ≥980MPa (GB/T3077 standard), some processes can reach 1080-1230MPa;
Yield Strength: ≥835MPa;
Elongation: ≥12%, some processes can reach 18%;
Impact Toughness: Impact energy ≥34J at -20℃, can reach over 180J in low-temperature applications.
(3) Heat Treatment Characteristics of 35CrMo Seamless Steel Pipe:
Quenching Temperature: 850-880℃, oil quenching can penetrate Φ15-40mm, water quenching can penetrate Φ28-60mm;
Tempering Temperature: 500-650℃, tempering holding time ≥90 minutes, to obtain tempered sorbite structure, balancing strength and toughness. (4) Application Areas of 35CrMo Seamless Steel Pipes:
Petroleum Industry: Drill collars, drill pipes, oil casing, subjected to high pressure and complex geological conditions;
Chemical Equipment: High-pressure vessels, reactors, heat exchanger pipes, resistant to corrosive media;
Power Industry: Boiler tubes, superheater tubes, operating stably in high-temperature and high-pressure steam environments for extended periods;
Machinery Manufacturing: Shaft parts, gears, connecting rods, subjected to alternating loads;
Extreme Environments: Polar oil and gas pipelines, railway rail fasteners in cold regions, maintaining ductile fracture characteristics even at -110℃.
Second, Corresponding Grades of 35CrMo Seamless Steel Pipes
The corresponding grades of 35CrMo seamless steel pipes in different standard systems are as follows:
Chinese Standard System GB, Grade 35CrMo conforms to GB/T3077-2015
American Standard System ASTM, Grade 4135, with similar chemical composition and properties
German Standard System DIN, Grade 34CrMo4/1.7220, with strong process compatibility
Japanese Standard System JIS, Grade SCM430 Applications in precision manufacturing
International standard system ISO, grade 35CrMo4, for easy international trade
Third, processing details of the 35CrMo seamless steel pipe
The processing of 35CrMo seamless steel pipe requires strict control of process parameters to ensure performance stability:
Production process flow of 35CrMo seamless steel pipe:
(1) Raw material preparation: Select high-quality 35CrMo alloy steel billet and control the content of harmful elements such as P and S;
(2) Hot rolling:
Heating temperature: 1100-1250℃, homogenization treatment;
Piercing and rolling: Piercing is completed by a three-roll skew rolling mill, and the initial tube shape is obtained after sizing.
(3) Cold drawing:
Multi-pass die stretching (elongation coefficient 1.3-1.5), grain size reaches ASTM Grade 8 or above; Inner wall honing: Surface roughness Ra≤0.8μm, reducing turbulence loss during fluid transport;
(4) Heat treatment:
Quenching: Oil quenching at 860-880℃ to form a uniform bainitic-martensite structure;
Tempering: Holding at 500-650℃ for ≥90 minutes, residual stress ≤120MPa;
(5) Finishing and inspection:
Eddy current testing: 100% non-destructive testing, flaw detection pass rate ≥99.93%;
Dimensional tolerances: Outer diameter tolerance ±0.15mm (for high-precision scenarios such as railway fasteners), wall thickness deviation ±5%;
Mechanical property verification: Tensile strength is measured using a tensile testing machine, and impact energy is measured using an impact testing machine.
(6) Key Process Control Points:
Quenching Temperature: Precisely controlled within the range of 860-880℃ to avoid structural defects;
Tempering Holding Time: ≥90 minutes to ensure full release of internal stress in the material;
Cold Drawing Elongation Coefficient: 1.3-1.5 to balance work hardening and plasticity;
Inner Wall Honing: Ra≤0.8μm to improve fluid transport efficiency;
Non-destructive Testing: Eddy current testing sensitivity ≥0.5mm to eliminate microcrack defects.
(7) Processing Equipment Requirements:
Hot Rolling Mill: Three-roll skew rolling mill equipped with an online temperature measuring instrument and a tension sensor;
Cold Drawing Machine: Four-pass die stretching system, supporting 6-120mm outer diameter processing;
Heat Treatment Furnace: Controlled atmosphere furnace, temperature uniformity ±5℃;
Testing Equipment: Rockwell hardness tester (HRC 28-32), direct-reading spectrometer (real-time monitoring of elemental content), coordinate measuring machine (geometric measurement of form and position tolerances).
Post time: Nov-20-2025