Product Overview
Our Grade 20 carbon seamless precision steel tube is manufactured from high-quality 20# steel through cold-drawn or cold-rolled precision processes. Featuring oxide-free inner and outer surfaces, leak-proof high-pressure resistance, no deformation in cold bending, and no cracking in flaring or flattening tests, this tube complies with GB/T 3639 (China's precision seamless tube standard, non-equivalent to DIN 2391), DIN 2391, and EN 10305-1. It is widely used in hydraulic systems, pneumatic components, automotive parts, construction machinery, oilfield equipment, and high-precision structural applications.
Core Advantages & Process Details
Ultra-High Dimensional Precision
Wall thickness tolerance: Commercial grade ±10%, precision grade ±5%; eccentricity controlled within ≤10% of nominal wall thickness.
High Surface Quality
Smooth inner and outer surfaces, scale-free; as-drawn surface roughness Ra 0.8–1.6μm; honed surface down to Ra 0.2–0.4μm; special requirements (SRB) reach Ra ≤0.2μm.
Reduces fluid friction and seal wear; ideal for hydraulic/pneumatic systems demanding high sealing performance.
Flexible Heat Treatment Delivery Conditions
Per GB/T 3639 and customer requirements, multiple delivery conditions are available:
BK (cold-drawn/cold-rolled as-processed): retains work-hardening.
BK+S (cold-drawn + stress-relief annealed): residual stress eliminated.
GBK (soft annealed): maximum plasticity, suitable for further cold working.
NBK (normalized): homogeneous microstructure, stable mechanical properties.
Tailored Tempering Processes
Depending on performance requirements, different tempering temperatures achieve target microstructure and properties:
| Tempering Type | Temperature Range | Microstructure | Hardness Range | Primary Applications |
|---|---|---|---|---|
| Low-Temp | 150–250℃ | Tempered Martensite | HRC 58–64 | Cutting tools, dies, bearings |
| Medium-Temp | 250–500℃ | Tempered Troostite | HRC 35–50 | Springs, hot-work dies (high yield + toughness) |
| High-Temp (Quenching + Tempering) | 500–650℃ | Tempered Sorbite | HB 200–330 | Gears, shafts, connecting rods, bolts (best combined properties) |
As-processed hardness ≤156HB; microstructure: ferrite + pearlite mixture.
Rigorous Non-Destructive Testing (NDT)
Full inspection services available: eddy current testing, ultrasonic testing, hydrostatic testing, metallographic examination, and high-precision C/S analysis ensure internal and surface integrity.
Flexible Customization
Non-standard dimensions, fixed lengths, special heat treatments, and surface coatings (anti-rust/zinc plating/chrome plating) available upon request.
Detailed Application Scenarios (by Industry)
Grade 20 precision seamless steel tubes are suitable for medium-to-low pressure (≤25MPa) and normal temperature (≤200℃) conditions, making them the preferred material for conventional hydraulic cylinders and mechanical structural parts. Key applications include:
| Industry Sector | Typical Uses | Operating Characteristics |
|---|---|---|
| Pneumatic Systems | Cylinder tubes, precision bushings, valve bodies | Low-pressure high-frequency cycling, tight tolerances |
| Automotive | Shock absorber tubes, steering columns, drive shafts, tail lift cylinders | Medium load, impact resistance, fatigue endurance |
| Construction Machinery | Mini excavators, loaders, forklift lift cylinders, crane telescopic cylinders | Pressure 16–25MPa, frequent reciprocating motion |
| Petrochemical | Instrument tubing, heat exchanger tubes, low-pressure process lines | Temperature ≤450℃, non-corrosive media |
| General Machinery | Machine tool clamp cylinders, packaging/printing feed cylinders, textile tension cylinders | Low pressure ≤16MPa, clean environments, high-frequency operation |
| Agricultural Machinery | Tractor/combine hydraulic suspension cylinders, header lift cylinders | Pressure 6–12MPa, outdoor exposure, requires anti-corrosion |
| Vehicle Modification | Reefer door cylinders, RV slide-out cylinders,环卫 truck hopper cylinders | Pressure ≤10MPa, low-load auxiliary cylinders |
⚠ Usage Limitation: Not recommended for high-pressure (≥31.5MPa) , heavy-impact, or high-temperature (≥200℃) primary actuators, such as large excavator main cylinders, heavy crane telescopic cylinders, or hot-rolling mill main cylinders. For such conditions, upgrade to 45# steel, 27SiMn, or alloy steel tubes.
Precision Tube vs. Ordinary Seamless Tube - Key Differences
Dimensional Precision: Precision tubes maintain strict tolerances (0.02–0.08mm) on ID and OD; ordinary seamless tubes have much looser tolerances.
Surface Quality: Precision tubes feature oxide-free, smooth surfaces; ordinary tubes have rough surfaces with scale.
Post-Processing Cost: Precision tubes are ready for assembly, significantly saving material, labor, and time in machining, and are progressively replacing solid round bars or ordinary tubes for precision-machined parts.
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