Introduction of Precision Bright Steel Tube
2026/08/17
Product Introduction
Precision tubes, also known as precision seamless steel tubes, are high‑precision steel tubular products manufactured from high‑quality carbon steel through cold rolling, cold drawing, non‑oxidative bright heat treatment (NBK condition), followed by straightening, non‑destructive testing, inner‑wall cleaning, anti‑rust oil coating and end‑cap sealing.
The tubes feature high dimensional accuracy: outer diameter tolerance ±0.05‑±0.1 mm, wall‑thickness tolerance within ±0.05 mm. The surface roughness Ra reaches 0.8‑1.6 μm with bright metallic luster, no oxide layer after heat treatment. They withstand high pressure, remain undeformed under cold bending, and resist cracking during flaring and flattening operations, suitable for complex forming and machining work.
Major applicable standards include GB/T 3639, DIN 2391‑94/C, EN 10305-1,EN 10305-4, ASTM A1519, JIS G3445. Typical delivery conditions: NBK(+N), GBK(+A), BK(+C), BKW(+LC), BKS(+SR).
1. Chemical Composition of Common Grades (mass fraction, %)
|
Grade |
C |
Si |
Mn |
S(max) |
P(max) |
Cr |
|
10# |
0.07‑0.13 |
0.17‑0.37 |
0.35‑0.65 |
0.035 |
0.035 |
— |
|
20# |
0.17‑0.23 |
0.17‑0.37 |
0.35‑0.65 |
0.035 |
0.035 |
— |
|
35# |
0.32‑0.39 |
0.17‑0.37 |
0.35‑0.65 |
0.035 |
0.035 |
— |
|
45# |
0.42‑0.50 |
0.17‑0.37 |
0.50‑0.80 |
0.035 |
0.035 |
— |
|
40Cr |
0.37‑0.44 |
0.17‑0.37 |
0.50‑0.80 |
0.035 |
0.035 |
0.08‑1.10 |
|
25Mn |
0.22‑0.29 |
0.17‑0.37 |
0.70‑1.00 |
0.035 |
0.035 |
≤0.25 |
|
37Mn5 |
0.30‑0.39 |
0.15‑0.30 |
1.20‑1.50 |
0.015 |
0.020 |
— |
2. Mechanical Properties under Different Delivery Conditions
Y: Cold‑finished hard; R: Cold‑finished soft; T: Stress‑relieved annealing;
σ_b: Tensile strength (MPa, minimum); δ_5: Elongation (%, minimum)
|
Grade |
Y (Cold‑finished hard) |
|
R (Cold‑finished soft) |
|
T (Stress‑relieved annealing) |
|
|
|
σ_b |
δ_5 |
σ_b |
δ_5 |
σ_b |
δ_5 |
|
10# |
410 |
6 |
375 |
10 |
335 |
12 |
|
20# |
510 |
5 |
450 |
8 |
430 |
10 |
|
30# |
590 |
4 |
550 |
6 |
520 |
8 |
|
45# |
645 |
4 |
630 |
5 |
610 |
7 |
3. Common Material Grades
|
Category |
Material Grades |
|
Carbon steel |
10#, 20#, 35#, 45#, 25Mn |
|
Alloy steel |
40Cr, 37Mn5, Q345B |
|
European standard |
St35(E235), St37.4, St45(E255), St52(E355) |
4. Typical Applications
|
Industry |
Application Items |
|
Pneumatic & hydraulic system |
Cylinders, hydraulic cylinders, hydraulic pipeline components |
|
Automobile industry |
Precision structural parts, chassis and transmission components |
|
General machinery |
High‑precision mechanical fittings, replace conventional seamless tubes / round bars to save machining cost |
|
Aerospace |
Light‑load precision tubular structural parts |
|
Medical equipment |
High‑cleanliness precision structural components |
|
Energy sector |
Precision fluid‑transport piping and instrument tubes |
Key Advantages Summary
1. Tight dimensional tolerance (2‑8 threads deviation), reduces material loss and machining time.
2. Bright oxide‑free inner & outer surface, high inner cleanliness.
3. Good formability: cold‑bendable, flaring and flattening without cracks, high pressure resistance.
