Overview
DIN 2391 is a German standard that specifies the technical delivery conditions for seamless, precision steel tubes. These tubes are characterized by their excellent dimensional accuracy, smooth surface finish, and high strength. They are typically cold-drawn (and sometimes cold-rolled) to achieve these precise tolerances.
The standard is divided into two main parts:
DIN 2391 Part 1: Covers seamless, cold-drawn precision steel tubes.
DIN 2391 Part 2: Covers welded, cold-drawn precision steel tubes.
While the standard covers various steel grades, it is most famously associated with carbon steel grades.
Key Features and Characteristics
High Dimensional Accuracy: These pipes have very tight tolerances on outer diameter (OD) and wall thickness. This makes them ideal for applications where components need to fit together precisely without further machining.
Excellent Surface Finish: The cold-drawing process results in a very smooth, scale-free surface, which is often sufficient for final use without additional finishing.
High Strength: The cold-working process (drawing or rolling) work-hardens the steel, increasing its yield strength and tensile strength compared to hot-finished tubes.
Seamless Construction (Part 1): The seamless variant has no weld seam, making it uniformly strong around its circumference and ideal for high-pressure applications.
Common Steel Grades and Chemical Composition
DIN 2391 specifies several steel grades. The most common carbon steel grades are:
| Steel Grade | Material Number (Werkstoffnummer) | Description | Equivalent Standard (Approx.) |
|---|---|---|---|
| St 35 | 1.0308 | Low-carbon steel, good weldability and formability. | ASTM A513 Type 1, EN 10305-1 E235 |
| St 52 | 1.0530 | Higher-strength carbon steel with higher yield strength. | ASTM A519 Grade 1020/1026, EN 10305-1 E355 |
| C 35 | 1.0506 | Medium-carbon steel, can be heat-treated for higher strength. | ASTM A519 1035 |
| C 45 | 1.0507 | Medium-carbon steel, higher strength and hardness. | ASTM A519 1045 |
Typical Chemical Composition (Example):
St 35: C max 0.17%, Mn max 0.70%, Si max 0.30%, P max 0.035%, S max 0.035%
St 52: C max 0.22%, Mn max 1.60%, Si max 0.55%, P max 0.035%, S max 0.035%
Mechanical Properties
The mechanical properties are significantly enhanced by the cold-working process.
| Steel Grade | Yield Strength (Re) Min. (MPa) | Tensile Strength (Rm) (MPa) | Elongation (A) Min. (%) |
|---|---|---|---|
| St 35 | 390 MPa | 490 - 690 MPa | 12% |
| St 52 | 490 MPa | 610 - 840 MPa | 10% |
Note: Actual values can vary based on the specific manufacturing process and tube dimensions.
Tolerances (Key Feature)
DIN 2391 pipes are known for their tight tolerances. For example, for common sizes:
Outside Diameter Tolerance: Typically h8 or h9 (very tight).
Example: For a 50 mm OD tube, the h8 tolerance is 0 / -0.046 mm.
Wall Thickness Tolerance: Usually around ±10% of the nominal wall thickness.
Applications
Due to their precision and strength, DIN 2391 pipes are used in a wide range of industries:
Hydraulic and Pneumatic Systems: For cylinders, pistons, and actuator housings.
Automotive Industry: Shock absorber cylinders, fuel injection systems, steering components.
Mechanical Engineering: Precision shafts, linear motion systems, bearing housings, machine guards.
General Precision Machinery: Any application requiring a high-quality, ready-to-use tube with minimal machining.
Equivalent and Superseding Standards
It's important to note that many national German standards (DIN) have been replaced by European Norm (EN) standards to harmonize specifications across Europe.
The direct successor to DIN 2391-1 is EN 10305-1. This standard, titled "Steel tubes for precision applications - Technical delivery conditions - Part 1: Seamless cold drawn tubes," covers the same product range.
When ordering or specifying, you might now see references to EN 10305-1 E235 (equivalent to St 35) or EN 10305-1 E355 (equivalent to St 52).
Summary
| Feature | Description |
|---|---|
| Standard | DIN 2391 (German Standard for precision steel tubes) |
| Type | Primarily seamless, cold-drawn (Part 1) |
| Material | Carbon Steel (e.g., St 35, St 52) |
| Key Advantage | High dimensional accuracy, excellent surface finish, high strength |
| Common Use | Hydraulic cylinders, automotive parts, precision mechanical components |
| Modern Equivalent | EN 10305-1 |
In conclusion, if you need a high-quality, precision carbon steel tube for a critical application where dimensions and surface finish matter, a pipe conforming to DIN 2391 / EN 10305-1 is an excellent choice.
