DIN 2391 ST45 Thick Wall High Precision Steel Tube
Sep 28, 2026
DIN 2391 ST45 (material number 1.0408) is a cold-drawn seamless precision steel tube supplied in the heavy-wall band with outside diameters from 4 to 260 mm and wall thicknesses from 0.5 to 25 mm. It holds a precise outside-diameter tolerance (±0.08 to ±0.45 mm by size) and ±10 % wall tolerance, so even at 8–25 mm walls it lands ready for machining without the scale and out-of-roundness of hot-rolled stock. The yield you design to is set by the delivery condition - ReH 255 MPa normalized (NBK) up to 375 MPa stress-relieved (BKS) - and St45 is the EN 10305-1 grade E275, not E355 or St52.
DIN 2391 ST45 seamless tube is a medium-carbon, cold-finished precision tube: the name "St45" signals a minimum tensile floor near 450 MPa, not the carbon level. It is the right choice when a shaft, sleeve, cylinder body or structural member needs tight size control and a clean surface, but does not need the higher yield of St52 (E355). Send your OD × wall, length and delivery condition to get a quoted lead time.
Technical Specifications
DIN 2391 ST45 dimensions span outside diameters of 4–260 mm and wall thicknesses of 0.5–25 mm, with the heavy-wall band (8–25 mm) as the focus of this page. The DIN 2391 ST45 wall thickness tolerance is ±10 % (minimum ±0.10 mm) even at heavy walls, and the DIN 2391 tolerance OD wall thickness is what separates precision tube from commodity pipe.
| Parameter | Capability |
|---|---|
| Standard | DIN 2391-1 / -2 (also supplied to EN 10305-1) |
| Grade / material no. | St45 / 1.0408 (EN 10305-1 E275; ASTM A519 1045; GB/T 3639 45#) |
| Outside diameter | 4 – 260 mm |
| Wall thickness | 0.5 – 25 mm (heavy-wall focus 8 – 25 mm) |
| Length | Up to 12 m (6 m stock common; cut-to-length available) |
| OD tolerance (precise class) | ±0.08 mm (4–30 mm) to ±0.45 mm (91–100 mm); wider on larger sizes |
| Wall tolerance | ±10 % (min ±0.10 mm); ±5 % special |
| Straightness | ≤1.5 mm/m standard; ≤1.0 / ≤0.5 mm/m on request |
| Delivery conditions | BK (+C), BKW (+LC), BKS (+SR), GBK (+A), NBK (+N) |
| Surface / protection | Drawn finish; rust-preventive oil, phosphating or varnish on request |
| Certification | EN 10204 3.1 MTC; third-party inspection (SGS/BV/TUV) available |
Chemical Composition
The DIN 2391 ST45 chemical composition below is the ladle-analysis limit set by the standard; the "45" is a tensile floor, not a carbon level.
| Element | St45 (1.0408) max/min | Note |
|---|---|---|
| Carbon (C) | ≤ 0.21 % | Medium-carbon; the "45" is not the carbon level |
| Silicon (Si) | ≤ 0.35 % | Deoxidation / strength |
| Manganese (Mn) | ≥ 0.40 % | DIN 2391 St45 minimum; EN 10305-1 E275 carries a different Mn bound |
| Phosphorus (P) | ≤ 0.025 % | Cleanliness control |
| Sulfur (S) | ≤ 0.025 % | Cleanliness control |
| Nb / Ti / V (optional) | ≤ 0.03 / ≤ 0.03 / ≤ 0.05 % | Micro-alloy additions permitted, total ≤ 0.05 % |
Every controlled element bounds a risk: carbon and manganese drive strength, while phosphorus and sulfur are kept low for cleanliness and consistent cold drawing. When you cross to EN 10305-1 E275, the manganese limit changes, so the material certificate must state the exact standard you ordered.
Mechanical Properties by Delivery Condition
DIN 2391 ST45 mechanical properties change with the delivery condition, which is why a single yield figure is misleading - the table lists every condition.
| Delivery condition | Symbol | Tensile Rm | Yield ReH | Elongation A5 |
|---|---|---|---|---|
| Cold-drawn hard | BK (+C) | ≥ 580 MPa | not specified | ≥ 5 % |
| Cold-drawn soft | BKW (+LC) | ≥ 520 MPa | not specified | ≥ 8 % |
| Cold-drawn, stress-relieved | BKS (+SR) | ≥ 520 MPa | ≥ 375 MPa | ≥ 12 % |
| Annealed | GBK (+A) | ≥ 390 MPa | not specified | ≥ 21 % |
| Normalized | NBK (+N) | 440 – 570 MPa | ≥ 255 MPa | ≥ 21 % |
The cold-drawn hard (BK) and soft (BKW) conditions quote only tensile and elongation; the standard does not set a yield for them. Only the stress-relieved (BKS) and normalized (NBK) conditions give a minimum ReH. Any single "St45 yield 300 MPa" figure is therefore incomplete unless it names the delivery condition - the most common misstatement we correct.
St35 vs St45 vs St52 Grade Ladder
| Grade (mat. no.) | EN 10305-1 | Min. tensile (typical) | ReH (stress-relieved) | Use when |
|---|---|---|---|---|
| St35 (1.0308) | E235 | ≈ 350 MPa | ≥ 315 MPa | Light forming, lowest strength need |
| St45 (1.0408) | E275 | ≈ 450 MPa | ≥ 375 MPa | Medium strength, good weldability, heavy wall |
| St52 (1.0580) | E355 | ≈ 520 MPa | ≥ 450 MPa | Higher yield required (high-pressure cylinders) |
St45 sits between St35 and St52. St45 vs St52 is the most common grade confusion on DIN 2391 drawings, so it is worth stating plainly: St45 is the EN 10305-1 grade E275 - not E355, which belongs to St52. If your drawing says "St45" and a supplier offers "E355 / St52" as "the same thing," the yield and elongation differ and the substitution should be rejected or re-approved by the designer.
St45 vs St52 vs St35 - which grade
| If your design needs… | Choose | Why |
|---|---|---|
| Highest yield, high-pressure cylinder | St52 (E355) | ReH ≥ 450 MPa stress-relieved |
| Medium strength + easy welding + heavy wall | St45 (E275) | ReH up to 375 MPa, simpler weld procedure |
| Light forming, lowest cost | St35 (E235) | Lower strength, best formability |
Within St45, the delivery condition - not the grade - sets the usable strength. Pick it by what happens after delivery:
Choosing the delivery condition
| Condition | ReH | Pick it when… |
|---|---|---|
| BK (+C) | not specified | Maximum hardness/spring, no further forming |
| BKW (+LC) | not specified | Light bending or flaring after delivery |
| BKS (+SR) | ≥ 375 MPa | Machining + moderate stress, highest usable yield |
| GBK (+A) | not specified | Maximum ductility for deep forming |
| NBK (+N) | ≥ 255 MPa | Balanced strength/ductility, weld-friendly base |
Applications
St45 precision tube is chosen where size control and surface quality drive the design more than peak strength. Five application groups cover most orders:
Hydraulic cylinder bodies and sleeves
St45 thick wall tube is a common parent for hydraulic and pneumatic cylinder barrels. The bore is later honed or roller-burnished; the heavy wall carries the hoop stress while the tight OD means the outer surface needs little correction.
Mechanical shafts and guide columns
For machine-tool spindles, guide rods and precision shafts, the cold-drawn surface and straightness (≤1.5 mm/m, tighter on request) let the tube go to machining with minimal stock removal.
Automotive and powertrain components
St45 is used for steering, suspension and drivetrain sleeves where repeatable dimensions cut assembly scrap. The stress-relieved (BKS) condition is the usual choice when the part is later bent or machined.
Structural and support members
In frames and fixtures the heavy-wall St45 tube gives stiffness at a lower cost than fully heat-treated alloy grades, while keeping the clean cold-drawn surface.
Tooling and jig bases
Because the wall can be held to ±10 % even at 8–25 mm, jig and fixture builders use St45 heavy-wall tube as a stable, drill-ready stock.
Why Source DIN 2391 ST45 from GNEE
As a DIN 2391 precision tube supplier with 18+ years of export experience, GNEE covers both legacy DIN 2391 and current EN 10305-1 specifications. What you get:
Dual-standard supply. We deliver to DIN 2391 or EN 10305-1 with the matching certificate, so legacy and new designs are both covered.
Heavy-wall stock and rolling. OD 4–260 mm, wall up to 25 mm, lengths to 12 m, with cut-to-length and end preparation.
Verification you can audit. EN 10204 3.1 MTC, third-party inspection (SGS/BV/TUV) and full heat-number traceability on every bundle.
Export experience. 18+ years supplying 60+ countries, with rust-preventive packing and documentation for sea freight.
Quality Control and Testing
Chemical analysis - ladle analysis against DIN 2391 St45 limits (C ≤0.21 %, Mn ≥0.40 %, P/S ≤0.025 %).
Tensile and flattening / drift-expanding tests - verify Rm, elongation and ductility per the ordered delivery condition.
Dimensional verification - OD, wall and straightness checked against the precise-class tolerances.
Non-destructive leak test - eddy current (transverse defects) and/or ultrasonic (longitudinal defects) testing; hydrostatic test available.
Surface and visual inspection - free of loose scale on heat-treated tubes; lubricant film noted on as-drawn tubes.
Material certificate - EN 10204 3.1 with grade, heat number and size for full traceability.
Send your OD × wall, length, delivery condition (BK/BKW/BKS/GBK/NBK) and any bore finish - our technical team will confirm the specification and return a quotation with lead time, typically within 24 hours. Contact GNEE today.
FAQ
What is DIN 2391 ST45?
DIN 2391 ST45 (material number 1.0408) is a cold-drawn seamless precision steel tube in a medium-carbon grade. It is supplied to tight outside-diameter and wall-thickness tolerances (OD ±0.08 to ±0.45 mm by size, wall ±10%) and is used where dimensional accuracy and a controlled surface finish matter more than bulk pipe strength.
Is DIN 2391 ST45 the same as E355 or St52?
No. St45 carries material number 1.0408 and maps to EN 10305-1 grade E275, while St52 (1.0580) maps to E355. The two grades have different yield strengths (St52 ReH ≥355 MPa; St45 ReH up to 375 MPa only in the stress-relieved condition) and are not interchangeable on a drawing.
What does the number 45 in St45 mean?
The 45 denotes the minimum tensile strength of about 450 MPa (the historic 45 kgf/mm² floor), not the carbon content. Carbon in St45 is capped at 0.21 %, so the grade name should never be read as 0.45 % carbon.
What delivery conditions are available for DIN 2391 ST45?
Five conditions are offered: BK (cold-drawn hard, +C), BKW (cold-drawn soft, +LC), BKS (stress-relieved, +SR, ReH ≥375 MPa), GBK (annealed, +A) and NBK (normalized, +N, ReH ≥255 MPa). The condition you choose sets the yield strength and elongation, not the grade.
What wall thickness counts as thick wall for ST45 precision tube?
Standard DIN 2391 covers wall thickness from 0.5 to 25 mm. We treat the 8–25 mm band as the heavy-wall range: at these walls the tube still holds ±10 % wall tolerance and precise OD, which a hot-rolled heavy-wall tube cannot match without machining.
Can DIN 2391 ST45 be used for hydraulic cylinder barrels?
Yes as the base precision tube; the bore is then honed or burnished to H7–H10 and Ra 0.2–0.8 µm. For the finished cylinder barrel many buyers specify EN 10305-1/-4 or a dedicated honed-tube specification, so confirm the bore finish requirement on the order.
Is DIN 2391 still a valid standard?
In the EU, DIN 2391 has been replaced by the harmonised EN 10305-1 for new designs, but DIN 2391 remains valid for legacy German drawings and is still widely specified in Asian and machinery markets. We can supply to either designation with identical product.
What is the chemical composition of ST45?
Per DIN 2391 St45: Carbon ≤0.21 %, Silicon ≤0.35 %, Manganese ≥0.40 %, Phosphorus ≤0.025 %, Sulfur ≤0.025 %. Small Nb/Ti/V additions (≤0.03–0.05 %) are permitted.
