DIN 2391 ST 44 Seamless Precision Steel Tubes — EN 10305-1 E235 | Manufacturer and Supplier

DIN 2391 ST 44 is a seamless cold-drawn carbon steel precision tube manufactured to the German DIN 2391 Part 2 standard, now superseded by EN 10305-1 E235. The "ST 44" designation indicates a minimum tensile strength of approximately 440 MPa and a minimum yield strength of 235 MPa. Unlike hot-finished tubes, DIN 2391 tubes are cold-drawn after seamless piercing, which produces tight OD tolerances (±0.30 mm on most sizes), a smooth internal bore (Ra ≤ 0.8 µm in bright-annealed condition), and consistent wall thickness all critical for hydraulic cylinder bore machining and pneumatic actuator applications. The grade is fully interchangeable with EN 10305-1 E235.

ST 52 (EN 10305-1 E355) has a minimum yield strength of 355 MPa and tensile strength of approximately 490–630 MPa, versus ST 44's 235 MPa yield and 340–480 MPa tensile. For medium-pressure hydraulic systems below 350 bar working pressure, ST 44 provides adequate strength at lower material cost. ST 52 is specified when higher working pressures, thinner walls, or weight reduction are priorities common in heavy construction equipment, truck hydraulics, and high-cycle press systems. ST 44 is preferred where machinability and formability matter more than ultimate strength, such as automotive steering tubes and pneumatic actuator bodies where the tube is further formed or welded.

Yes. DIN 2391 ST 44 is a low-to-medium carbon steel. The chemical composition limits maximum carbon to 0.17%, manganese to 1.20%, and phosphorus and sulphur each to 0.030%, with aluminium minimum 0.012% for grain refinement. No alloying elements (Cr, Ni, Mo) are added, making it a plain carbon steel easy to weld without pre-heat, compatible with standard metalworking lubricants, and straightforwardly recyclable. It does not offer corrosion resistance, so protective coatings (phosphate, zinc, paint) or dry storage are required for long-term protection.

The primary applications are hydraulic cylinder barrels and rod tubes, pneumatic actuator bodies, automotive steering columns, shock absorber housings, and precision mechanical assemblies requiring close bore tolerances. The tight OD tolerance and smooth bore enable direct honing to final hydraulic bore size without pre-boring, reducing machining steps and cycle time. In the automotive sector, ST 44 / E235 is also specified for crash-relevant structural tubes door intrusion beams, bumper reinforcements where the balance of strength and cold-formability is critical.

Yes this is the grade's primary industrial use. DIN 2391 ST 44 tubes are designed specifically for hydraulic cylinder manufacture. The cold-drawing process produces an internal surface roughness of Ra 0.4–1.6 µm depending on size and finish, which can be honed to the Ra ≤ 0.4 µm bore finish required for seal integrity with minimal metal removal. Working pressure suitability depends on OD, wall thickness, and safety factor a 50 mm OD × 4 mm wall ST 44 tube supports approximately 185 bar working pressure at a 4:1 safety factor under ISO 4413 guidelines. Always confirm with a pressure calculation for your specific bore and wall. For pressures above 350 bar, upgrade to ST 52 / E355.

Yes. Pneumatic actuators operating up to standard industrial supply pressures (6–10 bar) are well within ST 44 capacity even at thin walls. The smooth bright-annealed bore reduces friction and seal wear, extending actuator service life. ST 44 is also used for compressed air distribution lines in machine tools, medical-grade pneumatic equipment, and food-grade installations where bore cleanliness is important. For clean-room or food-grade applications, ask about ISO cleanliness certification (flushed and capped ends) available on request.

The principal industries are: (1) Hydraulic Equipment Manufacturing cylinder barrels, rod tubes, valve bodies; (2) Automotive OEM & Tier 1 steering columns, crash structures, suspension components; (3) Agricultural Machinery tractor lift hydraulics, implement rams; (4) Industrial Automation pneumatic actuators, pick-and-place robot arms; (5) Construction Equipment excavator and crane cylinder barrels; (6) Material Handling conveyor tubes, dock leveller cylinders; (7) Medical Devices syringe bodies and gas manifolds requiring precision bore. Any industry currently using SAE J526 / J2614 welded tubes or ASTM A519 Grade 1020 seamless for hydraulic or pneumatic service can typically switch to DIN 2391 ST 44 with equivalent performance.