Recently, a new batch of DIN 2391 St52 cold-drawn precision seamless steel tubes for India has been successfully completed. Before shipment, Botop Steel has carried out strict dimensional inspection to ensure that the product fully meets the customer's technical requirements and accuracy standards (photos of the inspection are attached at the end of the article).
Precision steel tubes are steel tubes with tight dimensional tolerances and high surface quality, which are widely used in hydraulic equipment, pneumatic systems, automotive parts and other applications requiring high fit accuracy.
The commonly used standards for precision seamless steel tubes include DIN 2391, EN 10305-1, and GB/T 3639. Among them, DIN 2391 St52 is a widely used grade, known for its good mechanical properties and excellent machinability.
Delivery condition is an important factor that affects the performance of precision steel tubes, as it involves different heat treatment processes applied to the tubes.
| DIN 2391 | EN 10305-1 and GB/T 3639 | Designation | Description |
| BK | +C | Cold finished (hard) | Tubes do not undergo heat treatment following the final cold forming and, thus, have a rather high resistance to deformation. |
| BKW | +LC | Cold finished (soft) | The final heat treatment is followed by cold drawing involving limited deformation. Appropriate further processing allows a certain degree of cold forming (e.g. bending expanding). |
| BKS | +SR | Cold finished and stress-relieved | Heat treatment is applied following the last cold forming process. Subject to appropriate processing conditions, the increase in the residual stresses involved enables both forming and machining to a certain degree. |
| GBK | +A | Annealed | The last cast cold forming process is followed by annealing in a controlled atmosphere. |
| NBK | +N | Normalized | The last cold forming process is followed by annealing above the upper transforming point in a controlled atmosphere. |
The BK (+C) and BKW (+LC) tubes are only cold worked and do not require heat treatment, while the BKS (+SR), GBK (+A), and NBK (+N) require a corresponding heat treatment process after cold working.
For this order, the customer requires DIN 2391 St52 precision seamless tubes in BK condition. The material properties of St52 in the different delivery states are described in more detail below.
| Steel grade | Chemical composition in % by mass | ||||
| C | Si | Mn | P | S | |
| DIN 2391 St52 | 0.22 max | 0.55 max | 1.60 max | 0.025 max | 0.025 max |
| Final Supply Condition | Tensile Strength Rm | Yield Strength ReH | Elongation A5 |
| BK | Min 640 Mpa | — | Min 4 % |
| BKW | Min 580 Mpa | — | Min 7 % |
| BKS | Min 580 Mpa | Min 420 Mpa | Min 10 % |
| GBK | Min 490 Mpa | — | Min 22 % |
| NBK | 490 – 630 Mpa | Min 355 Mpa | Min 22 % |
This order consists of several specifications, this time we are showing the specification of the tube with OD 100mm × ID 80mm. According to DIN 2391, the tolerance of OD and ID for this specification is ±0.45 mm, but in this case, the customer demanded a higher level of accuracy and specified a tolerance of ±0.2 mm. In order to meet the customer's requirements, Botop Steel has specially optimized the control of dimensional accuracy of this product, and inspected each steel pipe one by one before shipment to ensure that all the requirements are met.
Some of the actual inspection photos are attached below:
Outer Diameter Inspection (OD: 80 ±0.2 mm)
Inner Diameter Inspection (ID: 80 ±0.2 mm)
Length Inspection
Botop has been deeply engaged in the steel pipe industry for many years, and its insistence on quality and good reputation has won wide customer trust and market recognition. Through close cooperation with customers, the company continuously optimizes its products and services to meet the ever-changing market demands.
If you have any steel pipe needs, you can contact us, the professional team is ready to serve you.
Post time: May-09-2025