Seamless Precision Steel Tubes according to EN 10305-1
Standard: DIN2391 part 2 , DIN EN10305-1, DIN17175 etc;
Manufacturing method: cold-rolled / cold-drawn
Delivery condition: BK,BKS,SR,GBK,NBK.
Factory Certification: 2.2 according to EN
Acceptance Test Certificate:3.1 according to EN 10204
in bundles tied with steel strips. External packing by wooden cases if the wall thickness/OD ratio is low.
Oil-coating is generally necessary especially for export.
Used in hydraulic & pneumatic cylinder ,automobile and other mechanical device .Feature: high precision and high brightness, the inner and outer surface of the tubes have high cleanness without oxide, mechanical properties of the final tubes also come out excellent, promising no leakage under high pressure, no deformation after cold-bent and no cracks when flaring and flattening, ensuring the efficient operation in all service.
NBK means protective heat-treating under the non-oxidation environment to get a bright and smooth surface for the tubes.
DIN 2391-81 Part 2 Seamless Precision steel tubes(DIN2391-81)
Standard DIN 2391 defines the technical delivery conditions for seamless precision steel tubes according to DIN 2391 Part 1 which are made from the steel grades listed in section 5.
Tubes according to this Standard are mainly used where accuracy to dimension and, possibly, small wall thicknesses and good surface condition are required.
number Material number Mfg. Process C
St35 1.0308 S 0.17 0.35 0.4 0.05 0.05
St45 1.0408 S 0.21 0.35 0.4 0.05 0.05
St52 1.0508 S 0.22 0.55 1.6 0.05 0.05
Mechanical and technological properties
Code number Material number Cold-finished hard(BK) Cold-finished/soft (BKW) 3)
Rm(Mpa) A(%) Rm(Mpa) A(%)
St 35/E235 1.0308 480 6 420 10
St 45 1.0408 580 5 520 8
St 52/E355 1.0508 640 4 580 7
Code number Cold finished (soft)(BKW) Annealed (GBK) Normalized (NBK)
Rm(Mpa) ReH (Mpa) A(%) Rm(Mpa) A(%) Rm (Mpa) ReH (Mpa) A(%)
St 35/E235 420 315 14 315 25 340-470 235 25
St 45 520 375 12 390 21 440-570 255 21
St 52/E355 580 450 10 490 22 490-630 355 22
-The yield point for the annealed (GBK)condition on delivery is at least 50% of the (ultimate) tensile strength. Depending upon the degree of deformation in the drawing operation, the yield point of tubes delivered in the cold-finished/hard (BK)and cold-finished/soft(BKW) conditions, may be increased to a level close to the tensile strength.
-In calculating the yield point, the following values are recommended : cold-finished/hard condition on delivery > 80% of the tensile strength, cold-finished/soft condition on delivery > 70% of the tensile strength.
The tubes are supplied in the following quality grades :
A) precision steel tubes intended primarily for mechanical stressing, without any particular quality requirement and without acceptance test certificate.
B) precision steel tubes intended primarily for mechanical stressing, with special quirement and exclusively with acceptance test certificate.
C) precision steel tubes with special requirement according to section 12. Theses requirements and corresponding tests must be agreed, with the customer having to specify his requirements at the time of enquiry and on ordering.
Condition on delivery:
Term Symbol Explanation
(cold-finished as-drawn) BK No heat treatment after the last cold-forming process. The tubes therefore have only low deformability.
(lightly cold-worked) BKW After the last heat treatment there is a light finishing pass (cold drawing) With proper subsequent processing, the tube can be cold-formed (e.g. bent, expanded) within certain limits.
Annealed GBK After the final cold-forming process the tubes are annealed in a controlled atmosphere or under vacuum.
Normalized NBK The tubes are annealed above the upper transformation point in a controlled atmosphere or under vacuum.