Precision steel seamless tubes for the automotive industry

Standards and steel grades,
Tube sizes acc. to EN standard,
Tube sizes acc. to ASTM standard,
Tube sizes acc. to JIS standard.

Precision tubes for the automotive industry are made using the cold drawing process. The rolled seamless tubes are used as the semi-finished product. As an example, precision tubes are used for production of steering systems, cardan shafts, shock absorbers and air springs, parts of the chassis, axle shafts, construction parts of chassis and axles, steering components, seats construction, bracing for dashboard. Precision tubes are made from carbon and alloyed steel. Overview of dimensional standards and technical-delivery conditions of the precision tubes for the automotive industry is presented in a separate overview.

Tube dimensions for the automotive industry

Outside diameter ranges from 4 to 125 mm and wall thickness ranges from 0.5 to 13.0 mm. Precision steel tubes are delivered according to EN 10305-1, DIN 2391, BS 6323/4, NF A 49-310, UNI 7945. STN 42 6711 and 42 6712, ČSN 42 6711 and 42 6712, GOST 8734, 9567, 12132, PN-H 74240 a 74220, ASTM A519 and JIS G3445. Detailed overviews of produced dimensions are presented in dimensional tabled, according to EN standards, ASTM standards, and JIS standards.

Steel grades for precision tubes for the automotive industry

Precision tubes for the automotive industry are made from the following steels. According to STN and ČSN 42 0260; 11 353, 11 453, 11 503, 11 550, 11 650, 12 040, 12 050, 12 060, according to EN 10305-1; E215, E235, E255, E355, 26Mn5, C35E, C45E, 25CrMo4, 42CrMo4 and according to DIN 2391-2; St35, St45, St52. Additional steel grades according to BS 6323/1 and BS 6323/4, NF A 49-310 and NF A 49-312, UNI 7945, GOST 8733, GOST 21729, PN-H 74840, ASTM 519, JIS G3445, together with its chemical composition and its mechanical properties are presented in a separate table . Steels are produced in electric arc furnace and it is fully killed. Upon request other steel grades may be supplied.

Delivery condition and thermal processing of precision tubes for the automotive industry

Precision tubes are supplied in condition that is presented in the table below. It is marking for thermal processing according to EN 10305-1. Marking for material condition according to STN 42 0002 and STN 42 0004, ČSN 42 0002 and ČSN 42 0004, DIN 2391-2 and ASTM 519 may be found here.

+CCold drawn / hard. After the last cold forming no heat treatment.
+LCCold drawn / soft. After the last heat treatment follows the cold drawing there is a light finishing pass.
+SRCold drawn and stress relieved annealed. After the final cold drawing process the tubes are stress relieved annealed in a controlled atmosphere.
+A After the final cold drawing process the tubes are stress relieved annealed in a controlled atmosphere.
+NNormalized. After the last cold drawing process the tubes are annealed in a controlled atmosphere.

Length of precision tubes for the automotive industry

- random length precision tubes in the range of 3 – 7 (9) m
- approximate length with tolerance +/- 500 mm
- exact length with tolerance – 0 / +x mm (x upon agreement)
- tubes for the automotive industry may be delivered either as cut tubes or as bended tubes

Tolerances for precision tubes for the automotive industry

Tolerances of the precision tubes are in accordance with the appropriate dimensional tables of standards. Usual value for the outside diameter (D) is less than 0.5% (D) in no heat treatment process used (+C and +LC according to the European Standards). For the heat treated tubes the tolerance values are dependent upon the relation of the wall thickness and the tube diameter (t/D) up to a single or twofold. In tolerances of the outside diameter (D) the allowed deviation of circularity is included. When ordering based on the wall thickness, the tolerance is 10% from the wall thickness. Eccentricity of precision tube is included in the wall thickness tolerance.
Zeleziarne Podbrezova a.s. offers precision tubes with reduced tolerances, i.e. tolerances that are reduced compared to standard values. Reduced tolerances are presented in a separate table.

Wall thickness of precision tubes, according to the ASTM A450 Standard is presented in the BWG table and is converted to inches and millimeters. Usually the tubes are supplied with the wall thickness tolerance of –0 +20% (calculated from the minimal wall thickness). Upon agreement the precision tubes are supplied with the wall thickness tolerance of 10% (calculated from the medium wall thickness).

Straightness of precision tubes for the automotive industry

Straightness of the tubes is influenced by the mechanical properties of the tubes. For material having the yield point ReH <= 500 MPa is straightness 0,0015 x L (L – tube length) maximum, allowed straightness for one meter length is 1.5 : 1000. For material with the yield point ReH > 500 MPa the allowable straightness for the whole length of the tube is 0.0020 Xx L, allowed straightness of one meter is 2 : 1000.

Surface condition of precision tubes for the automotive industry

Surface condition of a tube meets the appropriate standards and depends upon the process of manufacturing the tube and its thermal processing. Precision tubes must have smooth outer and inner surface. The roughness value (Ra) is less or equals to 4 micrometers (0.004 mm) for the outer surface in the tubes in the +SR, +A and +N condition and is less or equals to 4 micrometers (0.004 mm) for the outer and inner surface of the tubes in the +C and +LC condition.

Ends of precision tubes for the automotive industry

Ends of the tubes are square to the longitudinal axis of the tubes and are free of burrs. Upon agreement the tubes may be supplied with mechanically machined ends. Likewise the ends of the tubes may be capped with plastic caps.

Marking of precision tubes and bundles of precision tubes

Marking of standard precision tubes is done according to standards or upon agreement by the InkJet system either in one spot or along the whole length of a tube. Bundle marking is done either by one or multiple labels with required data.

Surface protection of precision tubes for the automotive industry

Tubes are supplied with anticorrosion application. The type of protection is a subject of agreement.

Packaging of precision tubes for the automotive industry

Tubes are delivered in bundles with either circular or hexagonal shape weighing maximum 2000 kilograms.
Tubes are tied with steel band. Packaging into a plastic foil or wooden crated is possible upon agreement.

Testing of precision tubes for the automotive industry

Testing is performed according to the appropriate standards. Test selection is according to standards or as per agreement with customer. The mandatory tests for standard precision tubes are chemical analysis, tensile test, dimensional inspection and visual inspection.

Specific testing – acceptance testing certificate 3.1.B (3.1.A, 3.1.C).
Elective testing: flattening test or drift expanding test, roughness measurement and NDT to find longitudinal defects: eddy current (STN 01 5054, ČSN 01 5054, PRP 02-74, SEP 1925, ASTM E 309, EN 10246-3 Grade E3 for OD > 6 mm, WT > 0,5 mm), stray flux (STN 01 5047, ČSN 01 5047, SEP 1913, ASTM E 570, EN 10246-5 Grade F3 for OD > 32 mm, WT > 2 mm), and ultrasound (STN 01 5028, ČSN 01 5028, SEP 1915, ASTM E 213, EN 10246-7 Grade U3 for OD >10 mm, WT > 2 mm), NDT as a proof of tightness or leakage test by eddy current EN 10246-1.

Certificates for precision tubes

Certificates are issued according to standards, as an example we are showing: EN 10 204 (non-specified testing – 2.2, specified testing 3.1.B or 3.1.A, 3.1.C).

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