Standard DIN 2393 covers precision welded tubes produced from alloys like ST 52.3 BKS. this high precision tube is well suited for several applications like Auto and motorcycle shock absorber, Electric industry, Construction machinery, Gas spring, Hydraulic system steel tube, Heat exchanger as well as for Condenser. These industries prefer the use of DIN 2393 Grade St 52-3 tubes as they have the need for a dimensionally accurate product. In some instances, the St 52.3 DIN 2393 ISO H9 is also used where smaller wall thickness or a reliable surface condition is a mandate.

These letters decide the mechanical properties you actually receive. They are the most important line on your order.

Symbol	DIN term	Condition	Surface	Use
BK	Bright finished, cold finished	No heat treatment after final draw	Bright	Maximum strength, low ductility
BKW	Bright finished + light cold work	Light final pass	Bright	Some forming still possible
BKS	Stress relieved	Stress-relief annealed	Bright	Machining without distortion
GBK	Annealed	Soft annealed	Dark, scaled	Softest, best for bending
NBK	Normalised	Normalised above the transformation point	Dark, scaled	Uniform properties, weldable, machinable

NBK is the most requested condition for hydraulic and structural tube. Normalising removes the internal stress left by cold drawing, gives consistent properties along the whole length, and makes the tube safe to weld and machine. If your tube will be welded into a frame, order NBK.

Mechanical Properties (St52-3 / S355)

Thickness (mm)	Min. yield ReH (MPa)	Tensile Rm (MPa)	Min. elongation (%)
≤ 16	355	490 – 630	22
16 – 40	345	490 – 630	21
40 – 63	335	490 – 630	20
63 – 80	325	490 – 630	18
80 – 100	315	490 – 630	18
> 100	By agreement	490 – 630	By agreement

Chemical Composition (max %, DIN 17100 ladle analysis)

C	Si	Mn	P	S	N	Cu
0.20	0.55	1.60	0.040	0.040	0.012	0.55

Equivalent Grades

Standard	Grade
DIN 17100	St52-3 (1.0570)
EN 10025-2	S355J2 (1.0577); St52-3U → S355J0 (1.0553)
ASTM	A572 / A572M Grade 50
GB/T 1591	Q355C
JIS G3106	SM490B / SM490C
IS	2062 E350

A572 Gr. 50 guarantees 345 MPa, not 355. It is 10 MPa below St52-3. Do not substitute it into an existing St52-3 design without recalculating.

Surface and End Finish

Option	Detail
Bare / bright	As drawn or normalised
Black painted	Varnish coating for transport protection
Galvanized	Hot-dip or electro
Oiled	Internal and external rust prevention
3PE / FBE	Pipeline-grade corrosion coating
Ends	Plain, bevelled, threaded, capped

Typical Applications

Application	Condition usually ordered
Hydraulic cylinders, honed tubes	NBK / BKS
Shock absorbers, motorcycle and auto	NBK
Gas springs	NBK, tight ID tolerance
Construction machinery booms	NBK
Heat exchangers, condensers	NBK or GBK
Structural framing, welded frames	NBK

FAQ

1.Is St52-3 low-alloy steel?

No. It is an unalloyed (non-alloy) structural steel under DIN 17100. Low-alloy grades start with things like 16MnCr5 or 42CrMo.

2.Is St52-3 the same as S355?

Effectively yes, with a caveat. St52-3 was withdrawn in 2004 and replaced by S355 in EN 10025-2. St52-3 maps closest to S355J2. Your certificate will likely say S355.

3.What does NBK mean?

Normalised. The tube is heat-treated above its transformation point and cooled in air, giving uniform mechanical properties and removing the stress from cold drawing. It is the right choice when you will weld or machine the tube.

4.Which condition should I order for a hydraulic cylinder?

NBK or BKS. NBK for consistent properties and weldability; BKS if you need stress-relief without a full normalise.

5.Can I weld St52-3?

Yes, with all common processes. Use low-hydrogen consumables and preheat thicker sections. Ask for the CEV on the certificate first.

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