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H8 E355 Din2391 Metric Honed Tubing

H8 E355 DIN2391 metric honed tubing represents a class of high-precision cold-drawn seamless steel tubes specifically engineered for demanding hydraulic cylinder applications. Manufactured in strict compliance with the DIN 2391 standard, this tubing combines exceptional dimensional accuracy, superior mechanical properties, and optimized surface characteristics to meet the rigorous requirements of modern hydraulic systems.

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Description

The tubing utilizes E355 grade steel (equivalent to ST52), a non-alloy quality steel known for its excellent strength-to-weight ratio and weldability. Its chemical composition is carefully controlled, with maximum limits of 0.22% carbon, 0.55% silicon, and 1.6% manganese, while maintaining low levels of phosphorus and sulfur (≤0.025%) to ensure enhanced toughness and resistance to brittle fracture. The material undergoes cold drawing followed by stress-relieving treatment (BK+S condition), resulting in improved mechanical properties with minimum tensile strength of 600 MPa, yield strength of 520 MPa, and elongation of 14%, providing reliable performance under high-pressure conditions.

The H8 inner diameter tolerance classification ensures precise dimensional control, with specific tolerance values ranging from 0.033 mm for 30 mm ID to 0.089 mm for 315-400 mm ID tubes. This level of precision guarantees optimal piston fitment, reduces bypass leakage, and enhances overall cylinder efficiency. Available in metric dimensions, the tubing offers outer diameters from 40 mm to 480 mm with corresponding inner diameters ranging from 30 mm to 400 mm, with standard lengths extending up to 12 meters.

The honing process creates a superior internal surface finish achieving roughness values between Ra 0.4-0.8 μm, characterized by a cross-hatch pattern that promotes optimal oil retention and distribution. For applications requiring even smoother surfaces, additional Skived and Roller Burnished (SRB) processing can achieve surface roughness as low as Ra 0.1-0.4 μm. The tubing maintains straightness within 0.5-1 mm per meter and wall thickness tolerances of ±5% to ±10% depending on diameter.

These precision honed tubes are essential components in hydraulic cylinders for construction equipment, industrial machinery, material handling systems, and mobile applications where reliability, efficiency, and longevity are critical. The combination of E355 material properties, H8 precision tolerance, and DIN 2391 compliance ensures consistent performance, reduced maintenance requirements, and extended service life in even the most demanding operating conditions.

Quality assurance includes comprehensive testing of mechanical properties, dimensional verification, surface quality inspection, and compliance certification, ensuring that each length of tubing meets the exacting standards required for high-performance hydraulic applications across global industries.

1. Chemical Composition

Steel grade	Chemical composition %
	C	Si	Mn	P	S	Cr	Ni	V	AI
	C	Si	Mn	≤				≥
C20	0.17-0.24	0.17-0.37	0.15-0.65	0.035	0.025	0.250	0.250	/	/
CK45	0.42-0.5	0.17-0.37	0.5-0.8	0.025	0.025	0.250	0.300	/	/
Q355B	≤0.2	≤0.5	1.0-1.6	0.030	0.030	0.030	0.250	0.080	0.015
Q355D	≤0.2	≤0.5	1.0-1.6	0.030	0.025	0.250	0.250	0.150	/
E355(ST52)	≤0.22	≤0.55	≤1.6	0.025	0.025	0.250	0.250	/	/
SAE1026	0.22-0.28	0.15-0.35	0.6-0.9	0.040	0.050	/	/	/	/
4130	0.28-0.33	0.15-0.35	0.4-0.6	0.040	0.040	0.80-1.10	/	/	/
4140	0.36-0.43	0.15-0.35	0.705-1.0	0.040	0.040	0.80-1.10	/	/	/

2.Mechanical Property:

Delivery condition	Cold finished(hard)(BK)		Cold drawn and stress-relieved(BK+S)
Steel grade	Rm MPa	Elongation A5%	Rm MPa	ReH Mpa	Elongation A5%
C20	≥550	≥5	≥520	≥375	≥15
CK45	≥645	≥5	≥600	≥520	≥10
Q355B	≥640	≥5	≥600	≥520	≥14
Q355D	≥640	≥5	≥600	≥520	≥14
E355(ST52)	≥640	≥5	≥600	≥520	≥14
SAE1026	≥640	≥5	≥600	≥520	≥15

3.Tolerance:

Tolerance	I.D Tolerance			Tolerance of wall thickness
Size of I.D.	H8	H9	H10	<120mm(O.D) ≥120mm up to 210mm >210mm	±5% ±7.5% ±10%
30	0.033	0.052	0.084
>30-50	0.039	0.062	0.1
>50-80	0.046	0.074	0.12
>80-120	0.054	0.087	0.14
>120-180	0.063	0.1	0.16
>180-250	0.072	0.115	0.185
>250-315	0.081	0.13	0.21
>315-400	0.089	0.14	0.23

4.Processing Form

Processing form	I.Dmm	Length	Straightness	I.D tolerance	I.D Roughness (RA)
Honed	40-500	≤12M	0.5-1/1000	H8-H9	0.4-0.8um
SRB	50-250	≤12M	0.5-1/1000	H8	0.1-0.4um

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