GB/T 3639 honed hydraulic cylinder tubing is made from precision cold-drawn or cold-rolled seamless steel grades 10#, 20#, 35#, 45#, and 25Mn. It offers high dimensional accuracy, smooth surface, and various mechanical properties depending on delivery condition. Widely used in hydraulic cylinders, machinery, automotive, construction, and agricultural equipment.
GB/T 3639 specifies Honed Hydraulic Cylinder Tubing (grades 10#, 20#, 35#, 45#, 25Mn) used in hydraulic cylinders, mechanical systems, and automotive components.
Chemical Composition
Steel Grade
C (%)
Si (%)
Mn (%)
P (≤ %)
S (≤ %)
Notes
10#
0.07–0.10
0.17–0.37
0.35–0.65
0.035
0.035
Cu ≤ 0.20% for hot-press use
20#
0.17–0.23
0.17–0.37
0.35–0.65
0.035
0.035
—
35#
0.32–0.39
0.17–0.37
0.50–0.80
0.035
0.035
—
45#
0.42–0.50
0.17–0.37
0.50–0.80
0.035
0.035
—
Mechanical Properties
Grade
Condition
Tensile (MPa)
Yield (MPa)
Elongation (%)
10#
+C (BK)
≥ 410
—
≥ 6
+LC (BKW)
≥ 375
—
≥ 10
+SR (BKS)
≥ 335
—
≥ 12
+A (GBK)
≥ 335
—
≥ 24
+N (NBK)
—
≥ 205
≥ 24
20#
+C
≥ 510
—
≥ 5
+LC
≥ 450
—
≥ 8
+SR
≥ 430
—
≥ 10
+A
≥ 390
—
≥ 20
+N
—
≥ 245
≥ 20
35#
+C
≥ 590
—
≥ 4
+LC
≥ 550
—
≥ 6
+SR
≥ 520
—
≥ 8
+A
≥ 510
—
≥ 17
+N
—
≥ 315
≥ 17
45#
+C
≥ 645
—
≥ 4
+LC
≥ 630
—
≥ 5
+SR
≥ 610
—
≥ 7
+A
≥ 590
—
≥ 14
+N
—
≥ 355
≥ 14
Execution Standard
Standard: GB/T 3639. Manufacturing: cold-drawn or cold-rolled. Delivery states include +C, +LC, +SR, +A, +N.
Applications
Extensively used for hydraulic cylinders, precision mechanical components, automotive parts; honed varieties (20# and 45#) serve aerial work platforms, agriculture, construction machinery, hydraulic jacks, etc.