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GB 6653 HP325 steel, also written as GB/T 6653 HP325, GB/T6653-2017 HP325 and HP325 gas cylinder steel, is a weldable carbon-manganese steel for hot-rolled and cold-rolled plates and strips used to make welded gas cylinders. Gangsteel (HENAN GANG IRON AND STEEL) produces and exports HP325 hot-rolled coil, pickled strip, slit strip, cut plate and cold-rolled annealed sheet with EN 10204 3.1/3.2 certificates for LPG and industrial gas cylinder makers.
Data source: GB/T 6653-2017 Steel plates and strips for welded gas cylinders (issued 2017-12-29, effective 2018-09-01, replaces GB/T 6653-2008), Clauses 1, 3, 6 and Tables 1 and 2. The current edition covers five grades: HP235, HP265, HP295, HP325, HP345. Compared with 2008 it revised chemical composition, impact, inclusion and surface quality requirements. Always confirm the edition named on the purchase order.
| C max | Si max | Mn max | P max | S max | Nb max | V max | Ti max | Nb+V max | Als min |
|---|---|---|---|---|---|---|---|---|---|
| 0.20 | 0.35 | 1.50 | 0.025 | 0.012 | 0.05 | 0.10 | 0.06 | 0.12 | 0.015 |
Als may be replaced by total Al, in which case Al total ≥ 0.020%. Residual Cr, Ni and Mo are each ≤ 0.30% and Cu ≤ 0.20%. Rare earth elements may be added to improve internal quality, and product analysis tolerances follow GB/T 222. Steel is made in a converter or electric furnace and secondary refined.
| Grade | Lower yield strength ReL min (MPa) | Tensile strength Rm (MPa) | A80 min (%) t < 3 mm | A min (%) t ≥ 3 mm | 180° bend, mandrel D |
|---|---|---|---|---|---|
| HP325 | 325 | 490–600 | 18 | 22 | 2.0a (a = thickness) |
Tensile and bend test pieces are taken transverse to the rolling direction; Rp0.2 is used when yielding is not distinct, and the referee bend specimen width is 35 mm.
For HP325 plate and strip 6 mm and thicker a room-temperature Charpy V-notch test is made on transverse sub-size specimens (10 x 5 x 55 mm for 6–8 mm, 10 x 7.5 x 55 mm for over 8 to under 12 mm); the result is the average of three specimens and one value may be below the requirement but not below 70% of it. Material under 6 mm is not impact tested. Grain size must be No. 6 or finer to GB/T 6394. By agreement the buyer may add a -40°C Charpy test (replacing the room-temperature test), a yield ratio ReL/Rm ≤ 0.80 and a non-metallic inclusion rating to GB/T 10561. The 2017 edition revised the impact energy values; Gangsteel quotes the applicable Table 3 values on the order confirmation.
| Product | Thickness range (mm) | Delivery condition | Tolerance standard |
|---|---|---|---|
| Hot-rolled plate and strip | 2.0 – 14.0 | Hot rolled, controlled rolled or heat treated; hot rolled and pickled by agreement | GB/T 709 |
| Cold-rolled plate and strip | 1.5 – 4.0 | Annealed | GB/T 708 |
Each heat is analysed and each batch is tested for tensile and bend properties (plus impact for 6 mm and above). Surfaces must be free of cracks, scabs, folds, blisters, inclusions and laminations. Gangsteel supplies HP325 in coil, slit coil, cut plate and circular blanks, and SGS, BV or TUV witness inspection can be arranged.
HP325 is higher-strength welded cylinders and larger vessels such as vehicle LPG tanks, where wall thickness and tare weight are reduced. Cylinder makers form the heads by deep drawing and join them with submerged-arc or MAG circumferential seams, so the low carbon, low sulphur and fine-grain practice of GB/T 6653 is aimed at forming and weld quality.
| Standard | Comparable grade (approximate) |
|---|---|
| GB/T 6653 | HP325 |
| Foreign equivalents | JIS G3116 SG325/SG365 range, EN 10120 P310NB / P355NB range (approximate, no exact counterpart) |
| Other GB 6653 grades | HP235 | HP265 | HP295 | HP345 |
Equivalents are engineering references only; thickness range, chemistry limits and test rules differ, so dual certification requires the stricter combined limits on the order and the mill certificate.
HP325 is a carbon-manganese steel grade in GB/T 6653-2017, the Chinese national standard for steel plates and strips for welded gas cylinders. The letters HP come from the pinyin initials of 焊瓶 (welded cylinder), and 325 is the minimum lower yield strength in MPa.
The current edition is GB/T 6653-2017, issued on 29 December 2017 and effective from 1 September 2018, which fully replaced GB/T 6653-2008. It is a recommended (GB/T) standard, and it still contains the same five grades HP235, HP265, HP295, HP325 and HP345.
The heat analysis of HP325 is C 0.20% max, Si 0.35% max, Mn 1.50% max, P 0.025% max and S 0.012% max, with acid-soluble aluminium of at least 0.015%. Nb, V and Ti may be added up to 0.05%, 0.10% and 0.06% respectively, with Nb + V not exceeding 0.12%.
HP325 must reach a lower yield strength ReL of at least 325 MPa and a tensile strength of 490–600 MPa on transverse test pieces. Minimum elongation is 18% on A80 for thickness below 3 mm and 22% for 3 mm and above, and the 180° transverse bend test uses a mandrel diameter of 2.0a.
GB/T 6653-2017 covers hot-rolled HP325 plate and strip from 2.0 mm to 14.0 mm thick and cold-rolled plate and strip from 1.5 mm to 4.0 mm thick. Dimensions and tolerances follow GB/T 709 for hot-rolled and GB/T 708 for cold-rolled products.
Hot-rolled HP325 is delivered as hot rolled, controlled rolled or heat treated, and it can be supplied hot rolled and pickled when this is agreed in the contract. Cold-rolled HP325 is always delivered in the annealed condition.
A room-temperature Charpy V-notch test on transverse sub-size specimens is required only for HP325 plate and strip of 6 mm and thicker, and material below 6 mm is not impact tested. By agreement the buyer can specify a -40°C impact test instead, a yield-to-tensile ratio of 0.80 max and a non-metallic inclusion rating.
The nearest foreign grades to HP325 are JIS G3116 SG325/SG365 range, EN 10120 P310NB / P355NB range (approximate, no exact counterpart). These are engineering comparisons only, because thickness range, chemistry and test rules differ, so the order and mill certificate should name GB/T 6653 HP325.
HP325 is higher-strength welded cylinders and larger vessels such as vehicle LPG tanks, where wall thickness and tare weight are reduced.
State the standard number GB/T 6653-2017, the product type (plate or strip), the grade HP325, the delivery condition, the size and tolerance and the weight, plus any optional requirements such as -40°C impact or inclusion rating. For example: 200 t hot-rolled pickled strip 2.5 x 1250 mm C, GB/T 6653-2017 HP325, EN 10204 3.1.
Gangsteel supplies GB/T 6653 HP325 with a mill certificate to EN 10204 3.1 showing heat analysis, transverse tensile, bend and, where applicable, impact results, and 3.2 certificates with SGS, BV or TUV witness are available on request.
GB 6653 Hub | GB 6653 HP235 | GB 6653 HP265 | GB 6653 HP295 | GB 6653 HP325 | GB 6653 HP345 | EN 10120 | GB/T 713 | Boiler Steel Plate | Pressure Vessel Steel Plate
