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GB 6653 HP345 steel, also written as GB/T 6653 HP345, GB/T6653-2017 HP345 and HP345 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 HP345 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 |
|---|---|---|---|---|---|
| HP345 | 345 | 510–620 | 17 | 21 | 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 HP345 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 HP345 in coil, slit coil, cut plate and circular blanks, and SGS, BV or TUV witness inspection can be arranged.
HP345 is the highest-strength GB/T 6653 grade, used for lightweight welded cylinders, vehicle LPG tanks, fire-extinguisher bodies and thicker welded industrial gas cylinders up to 14 mm. 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 | HP345 |
| Foreign equivalents | EN 10120 P355NB, JIS G3116 SG365 (approximate) |
| Other GB 6653 grades | HP235 | HP265 | HP295 | HP325 |
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.
HP345 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 345 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 HP345 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%.
HP345 must reach a lower yield strength ReL of at least 345 MPa and a tensile strength of 510–620 MPa on transverse test pieces. Minimum elongation is 17% on A80 for thickness below 3 mm and 21% 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 HP345 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 HP345 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 HP345 is always delivered in the annealed condition.
A room-temperature Charpy V-notch test on transverse sub-size specimens is required only for HP345 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 HP345 are EN 10120 P355NB, JIS G3116 SG365 (approximate). These are engineering comparisons only, because thickness range, chemistry and test rules differ, so the order and mill certificate should name GB/T 6653 HP345.
HP345 is the highest-strength GB/T 6653 grade, used for lightweight welded cylinders, vehicle LPG tanks, fire-extinguisher bodies and thicker welded industrial gas cylinders up to 14 mm.
State the standard number GB/T 6653-2017, the product type (plate or strip), the grade HP345, 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 HP345, EN 10204 3.1.
Gangsteel supplies GB/T 6653 HP345 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.
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