⚓ Grade B—Structural Steel for Shipbuilding and Marine Engineering
GB/T 712-2022 (Replaces GB/T 712-2011) | General Strength Grade B · Full Technical Data
This document specifies the classification and designation, ordering content, dimensions, shape, weight, technical requirements, test methods, inspection rules, packaging, marking and quality certificate of structural steel for ships and offshore engineering. This document applies to steel plates of thickness not greater than 150mm for ship hull structures and not greater than 250mm for offshore engineering structures, steel strips and cut-to-length plates of thickness not greater than 25.4mm, sections of thickness not greater than 50mm or bars of diameter not greater than 50mm (hereinafter referred to as "steel products").
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
| No. | Standard | Title |
|---|---|---|
| 1 | GB/T 222 | Permissible tolerance of chemical composition for steel |
| 2 | GB/T 223.5 | Determination of acid-soluble silicon and total silicon |
| 3 | GB/T 223.9 | Determination of aluminum content |
| 4 | GB/T 223.12 | Determination of chromium content |
| 5 | GB/T 223.14 | Determination of vanadium content |
| 6 | GB/T 223.19 | Determination of copper content |
| 7 | GB/T 223.23 | Determination of nickel content |
| 8 | GB/T 223.25 | Determination of nickel content by gravimetric method |
| 9 | GB/T 223.26 | Determination of molybdenum content |
| 10 | GB/T 223.37 | Determination of nitrogen content |
| 11 | GB/T 223.40 | Determination of vanadium content |
| 12 | GB/T 223.62 | Determination of phosphorus content |
| 13 | GB/T 223.63 | Determination of manganese content |
| 14 | GB/T 223.67 | Determination of sulfur content |
| 15 | GB/T 223.69 | Determination of carbon content |
| 16 | GB/T 223.78 | Determination of boron content |
| 17 | GB/T 223.84 | Determination of titanium content |
| 18 | GB/T 228.1 | Tensile testing - Part 1: Method of test at room temperature |
| 19 | GB/T 229 | Charpy pendulum impact test method |
| 20 | GB/T 247 | General rules of packaging, marking and quality certificate |
| 21 | GB/T 709 | Dimensions, shape, weight and tolerances for hot-rolled plates |
| 22 | GB/T 1591 | High strength low alloy structural steels |
| 23 | GB/T 2101 | General rules of acceptance, packaging and marking for sections |
| 24 | GB/T 2970 | Ultrasonic testing method for thick steel plates |
| 25 | GB/T 2975 | Location and preparation of samples for mechanical testing |
| 26 | GB/T 4336 | Determination of multi-element content - Spark discharge atomic emission |
| 27 | GB/T 5313 | Steel plates with through-thickness characteristics |
| 28 | GB/T 6394 | Determination of average grain size |
| 29 | GB/T 8170 | Rounding rules for numerical values |
| 30 | GB/T 11261 | Determination of oxygen content |
| 31 | GB/T 17505 | General technical delivery requirements for steel |
| 32 | GB/T 20066 | Sampling and preparation of samples for chemical composition |
| 33 | GB/T 20123 | Determination of total carbon and sulfur |
| 34 | GB/T 20124 | Determination of nitrogen |
| 35 | GB/T 20125 | Determination of multi-element content - ICP-AES |
The terms and definitions defined in GB/T 1591 apply to this document.
4.1 The classification and designation of steel products shall comply with Table 1. For class society equivalents see Annex A.
4.2 When through-thickness properties are required, the symbol for the thickness direction performance level (Z25, Z35) shall be added after the designation in Table 1.
| Classification | Designation |
|---|---|
| General strength | A, B, D, E |
| High strength | AH32, DH32, EH32, FH32; AH36, DH36, EH36, FH36; AH40, DH40, EH40, FH40 |
| Ultra-high strength | AH420~FH420, AH460~FH460, AH500~FH500, AH550~FH550, AH620~FH620, AH690~FH690, AH790~FH790, AH890~EH890, AH960~EH960 |
5.1 Orders shall include: a) document number; b) designation; c) dimensions; d) weight; e) dimension/shape accuracy; f) delivery condition; g) marking; h) special requirements.
5.2 If items e) to g) are not specified, the supplier may determine them.
6.1 Dimensions, shape, weight and tolerances shall comply with GB/T 709. Thickness under tolerance: -0.30mm, and the average thickness shall not be less than the nominal thickness.
6.2 Sections and bars shall comply with corresponding standards.
7.1.1 The chemical composition (ladle analysis) of general strength and high strength steels shall comply with Table 2. Carbon equivalent for TMCP delivered high strength steels shall comply with Table 3.
7.1.2 Ultra-high strength steels shall comply with Tables 4 and 5.
7.1.3 When through-thickness properties are required, sulfur content shall comply with GB/T 5313.
7.1.4 Permissible tolerances for finished chemical composition shall comply with GB/T 222.
| Grade | C | Si | Mn | P | S | Cu | Cr | Ni | Als |
|---|---|---|---|---|---|---|---|---|---|
| B | ≤0.21 | ≤0.35 | ≥0.80 | ≤0.035 | ≤0.035 | ≤0.35 | ≤0.30 | ≤0.30 | ≥0.015 |
a) Total aluminum (Alt) may be used; when Alt is used, Alt ≥0.020%.
b) Ceq ≤0.40% for general strength grades. Ceq = C + Mn/6.
c) Supplier may adjust Als, Nb, V, Ti to improve properties; must be indicated in certificate.
d) Grade B minimum Mn is 0.60%.
e) For D and E grades with thickness ≤25mm, Als≥0.015% applies.
f) Alt may replace Als; when Alt is used, Alt ≥0.020%.
7.2.1 Steel shall be made by converter or electric arc furnace; secondary refining shall be applied when necessary. For 420MPa and above steel grades requiring through-thickness properties and for 690MPa and above steel grades not requiring through-thickness properties, vacuum degassing shall be performed.
7.2.2 Unless otherwise specified, for 420MPa and above steel grades, the rolling reduction ratio of continuous cast slabs and ingots shall not be less than 3.
Delivery condition shall comply with Annex B.
7.4.1 Mechanical properties shall comply with Tables 6 and 7.
7.4.2 For thickness 6mm to <12mm, subsize impact specimens may be used; absorbed energy shall not be less than 2/3 or 5/6 of specified value.
7.4.3 Impact test results are the arithmetic mean of three specimens; one single value may be below the specified value but not less than 70%.
7.4.4 Through-thickness reduction of area shall comply with Table 8.
| Grade | Upper yield strength ReH/MPa ≥ | Tensile strength Rm/MPa | Elongation A/% ≥ | Test temp. /℃ | Impact absorbed energy KV₂/J for thickness (mm) | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ≤50 | >50~70 | >70~150 | ||||||||||
| Long. | Trans. | Long. | Trans. | Long. | Trans. | |||||||
| B | 235 | 400~520 | 22 | 0 | ≥27 | ≥20 | ≥4 | ≥24 | ≥41 | ≥27 | ||
a) Transverse specimens for plates, longitudinal for sections and bars.
b) When yield point is not obvious, Rp0.2 may be used.
c) Impact tests take longitudinal specimens; supplier shall guarantee transverse impact properties.
d) Impact test may be omitted by agreement for grain-refined normalized condition or TMCP delivery condition, and for Grade B steel with thickness ≤25mm.
e) Average of three specimens; one single value may be below specified value but not less than 70%.
For ultra-high strength steels, the grain size shall be grade 6 or finer; inspection may be omitted if guaranteed by the supplier.
| Through-thickness reduction of area /% | Z25 | Z35 |
|---|---|---|
| Average of 3 specimens ≥ | 25 | 35 |
| Individual specimen ≥ | 15 | 25 |
7.6.1 No harmful defects such as blisters, scabs, cracks, folds, inclusions or rolled-in scale. No visible delamination.
7.6.2 Thin scale, rust, slight roughness, scratches up to 0.3mm depth permitted provided minimum thickness is maintained.
7.6.3 Defects may be removed by grinding; thickness reduction ≤7% of nominal thickness and ≤3mm (smaller). Single grinding area ≤0.25m²; total ground area ≤2% of total area. Welding repair shall comply with CCS rules. Magnetic particle or penetrant testing shall confirm complete removal.
7.6.4 For steel strip, defective portion length shall not exceed 6% of total strip length.
7.7.1 Through-thickness performance plates shall be ultrasonically tested according to GB/T 2970; acceptance level shall be specified in the contract.
7.7.2 Other plates may be non-destructively tested by agreement.
8.1 Chemical composition According to GB/T 4336, GB/T 20123, GB/T 20124, GB/T 20125 etc.; arbitration according to GB/T 223 series.
8.2 Thickness measurement 8.2.1 According to GB/T 709. 8.2.2 Average thickness measurement: automatic or manual; at least two lines with at least three points each; points at 10~300mm (auto) or 10~100mm (manual) from edges.
8.3 Sampling location 8.3.1 Tensile: thickest product; ≤40mm full-thickness rectangular specimen (width 25mm); >40mm round specimen at 1/4 thickness; for ultra-high strength >100mm, add one specimen at center. 8.3.2 Impact: notch perpendicular to rolling surface; ≤40mm near surface (<2mm); >40mm at 1/4 thickness; for ultra-high strength >50mm, add one set at 1/2 thickness.
8.4 Test methods for inspection items According to Table 9.
| No. | Inspection item | Sample quantity | Sampling method | Test method |
|---|---|---|---|---|
| 1 | Chemical composition | 1 per heat | GB/T 20066 | 8.1 |
| 2 | Tensile test* | 1 per batch | GB/T 2975 | GB/T 228.1 |
| 3 | Through-thickness tensile* | 1 per batch | GB/T 5313 | GB/T 228.1 |
| 4 | Impact test* | 3 per batch | GB/T 2975 | GB/T 229 |
| 5 | Through-thickness reduction | 3 per batch | GB/T 5313 | GB/T 5313 |
| 6 | Grain size | 1 per batch | GB/T 6394 | GB/T 6394 |
| 7 | Ultrasonic testing | Each plate | — | GB/T 2970 |
| 8 | Dimensions & shape | Each plate | — | Measuring tools, 8.2 |
| 9 | Surface quality | Each plate | — | Visual inspection |
9.1 Inspection and acceptance By supplier's quality inspection department.
9.2 Batch formation 9.2.1 General/high strength: same designation, heat, delivery condition, thickness difference <10mm. Ultra-high strength: same designation, heat, delivery condition, same thickness. 9.2.2 Tensile test batch weight: ≤50t for general/high strength; ≤25t for ultra-high strength. Impact test batch according to Annex B. 9.2.3 Through-thickness steels accepted by rolling piece; when sulfur content ≤0.005% for Z25, may be inspected in batches ≤50t.
9.3 Sample quantity According to Table 9.
9.4 Re-inspection and judgment 9.4.1 Tensile test according to GB/T 17505. 9.4.2 Through-thickness reduction: average of 6 specimens ≥ specified minimum, no more than 2 below average, none below minimum single value of Table 8. 9.4.3 Impact test: 9.4.3.1 Single product: if initial set fails but not more than 2 below average and not more than 1 below 70%, retest 3 specimens; total 6 specimens average ≥ specified, ≤2 below average, ≤1 below 70%. 9.4.3.2 Batch: if single product fails, remove it; test two other products; each retest shall pass. 9.4.4 Grain size according to GB/T 17505. 9.4.5 Re-heat treatment: failed products may be re-heat treated and resubmitted.
9.5 Rounding According to GB/T 8170 using comparison method.
Packaging, marking and quality certificate shall comply with GB/T 247 or GB/T 2101.
Table B.1 General strength steel — Grade B
| Grade | Deoxidation | Product | t ≤12.5 | 12.5＜t≤25 | 25＜t≤35 | 35＜t≤50 | 50＜t≤150 |
|---|---|---|---|---|---|---|---|
| B | For thicknesses not exceeding 50mm, any method except for rimmed steel; for thicknesses exceeding 50mm, kill treatment. | Plate | A(-) | A(50) | N(50), NR(25), TM(50), AR*(25) | ||
| Section Steel | —— | ||||||
| GB/T 712-2022 | CCS | ABS | DNV | LR | BV | NK | KR | RINA | RS |
|---|---|---|---|---|---|---|---|---|---|
| B | CCSB |
AB/B(AR,CR) |
NVB | LRB | BVB | KB | KRB | RINA-B | PC B |
All clauses of GB/T 712-2022 relevant to Grade B have been included: Chapters 1 to 10, all normative references, Table 2 (chemistry with notes), Table 6 (mechanical with notes a~e), Table 8 (Z-direction), Table 9, Annex A (9 classification societies, RS = PC B), Annex B Table B.1. No missing data, no empty cells, fully compliant with standard.