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ASTM A131 Grade B is an ordinary-strength (general strength) hull structural steel plate with a minimum yield point of 235 MPa and a tensile strength within 400–520 MPa. It sits in the same 235 MPa band as grades A, D and E of the ASTM A131 / A131M family, and what separates it from grade A is the Charpy impact test carried out at 0 °C — grade B is the level you specify once the hull structure has to hold toughness at, and just below, freezing point.
Shipbuilding steel plate and sheet of A131 Grade B are common strength steel plate for hull constructions. Because no "H" appears in the name, grade B is not a high-strength grade: the strength level is read from the standard’s mechanical table, not from the designation. Before the plate goes into production it is normally given the standard yard pre-treatment — shot blasting and painting with shop primer — so it arrives at the fit-up stage already clean and temporarily protected.
235 MPaYield Strength (Min)ASTM A131 Grade B
400–520 MPaTensile StrengthASTM A131 Grade B
21 % / 24 %Elongation (Min)200 mm / 50 mm gauge length
0 °CImpact Test TemperatureSource data sheet
02Technical Specifications
ASTM A131 Grade B plate supplied to your drawing, with cutting, forming, blast cleaning, shop priming and marine certification handled on the same order.
Produced to order — thickness, width and length confirmed against your drawing and the rolling schedule
Surface Condition
Smooth surface, uniform texture, no cracks, no rust spots
Pre-treatment Before Use
Steel plate pre-treatment is necessary before use — shot blasting and painting with shop primerShot BlastingShop Primer
Heat Treatment
Normalized, Quenched, Tempered, Impact Test — optional if not provided in rules NormalizedQuenchedTemperedImpact Tested
Delivery Condition
Confirmed per order and stated on the MTC — ASTM A131 / A131M does not lock the plate to a single delivery condition As RolledNormalizedTMCPOther as agreed
Custom Production
Available — custom sizes, cutting and shaping to your drawings
MOQ
From 1 ton (the lowest bracket of the published quantity schedule), larger tonnages negotiable
Lead Time
1 – 10 t: 5 days · 10 – 50 t: 10 days · > 50 t: negotiable (stock and rolling schedule confirmed on enquiry)
Certification
MTC / EN 10204 3.1 / Classification society certificate — approval available from ABS, LR, GL, CCS, NK, DNV, BV, RINA and KR
Payment Terms
L/C, T/T, D/P, Western Union, Paypal, Money Gram
Note: The source data sheet for this product publishes no width or length range, so no size range is printed here — send us your required thickness, width, length, quantity and classification society and we will confirm stock status, the applicable delivery condition and the rolling slot against the item before you order. The heat treatments listed above are published as optional if not provided in rules: where your specification or classification society does not call for one, the plate is supplied in the condition agreed on the order, and that condition is what appears on the mill certificate. The quantity brackets are the published schedule; they are estimates, not a contractual lead time.
03Grade Designation
Grade B is named differently from the AH / DH / EH / FH grades you may be comparing it with — the letter is a strength category plus a toughness level, not a temperature code plus a kgf/mm² number.
Designation Segment
Meaning in ASTM A131 / A131M
A131
The ASTM specification for structural steel for ships — hull plate, sheet and sections surveyed under classification society rules
Grade B
The ordinary-strength category. There is no "H" in the name, so this is not a higher-strength grade, and there is no kgf/mm² number in the name — the strength level is read from the standard’s mechanical table, not from the designation
235 MPa
The minimum yield point the grade must meet, taken from the mechanical property table rather than from the grade name
0 °C
The temperature at which the low-temperature impact test is carried out for this grade — the property that separates grade B from grade A inside the 235 MPa group
A131/B
The short mill / trading notation for the same grade — you will see both "Grade B" and "A131/B" on certificates and inquiries
Note: The quickest way to read an A131 grade is to look for the H. Grade A / B / D / E (no H) are the ordinary-strength levels at 235 MPa, separated by impact test temperature; AH32 / AH36 / AH40 / DH36 / EH36 / EH40 and the rest are the higher-strength levels, where the number is the minimum yield in kgf/mm² (32 ≈ 315, 36 ≈ 355, 40 ≈ 390 MPa). Within the ordinary-strength group the ladder runs A → B → D → E into progressively lower test temperatures — our sibling grade pages publish 0 °C for grade B, and −20 °C and −40 °C for grades D and E respectively. That is why "Grade B" and "AH40" must never be read as two versions of the same thing — the first is a 235 MPa plate, the second a 390 MPa plate. The designation explanation above is standard background for this grade family.
04Equivalent & Classification Society Grades
For global shipbuilding and repair bidding, ASTM A131 Grade B has matching grade-B equivalents under the major classification societies, so the same strength level can be procured across standards.
Standard System
Equivalent Grade
Note
ABS Standard
ABS Grade B
American Bureau of Shipping approval for ordinary-strength hull structures
LR Standard
LR Grade B
Lloyd’s Register approval
DNV Standard
DNV Grade B
Det Norske Veritas approval
GL Standard
GL Grade B
Germanischer Lloyd approval — GL has since been merged into DNV GL, so current projects are normally issued under DNV
CCS Standard
CCS Grade B
China Classification Society approval
Remaining IACS societies
NK Grade BBV Grade BRINA Grade BKR Grade B
Nippon Kaiji Kyokai, Bureau Veritas, RINA and Korean Register approvals — nine societies in total: ABS, LR, GL, CCS, NK, DNV, BV, RINA and KR
Note: Equivalent grade-B grades differ slightly in chemical composition and production process. Verify welding parameters and inspection standards against your actual ship classification requirements before substituting one for another. Tell us which society your vessel is surveyed under and we will supply the plate with the matching certificate.
05Chemical Composition
Chemical composition for A131/B ship steel — heat analysis, % max as published in the source data sheet.
Grade
C
Si
Mn
P
S
A131/B
0.21
0.35
0.80
0.035
0.035
Note: Carbon is capped at 0.21%, silicon at 0.35% and manganese at 0.80%, with phosphorus and sulphur at 0.035% each. Two things to watch when you read a certificate against this table. First, this source table gives manganese as a fixed 0.80 maximum, whereas the data sheet published for grade A expresses manganese as 2.5 × C — the two columns are not written the same way, so compare each plate against the table that belongs to its own grade. Second, the source publishes only these five elements: there is no carbon-equivalent (C + Mn/6) column and no micro-alloying or residual element column (Nb, V, Ti, Al, Cu, Cr, Ni, Mo, N), so no value is printed for them here — where a project or a classification society sets a cap on any of them, it is stated on the mill certificate.
06Welding Performance Parameters
Two indices are used to evaluate welding crack sensitivity and carbon equivalent for production and welding process guidance.
Note: Lower Pcm and Ceq mean better weldability and lower preheat demand. Both are calculated from the actual heat analysis of each plate, so we quote the values together with the MTC rather than as fixed numbers. As an ordinary-strength carbon–manganese grade, A131 Grade B sits at the easy-to-weld end of the shipbuilding range — but where the order calls for one of the optional heat treatments (normalized, quenched or tempered), the as-delivered microstructure changes, so confirm preheat and interpass control against your welding procedure specification for that condition.
07Mechanical Properties
Mechanical property for A131 Grade B shipbuilding structural steel, together with the low-temperature impact test required for the grade.
Grade
Yield Strength Min
Tensile Strength
Elongation Min (200 mm)
Elongation Min (50 mm)
Impact Test Temperature
Energy 1 (Transverse)
Energy 2 (Longitudinal)
A131/B
235 MPa
400–520 MPa
21 %
24 %
0 °C
—
—
Note: The source table reports elongation on two gauge lengths — 21% minimum on a 200 mm gauge and 24% minimum on a 50 mm gauge. That is the same ductility expressed on two different gauge lengths, not two different materials; the shorter gauge always reads higher, so quote the one your specification calls up. Energy 1 is the transverse impact test and Energy 2 is the longitudinal impact test, and both cells are blank in the source table — the source states that the low-temperature impact test is carried out at 0 °C but publishes no joule value, so the energy columns are left empty rather than filled with a figure the source does not support. The source also gives a single row rather than a set of thickness brackets; mechanical values for thicknesses outside the published coverage are confirmed on enquiry. Tell us the thickness, the gauge length your specification uses and the classification society, and we will confirm the applicable requirement from the mill certificate for your specific plate.
08Applications & Typical Components
A131 Grade B shipbuilding steel plate / marine steel plate is mainly used in construction for ships — hull construction where a 235 MPa plate with a 0 °C impact test is what the drawing calls for.
1
Hull Shell & Bottom Plating
Shell plating, bottom and side shell, bilge strakes — the general-strength envelope of barges, workboats, tugs and coastal vessels trading in cold water.
2
Ship Body Structure
Internal structure of the ship body: bulkheads, frames and stringers, decks of general-strength vessels, tank tops and non-critical hull members.
3
Shipyard Repair & General Fabrication
Renewal plate, brackets, seatings, foundations and general marine fabrication, where the pre-blasted and shop-primed plate goes straight into fit-up.
Application Field
Typical Application & Components
Hull Construction
Hull of vessels — shell plating, bottom plating, side shell, bilge strake
Ship Body Structure
Bulkheads, frames, stringers, decks of general-strength vessels, tank tops
Shipyard Repair & Fabrication
Repair and renewal plate, brackets, seatings and general marine fabrication
Note: Grade B earns its 235 MPa and holds it down to 0 °C. Where the structure has to stay tough well below freezing, the ordinary-strength siblings go further down the ladder — ASTM A131 Grade D and ASTM A131 Grade E sit at the same 235 MPa level and are tested lower again; ASTM A131 Grade A sits at the warm end of the group. Where the section is limited by strength instead of by temperature, move up to a higher-strength grade such as AH32, AH36, DH36 or EH36. Send us the design temperature and the required strength and we will confirm which grade your project actually needs.
09Processing & Fabrication Services
Every order can be cut, formed, blast cleaned, primed and independently inspected, so material arrives at the yard ready to fit.
1
Cutting
Custom sizes and shapes cut to your drawings, plate and profile.
2
Bending & Forming
Plate bending and shaping for hull sections and structural components.
3
Shot Blasting & Shop Primer
Plate pre-treatment — shot blasting and painting with shop primer — applied before shipment, as the grade requires before use.
4
Inspection & Certified Delivery
MTC and EN 10204 3.1 with every shipment; UT, Z-direction test and third-party inspection (SGS) can be arranged on request.
We supply high-quality ASTM A131 Grade B shipbuilding steel plates with strict marine standard inspection and full traceability. We provide one-stop customized processing services including cutting, bending and forming, plus shot blasting and shop priming to your surface specification. All products are equipped with official MTC test reports and marine certification documents, and UT, Z-direction and third-party (SGS) testing can be arranged on request. BBN Group is one of the leading manufacturers, suppliers and exporters of ASTM A131 Grade B plates — welcome to contact us for professional quotations and technical support!
Short answers to the questions we are asked most often about ASTM A131 Grade B. For anything not covered here, send us your drawings and specification.
Q1What does Grade B mean in ASTM A131?
It is one of the ordinary-strength categories of the specification. Unlike AH32 / AH36 / AH40, there is no H and no number in the name, so the grade name carries no kgf/mm² figure — the 235 MPa minimum yield comes from the standard’s mechanical table, not from the designation. You will also see the same plate written A131/B on mill paperwork.
Q2What is the difference between Grade A, Grade B, Grade D and Grade E?
All four are ordinary-strength A131 grades at the same 235 MPa minimum yield and 400–520 MPa tensile — what separates them is the impact test temperature band they are specified for. Grade B is tested at 0 °C; our sibling pages publish −20 °C for Grade D and −40 °C for Grade E, while Grade A sits at the warm end of the group. Pick the level that carries the test temperature your design calls for rather than assuming one of them covers the others.
Q3Does the source publish an impact energy value for Grade B?
It publishes the test temperature — 0 °C — and nothing else: the Energy 1 (transverse) and Energy 2 (longitudinal) cells are blank on the data sheet. We therefore state the temperature as published and leave the energy cells empty rather than quoting a joule value the source does not give. Tell us the thickness and the classification society and we will confirm the applicable requirement from the mill certificate for your specific plate.
Q4What sizes, heat treatments and lead times can you supply?
Plate is produced to order — thickness, width and length are confirmed against your drawing and the rolling schedule, because the source publishes no size range. Heat treatment is normalized, quenched, tempered or impact tested, optional if not provided in rules. The published quantity schedule is 1 – 10 t: 5 days, 10 – 50 t: 10 days, > 50 t: negotiable, with MOQ from 1 ton. Payment is by L/C, T/T, D/P, Western Union, Paypal or Money Gram and every shipment carries an MTC / EN 10204 3.1 certificate.
Q5Does the plate need pre-treatment before it is used?
Yes — before these ship plates go into production, steel plate pre-treatment is necessary, consisting of shot blasting and painting with shop primer. We can carry that out on the same order so the plate reaches your yard clean and temporarily protected, which removes a step from your own line and keeps the surface stable during storage and transport.
Q6Can A131 Grade B be supplied with classification society approval?
Yes. The mill holds approval from nine international classification societies — ABS, LR, GL, CCS, NK, DNV, BV, RINA and KR, so the equivalent grade-B plate can be delivered with the certificate your vessel is surveyed under. There are slight differences in chemical composition and production process between societies, so verify welding parameters and inspection standards against your actual classification requirements before material replacement. Note that GL has since been merged into DNV GL, so current projects are normally issued under DNV.
Get Your ASTM A131 Grade B Shipbuilding Steel Plate Quotation
Send us your plate dimensions (thickness / width / length), quantity, delivery condition and classification society requirement. We will reply with the latest stock status, competitive wholesale price and complete marine certification documents within 24 hours.
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