LR AH42 Steel Plate | LR/AH42 Marine Steel Plate

Technical Reviewer: Jack | SHH STEEL Material Solutions Department · Updated: 2026-10-27

LR AH42, often written LR/AH42 on mill certificates and plate markings, is an extra-high-strength hull structural steel under Lloyd’s Register Rules for the Manufacture, Testing and Certification of Materials. IACS Unified Requirement W16 covers this strength band (yield 420 N/mm²); LR implements corresponding requirements in its Materials rules. Minimum yield is 420 N/mm², tensile 530–680 N/mm², elongation 18 % min., with Charpy at 0 °C. It sits above the AH–FH 40 higher-strength family (max yield 390 N/mm² under UR W11). Commercial enquiries use LR AH42 or LR/AH42 marine steel plate.

Equivalent grades: LR AH42 ≈ ASTM A131 (no direct grade at this strength) ≈ ABS AH42 / AQ43 ≈ DNV NV A420 ≈ BV A420 ≈ CCS AH420 ≈ NK KA420 ≈ KR RA43 ≈ RINA A420 ≈ GB 712 Grade AH420 (all class-approved, stamped by the issuing society).

Naming note: Lloyd’s Register titles this strength band as AH42 / LR/AH42 (LR uses AH69, not AH70). DNV often titles the same yield as AH420 / DNV NV A420. ABS often titles AH42 (official ABS AQ43). ASTM A131 has no grade at this strength. Write LR/AH42 on the LR purchase order.

LR/AH42 is almost always produced TM or QT by an LR-approved mill to order rather than taken from open stock. SHH STEEL sources extra-high-strength plate from mills with Lloyd’s Register approval for the grade, under Surveyor attendance, with optional multi-class and EN 10204 3.2.

Maximum plate thickness depends on delivery condition and the mill’s LR approval sheet — typically TM up to about 100–150 mm and QT higher, but treat the approval limit as governing (UNCERTAIN without local LR PDF). Primary commercial scope we quote is within ~100 mm unless the mill approval and LR survey confirm otherwise.

Product (check) analysis column: LR Rules for Materials specify heat (ladle) limits; no numeric product-analysis tolerance is tabulated in the rule text reviewed, so product (check) limits are agreed on the order or taken from the approved mill specification and certificate.

Source: IACS UR W16 chemistry envelope as implemented by Lloyd’s Register for LR/AH42 — exact ladle limits depend on delivery condition (TM vs QT) and toughness letter. Values above are the rule envelope; the purchase order and mill approval sheet govern. Product analysis: as per standard and mill certificate. All intentionally added elements and Ceq (or CET/Pcm) are to be reported. Flagged UNCERTAIN where a local LR Materials PDF was not available to quote paragraph numbers.

Final acceptance values are as per standard and mill certificate under LR survey. For thick plate, additional mid-thickness tensile/impact positions may apply — confirm at enquiry. Test frequency is typically each heat-treatment batch of same cast/condition/thickness.

Charpy temperature is fixed by the grade letter: AH → 0 °C. Indicative average energy 42 / 28 J (L/T) from IACS UR W16 aligned tables — confirm exact figures on the LR-endorsed certificate. Unlike UR W11 higher-strength tables, EHS energies are usually stated as a single pair rather than rising through many thickness bands; thick-plate mid-thickness rules may still apply.

Allowed delivery conditions are primarily TM and QT within the mill’s approved thickness. Vacuum degassing is commonly required for higher categories and for thicker plate — follow the mill approval. State TM or QT on the PO; do not leave delivery condition blank for AH42.

Lloyd’s Register applies IACS UR W13 unless the PO states otherwise (confirm minus class on PO; see UNCERTAIN). Surface repair limits follow the applicable LR / UR rules; state primer/surface class on receipt if needed. For QT plate, avoid notching cut edges; follow mill cutting recommendations.

Extra-high grades such as LR/AH42 are rarely held as open stock; the table shows the size bands we quote against scheduled mill rolls. Quantities are indicative. All plates sold as LR class carry LR/AH42 marking and an LR-endorsed mill certificate. Typical mill lead time including LR survey is about 6–10 weeks (commercial estimate — confirm per quote). Send your size list and we will reply with the next available rolling slot.

Packing. Plates are bundled by size with steel strapping, marked with heat number, grade and LR stamp, and shipped in containers (up to about 11.8 m) or break bulk for longer plates.

These are comparisons, not substitutions. Always write the LR stamp LR/AH42 on the PO, plus any additional society stamps you need.

Use AH42 when scantlings need yield 420 N/mm². Do not substitute AH40/EH40 (390 N/mm² max under UR W11) without redesign. Within the 42 band, letter choice is toughness: AH 0 °C → DH −20 °C → EH −40 °C → FH −60 °C. Neighbouring strengths are AH–FH 40 / 46 — swapping strength needs class approval of the drawing change.

When LR LR/AH42 is the right choice: typical uses are higher-strength hull girder plating (deck, bottom, side shell) of bulk carriers, tankers and container ships in normal service where 0 °C toughness suffices at extra-high yield — weight-critical hull girder strakes, polar and ice-class primary structure, and offshore units where 420 N/mm² is specified. See offshore platform steel plates for related offshore grades.

Typical uses: higher-strength hull girder plating (deck, bottom, side shell) of bulk carriers, tankers and container ships in normal service where 0 °C toughness suffices at ReH 420 N/mm²; strength deck and shell of large container ships and gas carriers where EHS is specified; ice-belt and polar primary structure; selected offshore members. See offshore platform steel plates.

Welding: LR/AH42 is an extra-high-strength steel supplied TM or QT. Welding must follow a procedure qualified for this grade and approved by LR. Ceq/CET/Pcm from the ladle analysis govern hydrogen control, preheat, interpass and heat-input windows. Too much heat input can lower HAZ strength and toughness in QT plate. We send the certificate values before shipment so your welding engineer can confirm the procedure fits. We do not give generic preheat temperatures.

Processing notes: LR/AH42 owes its strength to TM or QT processing. Hot forming or stress relieving above the tempering temperature can lower the properties, so any heat treatment after delivery must be agreed with the mill and LR. Cold forming and bending radii should follow the mill’s data sheet. Thermal cutting parameters follow mill recommendations so the cut edge is not damaged.

LR survey at the mill; certificate includes ladle chemistry, Ceq/CET/Pcm as applicable, tensile (ReH ≥ 420, Rm 530–680, A ≥ 18 %), Charpy at 0 °C, delivery condition, UT if ordered, and plate identity. Optional EN 10204 3.2 and multi-class.

On receipt: verify LR/AH42 stamp, 0 °C impact data, energies ≥ ordered/certified minima, thickness within tolerance, Surveyor endorsement, UT report if required.

Charpy acceptance for LR/AH42 (IACS UR W16 aligned; actual results as per standard and mill certificate):

For thickness above ~100 mm, additional mid-thickness rules may apply — confirm at enquiry. If the PO asked for 3.2, the inspector’s report must name the witnessed tests and plate numbers.

• Ordering “LR 42” without the letter (AH) — toughness missing
• Writing ABS AH42 or DNV AH420 on an LR-class PO without arranging that society’s survey (wrong stamp)
• Leaving delivery condition blank (TM vs QT changes price, mill and properties)
• Expecting ASTM A131 dual-cert at this strength (A131 has no EHS grade)
• Skipping UT on thick EHS plate when the yard specification requires it
• Missing LR endorsement / assuming GB 712 Grade AH420 alone is class approval
• Confusing LR AH69 with ABS AH70 — same yield band, different society title

Write grade, TM/QT, impact temperature, UT level and certificate type into the PO.

Specify LR AH42 (LR/AH42), delivery condition TM or QT, thickness × width × length × qty, Z/U/UT level, multi-class, certificate type, port. Send to SHH STEEL.

Sample PO line: “Steel plate to Lloyd’s Register Rules for Materials, Grade AH42 (LR/AH42), delivery condition [TM/QT], 30 × 2500 × 12000 mm, 10 pcs, marked LR AH42 / LR/AH42, certificate endorsed by LR Surveyor, EN 10204 3.2 [if required], UT [EN 10160 / ASTM A578 level], CIF [port].”

LR AH42 / LR/AH42 is extra-high-strength hull steel (IACS UR W16 band): yield 420 N/mm², tensile 530–680 N/mm², Charpy at 0 °C, marking LR/AH42. Lock on the order: TM or QT, UT level, Ceq/CET/Pcm reporting, multi-class and 3.2.

SHH STEEL supplies LR/AH42 plate rolled by Chinese mills that hold Lloyd’s Register works approval for the grade, so every plate carries the LR/AH42 stamp and a Surveyor-endorsed certificate traceable to its heat. Sizes are scheduled into the mill rolling cycle with LR survey arranged at the mill. On request we add EN 10204 3.2 certificates with third-party witness (TÜV, SGS, BV or another agency) and joint certification with ABS, DNV, BV, CCS, NK, KR or RINA.

We accept T/T or L/C payment, with inspection before the balance is paid. Small quantities in several sizes, or LR/AH42 with neighbouring EHS sizes or higher-strength AH–FH 40 where the drawing allows, can be combined in one container. A dedicated coordinator sends production and shipping updates with photos, and our own workshop cuts to size, bevels, drills and machines plates before shipment so they arrive ready for fabrication.

Request a quotation: send SHH STEEL the grade (LR/AH42 / LR AH42), thickness, width, length, quantity per size and destination port, plus any multi-class, Z/U or 3.2 certificate requirement. We reply with price, available stock and lead time.