LR AH55 Steel Plate | AH55 Shipbuilding Steel Plate

LR AH55 steel plate, also written as LR/AH55, LR Grade AH55, Lloyd's Register AH55 or simply AH55 steel plate, is an extra-high-strength, fine-grain structural steel of the Lloyd's Register Rules for Materials (Ch 3, Section 10, high strength steels for welded structures) with 550 MPa minimum yield (t ≤ 50 mm), 640-820 MPa tensile strength and Charpy V-notch toughness at 0°C [32°F]. In the grade name "A" is the toughness class, "H" means high strength and "55" is the yield level (55 kgf/mm² class, i.e. 550 N/mm²); the IACS UR W16 designation is AH550. Gangsteel, a steel plate exporter, supplies LR AH55 plates in TM or QT condition, cut to size for offshore platforms, jack-up legs and racks, ship structures and other heavy marine steelwork.

Data source: LR Rules for the Manufacture, Testing and Certification of Materials (July 2022), Ch 3 Section 10, Tables 3.10.1-3.10.5, cross-checked with IACS UR W16 Rev.4 Corr.1 (2026). LR states these grades are primarily for marine and offshore structural applications; their use in a ship hull is approved case by case. Verify the current LR edition and the mill approval before ordering.

LR/AH55 Chemical Composition (Heat Analysis), %

Ladle (heat) analysis per LR Rules for Materials Ch 3, Table 3.10.2 / IACS UR W16 Table 1; all listed elements are to be reported. For TM and N/NR steels Nb+V+Ti ≤ 0.26% and Mo+Cr ≤ 0.65% (not applicable to QT). Total Al to N ratio at least 2:1 unless other nitrogen-binding elements are used. Higher Ni may be approved by LR. *TM vanadium: IACS UR W16 Rev.4 gives 0.12% max; the LR 2022 table text is ambiguous on this cell, so the IACS value is shown. Grades at this strength level are supplied only TM or QT (no N/NR route). Neither LR nor IACS UR W16 tabulates separate product (check) analysis limits for these grades, so no product analysis table is given. Values depend on IACS UR W16 / LR Rules for Materials.

LR AH55 Carbon Equivalent (Ceq, CET, Pcm), max %

Plates, per LR Table 3.10.3 / IACS UR W16 Table 2 (IACS splits the last column into 100-150 and 150-250 mm with the same plate values). Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15; CET = C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40 (H46 and above, at the manufacturer's discretion); Pcm = C + Si/30 + (Mn+Cu+Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B (TM and QT steels with C ≤ 0.12%). N/A means not applicable. Values depend on IACS UR W16 / LR Rules for Materials.

LR/AH55 Mechanical Properties

Per LR Table 3.10.4 / IACS UR W16 Table 4 for LR/AH55. Elongation on 5.65√S0: 16% min transverse, 18% min longitudinal. LR additionally limits the actual yield/tensile ratio to 0.94 max unless specially agreed. Where tensile properties must be maintained through the thickness (e.g. offshore racks), no reduction with thickness is permitted.

LR AH55 Elongation on 200 mm Gauge Length (25 mm wide flat specimen)

Transverse full-thickness specimens, per LR Table 3.10.5 / IACS UR W16 Table 5.

LR AH55 Charpy V-Notch Impact Requirements (0°C [32°F])

Per LR Table 3.10.4 / IACS UR W16 Table 4: average of three full-size specimens; the same energy applies over the whole thickness range. Plates wider than 600 mm are tested transverse; above 50 mm thickness, specimens are taken at t/4 and additionally at t/2.

Delivery Condition and Deoxidation

LR AH55 is fully killed and fine-grain treated, made to an LR-approved manufacturing specification. Permitted delivery conditions: TM or QT (TM includes TM with accelerated cooling and direct quench + tempering). Options by agreement: ultrasonic testing, Z15/Z25/Z35 through-thickness properties (vacuum degassed), and LR survey with 3.2 certificate stating the specified maximum Ceq, CET or Pcm.

Thickness Coverage

Maximum plate thickness: TM 150 mm, QT 150 mm (LR Table 3.10.1); thicker by special consideration. Typical mill sizes are about 8-150 mm thick, 1500-4000 mm wide and 6000-18000 mm long, subject to mill approval.

Equivalent Steel Grades of LR/AH55

All IACS members apply UR W16, so chemistry and properties are equivalent, but each plate needs a certificate from the vessel's or structure's own society; dual certification is possible when each surveyor witnesses the tests.

FAQ about LR AH55 Steel Plate

What is LR AH55 steel plate?

An extra-high-strength fine-grain structural steel to LR Rules for Materials Ch 3 Section 10 (IACS UR W16 grade AH550), with 550 MPa minimum yield, 640-820 MPa tensile strength and Charpy testing at 0°C [32°F].

What does AH55 mean?

A is the toughness class (A 0°C, D -20°C, E -40°C, F -60°C), H means high strength and 55 is the yield level in kgf/mm², i.e. 550 N/mm².

What is the yield strength of LR AH55?

550 MPa min up to 50 mm, 530 MPa for 50-100 mm and 490 MPa for 100-150 mm. Tensile strength is 640-820 MPa up to 100 mm and 590-770 MPa above.

What are the impact requirements for LR AH55?

Charpy V-notch at 0°C [32°F] with an average of at least 37 J transverse or 55 J longitudinal, for all thicknesses.

What is the maximum carbon equivalent for LR AH55?

For plate up to 50 mm, Ceq max is 0.48 (TM), 0.56 (QT); limits rise with thickness as tabulated above.

How is LR AH55 delivered?

TM or QT, fully killed and fine-grain treated, within the thickness limits of LR Table 3.10.1 and the mill's LR approval.

What is the difference between LR AH55 and LR DH55?

Same strength level; LR AH55 is impact tested at 0°C [32°F] while LR DH55 is tested at -20°C [-4°F].

What is LR AH55 equivalent to?

ABS AQ56, CCS A550, GL A550, DNV A550, BV A550, RINA A550, NK KA56 and KR RA56 (IACS AH550). ASTM A131 has no equivalent at this strength.

Is LR AH55 weldable?

Yes, with qualified procedures and LR-approved consumables of grade 3Y55 or higher (LR Rules for Materials Table 11.1.1); preheat is set from Ceq/CET or Pcm, thickness and restraint.

Other LR Steel Plate Grades

Ordinary and higher-strength grades (235-390 MPa): LR Grade A steel plate | LR Grade B steel plate | LR Grade D steel plate | LR Grade E steel plate | LR AH32 steel plate | LR AH36 steel plate | LR AH40 steel plate | LR DH32 steel plate | LR DH36 steel plate | LR DH40 steel plate | LR EH32 steel plate | LR EH36 steel plate | LR EH40 steel plate | LR FH32 steel plate | LR FH36 steel plate | LR FH40 steel plate

Extra-high-strength 420-500 MPa: LR AH42 steel plate | LR AH46 steel plate | LR AH50 steel plate | LR DH42 steel plate | LR DH46 steel plate | LR DH50 steel plate | LR EH42 steel plate | LR EH46 steel plate | LR EH50 steel plate | LR FH42 steel plate | LR FH46 steel plate | LR FH50 steel plate

Extra-high-strength 550-690 MPa: LR AH62 steel plate | LR AH69 steel plate | LR DH55 steel plate | LR DH62 steel plate | LR DH69 steel plate | LR EH55 steel plate | LR EH62 steel plate | LR EH69 steel plate | LR FH55 steel plate | LR FH62 steel plate | LR FH69 steel plate

Equivalent Class Society Grades

LR AH55 corresponds to the same grade under the other IACS member classification societies: CCS A550 steel plate, ABS AQ56 steel plate, GL A550 steel plate, DNV A550 steel plate, BV A550 steel plate, NK A56 steel plate, KR A56 steel plate, RINA A550 steel plate. ASTM A131 does not cover the 420-690 MPa extra-high-strength levels, so there is no A131 equivalent.