LR FH42 Steel Plate | FH42 Shipbuilding Steel Plate

LR FH42 steel plate, also written as LR/FH42, LR Grade FH42, Lloyd's Register FH42 or simply FH42 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 420 MPa minimum yield (t ≤ 50 mm), 520-680 MPa tensile strength and Charpy V-notch toughness at -60°C [-76°F]. In the grade name "F" is the toughness class, "H" means high strength and "42" is the yield level (42 kgf/mm² class, i.e. 420 N/mm²); the IACS UR W16 designation is FH420. Gangsteel, a steel plate exporter, supplies LR FH42 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/FH42 Chemical Composition (Heat Analysis), %

 

Element	TM	QT
C, max	0.14	0.18
Mn	1.00-1.70	1.70 max
Si, max	0.60	0.80
P, max	0.020	0.020
S, max	0.010	0.010
Al total, min	0.020	0.018
Nb, max	0.05	0.06
V, max	0.12*	0.12
Ti, max	0.05	0.05
Ni, max	2.00	2.00
Cu, max	0.55	0.50
Cr, max	0.50	1.50
Mo, max	0.50	0.70
N, max	0.025	0.015
B, max (if added)	0.005	0.005

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. FH grades are not listed for the N/NR route, so only TM and QT apply. 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 FH42 Carbon Equivalent (Ceq, CET, Pcm), max %

 

Strength level / condition	Ceq, t ≤ 50 mm	Ceq, 50 < t ≤ 100 mm	Ceq, 100 < t ≤ 250 mm	CET	Pcm
H42 TM	0.43	0.45	0.47	N/A	N/A
H42 QT	0.45	0.47	0.49	N/A	N/A

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/FH42 Mechanical Properties

 

Property	t ≤ 50 mm	50 < t ≤ 100 mm	100 < t ≤ 150 mm	150 < t ≤ 250 mm (N only)
Yield strength ReH, min	420 MPa [61 ksi]	390 MPa [57 ksi]	365 MPa [53 ksi]	365 MPa [53 ksi]
Tensile strength Rm	520-680 MPa [75-99 ksi]	520-680 MPa	470-650 MPa [68-94 ksi]	470-650 MPa

Per LR Table 3.10.4 / IACS UR W16 Table 4 for LR/FH42. Elongation on 5.65√S0: 19% min transverse, 21% 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 FH42 Elongation on 200 mm Gauge Length (25 mm wide flat specimen)

 

Thickness, mm	≤ 10	10-15	15-20	20-25	25-40	40-50	50-70
Elongation, % min	11	13	14	15	16	17	18

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

LR FH42 Charpy V-Notch Impact Requirements (-60°C [-76°F])

 

Grade	Test temperature	Transverse, avg min	Longitudinal, avg min
LR/FH42	-60°C [-76°F]	28 J	42 J

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 FH42 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: N 250 mm, NR 150 mm, 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/FH42

 

Society / standard	Equivalent grade
IACS UR W16	FH420
ABS	ABS FQ43
CCS	F420 (FH420)
GL / DNV / BV / RINA	F420
NK / KR	KF43 / RF43
ASTM A131	no equivalent (A131 stops at 390 MPa)

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 FH42 Steel Plate

What is LR FH42 steel plate?

An extra-high-strength fine-grain structural steel to LR Rules for Materials Ch 3 Section 10 (IACS UR W16 grade FH420), with 420 MPa minimum yield, 520-680 MPa tensile strength and Charpy testing at -60°C [-76°F].

What does FH42 mean?

F is the toughness class (A 0°C, D -20°C, E -40°C, F -60°C), H means high strength and 42 is the yield level in kgf/mm², i.e. 420 N/mm².

What is the yield strength of LR FH42?

420 MPa min up to 50 mm, 390 MPa for 50-100 mm and 365 MPa for 100-150 mm, and 365 MPa for normalized plate 150-250 mm. Tensile strength is 520-680 MPa up to 100 mm and 470-650 MPa above.

What are the impact requirements for LR FH42?

Charpy V-notch at -60°C [-76°F] with an average of at least 28 J transverse or 42 J longitudinal, for all thicknesses.

What is the maximum carbon equivalent for LR FH42?

For plate up to 50 mm, Ceq max is 0.43 (TM), 0.45 (QT); limits rise with thickness as tabulated above.

How is LR FH42 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 FH42 and LR EH42?

Same strength level; LR FH42 is impact tested at -60°C [-76°F] while LR EH42 is tested at -40°C [-40°F].

What is LR FH42 equivalent to?

ABS FQ43, CCS F420, GL F420, DNV F420, BV F420, RINA F420, NK KF43 and KR RF43 (IACS FH420). ASTM A131 has no equivalent at this strength.

Is LR FH42 weldable?

Yes, with qualified procedures and LR-approved consumables of grade 5Y42 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 FH46 steel plate | LR FH50 steel plate

Extra-high-strength 550-690 MPa: LR AH55 steel plate | 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 FH42 corresponds to the same grade under the other IACS member classification societies: CCS F420 steel plate, ABS FQ43 steel plate, GL F420 steel plate, DNV F420 steel plate, BV F420 steel plate, NK F43 steel plate, KR F43 steel plate, RINA F420 steel plate. ASTM A131 does not cover the 420-690 MPa extra-high-strength levels, so there is no A131 equivalent.