KR/R A51|KR A51 STEEL PLATE

KR A51 steel plate, also written as RA51, R A51, KR Grade A51 or market names such as AH50 / AQ51, is the extra-high-strength hull structural steel of Korean Register (KR) Rules for the Classification of Steel Ships (IACS UR W16 extra-high-strength family) with 500 MPa minimum yield, 610-770 MPa tensile strength and Charpy V-notch toughness at 0°C [32°F]. In the grade name, "A" is the toughness class, and "51" is the site strength label for about 500 MPa yield (ABS AQ51 family). Gangsteel, a steel plate exporter, supplies KR A51 / RA51 plates cut to size for shipbuilding, offshore platforms and marine structures.

Data source: Per IACS UR W16 (extra-high-strength hull structural steel) as adopted in KR Class hull structural steel rules, cross-checked with LR AH50 / ABS AQ51 sibling pages on gangsteel.net. Official mill/certificate grade is typically RA51 (R A51); KR A51 names the same class on this site. Verify the current KR Class edition before ordering.

KR A51 / RA51 Chemical Composition (Heat Analysis)

 

Element	C	Mn	Si	P	S	Al (acid sol.)
KR A51, %	0.21 max	1.70 max	0.10-0.55	0.035 max	0.035 max	0.015 min
Element	N	Nb	V	Ti	B	Notes
KR A51, %	0.020 max	0.02-0.05	0.04-0.10	0.02 max	0.005 max	Ni/Cu/Cr/Mo per delivery condition (N/TM/QT) in UR W16

Per IACS UR W16 / KR Class extra-high-strength rules. Exact maxima for Ni, Cu, Cr and Mo depend on delivery condition (N/NR, TM or QT). Carbon equivalent / CET / Pcm limits apply by thickness and condition; confirm on the mill certificate and current rule edition.

Product Analysis (Check Analysis)

 

When product analysis is required, apply ASTM A6/A6M Table A permitted variations to the heat limits unless the element is min-only or not listed in Table A.

Element	Heat analysis limit	Product analysis (heat ± A6)
C	0.21 max	0.25 max
Mn	1.70 max	see A6 Table A vs heat upper limit
Si	0.10-0.55	0.05–0.61 (approx. A6)
P	0.035 max	0.045 max
S	0.035 max	0.045 max
Al (acid sol.)	0.015 min	no A6 Table A tolerance; product value not tabulated
N	0.020 max	0.025 max (typical A6 +0.005)
Nb	0.02-0.05	0.010–0.060
V	0.04-0.10	0.030–0.110
Ti	0.02 max	0.03 max
B	0.005 max	product analysis often not applicable

Product analysis applies only when specified; for a range, results may not vary both above and below it.

KR A51 / RA51 Mechanical Properties

 

Grade	Yield strength, min	Tensile strength	Elongation, min
KR A51 / RA51	500 MPa [73 ksi]	610-770 MPa [88-112 ksi]	16%

Per IACS UR W16 / KR Class rules (common t≤50 mm values). Yield may step down for thicker plates per UR W16; confirm thickness-dependent values on the order.

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

 

Thickness	Test temperature	Longitudinal, avg min	Transverse, avg min
t≤50 mm	0°C [32°F]	50 J	33 J
50<t≤70 mm	0°C [32°F]	50 J	33 J
70<t≤100 mm	0°C [32°F]	50 J	33 J

Per IACS UR W16 / KR Class extra-high-strength practice. Average of three full-size specimens; transverse values apply when required. Thicker plates by agreement.

Delivery Condition and Deoxidation

Deoxidation: Killed, fine-grain practice. Delivery condition: typically TMCP or QT for extra-high-strength plates; N/NR may apply at lower extra-high levels per rules. A-class (R A51 / AQ51) grades may be as-rolled, controlled rolled, normalized or TMCP depending on thickness; thicker plates usually N or TMCP. Optional extras: UT, Z15/Z25/Z35, KR survey.

Thickness Coverage

Extra-high-strength KR A/D/E/F 43/47/51/56/63/70 plates (about 420-690 MPa family) are commonly supplied from about 6 mm to 100 mm thick (thicker by agreement under UR W16). Width 1500-4000 mm and length 6000-18000 mm are typical.

Equivalent Steel Grades of KR A51

 

Society / Standard	Equivalent grade
KR (Korean Register)	KR A51 / RA51 (LR AH50 / ABS AQ51)
LR (Lloyd's Register)	LR AH50 steel plate
ABS	ABS AQ51 steel plate
CCS	CCS A500 steel plate
GL	GL A500 steel plate
DNV	DNV A500 steel plate
BV	BV A500 steel plate
NK	NK A51 steel plate
RINA	RINA A500 steel plate

IACS societies align extra-high-strength hull grades under UR W16; naming differs (KR A51, LR AH50, ABS AQ51, DNV A500). Dual certification is common when ordered that way.

FAQ about KR A51 / RA51 Steel Plate

What is KR A51 (RA51) steel plate?

It is an extra-high-strength hull structural steel under KR Class Rules (IACS UR W16 extra-high-strength family), with 500 MPa minimum yield, 610-770 MPa tensile strength and Charpy toughness at 0°C [32°F].

What does KR A51 / RA51 stand for?

KR is Korean Register. The R prefix (RA51 / R A51) is the KR mill designation. The letter A is the toughness class (Charpy at 0°C [32°F]), and 51 is the yield-strength level in MPa. Market/LR naming often uses AH50; ABS often uses AQ51. This site uses ABS-like numbers (A43…A70), corresponding to about 500 MPa (ABS AQ51 / LR AH50 / DNV A500 family); there are no A420 paths under /kr/.

What is the yield strength of KR A51?

Minimum 500 MPa (73 ksi), tensile 610-770 MPa (88-112 ksi), elongation about 16% min (for the common thickness range).

What is the impact test temperature for KR A51 / RA51?

Charpy V-notch at 0°C [32°F]. Typical longitudinal average minimum is 50 J (transverse 33 J) for the tabulated thickness range on this grade page.

What is the difference between NK A51, D51, E51 and F51?

Same 500 MPa strength class. Toughness class differs: A at 0°C, D at -20°C, E at -40°C, F at -60°C. Chemistry (C, P, S, Mn) is tightened for colder classes.

How does KR A51 differ from higher-strength KR A40?

KR A40 is UR W11 higher-strength (390 MPa). KR A51 is UR W16 extra-high-strength (500 MPa) with different chemistry and delivery practice (often TM/QT).

Is KR A51 the same as LR AH50 or ABS AQ51?

They are IACS counterparts in the extra-high-strength family; exact chemistry/delivery options differ by society edition. Dual certification is available when surveys are arranged.

Is KR A51 weldable?

Weldable with approved procedures for extra-high-strength ship steel. Preheat, heat input and consumable matching are critical; follow the mill WPS and KR Class welding requirements.

What heat treatment is required for KR A51?

Extra-high-strength grades are typically delivered TMCP or quenched and tempered (QT), sometimes normalized/normalized-rolled depending on strength level and thickness. A-class (R A51 / AQ51) grades may be as-rolled, controlled rolled, normalized or TMCP depending on thickness; thicker plates usually N or TMCP. Optional extras: UT, Z15/Z25/Z35, KR survey.

What thickness is available for KR A51?

Common supply is about 6-100 mm (thicker by agreement under UR W16 / KR Class rules), 1500-4000 mm wide and 6000-18000 mm long.

Other KR Steel Plate Grades

KR Grade A steel plate | KR Grade B steel plate | KR Grade D steel plate | KR Grade E steel plate | KR A32 steel plate | KR A36 steel plate | KR A40 steel plate | KR D36 steel plate | KR D40 steel plate | KR E32 steel plate | KR E36 steel plate | KR E40 steel plate | KR F32 steel plate | KR F36 steel plate | KR F40 steel plate | KR A43 steel plate | KR A47 steel plate | KR A56 steel plate | KR A63 steel plate | KR A70 steel plate | KR D43 steel plate | KR D47 steel plate | KR D51 steel plate | KR D56 steel plate | KR D63 steel plate | KR D70 steel plate | KR E43 steel plate | KR E47 steel plate | KR E51 steel plate | KR E56 steel plate | KR E63 steel plate | KR E70 steel plate | KR F43 steel plate | KR F47 steel plate | KR F51 steel plate | KR F56 steel plate | KR F63 steel plate | KR F70 steel plate

Equivalent Class Society Grades

KR A51 / RA51 corresponds to extra-high-strength counterparts under other IACS societies (LR AH50, ABS AQ51, etc.): LR AH50 steel plate, ABS AQ51 steel plate, CCS A500 steel plate, GL A500 steel plate, DNV A500 steel plate, BV A500 steel plate, NK A51 steel plate, RINA A500 steel plate.