NK/K D40|NK D40 STEEL PLATE

NK D40 steel plate, also written as KD40, K D40, ClassNK D40, NK Grade D40 or market name DH40, is the higher-strength hull structural steel of ClassNK (Nippon Kaiji Kyokai) Rules for the Survey and Construction of Steel Ships (IACS UR W11 higher-strength family) with 390 MPa minimum yield, 510-650 MPa tensile strength and Charpy V-notch toughness at -20°C [-4°F]. In the grade name, "D" is the toughness class, and "40" refers to the strength level (historically about 40 kgf/mm²); ClassNK mill certificates commonly use the K prefix (KD40), while DH40 is the common IACS market name with "H" for higher strength. Gangsteel, a steel plate exporter, supplies NK D40 / KD40 plates cut to size for shipbuilding, offshore platforms and marine structures.

Data source: Per IACS UR W11 (ordinary/higher-strength hull structural steel) as adopted in ClassNK hull structural steel rules. Official mill/certificate grade is typically KD40 (K D40); NK D40 and DH40 name the same class on this site. Verify the current ClassNK edition before ordering.

NK D40 / KD40 Chemical Composition (Heat Analysis)

 

Element	C	Mn	Si	P	S	Al (acid sol.)
NK D40 / KD40, %	0.18 max	0.90-1.60	0.10-0.50	0.035 max	0.035 max	0.015 min
Element	Nb	V	Ti	Cu	Cr	Ni / Mo
NK D40 / KD40, %	0.02-0.05	0.05-0.10	0.02 max	0.35 max	0.20 max	0.40 max / 0.08 max

Per IACS UR W11 / ClassNK (NK) hull structural steel rules (higher-strength grades). Nb, V and Al grain-refining elements may be used singly or in combination; when used in combination the individual minima do not apply. Where acid-soluble Al is not less than 0.015%, the Si minimum does not apply. Carbon equivalent: Ceq = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 (%).

Product Analysis (Check Analysis)

 

IACS UR W11 / ClassNK rules do not separately tabulate product (check) analysis limits for higher-strength grades. When product analysis is required, the finished plate shall meet the heat limits subject to ASTM A6/A6M Table A permitted variations (same practice as other IACS societies).

Element	Heat analysis limit	Product analysis (heat ± A6)
C	0.18 max	0.22 max
Mn	0.90-1.60	0.81–1.72
Si	0.10-0.50	0.04–0.56
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
Nb	0.02-0.05	0.010–0.060
V	0.05-0.10	0.040–0.110
Ti	0.02 max	0.03 max
Cu	0.35 max	0.38 max
Cr	0.20 max	0.24 max
Ni	0.40 max	0.43 max
Mo	0.08 max	0.09 max

Per IACS UR W11 / ClassNK hull structural steel rules. Product analysis applies only when specified; for a range, results may not vary both above and below it.

NK D40 / KD40 Mechanical Properties

 

Grade	Yield strength, min	Tensile strength	Elongation, min
NK D40 (KD40)	390 MPa [57 ksi]	510-650 MPa [74-94 ksi]	20%

Per IACS UR W11 / ClassNK hull structural steel rules. Yield and tensile values apply for the full thickness range covered by the grade (typically up to 100 mm for these ship plates).

Charpy V-Notch Impact Requirements (-20°C [-4°F])

 

Thickness	Test temperature	Longitudinal, avg min	Transverse, avg min
t≤50 mm	-20°C [-4°F]	39 J	26 J
50<t≤70 mm	-20°C [-4°F]	46 J	31 J
70<t≤100 mm	-20°C [-4°F]	55 J	37 J

Per IACS UR W11 / ClassNK hull structural steel rules. Average of three full-size Charpy V-notch specimens; not more than one value below the average and none below 70% of it. Longitudinal values shown; transverse values apply when required by the rules or purchase order. Thicker plates (above 100 mm) may be supplied by agreement with adjusted impact requirements.

Delivery Condition and Deoxidation

Deoxidation: Killed, fine-grain practice. Delivery condition: D-class (K D40 / DH40) grades are typically normalized or TMCP; controlled-rolled delivery may apply within rule limits. Optional extras by agreement include ultrasonic testing, Z-direction (Z15/Z25/Z35) through-thickness testing and third-party ClassNK survey.

Thickness Coverage

Higher-strength NK A/D/E/F 32/36/40 plates are commonly supplied from about 6 mm to 100 mm thick (up to 150 mm by agreement). Width 1500-4000 mm and length 6000-18000 mm are typical.

Equivalent Steel Grades of NK D40

 

Society / Standard	Equivalent grade
NK (ClassNK)	NK D40 / KD40 (DH40)
LR (Lloyd's Register)	LR DH40 steel plate
ABS	ABS DH40 steel plate
CCS	CCS DH40 steel plate
ASTM A131/A131M	ASTM A131 DH40 steel plate
GL	GL DH40 steel plate
DNV	DNV D40 steel plate
BV	BV DH40 steel plate
KR	KR D40 steel plate

IACS member societies harmonize ordinary and higher-strength hull grades under UR W11; dual certification (for example NK + ABS, or NK + ASTM A131) is common when ordered that way.

FAQ about NK D40 / KD40 Steel Plate

What is NK D40 (KD40) steel plate?

It is a higher-strength hull structural steel under ClassNK (Nippon Kaiji Kyokai) Rules for the Survey and Construction of Steel Ships (IACS UR W11), with 390 MPa minimum yield, 510-650 MPa tensile strength and Charpy toughness at -20°C [-4°F]. The mill certificate grade is typically KD40 (K D40); NK D40 and market name DH40 refer to the same strength/toughness class.

What does NK D40 / KD40 / DH40 stand for?

NK (ClassNK) is Nippon Kaiji Kyokai. The K prefix on the mill grade (KD40) is the ClassNK designation. The letter D is the toughness class (Charpy at -20°C [-4°F]), and 40 is the strength level (historically about 40 kgf/mm², now 390 MPa min yield). DH40 adds "H" for higher strength in common IACS market naming.

What is the yield strength of NK D40?

Minimum 390 MPa (57 ksi), tensile 510-650 MPa (74-94 ksi), elongation about 20% min.

What is the impact test temperature for NK D40 / KD40?

Charpy V-notch at -20°C [-4°F]. Longitudinal average minima are 39 J up to 50 mm, 46 J for 50-70 mm and 55 J for 70-100 mm.

What is the difference between NK D40 and other 40-class grades?

Same 390 MPa strength class. NK A40 (KA40) at 0°C [32°F]; NK D40 (KD40) at -20°C [-4°F]; NK E40 (KE40) at -40°C [-40°F]; NK F40 (KF40) at -60°C [-76°F]. Delivery condition follows the toughness letter rules.

What is the difference between NK D40 and NK D32?

Same D-class toughness (Charpy at -20°C [-4°F]). NK D40 is strength class 40 (390 MPa min yield); NK D32 is strength class 32 (315 MPa min yield).

Is NK D40 the same as ABS DH40 or LR DH40?

Requirements are essentially harmonized under IACS UR W11. ABS DH40, LR DH40, DNV D40, BV DH40 and ASTM A131 DH40 (where listed) are counterparts; dual certification is common when ordered with the required surveys.

Is NK D40 weldable?

Yes. Controlled carbon and Ceq give good weldability; preheat may be required for thick sections depending on Ceq and restraint.

What heat treatment is required for NK D40?

D-class (K D40 / DH40) grades are typically normalized or TMCP; controlled-rolled delivery may apply within rule limits.

What thickness is available for NK D40?

Typical supply is about 6-100 mm thick (up to 150 mm by agreement), 1500-4000 mm wide and 6000-18000 mm long.

Other NK Steel Plate Grades

NK Grade A steel plate | NK Grade B steel plate | NK Grade D steel plate | NK Grade E steel plate | NK A32 steel plate | NK A36 steel plate | NK A40 steel plate | NK D32 steel plate | NK D36 steel plate | NK E32 steel plate | NK E36 steel plate | NK E40 steel plate | NK F32 steel plate | NK F36 steel plate | NK F40 steel plate

Equivalent Class Society Grades

NK D40 / KD40 (DH40) corresponds to the same grade under the other IACS member classification societies and ASTM A131: LR DH40 steel plate, ABS DH40 steel plate, CCS DH40 steel plate, ASTM A131 DH40 steel plate, GL DH40 steel plate, DNV D40 steel plate, BV DH40 steel plate, KR D40 steel plate.