R B|KR Grade B STEEL PLATE

KR Grade B steel plate, also written as R B, KR B or KR Grade B ship steel plate, is the ordinary-strength hull structural steel of Korean Register (KR) Rules for the Classification of Steel Ships (IACS UR W11 ordinary-strength family) with 235 MPa minimum yield, 400-520 MPa tensile strength and Charpy V-notch toughness at 0°C [32°F]. Gangsteel, a steel plate exporter, supplies KR Grade B / R B 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 KR Class hull structural steel rules. Official mill/certificate grade is typically R B; KR Grade B names the same class on this site. Verify the current KR Class edition before ordering.

KR Grade B / R B Chemical Composition (Heat Analysis)

 

Element	Heat analysis
C	0.21 max
Mn	0.80 min
Si	0.35 max
P	0.035 max
S	0.035 max

Per IACS UR W11 / KR Class hull structural steel rules (ordinary-strength grades). Grade A uses a manganese minimum tied to carbon (Mn ≥ 2.5×C) and a C + Mn/6 limit of 0.40%. Grades D and E require fine-grain practice with acid-soluble Al not less than 0.015% when used as the grain-refining element.

Product Analysis (Check Analysis)

 

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), unless a limit is min-only or calculated.

Element	Heat analysis limit	Product analysis (heat ± A6)
C	0.21 max	0.25 max
Mn	0.80 min	0.74 min (A6 lower)
Si	0.35 max	0.40 max
P	0.035 max	0.045 max
S	0.035 max	0.045 max

Per IACS UR W11 / KR Class hull structural steel rules. Product analysis applies only when specified.

KR Grade B / R B Mechanical Properties

 

Grade	Yield strength, min	Tensile strength	Elongation, min
KR Grade B / R B	235 MPa [34 ksi]	400-520 MPa [58-75 ksi]	22%

Per IACS UR W11 / KR Class 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 (0°C [32°F])

 

Thickness	Test temperature	Longitudinal, avg min	Transverse, avg min
t≤50 mm	0°C [32°F]	27 J	20 J
50<t≤70 mm	0°C [32°F]	34 J	24 J
70<t≤100 mm	0°C [32°F]	41 J	27 J

Per IACS UR W11 / KR Class hull structural steel rules. Average of three full-size Charpy V-notch specimens when impact testing is required; not more than one value below the average and none below 70% of it. For Grade A, impact testing is typically required only above 50 mm. Thicker plates (above 100 mm) may be supplied by agreement with adjusted impact requirements.

Delivery Condition and Deoxidation

Grade B is killed steel. Delivery may be as-rolled, controlled rolled, normalized or TMCP by thickness. Optional extras by agreement include ultrasonic testing, Z-direction (Z15/Z25/Z35) through-thickness testing and third-party KR survey.

Thickness Coverage

Ordinary-strength KR Grade A/B/D/E 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 KR Grade B

 

Society / Standard	Equivalent grade
KR (Korean Register)	KR Grade B / R B
LR (Lloyd's Register)	LR Grade B steel plate
ABS	ABS Grade B steel plate
CCS	CCS Grade B steel plate
GL	GL Grade B steel plate
DNV	DNV Grade B steel plate
BV	BV Grade B steel plate
NK	NK Grade B steel plate

IACS member societies harmonize ordinary-strength hull grades under UR W11; dual certification is common when ordered that way.

FAQ about KR Grade B / R B Steel Plate

What is KR Grade B (R B) steel plate?

It is an ordinary-strength hull structural steel under Korean Register (KR) Rules for the Classification of Steel Ships (IACS UR W11), with 235 MPa minimum yield, 400-520 MPa tensile strength and Charpy toughness requirements at 0°C [32°F] (by thickness).

What does KR Grade B / R B stand for?

KR is Korean Register. The R prefix (R B) is the KR mill designation. Grade B is the ordinary-strength toughness class tested at 0°C [32°F] (impact may be waived for Grade A at t≤50 mm per UR W11).

What is the yield strength of KR Grade B?

Minimum 235 MPa (34 ksi), tensile 400-520 MPa (58-75 ksi), elongation about 22% min.

What is the impact test temperature for KR Grade B / R B?

Charpy V-notch at 0°C [32°F]. See the impact table for longitudinal/transverse minima by thickness band.

What is the difference between KR Grades A, B, D and E?

Same 235 MPa ordinary-strength class. Toughness class differs: A at +20°C (often waived ≤50 mm), B at 0°C, D at -20°C, E at -40°C.

How does Grade B differ from higher-strength KR A32 / A36?

Grade B is ordinary strength (235 MPa). KR A32/A36/A40 families are higher-strength (315/355/390 MPa) under the same UR W11 framework.

Is KR Grade B weldable?

Yes. Ordinary-strength ship plates are widely welded with standard procedures; follow approved WPS for thickness and Ceq.

What heat treatment is required for KR Grade B?

Grade B is killed steel. Delivery may be as-rolled, controlled rolled, normalized or TMCP by thickness.

What thickness is available for KR Grade B?

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

Other KR Steel Plate Grades

KR Grade A 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 D63 / RD63 steel plate

Equivalent Class Society Grades

KR Grade B / R B corresponds to the same ordinary-strength grade under other IACS member classification societies: LR Grade B steel plate, ABS Grade B steel plate, CCS Grade B steel plate, GL Grade B steel plate, DNV Grade B steel plate, BV Grade B steel plate, NK Grade B steel plate.