Section 10 High strength steels for welded structures

10.1 Scope

10.1.1 Provision is made in this Section for hot-rolled, fine-grain treated, weldable high strength structural steels intended for use in marine and offshore structural applications. These requirements are not intended to apply to steels for the hull structure of ships.

10.1.2 The required notch toughness is designated by subdividing the strength levels into Grades AH, DH, EH and FH.

10.1.3 The steels may be supplied in eight strength levels with minimum yield stresses of 420, 460, 500, 550, 620, 690, 890 and 960 N/mm² respectively. For yield strength level of 890 and 960 N/mm² grade F is not applicable.

10.1.4 Steels covered by the scope of these Rules requirements may be supplied either in the normalised (N), normalising rolled (NR), thermomechanically controlled rolled (TM) or quench and tempered (QT) condition.

10.1.5 The requirements of this Section are primarily intended to apply to plates, wide flats, sections, bars and seamless tubulars, generally not exceeding the thickness limits given in Table 3.10.1 Maximum Thickness Limits. Steels with a thickness beyond the maximum thickness as given in Table 3.10.1 Maximum Thickness Limits are to be specially considered by LR.

Table 3.10.1 Maximum Thickness Limits

Steel Grade	Condition of supply	Maximum thickness (mm) (see Note 1)
		Plates	Sections	Bars	Tubulars
AH42, AH46	N	250	50	250	65
DH42, DH46	NR	150	(see Note 2)
EH42, EH46	TM	150	50	-	-
FH42, FH46	QT	150	50	-	50
AH50, AH55,	TM	150	-	-	-
AH62, AH69
DH50, DH55,	QT	150	-	-	50
DH62, DH69
EH50, EH55,
EH62, EH69
FH50, FH55,
FH62, FH69
AH89	TM	100	-	-	-
DH89
EH89	QT	100	-	-	-
AH96	QT	50	-	-	-
DH96
EH96
Note 1. Thicknesses in excess of these limits or those indicated by ‘-’ may be considered for approved applications. Note 2. The maximum thickness limits of sections and bars produced by the NR process route are generally lower than those applicable when manufactured by the N route and are subject to special consideration by LR.

10.2 Manufacture

10.2.1 The steel is to be made to a specification approved by LR which should include the manufacturing procedure, deoxidation practice, heat treatment and mechanical properties.

10.2.2 Vacuum degassing treatment shall be applied for all steels with enhanced through thickness properties and for grades with yield strength level of 690, 890 and 960 N/mm².

10.2.3 The steel is to be supplied in the fully killed and fine grain treated condition as detailed in the approved manufacturing specification.

10.3 Chemical composition

10.3.1 The chemical analysis is to be in accordance with the approved manufacturing specification. All the elements listed in Table 3.10.2 Chemical Composition are to be reported.

10.3.2 All alloying elements, including residuals, are to be as detailed in the approved manufacturing specification. Where Boron is added, this is not to exceed 0,005 per cent.

10.3.3 The steel shall contain nitrogen binding elements as detailed in the approved manufacturing specification.

Table 3.10.2 Chemical Composition

Chemical Composition	Condition of supply/Steel Grade
	N/NR		TM		QT
	AH42	EH42	AH42	EH42	AH42	EH42 FH42
	DH42	EH46	DH42	FH42	DH42	EH46 FH46
	AH46		AH46	EH46	AH46	EH50 FH50
	DH46		DH46	FH46	DH46	EH55 FH55
			AH50	EH50	AH50	EH62 FH62
			DH50	FH50	DH50	EH69 FH69
			AH55	EH55	AH55	DH89 EH89
			DH55	FH55	DH55	DH96 EH96
			AH62	EH62	AH62
			DH62	FH62	DH62
			AH69	EH69	AH69
			DH69	FH69	DH69
			AH89	DH89	AH89
				EH89	AH96
Carbon % max	0,20	0,18	0,16	0,14	0,18
Manganese %	1,0~1,70		1,0~1,70		1,70
Silicon % max	0,60		0,60		0,80
Phosphorus % max (see Note 1)	0,030	0,025	0,025	0,020	0,025	0,02
Sulphur % max (see Note 1)	0,025	0,02	0,015	0,010	0,015	0,010
Aluminium _total % min (see Note 2)	0,02		0,02		0,018
Niobium % max (see Note 2)	0,05		0,05		0,06
Vanadium % max (see note 3) 0,20	0,20		0,12		0,12
Titanium % max (see Note 3)	0,05		0,05		0,05
Nickel % max (see Note 4)	0,80		2,00 (see Note 4)		2,00 (see Note 4)
Copper % max	0,55		0,55		0,50
Chromium % max (see Note 3)	0,30		0,50		1,50
Molybdenum % max (see Note 3)	0,10		0,50		0,70
Nitrogen % max	0,025		0,025		0,015
Oxygen ppm max (see Note 5)	Not applicable		Not applicable	50	Not applicable	30
Note 1. For sections the P and S content can be 0,005 per cent higher than the value specified in the Table, Note 2. The total aluminium to nitrogen ratio shall be a minimum of 2:1, When other nitrogen binding elements are used, the minimum Al value and Al/N-ratio do not apply, Note 3. Total Nb+V+Ti ≤ 0,26 % and Mo+Cr ≤0,65%, not applicable for QT steels, Note 4. Higher Ni content may be approved at the discretion of LR, Note 5. The requirement on maximum Oxygen content is only applicable to DH89; EH89; DH96 and EH96.

10.3.4 The carbon equivalent value is to be calculated from the ladle analysis using the formula given below. Maximum values are specified in Table 3.10.3 Maximum Ceq, CET and Pcm values.

For steel grades H46 and higher, CET may be used instead of Ceq at the discretion of the manufacturer, and is to be calculated according to the following formula:

For TM and QT steels with carbon content not exceeding 0,12 per cent, the cold cracking susceptibility Pcm for evaluating weldability may be used instead of carbon equivalent of Ceq or CET at the manufacturer’s discretion, and is to be calculated using the following formula:

Table 3.10.3 Maximum Ceq, CET and Pcm values

Steel yield strength level/Condition of supply	Ceq (%)						CET (%)	Pcm (%)
	Plates			Sections	Bars	Tubulars	all	all
	t≤50 (mm)	50<t≤100 (mm)	100<t≤250 (mm)	t≤50 (mm)	t≤250 or d≤250 (mm)	t≤65 (mm)	all	all
H42N/NR	0,46	0,48	0,52	0,47	0,53	0,47	N/A
H42TM	0,43	0,45	0,47	0,44	N/A	N/A
H42QT	0,45	0,47	0,49	N/A	N/A	0,46
H46N/NR	0,50	0,52	0,54	0,51	0,55	0.51	0,25
H46TM	0,45	0,47	0,48	0,46	N/A	N/A	0,30	0,23
H46QT	0,47	0,48	0,50	N/A	N/A	0.48	0,32	0,24
H50TM	0,46	0,48	0,50	N/A		N/A	0,32	0,24
H50QT	0,48	0,50	0,54	N/A		0,50	0,34	0,25
H55TM	0,48	0,50	0,54	N/A		N/A	0,34	0,25
H55QT	0,56	0,60	0,64	N/A		0,56	0,36	0,28
H62TM	0,50	0,52	N/A	N/A		N/A	0,34	0,26
H62QT	0,56	0,60	0,64	N/A		0,58	0,38	0,30
H69TM	0,56	N/A		N/A	N/A	0,36	0,30
H69QT	0,64	0,66	0,70	N/A		0,68	0,40	0,33
H89TM	0,60	N/A		N/A	N/A	0,38	0,28
H89QT	0,68	0,75	N/A	N/A		N/A	0,40	N/A
H96QT	0,75	N/A				N/A	0,40	N/A
Note N/A = Not applicable

10.4 Mechanical tests

10.4.1 For steels in the normalising rolled (NR) or thermomechanically controlled rolled (TM) conditions, one tensile test is to be made for each batch of 25 tonnes or fraction thereof. Additional tests are to be made for every variation of 10 mm in the thickness or diameter of products from the same cast. One set of three Charpy V-notch impact tests specimens are to be taken from each piece. A piece is to be regarded as the rolled product from a single slab or billet, or from a single ingot if this is rolled directly into plates. Charpy V-notch impact test specimens from plates and flats with a finished width more than 600 mm are to have their axes transverse to the main rolling direction.

10.4.2 For normalised (N) and quenched and tempered (QT) plates, one tensile test piece and a set of three Charpy V-notch impact test specimens are to be taken from each plate as heat treated. Charpy V-notch impact test specimens from quenched and tempered plates and flats with a finished width more than 600 mm are to have their axes transverse to the main rolling direction.

10.4.3 For sections, bars and tubulars, one tensile test piece and one set of three Charpy V-notch impact test specimens are to be taken from each batch of 25 tonnes or fraction thereof. Additional tests are to be made for every variation of 10 mm in the thickness or diameter of products from the same cast. For sections, the thickness to be considered is the thickness of the product at the point at which samples are taken for mechanical tests. A piece is to be regarded as the rolled product from a single slab or billet, or from a single ingot if this is rolled directly into sections, bars or tubulars.

10.4.4 For material with a thickness in excess of 50 mm, impact tests shall be taken at the quarter thickness (t/4) location and additionally at mid-thickness (t/2) location. As an alternative to a full thickness or a sub-sized flat tensile specimen, the specimens are to be located at a position lying at a distance of t/4 from the surface and additionally at t/2 for thickness above 100 mm or as near as possible to these positions.

10.4.5 For steels designated with improved through thickness properties, through thickness tensile tests are to be performed in accordance with the requirement of Ch 3, 8 Plates with specified through thickness properties. Through-thickness tensile strength is required to be not less than 80 % of the specified minimum tensile strength.

10.4.6 The results of the tests are to comply with the appropriate requirements of Table 3.10.4 Mechanical Properties for acceptance purpose.

Table 3.10.4 Mechanical properties for acceptance purpose

Steel grade	Yield Stress N/mm² min (see Notes 1 and 2)				Tensile Strength N/mm²				Elongation on 5,65 %min (see Note 3)		Charpy V-notch impact test
	Nominal thickness (mm)								Elongation on 5,65 %min (see Note 3)		Average energy J Minimum
	≥3≤50	>50≤ 100	>100≤150	>150≤250	≥3≤50	>50≤ 100	>100≤150	>150≤250	T	L	T	L
AH42 DH42 EH42 FH42	420	390	365	365	520~680	520~680	470~650	470~650	19	21	28	42
AH46 DH46 EH46 FH46	460	430	390	390	540~720	540~720	500~710	500~710	17	19	31	46
AH50 DH50 EH50 FH50	500	480	440	-	590~770	590~770	540~720	-	17	19	33	50
AH55 DH55 EH55 FH55	550	530	490	-	640~820	640~820	590~770	-	16	18	37	55
AH62 DH62 EH62 FH62	620	580	560	-	700~890	700~890	650~830	-	15	17	41	62
AH69 DH69 EH69 FH69	690	650	630	-	770~940	770~940	710~900	-	14	16	46	69
AH89 DH89 EH89	890	830	-	-	940~1100	940~1100	-	-	11	13	46	69
AH96 DH96 EH96	960	-	-		980~1150	-	-	-	10	12	46	69
Symbols
T = Transverse
L = Longitudinal
Notes
Impact tests are to be made on the various grades at the following temperatures: AH grades 0°C DH grades -20°C EH grades -40°C FH grades -60°C Note 1. For tensile test either the upper yield stress (ReH) or where ReH cannot be determined, the 0,2 per cent proof stress (Rp0,2) is to be determined. Note 2. The ratio of actual yield strength to tensile strength shall not exceed 0,94. A higher yield strength to tensile strength ratio may be acceptable on a project specific basis, subject to special consideration. Note 3. For full thickness flat test specimens with a width of 25 mm and a gauge length of 200 mm the elongation is to comply with the minimum values shown in Table 3.10.5 Elongation minimum values for a width of 25 mm and a 200 mm gauge length.

Table 3.10.5 Elongation minimum values for a width of 25 mm and a 200 mm gauge length

Thickness (mm) (See Note 1)		≤10	>10 ≤15	>15 ≤20	>20 ≤25	>25 ≤40	>40 ≤50	>50 ≤70
Elongation (%)	Strength levels
	H42	11	13	14	15	16	17	18
	H46	11	12	13	14	15	16	17
	H50	10	11	12	13	14	15	16
	H55	10	11	12	13	14	15	16
	H62	9	11	12	12	13	14	15
	H69 (see note 2)	9	10	11	11	12	13	14
	H89 H96	See Note 3
Note 1. The tabulated elongation minimum values are the requirements for testing specimen in transversed direction. Note 2. Re-test can be carried out on the standards proportional test specimen witha gauge length of L₀=5.65√S₀ to meet the requirement of Table 3.10.4 Mechanical Properties for acceptance purpose when the elongation does not meeting the requirement in this table. See Ch 2, 2.4 Equivalent elongations. Note 3. Steel with strength level of 89 and 96 shall be tested by proportional specimens witha gauge length of L₀=5.65√S₀.

10.5 Identification of materials

10.5.1 The particulars detailed in Ch 3, 1.12 Identification of materials are to be marked on each piece which has been accepted and, for ease of recognition, are to be encircled or otherwise marked with paint.

10.6 Certification of materials

10.6.1 At least two copies of each test certificate are to be provided. They are to be of the type and give the information detailed in Ch 3, 1.13 Certification of materials and, additionally, are to state the specified maximum Ceq, CET or Pcm. As a minimum, chemical composition is to include the contents of any grain refining elements used and of the residual elements as detailed in Table 3.10.2 Chemical Composition.