Difference between LR DH55 and LR EH55 steel plate - Knowledge

LR DH55 and LR EH55 are high-strength, extra-high-strength shipbuilding steel plates classified by Lloyd's Register (LR) for marine structures, differing mainly in their required strength levels and processing (DH is normalized/controlled rolled, EH is quenched & tempered), offering excellent weldability and toughness, with minimum yield strengths around 550 MPa and tensile strengths of 670-830 MPa, crucial for ships and offshore platforms.

Chemical Composition

LR DH55 extra high Strength Chemical Composition
Grade	The Element Max (%)
Grade	C	Si	Mn	P	S	Al	N
LR DH55	0.20	0.55	1.70	0.030	0.030	0.015	0.020
	Nb	V	Ti	Cu	Cr	Ni	Mo
	0.02-0.05	0.03-0.10	0.02

LR EH55 extra high Strength Chemical Composition
Grade	The Element Max (%)
Grade	C	Si	Mn	P	S	Al	N
LR EH55	0.20	0.55	1.70	0.030	0.030	0.015	0.020
	Nb	V	Ti	Cu	Cr	Ni	Mo
	0.02-0.05	0.03-0.10	0.02

Mechanical Property

LR DH55 extra high strength property
Grade		Mechanical Property			Charpy V Impact Test
Grade	Thickness	Yield	Tensile	Elongation	Degree	Energy 1	Energy 2
LR DH55	mm	Min Mpa	Mpa	Min %	-20	J	J
	t≤50	550	670-830	18%		37	55
	50＜t≤70	550	670-830	18%		37	55
	70＜t≤100	550	670-830	18%		37	55
Note: Energy 1 is transverse impact test, Energy 2 is longitudinal

LR EH55 extra high strength property
Grade		Mechanical Property			Charpy V Impact Test
Grade	Thickness	Yield	Tensile	Elongation	Degree	Energy 1	Energy 2
LR EH55	mm	Min Mpa	Mpa	Min %	-40	J	J
	t≤50	550	670-830	18%		37	55
	50＜t≤70	550	670-830	18%		37	55
	70＜t≤100	550	670-830	18%		37	55
Note: Energy 1 is transverse impact test, Energy 2 is longitudinal

Key Characteristics

LR Grade: Both conform to Lloyd's Register (LR) rules for marine steels, with the "D" in DH55 often signifying normalized/controlled rolled, while "EH" signifies quenched & tempered, offering higher strength.

Strength: The "55" indicates a minimum yield strength of 550 MPa (Megapascals) for both grades.

Tensile Strength: Both typically have a tensile strength range of 670-830 MPa.

Toughness: They offer good toughness, vital for low-temperature marine environments.

DH55 and EH55 are high-performance shipbuilding steels, with EH55 generally being heat-treated (quenched & tempered) to achieve its strength, while DH55 relies on controlled rolling or normalizing, both meeting demanding LR standards for structural integrity in harsh marine conditions.