Difference between S275NL and S420NL steel plate - Knowledge

S275NL and S420NL are normalized/normalized rolled fine-grain structural steel grades specified under EN 10025-3, designed for heavily loaded welded structures operating at ambient and low temperatures . The "N" denotes normalized or normalized rolled delivery condition, while "L" signifies enhanced low-temperature toughness with mandatory Charpy V-notch impact testing at -50°C (minimum 27J longitudinal), compared to the -20°C requirement (40J) for non-L grades . Both grades are fully killed, fine-grain treated (grain size ≥6), ensuring excellent weldability and brittle fracture resistance.

S275NL is classified as a non-alloy quality steel with minimum yield strength of 275 MPa (≤16mm thickness), tensile strength of 370-510 MPa, and minimum elongation of 24% . Its maximum carbon equivalent (CEV) is 0.40% for thickness ≤63mm . Chemical composition limits include C ≤0.16% (for NL grade), Mn 0.50-1.50%, P ≤0.030%, S ≤0.025%, with microalloying elements (Nb ≤0.05%, V ≤0.05%) .

S420NL is classified as an alloy special steel offering substantially higher strength with minimum yield of 420 MPa (≤16mm), tensile strength of 520-680 MPa, but lower elongation of 19% . Its CEV is higher at 0.48% (≤63mm), reflecting increased alloy content: C ≤0.20%, Mn 1.00-1.70%, Si ≤0.60%, and permitted Ni ≤0.80%.

Key Differences:

Strength Level: S420NL provides approximately 53% higher yield strength (420 vs 275 MPa), enabling significant weight reduction in structural designs .

Steel Classification: S275NL is non-alloy quality steel; S420NL is alloy special steel with more stringent composition control .

Chemical Composition: S420NL permits higher carbon (0.20% vs 0.16%), manganese (1.70% vs 1.50%), and silicon (0.60% vs 0.40%) .

Carbon Equivalent: S420NL has higher CEV (0.48% vs 0.40% for ≤63mm), requiring more careful welding procedures .

Ductility: S275NL offers superior formability with 24% elongation versus 19% for S420NL .

Applications: S275NL suits general structural fabrication, storage tanks, and moderately loaded components in low-temperature environments. S420NL is preferred for highly stressed structures such as heavy machinery, offshore platforms, bridges, and arctic infrastructure where higher strength-to-weight ratios justify reduced section sizes.

Chemical Composition of S275NL Steel plate

Element	Symbol	Min (%)	Max (%)
Carbon	C	-	0.16
Silicon	Si	-	0.40
Manganese	Mn	0.50	1.50
Nickel	Ni	-	0.30
Phosphorus	P	-	0.025
Sulfur	S	-	0.020
Chromium	Cr	-	0.30
Molybdenum	Mo	-	0.10
Vanadium	V	-	0.05
Nitrogen	N	-	0.015
Niobium	Nb	-	0.05
Titanium	Ti	-	0.05
Aluminum	Al	-	0.020
Copper	Cu	-	0.55
CEV	-	-	0.42

Chemical Composition of S420NL Steel plate

Element	Ladle Analysis (max %)	Product Analysis (max %)
Carbon (C)	0.20	0.22
Silicon (Si)	0.60	0.65
Manganese (Mn)	1.00-1.70	0.95-1.80
Phosphorus (P)	0.025	0.030
Sulfur (S)	0.020	0.025
Nitrogen (N)	0.025	0.027
Aluminum (Al)	0.020 (min, total)	0.015 (min, total)
Niobium (Nb)	0.05	0.06
Vanadium (V)	0.20	0.22
Titanium (Ti)	0.05	0.06
Chromium (Cr)	0.30	0.35
Nickel (Ni)	0.80	0.85
Molybdenum (Mo)	0.10	0.12
Copper (Cu)	0.55	0.60

Mechanical Properties of S275NL Steel plate

Nominal Thickness (mm)	Yield Strength ReH Min (MPa)	Tensile Strength Rm (MPa)	Elongation A Min (%)	Charpy KV Longitudinal Min (J) at -50°C
≤ 16	275	370–510	24	27
16 < t ≤ 40	265	370–510	24	27
40 < t ≤ 63	255	370–510	24	27
63 < t ≤ 80	245	370–510	23	27
80 < t ≤ 100	235	370–510	23	27
100 < t ≤ 150	225	350–480	23	27
150 < t ≤ 200	215	350–480	23	27
200 < t ≤ 250	205	350–480	23	27

Mechanical Properties of S420NL steel plate

Thickness (mm)	Yield Strength (min, MPa)	Tensile Strength (MPa)	Elongation (min, %)	Impact Energy (min, J @ -50°C, Longitudinal)
≤16	420	520-680	19	27
16<t≤40	400	520-680	19	27
40<t≤63	390	520-680	19	27
63<t≤80	380	520-680	19	27
80<t≤100	360	520-680	19	27
100<t≤150	340	500-650	19	27
150<t≤200	330	500-650	19	27