S355NL and S420NL are normalized or normalized-rolled fine grain structural steel plates manufactured to the European standard EN 10025-3. The "N" indicates a Normalized or normalized-rolled delivery condition, and the "L" designates guaranteed impact toughness at low temperatures (down to -50°C or -60°C, depending on thickness). These grades are specified for welded structures operating in cold climates or requiring enhanced toughness, such as bridges, offshore structures, pressure vessels, and heavy construction equipment.
Key Differences:
The core distinction is their strength level. S355NL offers a minimum yield strength of 355 MPa, while S420NL provides a higher yield strength of 420 MPa (and a correspondingly higher tensile strength). This makes S420NL suitable for applications requiring greater load-bearing capacity.
To achieve the higher strength while maintaining fine grain structure and low-temperature toughness, S420NL utilizes a more carefully controlled chemical composition. This involves micro-alloying with elements like Niobium (Nb) and/or Vanadium (V), which provide grain refinement and precipitation strengthening during the normalizing process. Consequently, S420NL generally has a higher carbon equivalent (Ceq) compared to S355NL. This results in more demanding fabrication requirements for S420NL, particularly for welding. Welding S420NL often requires stricter control of preheating temperatures, the use of qualified low-hydrogen consumables, and careful management of heat input to preserve the material's toughness in the weld heat-affected zone.
Chemical Composition of S355NL
|
Element |
Ladle Analysis (max %) |
Product Analysis (max %) |
|---|---|---|
|
Carbon (C) |
0.18 |
0.20 |
|
Silicon (Si) |
0.50 |
0.55 |
|
Manganese (Mn) |
0.90-1.65 |
0.85-1.75 |
|
Phosphorus (P) |
0.025 |
0.035 |
|
Sulfur (S) |
0.015 |
0.025 |
|
Nitrogen (N) |
0.015 |
0.017 |
|
Aluminum (Al) |
0.020 (min, total) |
0.015 (min, total) |
|
Niobium (Nb) |
0.05 |
0.06 |
|
Vanadium (V) |
0.12 |
0.15 |
|
Titanium (Ti) |
0.05 |
0.06 |
|
Chromium (Cr) |
0.30 |
0.35 |
|
Nickel (Ni) |
0.30 |
0.35 |
|
Molybdenum (Mo) |
0.10 |
0.13 |
|
Copper (Cu) |
0.55 |
0.60 |
Chemical Composition of S420NL
|
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 S355NL
|
Thickness (mm) |
Yield Strength (min, MPa) |
Tensile Strength (MPa) |
Elongation (min, %) |
Impact Energy (min, J @ -50°C) |
|---|---|---|---|---|
|
≤16 |
355 |
470-630 |
22 |
27 |
|
16<t≤40 |
345 |
470-630 |
22 |
27 |
|
40<t≤63 |
335 |
470-630 |
22 |
27 |
|
63<t≤80 |
325 |
470-630 |
21 |
27 |
|
80<t≤100 |
305 |
470-630 |
21 |
27 |
|
100<t≤150 |
285 |
450-610 |
21 |
27 |
|
150<t≤200 |
265 |
450-610 |
21 |
27 |
|
200<t≤250 |
245 |
450-610 |
21 |
27 |
Mechanical Properties of S420NL
|
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 |
