DNV E420 and DNV E500 are DNV-classified high-strength hull structural steel plates for shipbuilding and offshore structures. Both belong to the E impact grade - Charpy V-notch tested at -40°C.
The meaningful difference between them is strength: E420 guarantees a minimum yield of 420 MPa, E500 of 500 MPa.
The original version of this article described E420 as having "excellent corrosion resistance" - that claim has been corrected: DNV rules do not assess corrosion resistance for these grades, and marine corrosion protection is provided by coating and cathodic protection per the design. This guide compares the two grades with data and explains when each one is the right choice.
Key Takeaways
- Same impact class, different strength: both are E grades (impact tested at -40°C); the numbers 420 / 500 are the minimum yield strength in MPa.
- E420: min yield 420 MPa, tensile 530–680 MPa, elongation min 18%. E500: min yield 500 MPa, tensile 610–770 MPa, elongation min 16%. Both impact-tested at -40°C (reference values, subject to DNV rules and MTC).
- Chemistry tables look identical by design: the values are industry-typical upper limits for the strength family. E500's extra strength comes from microalloy design and TMCP/QT processing - confirmed per heat on the MTC.
- No special corrosion allowance: choose E420/E500 for strength and toughness; manage corrosion with coating / cathodic protection per design.
- Choose E500 when weight saving justifies it and your fabrication shop can follow its stricter welding requirements.
1. What do DNV E420 and E500 mean?
DNV (Det Norske Veritas) classifies ship and offshore structures, and its rules (DNV-RU-SHIP, Pt.4 Ch.2) define the steel grades for hull structural use. The designation has two parts:
- The letter is the impact toughness grade: A = 0°C, D = -20°C, E = -40°C, F = -60°C (Charpy V-notch testing). The same letter scale is used by DNV, LR and other major classification societies - an "E" grade always means impact testing at -40°C.
- The number is the minimum yield strength in MPa: 420 for E420, 500 for E500. Both are "extra high strength" grades in the DNV classification system.
Cross-society equivalents exist for the same yield levels, but each society applies its own designation and rule details - confirm the accepted equivalent with your class surveyor rather than assuming it.
2. Chemical composition (industry-typical maxima)
DNV E420 and E500 share the same general composition limits shown below - the table gives industry-typical upper limits for the strength family. This is why the two grades' chemistry tables look identical: the specification caps are common, while the actual heat chemistry differs. The extra strength of E500 is achieved by the mill through microalloy design (Nb/V/Ti grain refinement) and controlled processing - TMCP or QT - details of which are shown on the DNV-approved drawings and the MTC.
Table 1 - Chemical composition, industry reference maxima (%, max unless shown as a range)
| Element | DNV E420 | DNV E500 | What it does |
|---|---|---|---|
| C | ≤ 0.20 | ≤ 0.20 | Strength; capped to protect weldability and toughness. |
| Si | 0.10 – 0.55 | 0.10 – 0.55 | Deoxidation and strength. |
| Mn | ≤ 1.70 | ≤ 1.70 | Strength and toughness at low temperature. |
| P | ≤ 0.030 | ≤ 0.030 | Impurity; kept low for toughness. |
| S | ≤ 0.030 | ≤ 0.030 | Impurity; kept low for ductility and through-thickness properties. |
| Al | 0.015 – 0.08 | 0.015 – 0.08 | Killed / fine-grain practice. |
| N | ≤ 0.020 | ≤ 0.020 | Capped to avoid strain-ageing embrittlement. |
| Nb | 0.02 – 0.05 | 0.02 – 0.05 | Grain refinement and precipitation strengthening - key to higher strength. |
| V | 0.04 – 0.10 | 0.04 – 0.10 | Precipitation strengthening, particularly in TMCP processing. |
| Ti | ≤ 0.02 | ≤ 0.02 | Nitride former for grain control, kept low. |
| B | ≤ 0.005 | ≤ 0.005 | Hardenability element, tightly controlled. |
Note: Cu, Cr, Ni and Mo are not listed with limits in the general table; controlled additions are made by the mill as needed for the strength/toughness design - see the approved drawings and MTC. Actual heat chemistry always governs over the table above.
3. Mechanical properties: E420 vs E500
Table 2 - Mechanical properties comparison (industry reference values)
| Property | DNV E420 | DNV E500 |
|---|---|---|
| Minimum yield strength (MPa) | 420 | 500 |
| Tensile strength (MPa) | 530 – 680 | 610 – 770 |
| Elongation, min | 18% | 16% |
| Charpy V-notch impact test, -40°C - transverse (J) | 28 | 33 |
| Charpy V-notch impact test, -40°C - longitudinal (J) | 42 | 50 |
| Typical delivery condition | As-rolled / Normalized / TMCP | TMCP / Quenched & Tempered |
Notes: (1) Impact values are industry reference values - transverse (Energy 1) and longitudinal (Energy 2) per the original page's convention; the binding acceptance criteria come from DNV rules and the MTC. (2) Requirements are thickness-dependent (e.g. t ≤ 50, 50 < t ≤ 70, 70 < t ≤ 150 mm bands apply per the rules) - confirm the applicable band for your plate thickness.
4. E420 vs E500: side-by-side difference
Table 3 - Difference comparison
| Aspect | DNV E420 | DNV E500 |
|---|---|---|
| Strength class | High strength (420 MPa yield) | Extra high strength (500 MPa yield) |
| Tensile / elongation | 530–680 MPa / ≥ 18% | 610–770 MPa / ≥ 16% |
| Impact grade | E - -40°C | E - -40°C |
| Typical processing | AR / N / TMCP | TMCP / QT |
| Typical applications | Hull shell, decks, bulkheads, offshore topsides - general high-strength hull construction | Heavily loaded hull members, offshore jack-up legs, crane and support structures, ice-strengthened areas |
| Welding demands | Standard low-hydrogen WPS per class rules | Stricter WPS: preheat, interpass and heat-input control, qualified consumables |
| Design benefit | Balanced strength, cost and weldability | Thinner plate at equal load - weight and weld-volume savings |
| Relative cost / lead time | Lower | Higher; availability varies by mill |
| Corrosion behaviour | No special allowance - coating / cathodic protection per design | Same |
5. Application and selection guide
- Choose DNV E420 for the majority of high-strength hull and offshore applications: shell and deck plating, bulkheads, stringers and topsides where -40°C toughness is required and 420 MPa yield is sufficient for the design. It offers the best balance of strength, weldability and cost.
- Choose DNV E500 when the structural design is strength- or weight-limited: heavy-lift structures, jack-up legs, highly loaded brackets and supports, ice-class reinforcements. The higher yield allows thinner plate at equal load, cutting weight and weld volume - worthwhile when the fabrication shop can follow the stricter welding procedure.
Selection checklist:
- Confirm the design yield requirement and thickness from the approved structural drawings.
- Check mill availability for the exact size range - E500 in heavy thicknesses is a more specialised rolling programme.
- Review your fabrication capability: preheat, heat-input control and qualified welders are more critical for E500 TMCP/QT plate.
- Specify class certificates (DNV), impact temperature, and any supplementary requirements (through-thickness Z, CEV limits) at enquiry; verify the MTC against DNV rules before release.
6. Welding notes
- Both grades require low-hydrogen consumables, qualified WPS/PQR per DNV rules, and control of preheat and interpass temperature; store consumables dry.
- For E500 supplied in TMCP or QT condition, keep heat input within the approved range - excessive heat input or post-weld overheating degrades HAZ toughness.
- Match consumables to the strength level of the parent plate and document the joint with the approved WPS and welder qualifications.
For thick plate, consider through-thickness (Z) requirements if the design has high restraint, and state them at enquiry.
7. FAQ
What does the "E" in DNV E420 and E500 mean?
E is the impact toughness grade: Charpy V-notch testing at -40°C, per the classification-society letter system (A = 0°C, D = -20°C, E = -40°C, F = -60°C). The numbers 420 and 500 are the minimum yield strength in MPa.
Is E500 simply a stronger version of E420?
In strength, yes - minimum yield 500 MPa vs 420 MPa. But E500 needs microalloy design and typically TMCP or QT processing, plus stricter welding control, to guarantee toughness and strength together.
Are E420 and E500 plates corrosion resistant?
No special corrosion allowance applies. Marine corrosion is normally managed by coating and cathodic protection per the design, not by the steel chemistry. The original article's "excellent corrosion resistance" wording was corrected.
Where do the mechanical values in this article come from?
The values shown are industry reference figures. The binding requirements come from the DNV rules (DNV-RU-SHIP Pt.4 Ch.2) and the Mill Test Certificate of the supplied heat.
Can I order lower-temperature impact toughness than -40°C?
Yes - F grades are tested at -60°C within the same strength families. Availability and pricing depend on the mill; confirm at quotation.
Need DNV E420 / E500 classified steel plate?
Send us: grade · size (thickness × width × length) · quantity · class society & certificate requirement (DNV) · impact temperature · supplementary requirements (through-thickness Z, CEV) · delivery port.
We will confirm mill availability, price and a realistic schedule.
- Email: alloy@gneesteelgroup.com
- Tel / WhatsApp: +86-15824687445
Gnee Steel (Tianjin) Co., Ltd - No.4-1114, Beichen Building, Beicang Town, Beichen District, Tianjin, China
Typical lead time 30–45 days subject to mill schedule - confirm at quotation.
All chemical and mechanical values are verified against the DNV-approved drawings and the Mill Test Certificate.
