ISO 630 vs EN 10025: Carbon Steel Plate Standards Compared

For international structural carbon steel plate procurement, two standards frequently appear on the same purchase order: ISO 630 and EN 10025. While they cover similar material grades, their grade designations, sub-categorization, and impact test requirements differ — and this matters for compliance, traceability, and project acceptance.

This guide explains both standards side by side and provides practical guidance for selecting the right one for your sourcing and project requirements.

Overview of the Standards

ISO 630 — Structural Carbon Steel Plates of High-Quality

ISO 630 (published by the International Organization for Standardization) covers high-quality structural carbon steel plates of thickness 3mm and over for general structural purposes. It is referenced globally for projects where the buyer wants a single internationally-recognized standard irrespective of country of origin.

The current edition is ISO 630:2023, which provides five grades — E185, E235, E255, E275, E355, and E460 — each available in multiple quality classes (A, B, C, D) corresponding to different impact test guarantees.

EN 10025 — Hot Rolled Products of Structural Steels

EN 10025 is the European standard series covering hot-rolled structural steel plate, sheet, and wide flats. Part 2 (EN 10025-2) covers non-alloy structural steels (the equivalent of ISO 630 grades), Part 3 covers normalized fine-grain, Part 4 covers thermomechanical rolled, and Parts 5 and 6 cover weathering and quenched-tempered grades respectively.

For most carbon steel plate buyers, EN 10025-2 is the relevant reference. Its grades (S235, S275, S355, S450) align with the same material properties as ISO 630 but use the European designation convention.

Side-by-Side Grade Comparison

Yield Strength Class	ISO 630 Grade	EN 10025-2 Grade	Min Yield (MPa, ≤16mm)
235	E235	S235JR / S235J0 / S235J2	235
275	E275	S275JR / S275J0 / S275J2	275
355	E355	S355JR / S355J0 / S355J2 / S355K2	355
460 (ISO 630 only)	E460	— (covered in EN 10025-4, -6)	460
185 (ISO 630 only)	E185	—	185
255 (ISO 630 only)	E255	—	255

Note: The EN 10025-2 series does not include 185 or 255 yield classes. ISO 630 carries these as legacy grades, allowing for traditional applications and regional compatibility. Conversely, ISO 630 does not cover 460 MPa yield; for very high-strength plate, EN 10025-4 or EN 10025-6 must be used.

Quality Classes and Impact Test Requirements

The ‘E’ prefix in ISO 630 grades stands for ‘Engineering.’ The letters A through D designate quality classes, each with progressively more stringent impact and deoxidation requirements.

Quality Class	Deoxidation	Impact Test Temp (Charpy)	Min Impact Energy	Equivalent EN 10025-2 Designation
AA	Rimmed or balanced (older grade)	Not required	—	—
A	Killed	+20°C	27J	JR
B	Killed, fine grain	0°C	27J	J0
C	Killed, fine grain	-20°C	27J	J2
D	Killed, fine grain, normalized or TMCP	-40°C or lower	27J	K2 (+N or +M delivery)

How the Letter Suffixes Map Across Standards

The logic is consistent: a higher letter (D in ISO, K2 in EN) means more stringent Charpy testing and finer grain structure, supporting use at lower service temperatures. The practical implication for buyers is that Quality Class C of ISO 630 is roughly equivalent to EN 10025-2 S355J2+N, while Class D aligns with S355K2+N or S355M/ML.

Chemical Requirements

Grade	C (max %)	Mn (max %)	P (max %)	S (max %)	Si (max %)	CEV (typical max)
E235 (ISO 630)	0.22	1.50	0.040	0.040	0.40	0.35
S235JR (EN 10025-2)	0.17	1.40	0.035	0.035	—	0.35
S275JR (EN 10025-2)	0.21	1.50	0.035	0.035	—	0.40
E355 (ISO 630)	0.24	1.60	0.040	0.040	0.55	0.45
S355J2 (EN 10025-2)	0.20	1.60	0.025	0.025	0.55	0.45
S355K2+N	0.20	1.70	0.025	0.020	0.55	0.45

Observation: EN 10025-2 generally has tighter P, S, and CE limits compared to the older ISO 630 wording. Buyers specifying ISO 630 should confirm with the supplier whether the mill standard is up to ISO 630 or whether the mill uses EN 10025-2 directly (most modern mills have moved to EN 10025 exclusively).

Mechanical Properties at Different Thicknesses

Yield Strength vs Thickness

Thickness (mm)	S235 (MPa, min)	S275 (MPa, min)	S355 (MPa, min)
≤16	235	275	355
16-40	225	265	345
40-63	215	255	335
63-80	215	245	325
80-100	215	235	315
100-150	195	225	295
150-200	185	215	285

The same thickness-dependent yield reduction applies to ISO 630 grades. The reduction is approximately 10-15% from nominal when going above 100mm thickness. Always check the MTC and confirm actual yield for the specific thickness delivered.

Delivery Conditions

EN 10025-2 Delivery Conditions

Symbol	Condition	Typical Use
+AR	As-rolled (no special rolling or heat treatment)	JR, J0 up to certain thicknesses
+N	Normalized (heated to ~920°C, air cooled)	J2, K2 grades
+M	Thermomechanical rolled	EN 10025-4 grades
+Q	Quenched and tempered	EN 10025-6 high-strength grades

Normalization (+N) is the most commonly specified delivery condition for S355 J2 and K2 grades. It refines the grain structure, ensuring reliable impact properties at -20°C and below. Thermomechanical rolling (+M) is the modern alternative — it delivers equivalent impact properties with a lower CEV, improving weldability and reducing the need for preheat.

Application Mapping

Application	Typical Specification	Notes
Light structural steel (beams, columns)	S235JR / E235A	As-rolled sufficient
General building frames	S275JR / E275A	Cost-effective strength
Industrial buildings & bridges	S355J2 / E355C (+N)	Normalized for impact
Cranes, mining equipment	S355K2 / E355D	Higher impact guarantee
Offshore platforms	EN 10025-4 S355M/ML	TMCP for sub-zero
Arctic structures	EN 10025-4 S355ML	Impact at -50°C
Welded pressure vessels	ASME equivalent (SA-36 / SA-572)	Not EN 10025
Ship hull plates	ABS / DNV / LR rules	Not EN 10025

International Equivalents

Region	S235 Equivalent	S355 Equivalent
ISO (International)	E235	E355
Europe (EN)	S235JR / S235J2	S355J2 / S355K2
USA (ASTM)	A36, A283 Gr.C	A572 Gr.50, A633 Gr.C
Japan (JIS)	SS400	SM490A / SM490YA / SM520
China (GB/T)	Q235B	Q355B / Q345B
India (IS)	IS 2062 E250	IS 2062 E350
Russia (GOST)	St3sp	17G1S, 09G2S

Procurement Pitfalls and Practical Tips

Mixing sub-grade implications: A buyer who orders “E355” without specifying Quality Class will receive material suitable for ambient use only. For Arctic or offshore, always confirm the class (C, D) and delivery condition (+N or +M).
ASTM-to-EN conversions: A36 is not the same as S235JR. Their chemistry and welding characteristics differ. Do not auto-substitute across regional standards without formal review.
Coating references: If galvanizing is required downstream (e.g., for coastal structures), consult ISO 14713 or EN ISO 1461 for galvanizing — and verify that the steel chemistry is suitable (silicon content matters).
MTC requirements: EN 10025-2 mandates EN 10204 3.1 mill certificates with full heat analysis and tensile data. Verify the MTC is from a recognized mill, not a stockist or re-roller without heat traceability.
Verification of impact at -20°C: For J2/C grades, Charpy values must be reported at -20°C per the standard. If the MTC shows no Charpy data or shows testing at 0°C only, the material is likely J0/B grade.

Inspection and Documentation Checklist

MTC EN 10204 3.1: Confirm standard, grade, quality class, delivery condition, and chemical/mechanical data
Charpy impact test: Three specimens per heat/lot at specified temperature, full-size specimen preferred
CEV report: Required for weldability assessment, especially when welding thick sections
Dimensional report: Plate thickness, width, length, squareness, flatness per EN 10029
Surface condition: Confirm mill scale, defects, edge condition per EN 10163
Markings: Each plate should carry heat number, grade designation, plate number, and mill mark
Third-party inspection: Optional but recommended for high-criticality applications (SGS / BV / TUV)

FAQ

Is ISO 630 the same as EN 10025?

No, but they cover the same family of structural carbon steels with very similar chemical and mechanical requirements. EN 10025-2 is more widely adopted by mills, particularly in Europe and Asia, and tends to have tighter chemical limits (P, S, CEV) than ISO 630. When a project allows either standard, EN 10025-2 is generally easier to source and typically matches ISO 630 grade-for-grade. Confirm with a mill comparison for critical parameters.

How do I choose between S355J2 and S355K2?

S355J2 guarantees 27J at -20°C and is typically supplied in as-rolled or normalized condition. S355K2 guarantees 40J (higher energy) at -20°C and must be supplied in normalized (+N) or thermomechanical (+M) condition. K2 is required when the design needs higher impact toughness or lower service temperatures, or when the customer specifies higher Charpy energy. The price difference between J2 and K2 is typically 4-8%.

What thickness range is covered?

ISO 630 and EN 10025-2 cover hot-rolled plate from 3mm up to typically 200mm in standard mill production. Above 200mm, the plates are usually produced by forging or special rolling processes, and the standards may reference supplementary requirements or a different specification altogether. Most mills stock 3-150mm thicknesses; 200mm and above often have lead time of 4-8 weeks.

Is E460 in ISO 630 still used?

E460 is in ISO 630 but is less common in modern procurement. Most high-strength plate procurement uses EN 10025-4 (thermomechanical, S420M / S460M) or EN 10025-6 (quenched and tempered, S460Q / S690Q / S960Q) for strength above 355 MPa. If your specification calls for E460, consider migrating to the equivalent EN grade for better mill availability and traceability.

Can I substitute GB/T 3274 (Chinese) for EN 10025?

GB/T 3274 covers Q235, Q275, Q345, and higher Chinese grades with chemical and mechanical requirements that closely parallel EN 10025-2. Many Chinese mills supply materials that meet both standards, with the MTC clearly stating compliance. However, mechanical property tolerances and acceptance criteria can differ. For European projects referencing EN 10025-2, request explicit dual certification on the MTC to avoid acceptance disputes at port.

Conclusion

ISO 630 and EN 10025-2 are alternative references for the same family of structural carbon steel plates, with EN 10025-2 being the modern, more detailed standard. Project specifications that call out one but expect the other are common — clarify at the inquiry stage. For procurement, EN 10025-2 tends to be the practical baseline because most international mills are tested and certified to it. The most important specifier decisions are the grade (S235/S275/S355), the quality class (JR/J0/J2/K2), and the delivery condition (+N or +M), not the choice between ISO 630 and EN 10025-2.

Need ISO 630 or EN 10025 carbon steel plate for your project? Contact Huaxia-Steel for mill-direct supply with full EN 10204 3.1 mill certification, dual-standard compliance (ISO 630 + EN 10025), third-party inspection arrangement, and global shipping from our ISO-certified mills.