1. Introduction
Steel plates are fundamental materials in modern industry and construction, and their quality standards have evolved into multiple systems worldwide. In China, steel plate products mainly comply with Chinese National Standards (GB, commonly referred to as "Guobiao"); in Europe, they comply with European Standards (EN). The two systems differ in standard framework, grade designation rules, chemical composition requirements, and mechanical property indices, yet there are also numerous grade equivalences. Understanding these similarities and differences is of great significance for international trade, engineering material selection, and material substitution.
2. Overview of the Main Standards
GB System
The main Chinese standards related to steel plates include:
GB/T 700 Carbon Structural Steels – specifies technical requirements for carbon structural steels, applicable to general structural steel.
GB/T 1591 High Strength Low Alloy Structural Steels – specifies technical requirements for high-strength low-alloy structural steels.
GB/T 3274 Hot-rolled steel plates and strips for carbon structural steels and low alloy structural steels – specifically for hot-rolled plates and strips.
EN System
The European standards for steel plates are centred on the EN 10025 series:
EN 10025-2 Hot rolled products of structural steels – Part 2: Technical delivery conditions for non-alloy structural steels – corresponds to the carbon structural steel category in GB.
EN 10025-3 Hot rolled products of structural steels – Part 3: Technical delivery conditions for normalized/normalized rolled weldable fine grain structural steels – corresponds to the high-strength low-alloy structural steel category in GB.
3. Differences in Grade Designation Rules
GB and EN follow completely different logics in grade designation, which is the most visible difference between the two.
GB Grade Designation
GB grades start with "Q", standing for "yield point" (yield strength), and the following number indicates the minimum yield strength (in MPa). The quality level is denoted by A, B, C, D, E, which successively correspond to different impact toughness requirements. For example:
Q235 – carbon structural steel with minimum yield strength of 235 MPa
Q355 – high-strength low-alloy structural steel with minimum yield strength of 355 MPa
EN Grade Designation
EN grades start with "S", standing for "Structural Steel", and the following number likewise indicates the minimum yield strength (in MPa). The quality level is expressed by codes such as JR, J0, J2, which indicate impact energy requirements. For example:
S235JR – structural steel with minimum yield strength of 235 MPa; JR indicates impact energy requirement at room temperature (20 °C)
S355J2 – structural steel with minimum yield strength of 355 MPa; J2 indicates impact energy requirement at –20 °C
It is worth noting that the EN standard embeds the toughness requirement directly into the grade name (e.g., S235JR), whereas GB separates the strength (Q355) from the quality level (B).
4. Main Differences between GB and EN Standards
4.1 Different Standard Architecture
GB standards are formulated according to steel categories (e.g., carbon structural steels and high-strength low-alloy structural steels each have their own separate standard), whereas EN standards are organized by product form and application. The EN 10025 series covers multiple parts for hot-rolled structural steels.
4.2 Different Grade Expression
As noted above, GB uses "Q + number + quality letter", while EN uses "S + number + quality code". This difference stems from their divergent philosophies regarding how to express strength and toughness.
4.3 Slight Differences in Chemical Composition Control
Taking S235JR and Q235B as examples, although they are very similar, there are minor differences in the upper limits of certain elements, carbon equivalent (CEV) calculation methods, etc. For S275JR, chemical composition is controlled by thickness ranges – for example, for thickness ≤16 mm, C ≤ 0.21% and Mn ≤ 1.50%.
4.4 Different Expression of Impact Toughness Requirements
GB uses letters A, B, C, D, E to indicate impact requirements at different temperatures, while EN directly uses codes such as JR (room temperature), J0 (0 °C), J2 (–20 °C) within the grade. This difference makes the EN grade itself directly reflect the toughness level of the steel.
4.5 Differences in Sampling and Testing Methods
With regard to sampling, Chinese and European standards are basically consistent, but they differ significantly from American standards. In mechanical property testing, as the tensile test rate increases, the strength indices increase while plasticity decreases.
5. Common Steel Plate Grade Equivalents
The following are the grade equivalences commonly used in engineering between GB and EN steel plates:
Carbon Structural Steels (General Structural Steels)
| GB Grade | EN Grade | Remarks |
|---|---|---|
| Q195 | S185 | Lowest strength grade, suitable for general structures |
| Q235A | S235JR | Grade A (no impact requirement) corresponds to JR (room temperature impact) |
| Q235B | S235JR | The most common equivalence; both can be substituted for each other in most applications |
| Q235C | S235J0 | Grade C (0 °C impact) corresponds to J0 (0 °C impact) |
| Q235D | S235J2 | Grade D (–20 °C impact) corresponds to J2 (–20 °C impact) |
| Q275 | S275JR | S275 is roughly equivalent to Q275 |
High Strength Low Alloy Structural Steels
| GB Grade | EN Grade | Remarks |
|---|---|---|
| Q345 (old designation) | S355 | Former equivalence: Q345 low-alloy steel corresponds to S355 |
| Q355 (new designation) | S355 | From 1 February 2019, Q345 was changed to Q355, aligning with S355 |
| Q355B | S355JR | General grade equivalence |
| Q355C | S355J0 | 0 °C impact requirement |
| Q355D | S355J2 / S355J2G3 | –20 °C impact requirement |
| Q355E | S355NL | –40 °C impact requirement, normalized rolled fine-grain steel |
Cold-rolled Steel Sheets
| GB Grade | EN Grade | Remarks |
|---|---|---|
| Quality carbon structural steel (GB/T 5213) | DC01 (EN 10130) | Cold-rolled low-carbon steel sheet and strip; similar mechanical properties |
6. Important Change: Q345 Adjusted to Q355
According to the national standard High Strength Low Alloy Structural Steels GB/T 1591-2018, effective from 1 February 2019, the Q345 steel grade was abolished and replaced by Q355. The main purpose of this adjustment is to align the GB grade with the European S355 steel grade, thereby promoting the internationalization of Chinese standard steels.
Q355 is a high-strength low-alloy steel with a yield strength of 355 MPa. In terms of chemical composition and mechanical properties, the new GB Q355B is already very close to European S355JR. This adjustment provides a technical basis for the application and promotion of Chinese standard steels in international engineering projects.
7. Recommendations for Material Selection and Substitution
In practical engineering applications, when substituting GB steel plates with EN steel plates (or vice versa), the following points should be noted:
Confirm the strength grade equivalence: Ensure that the yield strength levels correspond, e.g., Q235 corresponds to S235 series, Q355 corresponds to S355 series.
Check impact toughness requirements: According to the service environment and design temperature of the project, select the appropriate grade. The GB A/B/C/D/E levels must correspond one-to-one with EN JR/J0/J2/NL levels.
Pay attention to chemical composition differences: Although the requirements for major elements are similar, there may be differences in trace elements and carbon equivalent limits. Special attention should be paid for projects with high welding requirements.
Refer to authoritative comparison references: It is recommended to consult professional handbooks such as the Handbook for Quick Reference of Common Chinese and Foreign Steel Grades for more comprehensive grade equivalence information.
8. Conclusion
GB and EN, as two major mainstream steel plate standard systems, differ in system architecture, grade designation, and some technical requirements. However, they have become increasingly close in core strength grading and performance requirements. With the adjustment of GB Q355 to correspond to EN S355, the alignment of Chinese steel standards with international standards has been further improved. In actual engineering practice, as long as the grade equivalences are correctly understood and the subtle differences in technical requirements are taken into account, mutual substitution between GB and EN steel plates is entirely feasible.
