S355K2G2W Weathering Steel Old vs New Standard Comparison

The old standard: EN 10155 (1993).

Before EN 10025-5, weathering steels were covered under EN 10155. This standard specified S355K2G1W and S355K2G2W as separate grades. The main difference in that standard was phosphorus range. The G1W variant had lower phosphorus (≤0.035%), while G2W allowed higher phosphorus (up to 0.12%) for enhanced corrosion performance.

The new standard: EN 10025-5 (2004, updated 2019).

EN 10025-5 replaced EN 10155 and consolidated the weathering steel grades. S355K2G2W was retained, but several changes came along:

Grade consolidation. The transition unified testing and certification requirements across all weathering grades.

Impact testing. The J2 and K2 requirements were clarified, with K2 maintaining the 27J at -20°C and individual low limits.

Chemical limits. Phosphorus ranges were retained for G2W, with clearer definitions and tighter control on sulfur.

Delivery conditions. The new standard introduced more detailed requirements for normalized-rolled and thermomechanically rolled conditions.

What changed for S355K2G2W specifically.

Aspect    EN 10155 (old)    EN 10025-5 (current)
Phosphorus range    Up to 0.12%    Up to 0.12% (retained)
Copper range    0.25–0.55%    0.25–0.55% (unchanged)
Chromium range    0.40–0.80%    0.40–0.80% (unchanged)
Impact testing    K2 at -20°C    K2 at -20°C (clarified sampling)
Testing frequency    Per heat    Per heat + product analysis
Supplementary tests    Limited    Expanded options (UT, additional impacts)
What stayed the same.

Mechanical properties. Yield strength (355 MPa), tensile strength (470–630 MPa), and elongation remain unchanged.

Weathering chemistry. Copper, chromium, and nickel ranges are identical.

Impact toughness. The K2 requirement of 27J at -20°C with individual low limits remains the same.

What improved in the new standard.

Tighter tolerances. EN 10025-5 introduced more precise requirements for dimensional tolerances and surface quality.

Clearer certification. The new standard requires product analysis (not just heat analysis) for chemical verification—catching variations during rolling.

Supplementary testing. UT, additional impact tests, and bend tests are now clearly defined as options.

Traceability. The heat number system was standardized across all mills.

Practical impact for buyers.

Certificates now reference EN 10025-5. If your supplier sends a certificate with EN 10155, it's old stock or incorrectly documented.

Product analysis is now mandatory. The certificate should show both heat analysis and product analysis columns.

Grade naming is consistent. S355K2G2W is the same grade in both standards—no name change.

What about G1W?

In the old standard, G1W and G2W were separate. In EN 10025-5, both remain, but G2W (higher phosphorus) is often preferred for aggressive environments. The G1W variant (low phosphorus) is still available for weld-sensitive applications.

Transition note.

If your specification still references EN 10155, it's time to update. Most mills no longer certify to the old standard. For new projects, specify EN 10025-5:2019 (or the latest revision) to ensure compliance with current testing and certification requirements.

One common confusion.

Some buyers see "S355K2G2W" on an EN 10155 certificate and assume it's a different material than the EN 10025-5 version. It's not. The material is the same—the standard changed. But always verify the certificate's standard reference and ensure the testing meets current requirements.