S355J2WP Weathering Steel Impact Energy Requirements

At -20°C, S355J2WP must absorb at least 27 Joules in a Charpy V-notch test. That's an average across three specimens taken from the same plate. No single test value may fall below 20J.

Specimen size matters.

The 27J requirement applies to full-size specimens (10 × 10mm cross-section). But not all plates are thick enough to provide full-size samples.

For thinner plates:

Plate thickness    Specimen size    Required average (approx.)
≥10mm    10 × 10mm    27J
7.5–10mm    7.5 × 10mm    ~22J
6–7.5mm    5 × 10mm    ~14J
These are proportional requirements. The smaller the specimen, the lower the energy requirement. But the test temperature remains -20°C regardless of specimen size.

Why impact toughness matters for S355J2WP.

S355J2WP is used outdoors in bridges, railcars, and building structures. Cold weather can cause brittle fracture in steel with poor impact toughness. The J2 rating ensures that when winter arrives, the steel absorbs energy rather than fracturing.

Practical impact on design.

If your structure faces temperatures below -20°C, S355J2WP may not be suitable. Consider a grade with -40°C testing. For most European and North American temperate climates, -20°C is adequate.