Which ASTM grade corresponds to S355K2G1W

You have a European specification calling for S355K2G1W. Your steel supplier works in ASTM grades. Can you substitute? The short answer is yes, with adjustments. The long answer requires a careful look at what each standard actually guarantees.

The closest match: ASTM A588 Grade A

A588 Grade A is the standard weathering steel in the ASTM world. It offers:

Yield strength: 345 MPa minimum (50 ksi) for thicknesses up to 100mm

Tensile strength: 485 MPa minimum (70 ksi)

Weathering chemistry: Copper, chromium, nickel, and silicon for patina formation

That's very close to S355K2G1W's 355 MPa yield. For most structural applications, the 10 MPa difference is negligible in practice.

Where they diverge: Impact toughness

This is the critical difference. S355K2G1W guarantees 27J at -20°C with the K2 rating. Standard ASTM A588 Grade A has no mandatory Charpy impact requirement. You can order A588 with supplementary requirement S5 (Charpy V-notch impact testing), but typical temperatures are 0°F (-18°C) or sometimes -20°F (-29°C) depending on negotiation.

So to match S355K2G1W's low-temperature performance, you must:

Specify ASTM A588 Grade A

Add supplementary impact testing at -20°C (or -18°C as a practical equivalent)

Specify minimum energy absorption (typically 27J or 20 ft-lbs, which is roughly 27J)

What about phosphorus?

S355K2G1W keeps phosphorus low (≤0.035%). ASTM A588 Grade A allows up to 0.04% for Grade A, or 0.10% for Grade B (depending on thickness). This is actually closer to the G2W chemistry. For most applications, this difference doesn't matter. Only if your specification explicitly calls out the low-phosphorus G1 variant would you need to discuss with the mill.

Other ASTM grades to consider:

A709 Grade 50W: Bridge-specific weathering steel. Often includes impact testing options. Good for transportation structures.

A847: Cold-formed weathering steel tubing and shapes. Different product form, not a direct plate substitute.

A871 Grade 60 or 65: Higher strength weathering steel (415–450 MPa yield). Over-matching strength could cause unintended design issues.