Comparative Analysis of the Properties of S355K2G2W and JIS G3114 SMA490

So you have two weathering steel grades: one European, one Japanese. Both look similar on paper. But swap one for the other without checking the fine print, and you might run into trouble.

S355K2G2W follows EN 10025-5. Its name tells you a lot: minimum yield strength of 355 MPa, "K2" guarantees 27J impact energy at -20°C. SMA490 from JIS G3114 comes in several classes—A, B, C (e.g., SMA490AW, BW, CW). The "490" means minimum tensile strength of 490 MPa, with yield typically around 355 MPa, very close to its European cousin.

So where's the real difference? Impact toughness. SMA490 grades usually specify Charpy values at 0°C or sometimes -5°C, depending on the class. For most of Japan's temperate climate, that's fine. But if your project faces real winter cold—say, mountain bridges or northern European installations—S355K2G2W's -20°C guarantee gives you a clear edge.

Another difference: chemistry control. Japanese weathering steels often lean slightly more on copper and chromium, while European grades balance phosphorus and chromium differently. In practice, both develop a protective patina over time. Neither will rust through quickly in normal atmospheres.

Which one to choose? If your customer follows JIS standards or the structure stays in mild winter regions, SMA490 works well. If the job requires documented low-temperature toughness down to -20°C, S355K2G2W is the safer bet.