1. Manganese (Mn) – significantly improves low‑temperature toughnessMn is critical for balancing strength and toughness in S355J0WP.
It refines ferrite grains, making the microstructure finer and more uniform, which lowers the ductile‑brittle transition temperature (DBTT).
It combines with harmful sulphur to form stable MnS inclusions, eliminating brittle iron sulphide and avoiding hot cracking & low‑temperature brittleness.
It increases plastic deformation capacity and raises impact energy at 0 °C, ensuring the J0 impact requirement is met.
Moderate Mn also improves hardenability moderately without forming brittle phases.
2. Silicon (Si) – neutral to slightly harmful to low‑temperature toughnessSi is mainly added for deoxidation and solid‑solution strengthening.
Small amounts purify molten steel and enhance strength without obvious harm.
Excess Si promotes coarse ferrite and segregation, raises DBTT, reduces crack resistance at low temperatures.
Therefore, S355J0WP strictly limits Si content, to gain deoxidation benefits while minimizing toughness loss.
