Carbon steel and stainless steel are two main materials for construction fasteners. Each has unique strengths and limitations.
Carbon steel fasteners can reach very high mechanical strength at low cost. 8.8, 10.9 high strength bolts are carbon steel products. But carbon steel easily rusts, so anti-corrosion coating like zinc plating or HDG is required.
Stainless steel fasteners (A2, A4) have excellent natural corrosion resistance without extra coating. A4 stainless steel performs well under salt spray and coastal environment. The downside is higher price and lower tensile strength compared with high strength carbon steel bolts.
Balance cost, strength and corrosion requirement when choosing fastener material.