These are carbon steels that have additives eg. boron, manganese, chromium, silicon etc. SAE Grade 8 (Metric class 10.9,12.9) fasteners are generally manufactured out of alloy steel with AISI grades 4137, 4140 (B7), 4340 & 5140 and also ASTM A307 – Grade A/B/C, ASTM A194 Grade 4, 7, & 7M, ASTM A193 B7 & B7M, ASTM A320 Grade L7, L43 falling into this category.
