What are the common grades of round steel?

Common round steel grades vary by application and regional standards. In China, per GB/T 702, the most widely used grades include Q235B (yield strength ≥235MPa, for general structural parts like bolts and brackets), Q355B (yield strength ≥355MPa, for medium-load components such as mechanical shafts), and 45# steel (carbon structural steel with ~0.45% carbon, used for parts requiring quenching/tempering like gears). Internationally, ASTM A36 (USA, yield 250MPa, versatile in construction and machinery), EN 10025-2 S235JR/S355JR (Europe, equivalent to Q235B/Q355B), and JIS G3101 SS400 (Japan, for general industrial use) are prevalent. For high-precision or corrosion-resistant needs, grades like 304 stainless steel (ASTM A276, for food/medical equipment) and 40Cr (alloy structural steel, for high-torque shafts) are also common. These grades differ in chemical composition (e.g., 45# has higher carbon than Q235B) and mechanical properties, matching diverse usage scenarios.