40Cr (GB/T 3077) is a chromium-alloyed structural round steel valued for its heat-treatable strength, with mechanical properties tailored for heavy machinery:
Tensile strength: 800–1000 MPa after quenching (850°C) and tempering (520°C), enabling it to withstand high loads in gearboxes and crankshafts.
Yield strength: ≥700 MPa, ensuring minimal deformation under sustained stress-critical for components like connecting rods.
Impact toughness: ≥55 J at 20°C (Charpy V-notch), providing resistance to sudden impacts in industrial equipment.
Hardness: 241–286 HB after heat treatment, balancing wear resistance and machinability for complex parts.
These properties arise from its chemistry: 0.37–0.44% C, 0.17–0.37% Si, 0.50–0.80% Mn, and 0.80–1.10% Cr, which enhances hardenability. 40Cr is equivalent to ASTM 5140 (USA) and DIN 1.7035 (Germany), though it contains slightly more chromium than its Western counterparts. It is widely used in Chinese machinery manufacturing for gears, shafts, and bolts, with Made-in-China listings promoting it as "40Cr Alloy Steel Round Bar for Heavy Machinery."