GB/T 3077-1999 governs alloy structural round bars (e.g., 20Cr, 40Cr, 35CrMo) with comprehensive specifications to ensure performance:
Chemical composition: Strict limits for alloying elements (e.g., Cr 0.80–1.10% in 20Cr) to guarantee consistent hardenability and strength.
Heat treatment: Mandatory normalization or quenching/tempering for bars ≥16mm, with precise temperature ranges (e.g., 850–880°C for 40Cr quenching) to control microstructure.
Mechanical testing: Tensile, impact, and hardness tests for each heat of steel. Bars ≥12mm must pass a 180° bend test without cracking, ensuring ductility.
Surface quality: No cracks, folds, or segregation. Ultrasonic testing is required for bars ≥40mm used in critical applications (e.g., bridge bolts) to detect internal flaws.
The standard ensures alloy bars meet needs in automotive, aerospace, and energy sectors. It aligns with EN 10083 (EU) and ASTM A29 (USA) for global compatibility, making GB/T 3077-compliant bars popular in international projects.