The core function of ferro boron in steel is to improve hardenability via micro-addition. Based on this property, four main steel grades commonly require ferro boron addition:
1. Steel for High-Tensile Bolts & Automotive Components
Typical grades include 10B21 and 40B, used to manufacture high-strength bolts of Class 8.8 and above, steering knuckles and other auto parts. After boron addition, even thick bolts can achieve full hardening at the core, avoiding the defect of hard surface but soft core, thus preventing brittle fracture effectively.
2. Large-Size Spring Steel
Examples cover truck leaf springs and heavy machinery large springs. For thick cross-section springs, conventional spring steel cannot be fully hardened. Boron enables uniform hardness across the entire section, delivering superior elasticity and longer service life.
3. High-Temperature Resistant Steel for Power Station Equipment
Boiler and pipeline steel such as 12Cr1MoVB adopts boron not only for full hardening, but also to strengthen grain boundaries. It restricts high-temperature creep and deformation, extending the service life of high-temperature facility components.
4. Low-Alloy Structural Steel for Construction & Machinery
Applied to construction machinery booms and heavy structural parts. Boron enhances structural strength while cutting consumption of precious alloy metals, achieving excellent cost performance.
Important Reminder
Boron cannot be added arbitrarily. Molten steel must be thoroughly deoxidized and denitrified (usually pre-deoxidized with aluminum, then titanium is added for nitrogen fixation). Otherwise, boron will react with oxygen and nitrogen to form inclusions and lose effectiveness completely. Only refined clean steel is suitable for boron alloying; crude rimmed steel is totally incompatible with boron addition.
