Application of Continuous Casting Round Billets in Tricone Bit Forgings (part 2)

Process Flow

The trial production process for this round bar steel is as follows:

60t Electric Arc Furnace (EAF) Melting → Ladle Furnace (LF) Refining → Vacuum Degassing (VD) → Continuous Casting (400mm) → Reheating of Cast Bloom → Breakdown Forging with Hydraulic Press + Precision Forging (200mm) → Normalizing & Tempering → Visual Inspection → Ultrasonic Testing → Mechanical and Chemical Testing → Delivery

Key Process Controls and Measures

1) EAF Melting

Based on the designed chemical composition, the furnace charge consists of selected scrap steel, crop ends, Ni-containing steel chips, etc. All materials must be clean and dry before charging; unclassified scrap or pit-bottom residues are strictly prohibited. The content of five harmful elements (As, Sn, Pb, Sb, Bi) must each be controlled to ≤0.015%. To ensure continuous and compact production rhythm for continuous casting, the EAF adopts hot heel and slag-retaining operation. In the early stage of melting, a slag-free tapping method is used, with increased oxygen flow to accelerate decarburization and dephosphorization.

2) LF Refining

Non-metallic inclusions in steel have a significant negative effect on tricone bit performance. Therefore, refining — a critical process for inclusion removal — requires strict control. Throughout the LF refining process, argon gas usage must be optimized to avoid steel exposure and improve high-temperature molten steel kinetics. This enhances deoxidation and denitrification efficiency, ensures uniform temperature and chemical composition, and promotes the flotation and removal of gases and inclusions.

3) VD Degassing

During the VD vacuum degassing process, both vacuum degree and argon flow rate are dynamically controlled without slag overflow. This ensures deeper degassing and further removal of inclusions.

4) Continuous Casting

A two-strand vertical caster is used to produce 400mm section blooms. Protective casting is adopted throughout to prevent secondary oxidation of molten steel. Before casting begins, argon is used to purge the ladle shroud, with long nozzles used in the ladle and submerged nozzles in the tundish, sealed with argon protection.

5) Forging

To improve material utilization, continuous cast blooms are used instead of ingots for forging. Proper deformation methods must be employed to ensure internal quality of the forgings. Before forging begins, both the hammer head and bloom surface are cleaned to reduce the risk of surface cracks during deformation.