Be Extra Cautious with Acid-Based Furnaces for Aluminum Deoxidation

Brittle fracture is one of the common defects in investment castings. Especially when using induction furnaces (medium frequency induction furnace, low frequency induction furnace) with acidic furnace linings for melting and using aluminum for deoxidation, the cast steel parts are more prone to brittle fracture during pouring.

Ⅰ.Overview

The investment casting with brittle fracture is shown in Figure 1. The macroscopic fracture grains of brittle fracture castings are coarse and resemble rock sugar, as shown in Figure 2. The microstructure of brittle fracture castings is shown in Figure 3.

 Figure1. Brittle fracture of investment casting

FIG. 2 Macroscopic fracture of brittle fracture

                   Aluminides on grain boundaries 100X     Carbon-boron compounds at grain boundaries 160X

               FIG. 3 Microstructure of brittle fracture

Ⅱ. The cause