How to avoid bubble defects in large forgings?

Question

Accepted Answer

Bubbles are divided into two kinds: inner bubbles and subcutaneous bubbles:

The gas in the steel is fed from the charge, furnace gas, and air. When the deoxidation is poor during smelting and the boiling exhaust is insufficient, the gas content in the molten steel is excessive. During the solidification process, the gas solubility decreases with the decrease in the temperature of molten steel. Precipitate and form internal bubbles. When the ingot wall is damp, rusted, and the paint contains moisture or volatile substances, when the high temperature molten steel is injected, gas is generated and penetrates into the surface layer of the steel ingot to form subcutaneous bubbles.

After forging and deforming, the bubble collapses or expands into a crack.

1. The countermeasures for preventing air bubbles are:

Bubbles are divided into two kinds: inner bubbles and subcutaneous bubbles:

The gas in the steel is fed from the charge, furnace gas, and air. When the deoxidation is poor during smelting and the boiling exhaust is insufficient, the gas content in the molten steel is excessive. During the solidification process, the gas solubility decreases with the decrease in the temperature of molten steel. Precipitate and form internal bubbles. When the ingot wall is damp, rusted, and the paint contains moisture or volatile substances, when the high temperature molten steel is injected, gas is generated and penetrates into the surface layer of the steel ingot to form subcutaneous bubbles.

After forging and deforming, the bubble collapses or expands into a crack.

2. The countermeasures to prevent air bubbles are:

1) fully bake charge and gating system;

2) Full degassing during smelting and protective casting process;

3) high temperature diffusion, forging welding hole defects;

4) Burn off the surface cracks in time.

Separate baking charge and pouring system;

2) Full degassing during smelting and protective casting process;

3) high temperature diffusion, forging welding hole defects;

4) Burn off the surface cracks in time.