Zirconium modification principle
The zirconium modification principle is used for grain refinement and deoxidation in special alloys to improve the microstructure and toughness.
Physical-Chemical Mechanism of Action
Zirconia (ZrO2) is used in the molten weld pool as a strong deoxidizer. It binds oxygen, preventing porosity and increasing strength. Zirconia also promotes grain refinement through its microscopic crystal structure.
Metallurgical Relevance & Welding Risks
Too high a zirconia content can cause fusion issues, as it raises the liquidus temperature of the alloy. This can lead to distortion and uneven stresses in the weld. Conversely, insufficient zirconia can cause porosity and reduced mechanical properties.
Shop Practice & Action Points
• Deoxidation: Use zirconia in the flux to bind oxygen. Typical content is 0.1 to 0.5 %.
• Grain Refinement: Ensure optimal melt temperature and cooling time (t8/5 between 10 and 20 seconds) for fine grain structure.
• Monitoring: Continuously monitor zirconia content and deoxidation status to avoid porosity.