Oxygen Affinity Index
The oxygen affinity index indicates how strongly a metal reacts with oxygen. A higher index means stronger oxide formation. This affects the composition of the structure and the strength of the weld.
Physical-Chemical Mechanism of Action
The Oxygen Affinity Index (OAI) is a thermodynamic parameter that indicates how strongly a metal reacts with oxygen. It measures the chemical affinity of an element for oxygen and is given in eV (electron volts). A higher OAI means stronger oxide formation.
Metallurgical Relevance & Welding Risks
The OAI influences the microstructure composition in the melt and can lead to various problems. Too high an OAI can cause excessive oxidation and pore formation, which impairs the strength and mechanical properties of the weld. Too low an OAI can lead to insufficient oxide formation and sulfur formation, which also reduces weld quality.
Workshop Practice & Action Guidelines
To keep the OAI optimal, the melting conditions must be precisely controlled. This includes the correct choice of flux and maintaining the right temperature and time in the melt. For difficult-to-oxidize metals like steel, it's important to regulate the OAI so that sufficient oxide formation occurs without pores. This can be achieved by using deoxidizers and controlling the melting atmosphere.