Inclusion Formation in Low-Alloy Steel Welds
Outline
Certain inclusions promote acicular ferrite.
Models for inclusion formation
Fixed oxidation sequence and mass balance can be used to estimate the inclusion composition.
The oxidation sequence is related to chemical composition - Fe-X-O Deoxidation diagrams.
Thermodynamic calculations can describe the oxides that form as a function of temperature and composition.
Thermodynamic calculations are not capable of describing the process effects.
How do we consider effects of both weld composition and cooling rate?
Thermodynamic-Kinetic model is based on the calculation of extent of each oxide formation.
Fluid flow conditions in the weld may induce collision and coalescence of inclusions.
In addition, thermal fluctuations may lead to growth and dissolution of inclusions.
Application of the model - Use of thermodynamic calculations.
High Aluminum content in the welds leads to competition between AlN and Al2O3 reactions
High levels of aluminum in solution leads to incomplete _ ferrite to austenite transformation.
Application of the model - Use of thermodynamic-kinetic calculations.
Inclusion formation in autogenous Electron Beam (EB) and Laser Beam (LB) welds were studied.
Drastic change in inclusion distribution was observed between SA, LB, and EB welds.
What is the reason for the observed inclusion characteristics of EB and LB welds?
Approximate weld cooling curves were used for inclusion model predictions.
Calculated trends agree with experimental observations.
Calculated Al and Ti concentration in the inclusions agree with experimental trends.
Future Work
Application of these models to a wide range of welding conditions requires consideration of following issues.
Summary and Conclusions
We need to identify the relationship between inclusion characteristics and acicular ferrite transformation kinetics.
Future work
Email: babuss@ornl.gov
Home Page: http://babuss.ms.ornl.gov
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