DEVELOPMENT OF MACROSTRUCTURE AND MICROSTRUCTURE OF CARBON-MANGANESE LOW-ALLOY STEEL WELDS - INCLUSION FORMATION

Ladle steel deoxidation reactions are reviewed and the principles are extended to inclusion formation in steel weld metal. The dissolution o f oxygen, the stability of various oxides, and the nucleation and grow th of inclusions are discussed. Theoretical time-temperature transform ation (TTT) diagrams are calculated for various oxide inclusions based on an overall kinetics approach using nucleation and growth rare expr essions. These concepts are then extended to understand the developmen t of weld metal inclusion characteristics. A strong correlation betwee n the published inclusion composition and the stability of the oxides was found. An analysis of the TTT diagrams indicates that, during weld cooling, sequential oxidation of dissolved deoxidising elements takes place, which agrees with the reported layered morphology of inclusion s. The analysis indicates that the inclusion characteristics are quite sensitive to the oxygen content, the deoxidising element concent rati ons, the presence of performed inclusions, and the reaction temperatur e. Inclusion coarsening and elimination of inclusions from welds are d iscussed in relation to the final inclusion characteristics.