A new approach to quantifying steel response for welding procedure design

PhD candidate

P. F. Mendez
Director of CCWJ

Presented At: 
CWA Conference 2014

Minor changes in the composition of the steel defined in any welding procedure will have a major effect on the final properties of the welded part. Constant cooling transformation diagrams (CCT) are used to determine the final microstructure and hardness of steels; however, they are seldom available for weldable alloys. Creating CCT diagrams for custom steels is so difficult and expensive that the carbon equivalent concept is used as a proxy. Despite its practicality, this approach is incomplete. Ongoing research on phase transformations has enabled the use of precise temperature measurements during cooling to estimate the evolution of a newly formed phase with time/temperature. This method can go beyond any previous cooling curve analysis approach by quantifying partial transformations and making in-situ measurements of phase fractions in complex simultaneous phase transformations possible. This is possible because of a rigorous framework that reduces the number of unknown parameters to its minimum. This approach will be illustrated with examples of aluminum solidification with simultaneous precipitation and martensitic transformation in steel. The solidification/precipitation of aluminumA356 will be compared with Thermo-Calc Software TTAL7 Al-alloys database v7.1 predictions, and the martensitic transformation will be compared with dilatometry. A major benefit of this method is that it can be performed at negligible cost. Our conclusion is that quantification of intermediate stages of transformation in steels and other alloys is available to any lab with a furnace and a temperature recorder.

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