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Summary
This paper describes an investigation of SUS310S stainless steel weld metal to clarify the direction of grain boundary migration. A vertex dynamics model is used to calculate the transition process of grain growth in the base metal and grain boundary migration in the weld metal. The results are compared with observations of grain boundary migration in the weld metal. The results obtained may be summarised as follows.
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When the grain boundary migration behaviour of base metal grains is computer-simulated by vertex dynamics, the growth rule and number of grain sides distribution are found to be consistent with the actually observed growth behaviour. That is to say, when the friction coefficient of grain boundary migration is valued at the third power of the grain boundary length, grain growth is proportional to the 1/4 power of the growth time. The number of grain sides distribution is virtually identical in the grain growth process.
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The grain boundaries in the weld metal migrate from the heat affected zone (HAZ) towards the weld metal in the welding HAZ near the fusion boundary zone and from the axial crystals towards the columnar crystals at the weld metal centre. This is due to the fact that, at the grain boundary edges, the direction of the unit resultant vector of the grain boundary line extending from the grain boundary triple junctions faces towards the weld metal in the HAZ and towards the columnar crystals at the weld metal centre. The direction of grain boundary migration after solidification is therefore considered to be controlled by the migration of the grain boundary triple junctions on both edges, i.e. by the resultant direction of the unit vector of the grain boundary line extending from the grain boundary triple junctions.