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The segregation of phosphorus from the matrix to grain boundaries has been associated with increased brittleness in carbon-manganese submerged-arc weld metals, with the failure mode on the lower shelf and transition regime changing from cleavage to intergranular failure. The quantification of segregation and hence thermal embrittlement requires the knowledge of the energy decrease for an atom in the matrix moving to a grain boundary, ΔG. There is some evidence to suggest that the energy decrease depends on the level of alloying constituents and this paper considers a steel with 1.46 wt% manganese and 0.08% carbon. The value of ΔG was calculated as a function of temperature by measuring grain boundary segregation after annealings at constant temperature in the range 763–873K. The grain refined and columnar regions of the welds were analysed separately. The phosphorus grain boundary monolayer coverages observed were smaller than those reported for a PWR steel.
Submerged-arc weld, Thermal embrittlement, Phosphorus segregation, Auger examination
Research Officer, Magnox Electric plc, Berkeley Centre, Berkeley, Gloucestershire