Influence of Hot Straining Embrittlement on Brittle Fracture in Welded Steel Plates

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The metallurgical variables induced by welding often result in the decrease in fracture toughness of the materials used. Change in fracture toughness of material due to the hot straining during weld thermal cycle will influence the brittle fracture initiation in welded steel plates. Decrease in fracture toughness due to hot straining embrittlement may cause brittle fracture even in the range of service temperature. The present paper includes both analytical study on thermal stress and strain cycles in the vicinity of a notch tip during welding and experimental study on fracture toughness of materials subjected to hot straining during welding. The analytical study on thermal strain cycles is carried out based on the thermo-elasto-plastic analysis by the finite element method. Critical COD-values are obtained for high strength steels of 50, 60, 80 kg/mm^2 strength level and their weld fusion line subjected to weld thermal-strain cyces and to prestraining at elevated temperature. The hot straining embrittlement of material as well as residual stress due to welding elevates brittle fracture initiation temperature in comparison with the base metal. The influence of the hot straining during successive weld thermal cycles on fracture toughness can be estimated quantitatively by using notched bend COD test specimens cut from notched welded wide plate including a pre-existing notch. The elevation of the critical COD transition temperature in the material subjected to hot straining depends upon the kind of steels : mild steel and HT50 steel are sensitive to the hot straining embrittlement. The hot straining embrittlement is found in weld fusion line as well as base metal.
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Influence of Hot Straining Embrittlement on Brittle Fracture in Welded Steel Plates

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