The fracture toughness values of ship building mild steel measured over a temperature range -196Β°C to 28Β°C and crack tip strain rates ranging from IO-"/see to IO-'/set are examined in the light of the models recently proposed by Malkin and Tetelman.'The effect of a change in inclusion morphology brought about by electroslag refining on the fracture toughness of the steel is also evaluated. It is found that the stressinduced fracture criterion of the model applies for the case where the ratio u?/o,..~ < 3.94. This ratio is independent of the strain rate. In the strain induced fracture region of the model, the critical strain near the crack tip, E,(&) is a function of the yield stress irrespective of temperature and strain rate. Electroslag refining reduces significantly the size and volume fraction of the inclusions and changes their shape from prolate ellipsoid to spherical. Apparently the electroslag refining does not improve fracture toughness significantly if the fracture toughness of the as received material measured with the major axis of the inclusions perpendicular to the crack front, is taken as a basis of comparison. R. K. PANDEY. J. I). HARIDAS unit S. HANERJEE Microstructure C'ompoiition Mechanical pt-cqxrtic\ ASTM rr, Pj Material G.S. No. Ferrite P&lite C' Y.S.
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