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Elastic-plastic fracture toughness tests were carried out with HY-80 and ASTM A710 Grade A Class 3 steels, and crack arrest tests were carried out with the HY-80 steel. Metallurgical analyses were conducted to describe the local plastic fracture processes which contribute to ductile crack initiation and cleavage crack arrest. The fracture toughness, JIc, of the ASTM A710 steel was over two times that of the HY-80 steel. Large manganese sulfide (MnS) inclusions in the HY-80 steel controlled fracture by reducing local crack-tip constraint and promoting fast shear fracture in regions of high local strain. Fracture in ASTM A710 steel occurred by full void coalescence because of reduced inclusion content, a higher strain hardening capacity than that seen in HY-80, and discontinuous carbide distribution, which retarded local shear instabilities. A stress-modified critical strain model was observed to explain the relative fracture toughness of the two steels adequately, and this suggested a higher critical distance parameter for ASTM A710 steel, which was qualitatively verified. The micromechanisms of crack arrest in HY-80 include shear fracture of ligaments behind the crack-tip connecting noncoplanar regions of cleavage and, for the case of near upper shelf arrest, large deformations associated with the lateral spreading of cleavage.
HY-80 steel, ASTM A710 steel, high-strength low-alloy (HSLA) steel, elastic-plastic fracture, crack arrest, micromechanisms, nonlinear fracture mechanics, fracture mechanics
Professor, The Johns Hopkins University, Baltimore, MD