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FRACTURE OF METALS DURING DEFORMATION PROCESSING UNDER CONDITIONS OF HOT WORKING.
DREXEL INST OF TECH PHILADELPHIA PA DEPT OF METALLURGICAL ENGINEERING
The hot fracture of Inconel 600 and Waspaloy has been studied over the temperature range from 800 to 2200 F using a hot torsion tester that is capable of superimposing either axial tensile or compressive stresses on the torsional shearing stresses. Microscopic studies of fracture initiation have been made over the entire temperature region. From 800 to 1200 F fracture initiates at inclusions and propagates by transgranular shear. In the temperature region of minimum ductility, 1300-1500 F, fracture initiates at grain boundaries and propagates readily in an intergranular manner. At 1600 F and above, fracture initiates easily at grain boundaries, but because recrystallization intervenes crack propagation is difficult and strain to fracture is high. Microcracks initiate at the peak in the torque-twist curve. The higher the temperature the smaller is the strain at which fracture initiates. Correlations have been found between the stress state and the shearing strain at crack initiation and total fracture strain. These correlations show the strong influence of a compressive normal stress on retarding crack initiation and resisting crack propagation. Author
Final rept. 14 Nov 65-13 Nov 66,