A METALLOGRAPHIC INVESTIGATION OF THE FACTORS AFFECTING THE NOTCH TOUGHNESS OF MARAGING STEELS.
UNITED STATES STEEL CORP MONROEVILLE PA
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This report describes the results of an investigation of nine maraging steels with widely varying notch toughness 25 to 70 ft-lb Charpy V-notch energy at 190 ksi yield strength. Extraction fractography was used in conjunction with such techniques as light microscopy, thin-film electron microscopy, microprobe analysis, and electronand X-ray-diffraction analysis to identify the causes for the difference in toughness among the nine steels. The results of the investigation indicate that by examining extraction fractographs with metallographic, X-ray- and electrondiffraction, and microprobe techniques it is possible to isolate the major factors responsible for low notch toughness in maraging steels. Thin-film transmission-electron microscopy and analysis of insoluble residue, while generally substantiating the results obtained by analysis of the fractographs, are less definite and therefore less useful than the fractographic studies.