Accession Number : AD0486333

Title :   ON THE MICROSTRUCTURAL SENSITIVITY OF FRACTURE TOUGHNESS,

Corporate Author : AEROSPACE CORP EL SEGUNDO CA LAB OPERATIONS

Personal Author(s) : Raymond, Louis ; Gerberich, William W. ; Reuter, Walter G.

Report Date : MAY 1966

Pagination or Media Count : 41

Abstract : Deformation of a metastable 0.25C-5Cr-Mo-V austenite at 405 C, or about 40 C above the M sub s temperature, produced a two-phase microstructure of bainite and martensite. This microstructure exhibited abnormally high toughness at crack-instability (4000 in. -lb/sq. in. for 240-Ksi yield strength material) and a relatively low value at the initiation of crack propagation (70 in. -lb/sq. in.). Deformation at the M sub s or more than 100 C aboce the M sub s produced a one-phase martensite structure that exhibited toughness at crack-instability that was lower by a factor of 100. The uniaxial stress-strain curves were identical for both microstructures and thus contradict current continuum mechanics fracture theories derived from uniaxial tensile behavior. This anomaly is explained in terms of a model that considers the micromechanics of crack arrest and reinitiation in a two-phase microstructure where the bainite constituent is considerably tougher than martensite.

Descriptors :   (*STEEL, TOUGHNESS), (*FRACTURE(MECHANICS), MICROSTRUCTURE), STRESSES, AUSTENITE, HEAT TREATMENT, ROLLING(METALLURGY), BAINITE, MARTENSITE, PHASE STUDIES, SENSITIVITY, CHROMIUM ALLOYS, MOLYBDENUM ALLOYS, VANADIUM ALLOYS, CRYSTAL DEFECTS.

Subject Categories : Properties of Metals and Alloys

Distribution Statement : APPROVED FOR PUBLIC RELEASE