Effects of pre-existing grain boundary microvoid distributions on fracture toughness and fatigue crack growth in low alloy steel

Journal Article · Tue Sep 01 04:00:00 EDT 1987 · Acta Metall.; (United States)

DOI:https://doi.org/10.1016/0001-6160(87)90070-8· OSTI ID:5524757

Dauskardt, R H; Pendse, R D; Ritchie, R O

The role of dispersions of pre-existing grain boundary microvoids is investigated in fracture toughness and fatigue crack propagation behavior in a low alloy steel. Microvoid damage was achieved by prior exposure to gaseous hydrogen atmospheres at high temperatures and pressures where carbon reacts with hydrogen to nucleate methane bubbles along prior austenite grain boundaries (hydrogen attack). Whereas the crack initiation and crack growth toughness (i.e. K/sub lc/ and the tearing modulus) were degraded even for comparatively mild degrees of microvoid damage, rates of sub-critical crack growth by fatigue remained relatively unaffected. Such results are interpreted in terms of a mutual competition between microstructural damage generated by the grain boundary microvoids, which promotes crack growth by lowering the intrinsic resistance of the microstructure, and the resulting tortuous crack paths, which extrinsically retard crack growth at low stress intensities by lowering the local crack tip driving force (crack tip shielding). As shielding effects are minimized at high stress intensities, the degradation in intrinsic toughness is related to changes in ductility by means of a stress-modified critical strain model for ductile fracture where the presence of small microvoid clusters promotes coalescence through the easier onset of plastic strain localization. Fatigue behavior, conversely, is dominated by extrinsic shielding mechanisms and is modeled in terms of two-dimensional models of crack deflection and roughness-induced crack closure.

• Research Organization: Dept. of Materials Science and Mineral Engineering, Univ. of California, Berkeley, CA 94720
• OSTI ID: 5524757
• Journal Information: Acta Metall.; (United States), Journal Name: Acta Metall.; (United States) Vol. 35:9; ISSN AMETA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102 -- Metals & Alloys-- Structure & Phase Studies
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
CRACK PROPAGATION
CRYSTAL STRUCTURE
DUCTILITY
EMBRITTLEMENT
FATIGUE
FRACTURE PROPERTIES
GRAIN BOUNDARIES
HYDROGEN EMBRITTLEMENT
IRON ALLOYS
IRON BASE ALLOYS
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
MICROSTRUCTURE
NUCLEATION
STEELS
STRESSES
STRUCTURAL CHEMICAL ANALYSIS
TEMPERATURE EFFECTS
TENSILE PROPERTIES
THERMAL FATIGUE
THERMAL STRESSES
VOIDS