Further considerations on the inconsistency in toughness evaluation of AISI 4340 steel austenitized at increasing temperatures. [Stainless steel 4340 and 300-M]

Journal Article · Wed Mar 01 00:00:00 EST 1978 · Metall. Trans., A; (United States)

DOI:https://doi.org/10.1007/BF02646382· OSTI ID:6377917

Ritchie, R O ^[1]; Horn, R M

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1. Massachusetts Inst. of Tech., Cambridge

A study was made of the influence of austenitizing temperature on the ambient temperature toughness of commercial AISI 4340 ultrahigh strength steel in the as-quenched (untempered) and quenched and tempered at 200/sup 0/C conditions. A systematic trend of increasing plane strain fracture toughness (K/sub Ic/) and decreasing Charpy V-notch energy was observed as the austenitizing temperature was raised while the yield strength remained unaffected. This effect was seen under both static (slow-bend) and dynamic (impact) loading conditions, and was rationalized in terms of a differing response of the microstructure, produced by each austenitizing treatment, to the influence of notch root radius on toughness. Since failure in all microstructures was observed to proceed primarily by a ductile rupture (microvoid coalescence) mechanism, an analysis is presented to explain these results, similar to that reported previously for stress-controlled fracture, based on the assumption that ductile rupture can be considered to be strain-controlled. Under such conditions, the decrease in V-notch Charpy energy is associated with a reduction in critical fracture strain at increasing austenitizing temperatures, consistent with an observed decrease in uniaxial and plane strain ductility. The increase in sharp-crack fracture toughness, on the other hand, is associated with an increase in ''characteristic distance'' for ductile fracture, resulting from dissolution of void-initiating particles at high austenitizing temperatures. The microstructural factors which affect this behavior, in particular the specific role of retained austenite, is examined. No evidence was found that the enhancement of fracture toughness at high austenitizing temperatures was due to the presence of films of retained austenite.

• OSTI ID: 6377917
• Journal Information: Metall. Trans., A; (United States), Vol. 9:3
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
STAINLESS STEELS
FRACTURE PROPERTIES
AUSTENITE
CRACKS
CRYSTAL STRUCTURE
DUCTILITY
IMPACT SHOCK
STRAIN RATE
TEMPERATURE DEPENDENCE
TEMPERING
TENSILE PROPERTIES
VOIDS
ALLOYS
CARBON ADDITIONS
CHROMIUM ALLOYS
CORROSION RESISTANT ALLOYS
HEAT TREATMENTS
IRON ALLOYS
IRON BASE ALLOYS
MECHANICAL PROPERTIES
STEELS
360103* - Metals & Alloys- Mechanical Properties
360102 - Metals & Alloys- Structure & Phase Studies