The mechanical stability of austenite and cryogenic toughness of ferritic Fe-Mn-Al alloys

Journal Article · Tue Jun 01 00:00:00 EDT 1993 · Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States)

DOI:https://doi.org/10.1007/BF02668201· OSTI ID:6136529

Lee, Sang Woo ^[1]; Lee, Huchul ^[2]

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1. Research Inst. of Industrial Science and Technology, Pohang (Korea, Republic of)
2. Seoul National Univ., Kwanakku (Korea, Republic of). Department of Metallurgical Engineering

In an attempt to understand the role of retained austenite on the cryogenic toughness of a ferritic Fe-Mn-Al steel, the mechanical stability of austenite during cold rolling at room temperature and tensile deformation at ambient and liquid nitrogen temperature was investigated, and the microstructure of strain-induced transformation products was observed by transmission electron microscopy (TEM). The volume fraction of austenite increased with increasing tempering time and reached 54 pct after 650 [degree]C, 1-hour tempering and 36 pct after 550 [degree]C, 16-hour tempering. Saturation Charpy impact values at liquid nitrogen temperature were increased with decreasing tempering temperature, from 105 J after 650 [degree]C tempering to 220 J after 550 [degree]C tempering. The room-temperature stability of austenite varied significantly according to the ([alpha] + [gamma]) region tempering temperature; i.e., in 650 [degree]C tempered specimens, 80 to 90 pct of austenite were transformed to lath martensite, while in 550 [degree]C tempered specimens, austenite remained untransformed after 50 pct cold reductions. After tensile fracture (35 pct tensile strain) at [minus]196 [degree]C, no retained austenite was observed in 650 [degree]C tempered specimens, while 16 pct of austenite and 6 pct of [epsilon]-martensite were observed in 550 [degree]C tempered specimens. Considering the high volume fractions and high mechanical stability of austenite, the crack blunting model seems highly applicable for improved cryogenic toughness in 550 [degree]C tempered steel. Other possible toughening mechanisms were also discussed.

• OSTI ID: 6136529
• Journal Information: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Journal Name: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States) Vol. 24A:6; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102 -- Metals & Alloys-- Structure & Phase Studies
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
AUSTENITE
CARBON ADDITIONS
COLD WORKING
CRYOGENIC FLUIDS
CRYOGENICS
DEFORMATION
ELECTRON MICROSCOPY
ELEMENTS
FABRICATION
FERRITIC STEELS
FLUIDS
FRACTURE PROPERTIES
HEAT TREATMENTS
IMPACT TESTS
IRON ALLOYS
IRON BASE ALLOYS
MATERIALS TESTING
MATERIALS WORKING
MECHANICAL PROPERTIES
MECHANICAL TESTS
MICROSCOPY
MICROSTRUCTURE
NITROGEN
NONMETALS
PHASE TRANSFORMATIONS
STABILITY
STEELS
TEMPERING
TENSILE PROPERTIES
TESTING
TRANSMISSION ELECTRON MICROSCOPY