Nb modification of microcomposite Fe/C/Cr/Mn steel

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:6754874

Kim, J

The present work is concerned with obtaining superior combinations of mechanical properties by adding the microalloy element of niobium to the basis quaternary alloy of Fe/2.0 wt% Cr/1.2 wt% Mn/0.25 wt% C and by applying controlled rolling practice to processing of the experimental alloys to attain fine austenite grains, giving rise to high Charpy V-notch impact toughness. Continuous cooling transformation diagrams of the basic quaternary and the niobium bearing alloys have been determined to predict the appropriate cooling rate required for martensitic transformation by dilatometry method. Niobium effected a considerable increment of martensitic hardenability, which alleviates the otherwise stringent quenching rate arising from the reduced alloy contents and which is needed to obtain the composite microstructure. Heavy deformation is added just above the recrystallization temperature in order to obtain fine and recrystallined austenite grains which result in fine microcomposite structures. As for the microalloy element, 0.02 wt% of niobium is added to utilize the interactions of microalloyed element precipitation and austenite recrystallization kinetics during hot rolling. Application of controlled rolling practice to Fe/0.25 wt% C/2.0 wt% Mn/0.02 wt% Nb alloy resulted in a great enhancement of Charpy impact toughness by about 15 joules than alloy without addition of niobium. The Nb bearing alloy showed an excellent plane strain fracture toughness value reaching 155 MPa{radical}m, after tempering but even 147 MPa{radical}m directly quenched on-line.

• Research Organization: California Univ., Berkeley, CA (USA)
• OSTI ID: 6754874
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
360103 -- Metals & Alloys-- Mechanical Properties
ALLOY SYSTEMS
ALLOYS
AUSTENITE
CARBON ADDITIONS
CHROMIUM ALLOYS
CRYSTAL STRUCTURE
CRYSTALLIZATION
DEFORMATION
DIAGRAMS
DILATOMETRY
ELEMENTS
FABRICATION
FRACTURE PROPERTIES
GRAIN SIZE
HARDNESS
IMPACT STRENGTH
IRON ALLOYS
IRON BASE ALLOYS
MANGANESE ALLOYS
MARTENSITIC STEELS
MATERIALS WORKING
MECHANICAL PROPERTIES
METALLURGICAL EFFECTS
METALS
MICROSTRUCTURE
NIOBIUM
NIOBIUM ADDITIONS
NIOBIUM ALLOYS
PHASE DIAGRAMS
PHASE TRANSFORMATIONS
QUATERNARY ALLOY SYSTEMS
QUENCHING
ROLLING
SIZE
STEELS
THERMAL ANALYSIS
TRANSITION ELEMENTS