Effect of holding time in the ({alpha} + {gamma}) temperature range on toughness of specially austempered ductile iron

Journal Article · Mon Jul 01 04:00:00 EDT 1996 · Metallurgical Transactions, A

OSTI ID:282245

Kobayashi, T; Yamada, S ^[1]

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1. Toyohashi Univ. of Technology (Japan). Dept. of Production Systems Engineering

Austempered ductile iron (ADI) finds wide application in the industry because of its high strength and toughness. The QB{prime} process has been developed to produce a fine microstructure with high fracture toughness in ADI. This process involves reaustenitizing a prequenched ductile iron in the ({alpha} + {gamma}) temperature range followed by an isothermal treatment in the bainitic transformation temperature range. In the present work, the effect of holding time in the ({alpha} + {gamma}) temperature range on the structure and un-notched toughness of ADI has been studied. Prior to the austempering treatment, the as-cast ductile iron was heat treated to obtain martensitic, ferritic, and pearlitic matrix structures. In the case of prequenched material (martensitic matrix), the un-notched impact toughness increased as a function of holding time in the ({alpha} + {gamma}) temperature range. The reaustenitization heat treatment also resulted in the precipitation of fine carbide particles, identified as (Fe,Cr,Mn){sub 3}C. It was shown that the increase in holding time in the ({alpha} + {gamma}) temperature range leads to a reduction in the number of carbide particles. In the case of a ferritic prior structure, a long duration hold in the ({alpha} + {gamma}) temperature range resulted in the coarsening of the structure with a marginal increase in the toughness. In the case of a pearlitic prior structure, the toughness increased with holding time. This was attributed to the decomposition of the relatively stable carbide around the eutectic cell boundary with longer holding times.

• OSTI ID: 282245
• Journal Information: Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 7 Vol. 27; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CARBIDES
CARBON
CHEMICAL COMPOSITION
CHROMIUM ADDITIONS
FERRITE
FRACTURE PROPERTIES
HEAT TREATMENTS
IRON BASE ALLOYS
MANGANESE ADDITIONS
MARTENSITE
MICROSTRUCTURE
NICKEL ALLOYS
PEARLITE
PRECIPITATION
SILICON ALLOYS
TEMPERATURE DEPENDENCE
TEMPERING
TIME DEPENDENCE