The hot workability of lnconel Alloy 706 (IN 706) extends over a temperature range of 1700°F to 21OO'F (925°C to 1150°C). The good hot workability of IN 706 in relatively large ingot sizes makes this alloy fabricable into large forgings utilized by important end markets including power generation, chemical processing, and others. Successful utilization of large IN 706 forgings in critical components requires control of important microstructural and mechanical property features. Grain size, grain boundary precipitates, and matrix precipitates vary widely in IN 706 as a result of fabrication history and post-fabrication thermal treatments (TMP). TMP conditions which favor heavy grain boundary precipitates, such as y, y and 6 or n phases, affect ductility (elongation or reduction in area [RA]) and impact toughness (Charpy V-notch [CVN]) properties. Coarse matrix precipitates may also be observed. While tensile yield and ultimate strengths may increase slightly due to within grain and/or grain boundary precipitates, thicker, more continuous grain boundary precipitates result in lower ductility and toughness.Presented are fractographic and microscopic evaluations of IN 706 forgings illustrating key relationships between microstructure and ductility and fracture-related properties.Fracture behavior changes as grain interior and/or grain boundary precipitate and morphological features are changed. Critical impact properties of IN 706 are rationalized by microstructural observations. Backaround lnconel Alloy 706 (IN 706) is an important superalloy material for very large, commercial scale forgings utilized in several critical applications including power generation and chemical processing.Triple melted, VIM-ESR-VAR ingots, 32 to 36 in. (81 to 91 cm.) weighing over 30,000 Ibs. (13,600 Kg.), are now routinely produced by several metal producers for fabrication into the large forgings specified for these applications, Casting of IN 706 ingots of this large size are feasible due the alloy's reduced propensity for segregation in comparison to lnconel Alloy 718. The composition and processing of the alloy provides excellent property combinations for highly stressed parts, including rotating components, in elevated temperature and/or corrosive environments. IN 706's reduced segregation potential may be linked to lower hardening element contents: 1) Nb -nominal 2.9% vs. 5.25% for IN 718 and (2) Al -0.4% maximum vs. nominal 0.6% for IN 718. For adequate strength development, Ti content of IN 706 is higher than IN 718, e.g. nominal 1.75% vs.
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