Evolution of Microstructure and Texture During Hot Compression of a Ni-Fe-Cr Superalloy
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INCREASING energy demands are forcing oil producers to drill in harsh environments requiring improved structural materials. The current demand for forged rod from the oil industry is significant, and the ability to produce consistent, quality product is key for producers. The demand for improved materials is continuously pushing producers to optimize properties through microstructural control. For forged superalloy rod, such requirements call for fine grains and grain size uniformity. Understanding flow and recrystallization behavior is critical for optimizing forging and annealing practices to meet these requirements. Most high-temperature superalloy forging studies have been conducted on alloy 718. However, other alloys are being developed to meet strength and corrosion requirements of the oil industry. One example is INCOLOY alloy 945 (Special Metals Corporation, Huntington, WV), a newly developed hybrid alloy with strength comparable to alloy 718 and corrosion resistance comparable to alloy 925. The effect of alloying on flow behavior and microstructural evolution has not been studied comprehensively for this class of alloys. In general, the results from S.P. CORYELL, Product and Applications Development Engineer, is with the PCC Energy Group, Special Metals Corporation, Huntington, WV 25705. K.O. FINDLEY, Assistant Professor, is with the Colorado School of Mines, Golden, CO 80401. Contact e-mail: kfi[email protected] M.C. MATAYA, now retired, was formerly Senior Lecturer with the Colorado School of Mines. E. BROWN, Consultant, is with the EB Scientific Enterprises LLC, Golden, CO 80401. Manuscript submitted December 21, 2010. Article published online September 23, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
hot deformation studies in a single-phase field are applicable to a wide range of metallic systems with similar stacking fault energy including those with nickel-, iron-, or nickel-iron-based compositions. Recovery and recrystallization are the two most common softening mechanisms during and after hot deformation. However, in materials with low-to-medium stacking fault energies, such as nickel superalloys, recovery occurs more slowly and is less common. Therefore, dislocation density increases to appreciably higher levels during deformation, permitting the nucleation of recrystallization before significant recovery.[1] Recrystallization during hot deformation can occur through dynamic recrystallization (DRX). Metadynamic recrystallization (MDRX) starts during hot deformation and continues during hold times between deformation passes. Static recrystallization (SRX) occurs during hold times at high temperatures between deformation passes or during sufficiently slow cooling. It can be difficult to distinguish among grains recrystallized by DRX, SRX, or MDRX, which has led to inconsistent interpretations of nickel alloy recrystallized microstructures in literature. However, electron backscatter diffraction (EBSD) imaging combined with other optical and electron microscopy imaging techniques can help resolve which r
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