Heat Treatment Effects on Pristine and Cold-Worked Thin-Walled Inconel 625

Gabriel Demeneghi,Annette Gray,Skylar Elliott,Ellen Rabenberg,Gregory Jerman,Ayman Girgis,William Tilson

doi:10.3390/met11111746

Abstract

Thin-walled Inconel 625 sheet metal was sectioned into tensile specimens, plastically strained, and then heat treated. Specimens were pulled to a targeted strain, unloaded, and then subjected to one of two heat treatments with the goal of restoring the full ductility and total plastic strain capability of the material. Post-heat treatment tensile testing was performed at room temperature to evaluate the heat treatment efficacy and then followed by hardness and microstructural analysis. The results showed the amount of material recovery was affected by the initial amount of plastic strain imparted to the tensile specimen before heat treatment. Although recrystallization was not observed, grains did elongate in the load direction, and the Kernel average misorientation (KAM) increased with heat treatment. Furthermore, specimens prestrained to 40% and heat treated at 980 °C successfully recovered 88% of pre-heat treatment strain capability prior to fracturing.

Highlights

Inconel 625 is a solid solution strengthened nickel-based superalloy commonly used to manufacture components requiring high temperature strength, excellent corrosion resistance, good weldability, and processability in harsh environments [1,2,3]
The improved low cycle fatigue (LCF) properties are the result of controlled microstructures with fine grain sizes (American society for testing materials (ASTM) No 5 or finer), which are achieved by appropriate heat treatments and tight control of impurities [4]
The tensile specimens were used to investigate the effects of both heat treatments by subjecting them to varying degrees of prestrain before undergoing one of the heat treatments

Summary

Introduction

Inconel 625 is a solid solution strengthened nickel-based superalloy commonly used to manufacture components requiring high temperature strength, excellent corrosion resistance, good weldability, and processability in harsh environments [1,2,3]. Inconel 625LCF is a special grade of Inconel 625 used in applications requiring improved low cycle fatigue (LCF) properties. The material might undergo several machining, forming, and shaping processes to obtain its final shape. These processes introduce significant deformation in the part, leading to hardening, with an associated increase in strength and reduction in ductility, presenting properties that may significantly differ from the baseline material properties

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Results

Conclusion