Austempering Time and Its Influence on the Mechanical Performance of Inverse Bainite: Insights from Hardness, Toughness, and Strength Testing

Aqil Inam; Muhammad Ishtiaq; Waqas Dilawar; Muhammad Haseeb Hassan; Faraz Hussain; Inam Ullah

Authors

Aqil Inam Institute of Metallurgy & Materials Engineering, University of the Punjab, 54590, Lahore, Pakistan
Muhammad Ishtiaq University of the Punjab, Lahore
Waqas Dilawar Institute of Metallurgy & Materials Engineering, University of the Punjab, 54590, Lahore, Pakistan
Muhammad Haseeb Hassan Institute of Metallurgy & Materials Engineering, University of the Punjab, 54590, Lahore, Pakistan
Faraz Hussain Institute of Metallurgy & Materials Engineering, University of the Punjab, 54590, Lahore, Pakistan
Inam Ullah Institute of Metallurgy & Materials Engineering, University of the Punjab, 54590, Lahore, Pakistan

Keywords:

Inverse Bainite, Austempering Time, Hardness, Impact Strength, Mechanical Properties

Abstract

This study examines the impact of austempering time on the mechanical properties of 0.8C experimental steel with inverse bainitic microstructures. Samples were austenitized at 900 °C and austempered at 420 °C for 30, 60, 90, and 120 minutes. The effects on hardness, impact toughness, and (UTS) were analyzed. Microstructural evaluations by optical microscope, scanning electron microscope, and energy dispersive spectroscopy confirmed the formation of inverse bainite. Mechanical testing showed that increasing austempering time leads to higher hardness due to cementite lath growth and reduced ferrite content, but also results in lower Charpy impact energy, indicating reduced toughness. While UTS initially decreases, it increases sharply after 120 minutes, accompanied by brittle fracture. This study suggests that prolonged austempering enhances hardness and strength but increases brittleness, making these structures less suitable for applications involving sudden forces.

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