Acoustic emission monitoring of immersion quenching bath attributes

Abstract

This paper describes the use of acoustic emission (AE) testing for monitoring immersion quenching bath attributes. Immersion quenching is a heat treatment process used to change the mechanical properties of metallic workpieces. The quenching bath cooling attributes degrade with prolonged use, thus affecting the workpiece mechanical properties. A non-destructive monitoring method of the quenching bath is required. An AE measurement system is proposed for this purpose. Steel specimens are quenched in tap water, deionized water, 5 % NaCl-water solution and 5 % detergent-water solution. AE is measured with four piezoelectric sensors. The influence of quenching bath attributes on specimen cooling is described together with the measured AE signals. AE signal peak amplitude diagrams are evaluated. A reference AE peak amplitude signal is presented with the measurements. The quenching bath attribute assessment method is established by monitoring the amount of outlying AE signals in regard to the reference AE signal. The results confirm that AE monitoring provides a decent way of assessing quenching bath attributes and thus also the quenched specimen mechanical properties.