Evaluation of Thermal Damage Impact on Microstructure and Properties of Carburized AISI 9310 Gear Steel Grade by Destructive and Non-Destructive Testing Methods

Abstract

Advanced aircraft gearboxes operate under high mechanical loads. Currently, aircraft gears are manufactured from chromium–nickel–molybdenum steel grades such as AISI 9310 or Pyrowear 53. The major causes of gear failure are wear and fatigue cracking. As the crack initiation occurs predominantly on the component surface, the gears are routinely subjected to surface hardening processes such as low-pressure carburizing and case hardening. The gears are manufactured in a multiple operation process, in which teeth grinding is a crucial step. Selection of improper grinding conditions can lead to local heat concentration and creation of grinding burns, which are small areas where microstructure and properties changes are induced by high temperature generated during grinding. Their presence can lead to significant reduction of gear durability. Therefore destructive and non-destructive (NDT) quality-control methods such as chemical etching or magnetic Barkhausen noise (MBN) measurements are applied to detect the grinding burns. In the area of a grinding burn, effects related to the over-tempering or re-hardening of the carburized case may occur. In this paper, the results of the studies on the characterization of microstructure changes caused by local heating performed to simulate grinding burns are presented. The areas with the over-tempering and re-hardening effects typical for grinding burns were formed by laser surface heating of carburized AISI 9310 steel. Analyses of the microstructure, residual stresses, retained austenite content, and non-destructive testing by the MBN method were performed. The correlation between the MBN value and the properties of the modified surface layer was identified. It was also found that the re-hardened areas had similar characteristics of changes in the Barkhausen noise intensity, despite the significant differences in the width of the overheated zone, which depended on the laser-heating process conditions.

An improved hidden Markov model with magnetic Barkhausen noise and optimized Gaussian mixture feature for fatigue prediction

“…Owing to the electromagnetic response of domain walls to an external magnetic field, MBN signals are intricately linked to the microstructure of ferromagnetic materials [8,9], which may change under varying stress and repeated loading. Dychton et al [10] and Ducharne et al [11] highlighted the effectiveness of MBN to monitor fatigue in ferromagnetic materials. Moorthy [12] utilized the MBN method to study fatigue damage in various steels, revealing that MBN signals can capture characteristic changes in material microstructures.…”

Towards Understanding Subsurface Characteristics in Burn Process of Gear Profile Grinding

“…The parameter thresholds for avoiding grinding burns were first determined by metallographic analysis, and then the parameters were optimized to improve the machining accuracy of gears. In order to specifically study the effects caused by grinding burns, Dychtońet et al [ 17 ] used laser heating to simulate the effect of excessive tempering and secondary hardening caused by grinding burns in aerospace gears and investigated the effect of burns on microstructure and residual stresses by Barkhausen noise nondestructive testing. For high-strength gear steel materials, Wang et al [ 18 ] conducted an experimental study on the characteristics and formation mechanisms of grinding burns and cracks in 20 CrMnTi steel gears, and analyzed the changes in tissue transformation, hardness, and residual stresses for tempered burns and quenched burns, respectively.…”

Grinding Burn Detection via Magnetic Barkhausen Noise Analysis Independently of Induction Hardened Depth

“…The magnetic Barkhausen noise (MBN) signal can be used successfully to detect grinding burns non-destructively and to identify the intensity of the grinding burns [3,4], and this is possible because the MBN signal is sensitive to the hardness and residual stress of a steel part. Overall, a decrease in hardness increases the amplitude of the peak of the MBN envelope and shifts the peak position to lower levels of the applied magnetic field, whereas an increase in hardness decreases the peak amplitude and moves the position of the peak towards higher levels of the applied field [5][6][7].…”