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<p>To ensure the quality and load-carrying capacity of case-hardened (or carbonitrided) gears, the permissible retained austenite content is limited to a&#xa0;maximum of 30 vol.-% in common design standards, such as ISO 6336 or ANSI/AGMA 2101. In recent years, however, it has been shown repeatedly in several research projects that an increased retained austenite content in carbonitrided gears does not necessarily lead to a&#xa0;decrease in the tooth root load-carrying capacity but can result in an increase. This can be observed in particular on gears that have undergone a&#xa0;shot blasting or peening treatment before being subjected to stress in operation. It is assumed that a&#xa0;residual austenite transformation into martensite that occurs during operating under mechanical stress leads to a&#xa0;decrease of the load-carrying capacity. It is therefore very important to comprehensively stabilize the retained austenite in the surface layer by a&#xa0;shot blasting or peening before operating gears in order to avoid further transformation under operating conditions.</p><p>To investigate the stability behavior of retained austenite, gears of several case-hardening steels were therefore carbonitrided with specific heat treatment parameters as part of a&#xa0;research project, so that increased retained austenite contents of up to 70 vol.-% are achieved in the surface layer of the material. The test variants were then subjected to various shot blasting and peening treatments for retained austenite transformation respectively stabilization and afterwards examined in a&#xa0;pulsator test rig with regard to their tooth root load-carrying capacity. By means of x‑ray diffraction, a&#xa0;significant transformation of retained austenite into martensite by the blasting treatment can be verified and that retained austenite content does not decrease further during the test runs. Compared to case-hardened and subsequently shot blasted reference variants according to the state of the art, the test variants consistently show significant increases in tooth root load-carrying capacity. It can therefore be concluded that increased retained austenite contents &gt; 30 vol.-% on carbonitrided and subsequently shot blasted or peened gears can increase their tooth root load-carrying capacity.</p>

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Investigations on the tooth root load-carrying capacity of carbonitrided gears containing high amounts of retained austenite

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  • 发表日期：

    2025年9月2日

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  • A. Sorg,
  • M. T. Boyraz,
  • T. Tobie,
  • M. Steinbacher,
  • K. Stahl,
  • R. Fechte-Heinen

摘要

To ensure the quality and load-carrying capacity of case-hardened (or carbonitrided) gears, the permissible retained austenite content is limited to a maximum of 30 vol.-% in common design standards, such as ISO 6336 or ANSI/AGMA 2101. In recent years, however, it has been shown repeatedly in several research projects that an increased retained austenite content in carbonitrided gears does not necessarily lead to a decrease in the tooth root load-carrying capacity but can result in an increase. This can be observed in particular on gears that have undergone a shot blasting or peening treatment before being subjected to stress in operation. It is assumed that a residual austenite transformation into martensite that occurs during operating under mechanical stress leads to a decrease of the load-carrying capacity. It is therefore very important to comprehensively stabilize the retained austenite in the surface layer by a shot blasting or peening before operating gears in order to avoid further transformation under operating conditions.

To investigate the stability behavior of retained austenite, gears of several case-hardening steels were therefore carbonitrided with specific heat treatment parameters as part of a research project, so that increased retained austenite contents of up to 70 vol.-% are achieved in the surface layer of the material. The test variants were then subjected to various shot blasting and peening treatments for retained austenite transformation respectively stabilization and afterwards examined in a pulsator test rig with regard to their tooth root load-carrying capacity. By means of x‑ray diffraction, a significant transformation of retained austenite into martensite by the blasting treatment can be verified and that retained austenite content does not decrease further during the test runs. Compared to case-hardened and subsequently shot blasted reference variants according to the state of the art, the test variants consistently show significant increases in tooth root load-carrying capacity. It can therefore be concluded that increased retained austenite contents > 30 vol.-% on carbonitrided and subsequently shot blasted or peened gears can increase their tooth root load-carrying capacity.