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Fatigue Failure of Through Hardened Gear Teeth

Background: TLE inlet tubesheet tube failure associated with localized material loss. A metallurgical failure analysis was conducted to identify the failure mechanism.

Fatigue Failure of Through Hardened Gear Teeth


Figure 2: SEM Micrograph of Manganese Sulphide Inclusion in the Fatigue Crack Region


The failure of the gear teeth was caused by the presence of manganese sulfide (MnS) inclusions leading to fatigue cracking and brittle overload of the through hardened gear teeth. Inclusions were found in the fatigue crack regions which EDS revealed to be manganese sulfide (MnS) streamers. These inclusions serve as fatigue crack initiation locations and are known to be highly detrimental to the fatigue properties of through hardened steels. In a through hardened gear there is very little ductility or toughness, so once a fatigue crack was initiated at the inclusions the failure of the gear teeth was very likely.

Take Away:

Steel quality is critical to the longevity of materials, especially high strength materials. Metallurgical analysis of the gear teeth was able to identify the presence of inclusions in the steel that were detrimental to the material properties and led to the failure of the gear.

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