Review links critical inclusions to fatigue in high-strength steels

A review of inclusion-controlled fatigue concludes that the fatigue limit of high-strength steels is often governed by the maximum dangerous defect or another high-risk defect within a highly stressed volume, rather than by average cleanliness. The findings explain why nominal strength alone cannot fully characterize fatigue performance: inclusions form a statistical population that varies in size, spatial distribution and type, and their potential to initiate fatigue failure depends on more than their average abundance.

Extreme-value statistics provides the framework for examining this problem. Rather than characterizing inclusions only through average size or average cleanliness, the statistical approach focuses on the upper tail of the defect population and the occurrence of unusually harmful features. This matters because a single large or otherwise high-risk inclusion may control fatigue behavior even when the overall inclusion population appears relatively clean. The review identifies three-dimensional statistical characterization of inclusions and classification-based evaluation of critical defects as important directions for future research.

The review also finds that a defect’s harmfulness is determined by several interacting characteristics. Relevant factors include inclusion type, morphological sharpness, interfacial bonding state and local stress concentration. Size remains important, but it does not provide a complete description of danger. A material with fewer inclusions may not necessarily outperform one with more inclusions if the defects differ in type, shape or bonding conditions. The available evidence therefore supports assessing dangerous defects as classified, three-dimensional features rather than reducing risk to a single average cleanliness measure.

Strength, toughness and fatigue resistance must be considered together. Increasing strength can improve the load-bearing capacity of the steel matrix, but excessive strengthening can increase sensitivity to defects. Toughness, by contrast, can improve defect tolerance through crack-tip plastic dissipation, crack deflection and crack closure. The review therefore proposes a shift from strength-dominated fatigue design toward coordinated consideration of strength, toughness and defect tolerance, supported by multifactorial fatigue-life models and damage-tolerant design methods. These conclusions are a synthesis of the reviewed evidence rather than results from a new experimental or clinical study, and the review identifies the need for further work on critical-defect evaluation, coupled life models and engineering design methods.

Subject of Research: Inclusion-controlled fatigue in high-strength steels

Article Title: Inclusion-controlled fatigue in high-strength steels: extreme value statistics to the interplay among strength, toughness and fatigue

Article References: Li, M., Cui, B., Wei, G., Xiu, W., & Sarman, A. M. (2026). Inclusion-controlled fatigue in high-strength steels: extreme value statistics to the interplay among strength, toughness and fatigue. Journal of Materials Science, 61(41), 31472-31500. https://doi.org/10.1007/s10853-026-13600-3

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13600-3

Keywords: high-strength steels, fatigue failure, non-metallic inclusions, extreme-value statistics, steel cleanliness, toughness, defect tolerance, fatigue life, Inclusion-controlled, fatigue, high-strength, steels