Mechanical Properties of High Strength Steel at Elevated Temperatures

High strength steels (HSS), characterised by yield strengths above 355 MPa, are increasingly employed in demanding structural applications—from high-rise buildings to automotive frameworks—owing to their superior strength-to-weight ratio. However, under elevated temperatures such as those encountered in fires or industrial processes, their mechanical properties exhibit pronounced degradation that often diverges from established design code assumptions based on mild steel. Key parameters including yield strength, ultimate tensile strength and Young’s modulus diminish at rates dependent on alloy chemistry, microstructure and thermal history. For instance, quenched-and-tempered grades such as S700MC or direct-quenched S960 may retain less than 60 % of ambient yield strength at temperatures around 600 °C, while weld heat-affected zones can undergo additional softening due to phase transformations. To address these complex responses, researchers employ both steady-state and transient tensile testing up to 1000 °C, real-time strain measurement techniques and the development of temperature-dependent constitutive models. These efforts underpin performance-based design methods, improve fire safety assessments, facilitate accurate post-fire damage evaluation and guide the optimisation of resilient steel structures worldwide.

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Mechanical Properties of High Strength Steel at Elevated Temperatures publication trend

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Technical terms

Yield strength: Stress at which material begins to deform plastically.

Ultimate tensile strength: Maximum stress a material can withstand before failure.

Young’s modulus: Ratio of stress to elastic strain in the linear region of deformation.

Proportional limit: Stress at which stress–strain response departs from linearity.

Reduction factor: Ratio of a mechanical property at elevated temperature to its ambient value.

Constitutive model: Mathematical description of a material’s stress–strain relationship under specified conditions.

Ultrahigh-strength steel (UHSS): Steel grades with yield strengths above approximately 690 MPa.

References

1. Experimental studies on mechanical properties of S700 MC steel at elevated temperatures. Fire Safety Journal (2020).
2. Ultrahigh-strength steels at elevated temperatures. Journal of Constructional Steel Research (2021).
3. Mechanical properties of butt-welded ultra-high strength steels at elevated temperatures. Journal of Constructional Steel Research (2022).
4. Application of Machine Learning to predict the mechanical properties of high strength steel at elevated temperatures based on the chemical composition. Structures (2023).