Post-fire mechanical properties of austenitic stainless steel rebars under air, water and furnace cooling

Purpose This study aims to investigate the post-fire mechanical properties of austenitic stainless steel rebars (ASSR) (EN1.4301, EN1.4401 and EN1.4436) subjected to temperatures up to 900 °C and cooled by air (CIA), water (CIW) or furnace (CIF) methods. Unlike carbon steels, these alloys retain a stable austenitic structure without quenching effects. Through tensile testing and empirical modeling, the work quantifies residual strength, stiffness and ductility, revealing critical temperature–cooling interactions. The findings provide a new evidence base for assessing fire-damaged stainless reinforcement and propose predictive equations to support safety evaluation and repair strategies in structural engineering. Design/methodology/approach ASSR (EN1.4301, EN1.4401 and EN1.4436) were heated to 100–900 °C in an electric furnace at a controlled rate (15 °C/min) and held for 20 min. Three cooling regimes – CIA, CIW and CIF – were applied to replicate realistic post-fire scenarios. Tensile tests were performed using a displacement-controlled Instron machine in accordance with International Organization for Standardization 6892-1, measuring yield strength, ultimate strength, elastic modulus and elongation. Reduction factors were derived and compared with existing provisions. Empirical equations with R2 > 0.95 were developed to predict residual properties as functions of temperature and cooling method. Findings ASSR exhibited stable post-fire behavior up to 500 °C, with strength enhancement due to dynamic strain aging. Beyond 700 °C, significant strength loss occurred, with residual yield strength reduced to 38–46% at 900 °C. The cooling method had a negligible influence on strength and stiffness but markedly affected ductility, with water quenching increasing elongation to over 260%. EN1.4436 showed the best thermal stability, attributed to higher nickel and molybdenum content. Empirical models (R2 > 0.95) accurately predicted temperature-cooling interactions, confirming that stainless rebars resist quenching effects unlike carbon steels. Originality/value This study is the first to systematically evaluate the combined effects of temperature and three practical post-fire cooling regimes on ASSR. Unlike prior work focused only on heating, it demonstrates the absence of a quenching effect, quantifies critical temperature-ductility interactions and provides validated prediction equations (R2 > 0.95). The findings establish a new evidence base for post-fire assessment of stainless reinforcement, offering engineers reliable tools to evaluate residual capacity and guiding repair or reuse strategies. The originality lies in bridging experimental insight with practical modeling for structural fire safety design.