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Towards enhanced fatigue performance of advanced high-strength medium-carbon low-alloy steels: A comparative study between banded ultrafine bainitic and martensitic steels.

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Title: Towards enhanced fatigue performance of advanced high-strength medium-carbon low-alloy steels: A comparative study between banded ultrafine bainitic and martensitic steels.
Authors: Mweene, Bright1 (AUTHOR), Ghosh, Sumit2 (AUTHOR), Somani, Mahesh2 (AUTHOR), Chauhan, Ankur1 (AUTHOR) ankurchauhan@iisc.ac.in
Source: Materials Science & Engineering: A. Nov2025, Vol. 946, pN.PAG-N.PAG. 1p.
Subjects: High strength steel, Bainitic steel, Alloy fatigue, Martensitic structure, Microstructure, Low alloy steel, High cycle fatigue
Abstract: To explore the strategies for improving the fatigue resistance in advanced high-strength medium-carbon low-alloy steels, two variants were examined: one with segregation-induced martensite-austenite (MA) bands in an ultrafine bainitic (UFB) matrix produced via low-temperature bainitization, and another with MA bands in a martensitic matrix processed by direct quenching and partitioning (DQ&P). UFB contained 20.8 % retained austenite (RA), while DQ&P had 15.8 % RA with finer, more closely spaced MA bands. Owing to its martensitic matrix with finer laths and higher dislocation density, DQ&P showed higher hardness and yield strength (1237 MPa vs. 914 MPa). Low-cycle fatigue (LCF) tests at room temperature under fully reversed loading aligned with the MA bands revealed initial cyclic hardening followed by softening in both steels, driven by strain-induced RA-to-martensite transformation and dislocation-mediated plasticity. DQ&P exhibited consistently higher stress amplitudes, though both steels showed similar fatigue lives at lower strain amplitudes. At the highest strain amplitude, UFB's fatigue life is nearly double that of DQ&P. Cracks initiated at surface defects and propagated through microstructural features, with pronounced deflection, branching, and arrest at high-angle grain boundaries, including prior austenite grain boundaries (PAGBs), and MA islands. Deflection angles often exceeded 15°, with some reaching ∼90° near stiff MA islands close to PAGBs. Total strain-life and stress-life curves indicated similar fatigue performance. In contrast, plastic strain-life and hysteresis loop energy analysis revealed higher intrinsic fatigue resistance/toughness in UFB and better damage dispersion in DQ&P due to its finer MA band structure. The findings highlight that incorporating finer and more uniformly distributed bands, as seen in the DQ&P steel, into the tougher UFB matrix could be a promising strategy to enhance fatigue resistance. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:To explore the strategies for improving the fatigue resistance in advanced high-strength medium-carbon low-alloy steels, two variants were examined: one with segregation-induced martensite-austenite (MA) bands in an ultrafine bainitic (UFB) matrix produced via low-temperature bainitization, and another with MA bands in a martensitic matrix processed by direct quenching and partitioning (DQ&P). UFB contained 20.8 % retained austenite (RA), while DQ&P had 15.8 % RA with finer, more closely spaced MA bands. Owing to its martensitic matrix with finer laths and higher dislocation density, DQ&P showed higher hardness and yield strength (1237 MPa vs. 914 MPa). Low-cycle fatigue (LCF) tests at room temperature under fully reversed loading aligned with the MA bands revealed initial cyclic hardening followed by softening in both steels, driven by strain-induced RA-to-martensite transformation and dislocation-mediated plasticity. DQ&P exhibited consistently higher stress amplitudes, though both steels showed similar fatigue lives at lower strain amplitudes. At the highest strain amplitude, UFB's fatigue life is nearly double that of DQ&P. Cracks initiated at surface defects and propagated through microstructural features, with pronounced deflection, branching, and arrest at high-angle grain boundaries, including prior austenite grain boundaries (PAGBs), and MA islands. Deflection angles often exceeded 15°, with some reaching ∼90° near stiff MA islands close to PAGBs. Total strain-life and stress-life curves indicated similar fatigue performance. In contrast, plastic strain-life and hysteresis loop energy analysis revealed higher intrinsic fatigue resistance/toughness in UFB and better damage dispersion in DQ&P due to its finer MA band structure. The findings highlight that incorporating finer and more uniformly distributed bands, as seen in the DQ&P steel, into the tougher UFB matrix could be a promising strategy to enhance fatigue resistance. [ABSTRACT FROM AUTHOR]
ISSN:09215093
DOI:10.1016/j.msea.2025.149080