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Influence of microstructure and retained austenite on the abrasive wear performance of bainitic 9260 and 6150 steels
Brown, Casey S.
Brown, Casey S.
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2025
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The influence of retained austenite content and morphology on the abrasive wear resistance of 9260 and 6150 bainitic steels was evaluated. Two carbide free bainitic (CFB) microstructures were developed with the 9260 alloy to achieve differences in retained austenite content and morphology. These were compared with lower bainitic microstructures from the 6150 alloy and quench and tempered (Q&T) martensitic conditions of similar hardness, for a total of eight microstructures studied at hardness levels of 37 and 50 HRC.
Microstructural characterization was performed using field-emission scanning electron microscopy, electron backscatter diffraction, X-ray diffraction (XRD), hardness testing, and Charpy impact testing. Abrasive wear resistance was evaluated through single and multi-pass scratch tests, dry sand/rubber wheel (DSRW) testing, and Bond abrasion testing.
Microstructural analysis revealed that the 50 HRC CFB sample was comprised of 17.8 vol pct retained austenite, mostly in the form of thin-films between bainitic ferrite. The 37 HRC CFB sample contained 27.3 vol pct of larger retained austenite regions and more coarse bainitic ferrite laths. The 6150 alloy formed lower bainite upon austempering heat treatments with visible inter- and intra-lath cementite. The Q&T microstructures featured tempered martensite laths with carbides both within and between these laths.
The scratch test results showed that the Q&T microstructures outperformed bainitic microstructures of similar hardness. However, in DSRW and Bond abrasion wear testing, bainitic microstructures exhibited superior wear resistance. The Bond abrasion test showed the most significant indication of a transformation induced plasticity (TRIP) mechanism in the CFB steels, evidenced by the combination of hardness and XRD data, improving the wear resistance over lower bainitic and Q&T microstructures. This effect was most pronounced in the CFB sample that had larger, unstable austenite which showed a 24 pct increase in hardness and 75 pct decrease in austenite content, compared to the sample with more stable, thin-film austenite. In wear tests where TRIP did not induce significant hardening, such as the DSRW test, the lower bainitic samples showed improved wear resistance compared to CFB and Q&T microstructures.
Lower Si-containing alloys such as 6150 can produce abrasion-resistant bainitic microstructures suitable for low-stress or elevated-temperature applications where TRIP is not expected. However, in higher stress or impact conditions, higher-Si alloys such as 9260 show superior wear performance.
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