Elsevier

Wear

Volumes 456–457, 15 September 2020, 203386
Wear

Characteristics of carbide-free medium-carbon bainitic steels in high-stress abrasive wear conditions

https://doi.org/10.1016/j.wear.2020.203386Get rights and content
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Highlights

  • Fifteen different medium-carbon carbide-free bainitic steels were designed.

  • Three ausforming routes resulted in steels with varying fractions of different phases.

  • Tensile strengths up to 1900 MPa and hardness up to 500 HV were achieved.

  • Experimental bainitic steels showed extremely high work-hardening in wear testing.

  • Abrasive wear resistance correlated with the deformed wear surface hardness.

Abstract

This study encompasses a comprehensive account of the abrasive wear properties of carbide-free, ultrahigh-strength bainitic steels processed through ausforming at three different temperatures well below the recrystallization stop temperature followed by bainitic transformation at temperatures close to the Ms temperature. Five medium-carbon, high-silicon compositions were designed for the study by suitably varying the alloying levels of carbon, vanadium, niobium, molybdenum, and aluminum. While ausforming at lower temperatures enabled a large number of nucleation sites leading to significant refinement of bainitic laths, the decomposition of austenite at relatively low transformation temperatures was accelerated due to the presence of a high dislocation density, thus enabling completion of bainitic transformation in a reasonable length of time. The steels were characterized in respect of microstructural features and mechanical properties, besides evaluation of wear resistance through a high-stress abrasive wear testing method with natural granite abrasives. The microstructures comprised different fractions of bainitic ferrite and/or granular bainite (56–68%), martensite (0–25%), besides a significant fraction of retained austenite (20–34%) manifesting as pools and also interlath films, depending on the ausforming conditions and subsequent cooling paths. A tensile strength of 1900 MPa level was achieved with hardness exceeding 500 HV for the medium-temperature ausformed steel containing a high carbon content that also showed lowest mass loss in the wear test. The hardness-to-mass loss ratio appeared highly promising with some of the carbide-free bainitic steels on par with or better than the reference martensitic steel. The high work-hardening capability as a consequence of the strain-induced austenite to martensite transformation was considered as the main factor for the superior abrasive wear resistance of the carbide-free bainitic steels.

Keywords

Steel
Bainite
Wear testing
Abrasion
Microstructure

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