Influence of thermal and thermal-mechanical treatments on microstructure and mechanical properties of the multicomponent alloy FeCrMnNiCo0.85C0.15

The multicomponent FeCrMnNiCo alloy, known as the Cantor alloy, has a single-phase austenitic structure (with an fcc crystal lattice) and high ductility and toughness. However, at room temperature, the yield strength of the Cantor alloy is rather low (≈200 MPa). Alloying of the FeCrMnNiCo multicomponent alloy with carbon can significantly increase its strength properties due to solid solution hardening of the austenitic phase and precipitation hardening. But for alloys with interstitial atoms, high values of the configurational entropy do not provide the formation of a single-phase structure in the cast state. The formation of large incoherent M7C3 / M23C6 carbides occurs during crystallization and their presence adversely affects the plasticity of cast carbon-alloyed multicomponent alloys. Achievement of a high-strength state without the loss of plasticity is possible by modifying the microstructure of carbon-alloyed alloys using thermal and thermomechanical treatments. We studied the structure, phase composition, and mechanical properties of the FeCrMnNiCo0.85C0.15 alloy in the cast and annealed (at 1200°C, 1 h) states, as well as after multistage thermomechanical treatments, including high-temperature annealing, hot forging, and cold rolling. It was found that alloying with carbon leads to an increase in the yield strength and a sharp drop in the ductility of the cast FeCrMnNiCo0.85C0.15 alloy (σ0.2 = 315 MPa, δ =12 %) as compared to the reference Cantor alloy containing no carbon atoms (σ0.2 =180 MPa, δ = 62 %). Cast FeCrMnNiCo0.85C0.15 alloy has an inhomogeneous structure consisting of an austenitic phase and large carbides. Annealing promotes partial dissolution of carbides, is accompanied by an increase in the yield stress, but does not contribute to an increase in the plasticity of the alloy (σ0.2 = 355 MPa, δ = 9 %). Thermomechanical treatments do not provide the formation of a single-phase austenitic structure, but contribute to a significant dissolution of carbides and an increase in the solid solution hardening of the austenite phase. Such alloys have significantly higher strength and ductility values (σ0.2 = 434 – 436 MPa, δ = 35 – 37 %) in comparison with cast alloy and Cantor alloy.

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1. Russian Science Foundation - project No. 20-19-00261