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Effect of Sintering Holding Time and Cooling Rate on the Austenite Stability and Mechanical Properties of Nanocrystalline FeCrC Alloy

Kim Gwanghun, Jeon Junhyub, Seo Namhyuk, Choi Seunggyu, Oh Min-Suk, Son Seung Bae, Lee Seok-Jae

Archives of Metallurgy and Materials

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2021

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Vol. 66, iss. 3

759--763

EN

The effects of the sintering holding time and cooling rate on the microstructure and mechanical properties of nanocrystalline Fe-Cr-C alloy were investigated. Nanocrystalline Fe-1.5Cr-1C (wt.%) alloy was fabricated by mechanical alloying and spark plasma sintering. Different process conditions were applied to fabricate the sintered samples. The phase fraction and grain size were measured using X-ray powder diffraction and confirmed by electron backscatter diffraction. The stability and volume fraction of the austenite phase, which could affect the mechanical properties of the Fe-based alloy, were calculated using an empirical equation. The sample names consist of a number and a letter, which correspond to the holding time and cooling method, respectively. For the 0A, 0W, 10A, and 10W samples, the volume fraction was measured at 5.56, 44.95, 6.15, and 61.44 vol.%. To evaluate the mechanical properties, the hardness of 0A, 0W, 10A, and 10W samples were measured as 44.6, 63.1, 42.5, and 53.8 HRC. These results show that there is a difference in carbon diffusion and solubility depending on the sintering holding time and cooling rate.

2

Microstructural and Mechanical Characteristics of Non-Equiatomic High Entropy Alloy FeMnCoCr Prepared by Spark Plasma Sintering

Seo Namhyuk, Jeon Junhyub, Choi Seunggyu, Moon Young Hoon, Shon In-Jin, Lee Seok-Jae

Archives of Metallurgy and Materials

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2020

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Vol. 65, iss. 3

1005--1009

EN

In this study, a non-equiatomic high entropy alloy was fabricated using the spark plasma sintering method, and its microstructural features and mechanical properties were investigated. The chemical composition of FeMnCoCr was determined by using the entropy calculation related to the design of high entropy alloys. A bulk sample with the same composition was also prepared using the conventional metallurgical processes of casting and hot rolling. The microstructures of the samples fabricated by these different processes were compared by microscope observation, and a quantitative phase analysis was carried out using FE-SEM. Hardness measurement was used to evaluate mechanical properties. Particular attention was paid to microstructural changes due to heat treatment, which was analyzed by considering how austenite stability is affected by grain refinement.

3

Effects of TiC Addition on Strain-Induced Martensite Transformation and Mechanical Properties of Nanocrystalline Fe-Mn Alloy Fabricated by Spark Plasma Sintering

Jeon Junhyub, Choi Seunggyu, Seo Namhyuk, Moon Young Hoon, Shon In-Jin, Lee Seok-Jae

Archives of Metallurgy and Materials

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2020

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Vol. 65, iss. 4

1249--1254

EN

The effect of TiC content on the microstructure and mechanical properties of a nanocrystalline Fe-Mn alloy was investigated by XRD analysis, TEM observation, and mechanical tests. A sintered Fe-Mn alloy sample with nano-sized crystallites was obtained using spark plasma sintering. Crystallite size, which is used as a hardening mechanism, was measured by X-ray diffraction peak analysis. It was observed that the addition of TiC influenced the average size of crystallites, resulting in a change in austenite stability. Thus, the volume fraction of austenite at room temperature afterthe sintering process was also modified by the TiC addition. The martensite transformation during cooling was suppressed by adding TiC, which lowered the martensite start temperature. The plastic behavior and the strain-induced martensite kinetics formed during plastic deformation are discussed with compressive stress-strain curves and numerical analysis for the transformation kinetics.

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Effect of Composition on Strain-Induced Martensite Transformation of FeMnNiC Alloys Fabricated by Powder Metallurgy

Choi Seunggyu, Jeon Junhyub, Seo Namhyuk, Moon Young Hoon, Shon In-Jin, Lee Seok-Jae

Archives of Metallurgy and Materials

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2020

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Vol. 65, iss. 3

1001--1004

EN

We investigated the austenite stability and mechanical properties in FeMnNiC alloy fabricated by spark plasma sintering. The addition of Mn, Ni, and C, which are known austenite stabilizing elements, increases its stability to a stable phase existing above 910°C in pure iron; as a result, austenitic microstructure can be observed at room temperature, depending on the amounts of Mn, Ni, and C added. Depending on austenite stability and the volume fraction of austenite at a given temperature, strain-induced martensite transformation during plastic deformation may occur. Both stability and the volume fraction of austenite can be controlled by several factors, including chemical composition, grain size, dislocation density, and so on. The present study investigated the effect of carbon addition on austenite stability in FeMnNi alloys containing different Mn and Ni contents. Microstructural features and mechanical properties were analyzed with regard to austenite stability.