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1
Content available Austenitic Stability and Strain-Induced Martensitic Transformation Behavior of Nanocrystalline FeNiCrMoC HSLA Steels
Park Jungbin, Jeon Junhyub, Seo Namhyuk, Kim Gwanghun, Son Seung Bae, Jung Jae-Gil, Lee Seok-Jae
Archives of Metallurgy and Materials
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2023
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Vol. 68, iss. 1
77--80
EN
The austenitic stability and strain-induced martensitic transformation behavior of a nanocrystalline FeNiCrMoC alloy were investigated. The alloy was fabricated by high-energy ball milling and spark plasma sintering. The phase fraction and grain size were measured using X-ray diffraction. The grain sizes of the milled powder and the sintered alloy were confirmed to be on the order of several nanometers. The variation in the austenite fraction according to compressive deformation was measured, and the austenite stability and strain-induced martensitic transformation behavior were calculated. The hardness was measured to evaluate the mechanical properties according to compression deformation, which confirmed that the hardness increased to 64.03 HRC when compressed up to 30%.
2
Content available 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.
3
Content available 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.
4
Content available 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.
5
Content available Influence of Carbon Content on Austenite Stability and Strain-induced Transformation of Nanocrystalline FeNiC Alloy by Spark Plasma Sintering
Oh Seung-Jin, Kim Byoung-Cheol, Suh Man-Chul, Shon In-Jin, Lee Seok-Jae
Archives of Metallurgy and Materials
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2019
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Vol. 64, iss. 3
863--867
EN
The effects of carbon content on the austenite stability and strain-induced transformation of nanocrystalline Fe-11%Ni alloys were investigated using X-ray analysis and mechanical tests. The nanocrystalline FeNiC alloy samples were rapidly fabricated using spark plasma sintering because of the extremely short densification time, which not only helped attain the theoretical density value but also prevented grain growth. The increased austenite stability resulted from nanosized crystallites in the sintered alloys. Increasing compressive deformation increased the volume fraction of strain-induced martensite from austenite decomposition. The kinetics of the strain-induced martensite formation were evaluated using an empirical equation considering the austenite stability factor. As the carbon content increased, the austenite stability was enhanced, contributing to not only a higher volume fraction of austenite after sintering, but also to the suppression of its strain-induced martensite transformation.
6
Content available Effect of Ni Content on the Austenite Stability and Mechanical Properties of Nanocrystalline Fe-Ni Alloy Fabricated by Spark Plasma Sintering
Park D., Oh S.-J., Shon I.-J., Lee S.-J.
Archives of Metallurgy and Materials
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2018
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Vol. 63, iss. 3
1477--1480
EN
The mechanical behavior and the change of retained austenite of nanocrystalline Fe-Ni alloy have been investigated by considering the effect of various Ni addition amount. The nanocrystalline Fe-Ni alloy samples were rapidly fabricated by spark plasma sintering (SPS). The SPS is a well-known effective sintering process with an extremely short densification time not only to reach a theoretical density value but also to prevent a grain growth, which could result in a nanocrystalline structures. The effect of Ni addition on the compressive stress-strain behavior was analyzed. The variation of the volume fraction of retained austenite due to deformation was quantitatively measured by means of x-ray diffraction and microscope analyses. The strain-induced martensite transformation was observed in Fe-Ni alloy. The different amount of Ni influenced the rate of the strain-induced martensite transformation kinetics and resulted in the change of the work hardening during the compressive deformation.
7
Content available remote Deformation behavior of bulk TRIP steel
Zrnik J., Muransky O., Novy Z., Slama P.
Journal of Achievements in Materials and Manufacturing Engineering
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2015
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Vol. 68, nr 2
59--63
EN
Purpose: Experimental verification of various thermo-mechanical (TM) processing schedules, with aim to modify the structure characteristics using press forging of Si-Mn TRIP (Transformation Induced Plasticity) steel, was described. Design/methodology/approach: High strength and ductility of TRIP steels is attributed to the TRIP effect resulting from the strain induced martensitic transformation of the retained austenite in the multiphase (ferrite, bainite, martensite) microstructure. In order to rationalize the retained austenite (RA) volume fraction in steel microstructure, several TM schedules were employed at experiment where different austenite conditioning was considered. Findings: The various multiphase structure characteristics were then resulting after TM processing of steel, where different volume fractions of ferrite, bainite and RA were received in the steel. The modification of structural characteristics of steel then influenced the deformation behavior and mechanical properties TRIP steel. Research limitations/implications: The present work also focused on monitoring of RA transformation during incremental mechanical straining using in-situ neutron diffraction technique. Originality/value: This non-convenient experimental method was used to characterize the kinetics of RA transformation and its stability during consecutive straining.
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