산화물 분산 강화(ODS) 합금 강의 미세조직 및 고온 특성에 미치는 분말 밀링 공정의 영향 Effects of powder milling process on the microstructure and high temperature properties of oxide dispersion strengthened (ODS) steel원문보기
This study investigated the effects of powder milling process(Cryomilling, Combination milling) on the microstructures and high temperature properties of oxide dispersion-strengthened steel. Firstly, Cryomilling was newly tried on this ODS steel to control grains, oxides, and dislocation microstruct...
This study investigated the effects of powder milling process(Cryomilling, Combination milling) on the microstructures and high temperature properties of oxide dispersion-strengthened steel. Firstly, Cryomilling was newly tried on this ODS steel to control grains, oxides, and dislocation microstructures. Fe-14Cr-3W-0.4Ti (wt.%) alloy powder and 0.3wt.%Y2O3 powder were mixed and were mechanically alloyed through ball milling at each of room temperature (RT) and cryogenic temperature (-150°C) and then hot isostatic pressing, hot rolling, and annealing processes were implemented to manufacture two types of ODS ferritic steel, K1 (RT) and K4 (-150°C). The grain size of K1 was 0.5~1.5μm and K4 was 300nm on average. Oxide particles were shown to be finer and more uniformly distributed in K4 (5~10nm size distribution) than in K1 (average size 30nm). The two alloys were subjected to high temperature compression (RT~900°C) and creep (650°C) tests. K4 represented higher yield strength under all temperature conditions. However, K4 showed rapid strength decreases at high temperatures exceeding 700°C and showed similar levels of strengths to K1 at 900°C. In the case of creep properties, steady-state creep rates of K4 were lower than K1 in the same stress range. Stress exponent was almost similar values K1(n=4.15) and K4(n=4). Although cryomilling increased the number density of oxide particles, it simultaneously reduced grain sizes too much, so that grain boundary weakening at high temperatures could not be sufficiently prevented. Also, this study investigated the long-term high-temperature oxidation property of K1, K4. Long-term high-temperature oxidation tests were conducted at 800°C for up to 6000hours in atmospheric air. The weight gains after 6000h oxidation tests for K1, K4 were 1.5, 0.3 mg/cm2, respectively. K4 showed significantly better oxidation resistance than K1. Oxide scales of Cr2O3, Fe2O3, and Fe2TiO4 were formed after oxidation tests. Microstructural features and reactive element effect were found to be important in improving the oxidation resistance of ODS steels. Meanwhile, Combination milling is a process attempt for mutual enhancement of strength and toughness of ODS steel. KB ODS steel was manufactured through planetary milling, cryomilling and conventional drum milling. The grain size was 0.5~0.7μm with annealing heat treatment and oxide particles size was 5~25nm. This alloy was subjected to high temperature compression (RT~900°C). KB represented relatively low yield strength and very high tensile strength. It showed strength decreases at high temperatures exceeding 700°C but high temperature strength was improved than other ODS steel manufactured by single milling.
This study investigated the effects of powder milling process(Cryomilling, Combination milling) on the microstructures and high temperature properties of oxide dispersion-strengthened steel. Firstly, Cryomilling was newly tried on this ODS steel to control grains, oxides, and dislocation microstructures. Fe-14Cr-3W-0.4Ti (wt.%) alloy powder and 0.3wt.%Y2O3 powder were mixed and were mechanically alloyed through ball milling at each of room temperature (RT) and cryogenic temperature (-150°C) and then hot isostatic pressing, hot rolling, and annealing processes were implemented to manufacture two types of ODS ferritic steel, K1 (RT) and K4 (-150°C). The grain size of K1 was 0.5~1.5μm and K4 was 300nm on average. Oxide particles were shown to be finer and more uniformly distributed in K4 (5~10nm size distribution) than in K1 (average size 30nm). The two alloys were subjected to high temperature compression (RT~900°C) and creep (650°C) tests. K4 represented higher yield strength under all temperature conditions. However, K4 showed rapid strength decreases at high temperatures exceeding 700°C and showed similar levels of strengths to K1 at 900°C. In the case of creep properties, steady-state creep rates of K4 were lower than K1 in the same stress range. Stress exponent was almost similar values K1(n=4.15) and K4(n=4). Although cryomilling increased the number density of oxide particles, it simultaneously reduced grain sizes too much, so that grain boundary weakening at high temperatures could not be sufficiently prevented. Also, this study investigated the long-term high-temperature oxidation property of K1, K4. Long-term high-temperature oxidation tests were conducted at 800°C for up to 6000hours in atmospheric air. The weight gains after 6000h oxidation tests for K1, K4 were 1.5, 0.3 mg/cm2, respectively. K4 showed significantly better oxidation resistance than K1. Oxide scales of Cr2O3, Fe2O3, and Fe2TiO4 were formed after oxidation tests. Microstructural features and reactive element effect were found to be important in improving the oxidation resistance of ODS steels. Meanwhile, Combination milling is a process attempt for mutual enhancement of strength and toughness of ODS steel. KB ODS steel was manufactured through planetary milling, cryomilling and conventional drum milling. The grain size was 0.5~0.7μm with annealing heat treatment and oxide particles size was 5~25nm. This alloy was subjected to high temperature compression (RT~900°C). KB represented relatively low yield strength and very high tensile strength. It showed strength decreases at high temperatures exceeding 700°C but high temperature strength was improved than other ODS steel manufactured by single milling.
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