각종 질화법으로 질화 처리한 발전 플랜트용 스팀밸브계 부품소재들의 표면특성 비교평가
Study of Surface Property Modification of Steam Turbine Valve Materials after Various Nitriding Treatments
질화법 질화 처리 발전 플랜트 스팀밸브 부품소재 표면특성 습증기 산화 고온마모;
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The effect of nitriding treatment on the wear resistance, corrosion resistance and high temperature-high pressure oxidation resistance was studied on various alloys for power plants. Plasma nitriding treatment of Nimonic 901 alloy at 650℃ has resulted in a nitrided layer of CrN, whose hardness was Hv 1150. The oxides on the specimen were analyzed by using X-ray diffractometer (XRD) and the weight change was measured after oxidation at 283℃, 10MPa under the steam conditions of nuclear power generation. The oxidation behaviors of the two alloys (ASTM A355, SUS422), with and without nitriding treatments, were clearly different. XRD analysis revealed formation of nitrides such as CrN, Fe_(4)N, and Fe_(2)-_(3)N. Also, it was found that nitrided layer hardness was decreased to Hv 425 at 283℃ from Hv 1150 at room temperature. The wear characteristics of the ASTM A355, Type SUS422 and Nimonic 901 steels were evaluated after nitriding. The wear resistance of the specimens nitrided under different methods and conditions were measured by the ring on disk type test at the operation temperatures for the power plant, i. e., 399-593℃. The wear properties, such as the wear coefficient, amount of wear, shape and composition of wear debris, were analyzed at 200N load, 120 rpm, and 40 min. holding time. Compared with non-nitrided specimens, the amount of wear and wear coefficients of the nitrided specimens were decreased remarkably. In addition, the surface hardness and ductility were increased and less debris was formed in the nitrided specimen.