Resistencia a la corrosión de aleaciones Ni-Cr-Mo en diferentes condicionesmetalúrgicas
2010
Tesista | Natalia Silvina ZADOROZNE Ingeniera Química - Universidad Nacional de Misiones - Argentina Magíster en Ciencia y Tecnología de Materiales - Instituto Sabato UNSAM/CNEA - Argentina |
Director | Dr. Ricardo M. CARRANZA. CNEA, UNSAM - Argentina |
Codirector | Dr. Martín Alejandro RODRÍGUEZ. CNEA, UNSAM, CONICET - Argentina |
Lugar de realización | División Corrosión - Departamento Materiales - - Centro Atómico Constituyentes - CNEA - Argentina |
Fecha Defensa | 25/03/2010 |
Jurado | Dra. Silvia Beatriz FARINA. CNEA, UNSAM, CONICET - Argentina Dra. Silvia REAL. INIFTA, UTN, CONICET - Argentina Dra. Marcela VÁZQUEZ. INTEMA, UNMdP, CONICET - Argentina |
Código | IS/T 121/10 |
Título completo
Resistencia a la corrosión de aleaciones Ni-Cr-Mo en diferentes condicionesmetalúrgicas
Resumen
Complete Title
Corrosion resistance of Ni-Cr-Mo alloys in different metallurgical conditions
Abstract
Alloy C-22 (Ni-22Cr-13Mo-3W) shows an outstanding corrosion resistance in a wide variety of highly-corrosive environments. Due to its excellent corrosion resistance in oxidizing and reducing environments, Alloy C-22 has been selected as a candidate for the fabrication of the corrosion-resistant outer shell of the high-level nuclear waste containers. New Ni-Cr-Mo alloys have been developed due to the increasing demand of the industry for corrosion resistant alloys with particular properties. Alloy C-22HS (Ni-21%Cr-17%Mo) is a new high-strength corrosion resistant material which provides an excellent corrosion resistance and improved mechanical properties. Alloy HYBRID-BC1 (Ni-22%Mo-15%Cr) is intended for filling the gap between Ni-Mo and Ni-Cr-Mo alloys. This novel alloy is able to withstand HCl and H2SO4, even in the presence of dissolved oxygen and other oxidizing species in the environement.
The Mill Annealled condition (MA) ot the Ni-Cr-Mo alloys is an fcc solid solution. Thermal aging of Ni-Cr-Mo alloys leads to microstructure changes depending on the temperature range and exposure time at temperature. A Long Range Ordering (LRO) reaction can occur in the range of 350ºC to 600ºC. This homogeneous ordering reaction does not seem to affect the corrosion resistance and produces only a slight loss in ductility. Topollogically or Tetrahedrally Closed Packed (TCP) phases, like μ, σ and P, may form when Ni-Cr-Mo alloys are exposed in the range of 600ºC to 1100 ºC. These phases could have a detrimental effect upon corrosion resistance and cause a loss of mechanical ductility. The precipitation of TCP phases is heterogeneous and starts at grain boundaries. The sensitized alloy is prone to intergranular attack in certain environments.
The aim of the present work was to compare the general corrosion rate and the crevice corrosion susceptibility of alloys C-22, C-22HS and HYBRID-BC1 in different metallurgical conditions when exposed to 1M NaCl and 1M HCl at 90ºC. The effects of the alloy composition and different heat treatments were assessed.
Corrosion rates of approximately 0.1 µm/yr were found in 1M NaCl for all the tested alloys in the studied metallurgical conditions. In 1M HCl, alloys C-22 and C-22HS showed corrosion rates in the range of 1 to 3 mm/yr, while alloy HYBRID-BC1 showed corrosion rates of ca 10 µm/yr. None of the performed thermal aging treatments affected the corrosion rate of the tested alloys in the studied conditions. Alloy HYBRID-BC1 showed lower crevice corrosion susceptibility than alloys C-22 and C-22HS in 1M NaCl at 90ºC. Thermal aging treatments performed to alloy C-22 did not affect its crevice corrosion resistance, while the age hardening treatment performed to alloy C-22HS slightly reduced its crevice corrosion resistance. The better performance of alloy HYBRID-BC1 in 1M HCl and its higher crevice corrosion resistance in 1M NaCl were attributed to its higher molybdenum content.
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