Microestrutura, corrosão e propriedades mecânicas de um aço com alto teor de manganês (27%p) para aplicações criogênicas

Abstract

Natural gas is a very promising alternative energy source, and may well be the main fuel in the coming decades, has a vast resource base and its environmental advantages are widely recognized. Because of this, the storage and transportation of liquefied natural gas (LNG) is increasingly important. For the manufacture of the storage tank and transport of LNG are used aluminum alloys, austenitic stainless steels, alloy 9% Ni, among others. But all these materials have disadvantages, such as expensive welding consumables, welding difficulties, and its high manufacturing cost. Alloys with high Mn content can be an attractive alternative to such an application. Manganese is part of the group of stabilizing elements of austenite in steels. Mn-based alloys have low production costs compared to those currently used. The alloy characterized was Fe27Mn1Si. The rolling and solubilization heat treatment temperatures were obtained from the phase diagrams plotted in the Thermo-Calc® software. Hot laminations were carried out at temperatures of 700oC and 1100oC. Reductions of 80% and 60% of the initial thickness were applied. Coolings were made in water, air and furnace. The microstructure of the Fe27Mn1Si alloy was characterized by scanning electron and optical microscopy techniques. The presence of the Austenite and Martensite- phases was observed. The phases were analyzed and quantified using the EBSD and XRD techniques. An increase of the Martensite- phase was observed for a lower cooling rate. The mechanical properties of the Fe27Mn1Si alloy were investigated. The traction and Charpy impact energy tests were performed at room temperature and cryogenic (-196°C). The alloy with high Mn content combined high strength with good ductility. The corrosion resistance in 0.001M NaCl solution was analyzed by OCP techniques and polarization curves.