MICROSTRUCTURE EVOLUTION STUDY OF FERRITIC STEEL Fe-14Ni-9Al-7.5Cr-1Mo AT TEMPERATURE 800, 900, AND 1000OC

• Main Author: BACHRI (NIM : 12514032), SYAIFUL
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/31180
• Institution: Institut Teknologi Bandung

World population growth is projected to grow to 9.8 billion by 2050. This population growth leads to a 60% increase in world electricity demand between 2015 and 2040. Continued efficiency improvements are made in power generation by developing materials that can be used at higher temperatures and pressures. The ferritic steel can be used as an alternative to the heat exchange component of the boiler because it has high thermal conductivity, low thermal expansion and lower price compared to nickel-based super-alloys. However, the use of ferritic steel is still limited to temperatures of 620-630oC due to consideration of creep resistance and high-temperature corrosion. One method that can be used to strengthen ferritic steel is precipitation strengthening. In this study, studied the effect of aging on microstructural changes and the mechanical properties of ferritic steel alloys reinforced by B2- (Fe, Ni) Al precipitates. <br /> <br /> Alloy with Fe-14Ni-9Al-7.5Cr-1Mo (% weight) composition is melted with DC Mini Arc Furnace to form button. Furthermore, the button is homogenized at 1100°C for 24 hours with tube furnace. Aging treatment was given to the test sample with temperature variations of 800, 900, 1000oC for 6, 20, and 48 hours. Samples that have been subjected to aging treatment are observed by the results of changes in microstructure using optical microscopy, scanning electron microscope (SEM), and to see the alloy phase composition using energy dispersive spectroscopy (EDS). Hardness values were obtained using a vicker hardness test. <br /> <br /> The experimental results show that the phases formed in Fe-14Ni-9Al-7.5Cr-1Mo (% weight) alloys are &#945;-Fe as the matrix and &#946; 'as B2-ordered (Fe,Ni)Al precipitates. Alloys increase in volume fraction and average size with increasing aging time at each temperature. The precipitate morphology of the aging temperature at 800oC for 6 hours has a majority of rounded cuboidal shape and turns into spherical as the aging time increase while aging at 1000oC for 6 hours has a spherical majority shape that will enlarge with aging time increase. The coarsening rate coefficient value obtained is greater with increasing temperature aging ie 5.7 x 104 nm3/h and 2,1 x 106 nm3/h at temperature 800 and 1000oC. The highest hardness value was in the aging sample at 1000°C for 6 hours is 520 HVN.