Study of Microstructural Evolution for Advanced Ferritic Steel Alloy Fe-14Ni-9Al-7,5Cr-0,5Nb with Aging at 800, 900, 1000OC

• Main Author: Nusantara (NIM : 12514053), Prawira
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/29974
• Institution: Institut Teknologi Bandung

The main issue in the operation of the steam power plant is the need to reduce CO2 emissions generated from coal combustion, increase energy efficiency and decrease fuel consumption. This issue can be overcome by operating at higher temperatures. This requires the readiness of materials to be able to be used at these temperatures. Various studies have been undertaken to develop advanced Fe-Ni-Al-Cr ferritic steel as an alternative material used, since the presence of a B2- (Ni, Fe)Al coherent precipitate phase can increase strength at elevated temperatures, and with the addition of niobium (Nb) microalloying can increase the volume fraction of the precipitate. In this study, we studied the effect of temperature and time of aging on advanced ferritic steel alloys. A series of experiments were conducted to study the effect of a combination of variations in temperature and time aging on microstructural evolution, volume fraction and particle size of B2 precipitate and coarsening rate, and the hardness properties of Fe-14Ni-9Al-7,5Cr-0,5Nb (wt.%). Making alloys is done by melting raw materials on the DC Mini Arc Furnace to form a button. The alloy is then homogenized and aging testing is carried out at 800, 900, 1000oC for 6, 20, 48 hours. Microscopic observation was performed by optical microscope and scanning electron microscope (SEM), examination of alloying composition using energy dispersive spectroscopy (EDS), and hardness test tester on hardness test. The results of the experiment showed the formation of coherent precipitate phase B2- (Ni, Fe)Al at homogenization results. An increase in aging temperature causes morphological evolution, successively from spherical, cuboidal and elliptical, due to increased lattice misfit. An increase in the aging time will increase the number of semi-coherent precipitates in rectangular“bone-like” and rod form, which are consecutively a coarsening product of cuboidal and elliptical morphology. In addition, the phenomenon of nanoprecipitate formation results in homogenization and aging 1000oC, the formation of the third phase with the dominant element Nb, then there is the phenomenon of the spread of small precipitates on the grain boundaries and the middle grains, and also the phenomenon of hierarchical precipitate formed at ageing 1000oC. The coarsening rate at ageing 800oC is 0.093 μm3/hr and at ageing 1000oC is 0.1811 μm3/hr. The highest volume fraction was obtained when aging 800oC for 6 hours was 27.48%, and the highest hardness value was reached when aging 1000oC for 20 hours was 559,12 HVN.