REKAYASA PADUAN Fe-Al-Mn-C SEBAGAI PENGGANTI BAJA TAHAN KARAT KONVENSIONAL SS 304

Abstract

Conventional stainless steel is austenitic stainless steel (Fe-Cr-Ni alloy) which is the most widely used in industry. Weakness of stainless steel is the high cost of production and limited reserves, so that it is necessary to find new alloys which can replace the conventional stainless steel. The Fe-Al-Mn alloy system is very interesting as a potential candidate to replace the conventional stainless steel, where Al and Mn replace Cr and Ni, respectively. This study aims to find composition of the Fe-Al-Mn-C alloy which completely replaces SS 304 austenitic stainless steel. The alloy was prepared from mild steel scrap, medium carbon ferromanganese, high purity aluminum and ferrocarbon. The alloy was fabricated in a high frequency induction furnace. Melting experiments was carried out to find the right process that can achieve the target composition. Characterization was carried out to determine the effect of Al content in the Fe-Al-C alloy and Mn content in the Fe-Al-Mn-C alloy. In the last stage, the Fe-Al-C and Fe-Al-Mn-C alloy were compared with the SS 430 and as cast of SS 304 conventional stainless steel. Sensitization and transition temperature properties of the Fe-Al-Mn-C alloy were investigated in detail. The results show that the Fe-Al-C and Fe-Al-Mn-C alloys can be alloyed in a high frequency induction furnace under argon atmosphere. The level of Al in the Fe- Al-Mn-C alloy is 7.5% because it has high corrosion resistance. Microstructures of as cast Fe-Al-C alloy are ferrite and pearlite. Enhancement of Al causes fraction of ferritic in these alloys. Enhancement of Al also decreases density and toughness, but increases hardness, tensile strength and corrosion resistance significantly. Microstructure of as cast Fe-Al-Mn-C alloy up to 20% Mn is ferrite and austenite. Fully austenitic microstructure is achieved at 25% Mn. Addition of Mn to Fe-Al-C alloy increases density, hardness, tensile strength and corrosion resistance significantly. The Fe-Al-C and Fe-Al-Mn-C alloy have no sensitization at a temperature of 600oC, and no brittle-ductile transition in the range of-90oC to 90oC. Both alloys are not hardenable. The Fe-7.5Al-25Mn-0.6C alloy is recommended to completely replace SS 304 conventional stainless steel