The abundant reserve of lateritic ores in Indonesia is currently processed and studied to fulfil the national steel demand in several sectors, one of which is for railway application. The development of lateritic steel (Fe-Ni) as carbide free bainitic steel is carried out by adding Al to the Fe-Ni alloy. In this research, the effect of warm rolling and Al addition to the formation of carbide, phases development and mechanical properties was studied. The warm-rolled thermomechanical process (TMCP) was carried out by heating the material at 945°C for 20 minutes followed by second heating to 400°C, 450°C and 500°C with holding time for 30 minutes. The materials then warm rolled with 50% and 70% reductions using 20 tons capacity roller machine and then air cooled outside the furnace chamber. The microstructure of the as-rolled materials was characterized using optical microscope (OM) and scanning electron microscope (SEM), while the phases, the chemical distribution and the possibility of carbide formation were examine using X-Ray Diffraction (XRD) pattern and energy dispersive X-Ray spectroscopy (EDS). The mechanical properties of the material were observed using macro Rockwell hardness test. It was revealed that the addition of Al altered the phases of Fe-Ni lateritic steel significantly. Furthermore, Al addition gives positive effects to the Fe-Ni lateritic steel by increasing hardness. The reductions applied during warm rolling were observed to have effect on the growth of the grains in the Fe-Ni-Al lateritic steel.

The effects of Cr addition and cold deformation in increasing strength and altering the austempered structure of a FeNi steel is discussed. Cr content in the steel was varied from 2 to 3 wt% whilst cold deformation was undertaken on the material at either, 10% or 50%. The cold deformed steel was then subjected to austempering treatment at 400 °C for 30 min to obtain bainite structure in the samples. Post-austempering scanning electron microscopy (SEM) images of the FeNi-Cr samples showed the formation of lower bainite (LB) and martensite/retained austenite (M/RA) in the microstructure, whilst, in the FeNi sample showed the presence of ferrite in addition to LB and M/RA. The hardness and strength of the austempered FeNi-Cr samples increased significantly with increasing Cr content. Hardness and strength values of up to 46 HRC (from ⋘<20 HRC in FeNi) and above 1400 MPa (from ~800 MPa in FeNi), respectively, were obtained in 50% cold-deformed austempered FeNi-3 wt% Cr sample. However, the elongation decreased with increasing Cr content from 22% in the FeNi to 17% in the FeNi-3 wt% Cr sample. These findings suggest that while strength and hardness increase in cold-deformed austempered FeNi with increasing Cr content, the ductility decreases.

Baja laterit merupakan baja berbahan dasar bijih nikel laterit. Bijih nikel laterit biasa diabaikan penambang karena faktor ekonomis dan lebih mencari nikel yang berada dibawah lapisan limonit. Tujuan penelitian ini adalah mengetahui karakteristik baja laterit yaitu sifat kekerasan, ketangguhan, struktur mikro, dan struktur patahan baja laterit dengan variasi beban pada proses penempaan panas (hot forging). Penempaan panas menggunakan 3 variasi beban tempa yaitu 50, 75, dan 100 ton serta bahan awal (As Cast) dengan 1 kali penempaan pada temperatur pemanasan 1200°C. Penempaan panas menghasilkan reduksi As Cast (0%), 50 ton (18.06%), 75 ton (31.02%), dan 100 ton (31.72%). Hasil pengujian karakterisasi material menunjukkan bahwa nilai kekerasan tertinggi dan nilai impak tertinggi pada reduksi 31.02% sebesar 61.21 HRC dan 0.21 Joule/mm². Struktur mikro yang terbentuk pada As Cast adalah ferit dan perlit sedangkan pada hasil penempaan panas adalah bainit. Hasil struktur patahan menggunakan Scanning Electron Microscope menunjukkan bahwa ukuran butir semakin halus dan pipih seiring bertambahnya beban tempa panas.