AISI 410-3Mo-3Ni stainless steel is a martensitic steel which limited in using when compared to austenitic and ferritic stainless steels. Martensitic steel has an essential role in specific components due to a combination of strength, toughness and excellent corrosion resistance. However, martensitic steel tends to undergo decreasing in mechanical properties and microstructure after the forging process. In this study, mechanical properties and microstructure of the forged AISI 410 after receiving annealing heat treatment will be studied. Annealing aims to reduce material hardness and increase grain refinement of material. Annealing heat treatment is carried out by varying the annealing temperature and time. Annealing temperature variations are 7000, 7600, and 8000C. The annealing time variation is 3 hours and 6 hours. The effect of annealing time and temperature will be studied on the hardness and microstructure of the AISI 410 modified material. The optimum hardness of 35.9 HRC in sample with annealing treatment in 760°C for 6 hours. The microstructure shows delta ferrite, martensite, austenite, and carbide phases which affect hardness value of annealed samples.

No abstract

Baja mangan austenitik merupakan baja yang digunakan secara luas pada industri tambang dan mineral karena memiliki ketahanan aus dan ketangguhan yang tinggi. Secara umum, baja mangan austenitik yang dibuat melalui proses pengecoran memiliki kecenderungan getas dengan ketangguhan yang rendah karena terbentuknya formasi karbida. Proses solution treatment diikuti dengan pendinginan cepat menjadi hal penting untuk melarutkan karbida sehingga menjamin terbentuknya  struktur full austenit pada temperatur kamar. Penelitian ini bertujuan untuk mengetahui pengaruh variasi holding time dan media pendingin pada proses solution treatment terhadap kekerasan dan ketangguhan paduan baja Fe12Mn1.5Mo. Pada penelitian ini, karakteristik baja Fe12Mn1.5Mo hasil cor diinvestigasi lebih lanjut setelah dilakukan proses solution treatment dalam dua tahap, yaitu memanaskan dari temperatur ruang sampai 700oC dengan holding time 3 jam, kemudian dinaikkan sampai temperatur 1000 oC dengan variasi holding time selama 1 jam, 2 jam dan 3 jam diikuti dengan quenching menggunakan 3 media pendingin berbeda (air, larutan garam 1.5% dan 3%). Pada pendinginan menggunakan larutan garam 1.5% dan 3% menunjukkan bahwa semakin lama holding time, maka nilai kekerasan dan nilai impak juga semakin meningkat. Sementara itu, spesimen yang didinginkan menggunakan air menghasilkan nilai yang berfluktuasi untuk kedua sifat mekanik. Nilai kekerasan tertinggi sebesar 344 BHN pada variasi holding time 2 jam diikuti dengan pendinginan air, sementara nilai impak tertinggi sebesar 73.7 J/cm2 dihasilkan pada variasi holding time 1 jam dengan pendinginan air.  Nilai impak terendah sebesar 48.8 J/cm2 dihasilkan pada variasi holding time 1 jam dengan pendinginan larutan garam 3%. Hasil metalografi menunjukkan bahwa struktur mikro matriks austenit yang mengakibatkan nilai kekerasan yang rendah sedangkan karbida tak terlarut yang terdispersi di batas butir dan di dalam butir yang mengakibatkan nilai kekerasan yang tinggi. Di sisi lain, Proses solution treatment yang berlangsung kurang sempurna berakibat pada menurunnya ketangguhan karena terbentuknya presipitasi karbida.

Fatigue failure of turbine blades originating from pitting corrosion is a critical issue for power plant. Herein, we study the pitting corrosion resistance of cast CA6NM as turbine blade material in simulated geothermal environment with and without CO2 gas by using cyclic polarization measurement. Three different molybdenum and nitrogen content of CA6NM were used for experiments: (i) CA6NM with a molybdenum content of 1 wt.% and without addition of nitrogen, (ii) CA6NM with a molybdenum content of 2 wt.% and without addition of nitrogen, (iii) CA6NM with a molybdenum content of 2 wt.% and nitrogen content 0.1 wt.%. The measurement reveals CA6NM with molybdenum 2 wt.% and nitrogen 0.1 wt.% is the most resistance to pitting corrosion in simulated artificial geothermal brine with and without CO2 gas.

Pitting corrosion is an importance phenomena in power generation steam turbine, as it is one of the main causes for blade failure, particularly in the last row of low pressure blading. In this work, the pitting corrosion resistance of the widely used blading alloy of wrought 410 stainless steel and that of the candidate alloy of cast CA6NM stainless steel were investigated. Cyclic polarization measurements for all samples were conducted in simulated solution of thermal and geothermal power plants. The experimental results show that the pitting potentials of the cast CA6NM steel were higher compared to those of the wrought 410 steel in all simulated solution. Both steels exhibited higher pitting potentials in CO2 containing simulated geothermal water than those in the other solutions. These results were correlated with microstructure of the steels observed by Scanning Eectron Microscope (SEM).