In the present investigation, low temperature nitriding has been attempted on AISI 316L austenitic stainless steel by using a laboratory fluidized bed furnace. The nitriding was performed in temperature range between 400°C and 500°C. X-ray diffraction, metallography, and corrosion tests were used to characterize the resultant nitrided surface and layers. The results showed that fluidized bed process can be used to produce a precipitation-free nitrided layer characterized by the S phase or expanded austenite on austenitic stainless steel at temperatures below 500°C. But there exists a critical temperature and an incubation time for effective nitriding, below which nitriding is ineffective. The corrosion behaviour of the as-nitrided surfaces is significantly different from that previously reported for low temperature plasma nitriding. This anomaly is explained by the formation of iron oxide products and surface contamination during the fluidized process.
A comprehensive study of fluidized bed nitriding was performance on a carbon steel (grade AISI St 41) and low alloy steel (grade AISI 4140) at 550 0 C in 20 % N 2 and 80 % NH 3 atmosphere at a flow rate gasses of 0.7 m 3 /hr. Various surface roughness were used to incorporate nitrogen into these steels. The nitride layer formed at AISI 4140 showed better surface roughness and surface hardness than AISI St 41. With low chromium alloy (grade AISI 4140), nitrogen diffusion is more uniform in the lower surface roughness after nitriding process. It has been found that the surface microhardness of the compound layer increases with decreasing surface roughness and chromium alloy contents. The layer nitride has a decrease surface roughness ranging from 50 % at 0,1 µm to about 17 % at 0,5 µm. On the contrary, the carbon steel without chromium alloy (grade AISI St 41) sample show an enhance surface roughness between 1.3 to 2.5 times after nitriding process, but on 0.5 µm surface roughness sample show a decrease surface roughness of about 10%. All sample show an enhanced surface microhardness after nitriding significantly. Chromium alloy is found to enhanced the nitriding efficiency. Without chromium in the steel, a lower surface roughness provides a supplementary amount of implanted nitrogen available for further diffusion, and the uniform of the surface passive oxide. So, with limited surface roughness, more uniform layers with higher amounts of nitrogen can be achieved by low chromium alloy. However, with limited solubility of nitrogen atom in α-Fe into iron nitride form, the nitrogen becomes supersaturated reaction and nitride layer is more brittle and porosity. It is can be ascribed to the nitrogen solubility in the nitride layer, which at AISI St 41 is higher due to the formation of porosity phase while at AISI 4140 a phase rich in nitrogen (ϒand ε phases) is formed.
Besi cor kelabu, jenis cor ini sering dipakai karena memiliki banyak kelebihan. Kelebihan tersebut adalah mudah dituang atau dicor menjadi bentuk yang rumit, mudah dilakukan proses permesinan, tahan aus karena grafit dapat berfungsi sebagai pelumas, mempunyai kemampuan meredam getaran yang tinggi, mempunyai kekuatan tekan tinggi, sifat ketahan korosinya baik dibandingkan dengan baja konstruksi biasa, Spesimen yang sebelum proses diperoleh kekerasan tertiinggi yaitu 284,4 HV dengan kedalaman 30 μm, setelah diproses nitridisasi dengan temperature 6500C dengan holding 1,2, dan 3 jam, maka didapat kekerasan tertinggi sebesar 277,2 HV, 261,1 HV, 273,4 HV kekerasan naik pada holding 1 jam itu disebabkan karena reaksi kimia antara nitrogen dengan spesimen sehingga konsentrasi nitrogen pada permukaan spesimen yang berasal dari difusi nitrogen akan lebih banyak membentuk lapisan nitride. Pada pengujian spesimen dengan holding 1 jam didapat ketebalan lapisan 10, 20, 30, 40 μm dan permukaan tepi dari inti tidak merata sehingga lapisan menjadi tidak merata atau bergelombang, sedangkan pada temperatur 6500C dengan waktu 2 jam ketebalan ditunjukan hanya sampai pada 30 μm dan 40 μm, garis grafik mengalami kenaikan dikarenakan lapisan nitride dan permukaan tepi dari inti tidak merata sehingga lapisan menjadi bergelombang. Struktur mikro diperoleh dari hasil metalografi row material dan spesimen yang sesudah mengalami proses nitridisasi. Hasil dari struktur mikro sudah terlihat grafit berbentuk serpih keabu-abu an dan terlihat adanya sedikit korosi dikarenakan spesimen belum dilakukan proses
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