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Abstrak :
Nb (CN) particle in Nb-HSKA steels plays important role to retard recrystallisation process and to strengthen the mechanical properties by precipitation hardening. The behavior od NB (CN) particle growth after deformation needs to evaluate in order to optimize the production process. HSLA steel containing 0.03% Nb is used and the thermomechanical treatment including reheating air cooling, finishing and relaxation is applied to the test steels. The results obtained in this way shows that the kinetics coarsening of NB (CN) particle after deformation at 900C is considerably accelerated compared with when the coarsening is controlled by a bulk diffusion process.

Abstrak :
Paduan biner Mg-Gd memiliki potensi sebagai material implan yang mudah larut dalam tubuh. Penambahan sedikit gadolinium dapat memperbaiki sifat mekanik dan laju korosi sehingga memenuhi syarat sebagai material implan yang sesuai dengan kondisi tubuh. Penelitian ini bertujuan untuk merancang paduan Mg-1,6Gd sebagai material implan yang mudah larut yang memiliki sifatsifat mekanik yang baik dan laju korosi terkontrol setelah diproses termomekanik. Paduan tersebut diproses melalui ekstrusi panas dan canai panas dalam rentang temperatur 300-550°C dengn variasi reduksi ketebalan. Sampel diekstrusi panas dengan kecepatan 1 mm/s dengan ratio ekstrusi 30dan sampel canai panas dengan reduksi 30% dan 95%, kecepatan 10 m/min. Proses canai dilakukan dengan dua metode yaitu canai searah dan canai silang. Canai searah dilakukan searah dengan putaran rol, sesuai dengan reduksi dan canai silang membentuk sudut 90° dari setiap tahap rol. Pada rol reduksi 30% dilakukan sekali rol, sementara rol reduksi 95% searah dilakukan multi pass (40%, 40 %, 15% setiap tahap) dan rol reduksi 95% silang dilakukan 23,75% setiap tahap. Paduan Mg-1,6Gd membentuk senyawa intermetallik (Mg5Gd) menyebar di dalam dan dibatas butir untuk semua proses termomekanik. Ekstrusi menghasilkan ukuran butir terkecil dibanding kedua proses canai yaitu mencapai 14um dengan kekerasan 48,7 HVN. Kekuatan tarik dan luluh juga dihasilkan paling tinggi pada proses ini yaitu 232 MPa dan 142 MPa. Sementara proses canai hanya memilki ukuran butir dalam rentang 50-400 um, namun kekerasan rata-rata proses canai lebih tinggi dari ekstrusi yaitu 40-66 HVN. Canai searah 95% menghasilkan kekuatan tarik dan luluh lebih tinggi dari canai 30% yaitu adalah 197 MPa, 157 MPa dan keuletan 26 %. Pada awal perendaman paduan Mg-1,6Gd memiliki laju korosi yang tinggi untuk kedua larutan (SBF dan Ringers). Selanjutnya pada perendaman lama (14 hari) laju korosi cenderung menurun, dikarenakan telah terbentuk lapisan pasif. Ekstrusi menghasilkan laju korosi yang tertinggi dibanding canai yaitu 4.4 mmpy setelah imersi 3 hari dalam larutan Ringers. Melalui polarisasi, canai 95% menghasilkan laju korosi tertinggi (5,7 mmpy). Pengujian sitotoksisitas untuk ketiga proses termomekanik menunjukkan sampel ini tidak menghasilkan toksin karena ratarata hasil % viabilitas diatas viabilitas kontrol (75%). Paduan Mg-1,6Gd setelah proses termomekanik mampu memiliki sifat-sifat mekanik yang baik, laju korosi terkontrol dan tidak toksik untuk digunakan sebagai material implan mampu luruh sesuai kondisi tubuh.

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Binary Mg-Gd alloys have been the potential as biodegradable implant materials. The small addition of element Gd could improve the mechanical properties and corrosion rate that the alloy can be used as implant materials for the body condition. This study aims to design the Mg-1.6Gd alloy as degradable implant that it has good mechanical properties and corrosion rate after thermomechanical process. The Mg-1,6Gd alloys is processed by the hot extrusion and the severely hot rolled in the temperature range 300-550°C with the different reduction. The samples were hot extruded with a speed of 1 mm/s, a ratio of 30 and a hot rolled with a reduction of 30% and 95% and a speed of 10 m/min. The rolling process is done by two methods: Unidirectional rolling (UR) and cross-rolling (CR). UR is carried out in the direction of rotation of the rolland CR formed an angle of 90 from each stage of the roll. The roll of 30% reduction is done only one roll, while the UR of 95% reductionis done multi pass (40%, 40%, 15% each stage) and the CR of 95% reduction is done at 23.75% per stage.The Mg-1.6Gd alloys forms intermetallic compounds (Mg5Gd) and spread inside and grain boundaries for all thermomechanical processes. The hot extrusion resulted the smallest grain size compared to both the rolling process, which the grain size of 14 um and the hardness of 48.7HVN. The highest strength and yield are 232 MPa and 142 MPa for this the extrusion process.The hot rolled samples have the grain size of 50-130um but the average hardness of the this process is higher than that of 40-66 HVN. The hot rolled with the 95% reduction has the higher tensile strength and yield strength than the 30 % reduction, were 197 MPa and 157 MPa, respectively, while the ductility is 26 %.The highest corrotion rate occur on the short time for the both solutions. Furthermore, in the long immersion (14 days) the corrosion rate tends to decrease, because it formed a passive layer. Extrusion process produced the highest corrosion rate of 4.4 mmpy after 3 days of imersion in the Ringer's solution. The hot rolled of the 95% reduction resulted the high corrosion rate of 5,7 mmpy on the polarization test. The cytotoxicity test for all three thermomechanical processes showed the sample have no cytotoxicity because the % viability result was above viability control (75%). The Mg-1.6Gd alloy after thermomechanical process produced good mechanical properties, corrosion rate and no toxins to be used as degradable implant for the body condition.

Abstrak :
Material baja khususnya baja paduan rendah kekuatan tinggi (HSLA) dalam kebanyakan aplikasi membutuhkan kombinasi dari kekuatan dan kekerasan. Sifat ini dapat dicapai dengan kontrol terhadap proses pada saat pembuatan baja. Salah satu proses yang biasa diterapkan adalah proses Thermomechanical Treatment atau pengerolan terkendali. Proses ini akan menyebabkan peningkatan kekuatan dan kekerasan baja HSLA melalui mekanisme penghalusan butir ferit dan juga pengerasan presipitat. Adapun tujuan dari penelitian ini adalah untuk mengetahui perilaku butir ferit dan hubungannya dengan ketahanan korosi benda uji sebelum dan sesudah pencanaian. Benda uji berupa baja paduan rendah kekuatan tinggi (HSLA) berukuran 100x6x60 mm dengan kandungan 0.029% Nb, 0.01% N, 0.087% C dan sejumlah kecil paduan lainnya dipersiapkan untuk proses pencanaian. Benda uji kemudian dipanaskan hingga temperatur 1200 °C dan ditahan selama 60 menit. Proses pencanaian dilakukan dengan deformasi sebesar 30% menggunakan mesin rol berkapasitas 20 ton dan dilanjutkan dengan pendinginan udara. Larutan nital 2% digunakan untuk mengamati butir ferit sedangkan picral digunakan untuk mengamati butir austenit. Perhitungan besar butir dilakukan menggunakan metode planimetri sesuai ASTM E 112. Untuk mengamati ketahanan korosi, uji sembur kabut garam dilakukan menggunakan larutan NaCl 3.5% , pH 6.8 dan temperatur 28°C selama 48 jam sesuai standar ASTM B 117, benda uji dibersihkan menggunakan 1000 ml HCl, 20 gr antimony (III) trioxide, dan 60 gr tin (II) chloride dihydrate sesuai standar JIS Z 2371 dan perhitungan laju korosi dilakukan menggunakan metode kehilangan berat. Hasil pengujian menunjukkan bahwa ukuran butir ferit sesudah deformasi menurun dari 17.2 ± 0.92 µm menjadi 15.4 ± 0.17 µm sedangkan laju korosi meningkat dari 106.82 mpy menjadi 114.45 mpy. ......Good mechanical properties, such as strength and hardness, is a must have charecteristics for high strength low alloy steel in many application. This excellent properties can be achieved through controlling final microstructure. Therefore, thermomechanical treatment was worked out in order to get those properties through grain refinement and precipitation hardening that formed after this process applied. The main objective of this experiment was to measure the ferrite grain size before and after hot rolling process and to calculate the corrosion rates between rolled and un-rolled specimens. A 100x6x60 mm rolling specimen was cutted from HSLA slab containing 0.029 wt% Nb, 0.01 wt% N, 0.087 wt% C and some other micro alloying elements. Specimen then reheated at temperature of approximately 1200 0C then soaked in 60 mins. Specimens then rolled using 20 ton rolling machines and slowly cooled to room temperature at about 6.670C/min. Metallographic technique was implemented in order to observe the final microstructure. 2% nital etch was used to observe final ferrite size and morphologies while picral used for austenite phase. Grain size was measured using jefferies or planimetric methods according to ASTM E 112. Corrosion test was worked out using salt spray fog test (ASTM B 117). Using 3.5% NaCl with 6.8 pH as a salt solution. The specimens then exposed in the chamber for 48 hours and cleaned using 1000 ml HCl, 20 gr antimony (III) trioxide, dan 60 gr tin (II) chloride dihydrate to remove corrosion products. Specimens then weighed to calculate the corrosion rates using weight loss methods. The results of this experiments show that after hot defromation final ferrite grain size was decreased from 17.2 ± 0.92 µm to 15.4 ± 0.17 µm while corrosion rates increased from 106.82 mpy to 114.45 mpy.

Abstrak :
This book summarizes the results of experimental work on the development of technologies for the manufacture of sour service line pipe steels. It presents the latest theories on the mechanisms of cracking and factors affecting fracture resistance in H2S-containing media of low-alloy pipe steels. The authors propose methods for improving the quality of continuously cast slabs and show the effect of the chemical composition on the microstructure and properties of rolled plates for pipes. Considerable attention is paid to the metallurgical aspects of microstructure formation and its mechanical properties, as well as the enhancement and cracking resistance of sour service sheets under thermomechanical rolling with accelerated cooling. In brief, the book presents a cutting-edge overview of sour service sheet and pipe production.