No abstract

Bu çalışmada; doğalgaz ve petrol boru hatlarında kullanılan API 5L X65 kalitesindeki çelik malzemeler, MAG kaynak yöntemiyle özlü rutil tel ile birleştirilmiştir. Birleştirmelerden alınan numunelerin mikroyapı ve mekanik özelliklere etkileri incelenmiştir. Deneysel çalışmalarda makro ve mikroyapısal olarak, ana malzeme, ITAB) ve kaynak metali incelenmiş, oluşan yapıların tipik kaynak işlem özelliklerine sahip yapılar olduğu tespit edilmiştir. Çekme, çentik darbe, sertlik ve eğme testlerinde kaynak işlemi kusursuz özellikler sergilemiştir. Elde edilen tüm sonuçlar, kaynak işleminin mikroyapısal ve mekanik olarak kendinden beklenen lokal özellikleri karşılayabilecek bir tavır sergilediğini göstermiştir.

Bu çalışmada; doğalgaz ve petrol boru hatlarında kullanılan API 5L X65 kalitesindeki çelik malzemeler, elektrik ark kaynak yöntemiyle, bazik elektrod kullanılarak birleştirilmiştir. Birleştirmelerden alınan numunelere makroyapımikroyapı analizleri ve çekme, % uzama, kırılma tokluğu, eğme ve mikrosertlik ölçümleri yapılmıştır. Deneysel çalışmalarda makro ve mikroyapısal olarak, ana malzeme, ITAB ve kaynak metali incelenmiştir. Mekanik incelemelerde ise, kaynak işleminin mekanik performansı irdelenmiştir. Çekme, çentik darbe, sertlik ve eğme testlerinde kaynak işlemi başarılı bir performans göstermiştir. Çekme testlerinde ortalama 579MPa maksimum çekme kuvveti ve % 22 uzama ile kopma ana malzemelerde gerçekleşerek, çalışmada istenilen mukavemet özelliklerinin sağlandığı tespit edilmiştir. 0°C'de yapılan çentik-darbe deneylerinde ise ortalama 74 Joule' lük bir kırılma tokluğu enerjisi ölçülmüştür. Sertlik ölçümlerinde en yüksek sertlik değeri kaynak metalinde 310 HV olarak ölçülürken, en düşük değer ise yaklaşık 205 HV olarak ITAB'da ölçülmüştür. Eğme testlerinde ise kaynaklı bölgede herhangi bir hataya rastlanmamıştır. Sonuçlar incelendiğinde; kaynak işleminin kendinden beklenen özellikleri sergileyerek, başarılı bir mekanik tavır gösterdiği görülmüştür.

In this study, effects of holding in liquid nitrogen and cryogenic methods applied onto the SAE 4140 steel were empirically investigated. In this context, austempering, holding in liquid nitrogen, the conventional cryogenic process and tempering processes were applied in different orders and combinations. The temperature of the samples to be tempered in liquid nitrogen was decreased from room temperature to-196°C at the average rate of 1.6°C/min and held at this temperature for 24 h. The temperature of the samples to undergo the traditional cryogenic process was decreased from room temperature to-140°C at a constant rate of 2°C/min and held at this temperature for 24 h. After a microhardness analysis and tensile tests, it was observed that the toughness was increased without the hardness being changed during both cooling processes carried out after austempering processes. The most obvious improvement in terms of toughness was observed on the samples, to which austempering was applied, exibiting an increase of 32.83 %, followed by the samples undergoing the cryogenic process and, lastly, the ones undergoing the tempering process. The largest increase in the tensile strength also occurred in the samples subjected to austempering, exhibiting a 66 N/mm 2 improvement. In terms of the properties investigated during this study, it was seen that the process of holding steel in liquid nitrogen could consitute an alternative to the cryogenic process using different rates.

In this experimental study, composite samples containing silicon are produced with powder metallurgy technique by sintering under argon atmosphere. The effect of cutting speeds, feed rates and different cutting tool types on cutting forces and surface roughness are investigated in the face milling operation of silicon carbide particle reinforced aluminium metal matrix composites. Machining operations are conducted using coated and uncoated tools. Main cutting force (F x ) and surface roughness (Ra) are measured for at four different cutting speeds (300, 350, 400 and 450 m/min) and three different feed rates (0.1, 0.15, 0.20 mm/tooth) and two depth of cut (0.5, 1 mm). As a result of experimental evaluation for coated and uncoated tools, main cutting force increased with increasing feed rate and depth of cut whereas, it is decreased significantly by higher cutting speed. On the other hand, Al-SiC produces the worst surface finish with increasing feed rate and depth of cut in the uncoated tools whereas, the surface roughness in the coated tools are decreased under the same cutting conditions. The best surface roughness is obtained with increasing cutting speed for both uncoated and coated tools.Key words: Metal matrix composite, face milling, machining, cutting forces, surface roughness. INTRODUCIONRecently, the reinforced metal matrix composites (MMCs) are widely used in aerospace, automotive, electronic and medical industries. Silicon carbide (SiC) and alumina (Al 2 O 3 ) as the matrix phase in the production of metal matrix composites are used the popular reinforcement in the literature (Rohatgi, 1990;Monaghan, 1994;El-Gallab and Sklad, 1998;Koczak et al., 1993). Net shaping and good surface finish of particulate metal matrix composites (PMMCs) are very important for machining operations. However, PMMCs show poor machinability because of the fact that their reinforcements cause serious abrasive tool wear and the worst surface finish during machining