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Östenitik paslanmaz çelikler, düşük sıcaklıklarda bile çok iyi şekillendirilebilirlik, iyi mekanik özellikler ve yüksek korozyon direnci gibi özelliklere sahiptir. Bunun sonucu, tüm paslanmaz çelikler içerisinde en fazla üretilen ve kullanılan türdür. Ancak bu çeliklerin kaynağında birçok problem söz konusudur. Bunların başında, krom karbür oluşumu sonucu ısıdan etkilenmiş bölgede korozyon direncinin düşmesi gelmektedir. Bu çalışma, gaz tungsten ark kaynağı yöntemi ile AISI 316L levhalarda kaynak hatası içermeyen bağlantıların üretilmesini amaçlamaktadır. Bu amaca yönelik, 10 mm kalınlığında AISI 316L levhalar, 2,4 mm çapında ER316L dolgu teli kullanılarak beş pasoda kaynaklanmıştır. Elde edilen kaynaklı levhanın mikroyapısal ve mekanik özelliklerini araştırmak ve karakterize etmek için çekme testi yanında detaylı optik mikroskop çalışmaları ve mikro sertlik ölçümleri gerçekleştirilmiştir. Çok pasolu kaynağın mikroyapısal değişim üzerindeki etkisi ve dolayısıyla üretilen bağlantının mekanik davranışını nasıl etkilediği de araştırılmıştır. Yapılan çalışma sonucunda, kaynak bölgesinde herhangi bir hata gözlenmemiş olup, kaynaklı bağlantının çekme mukavemeti ve uzama açısından sırası ile %104 ve %58 lik bir kaynak performansı sergilediği tespit edilmiştir. Ayrıca, ergime bölgesinde ve ısıdan etkilenen bölgede sertlik artışı gözlemlenmiştir.

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In this study, 316L austenitic stainless samples were applied low temperature (400-500 °C) plasma nitriding to improve mecanical and material properies on the surface of material without deterioration of its corosion properties. Experiments could be seperate two groups. Some of nitridation were performed at %10 N2 - %90 H2 gas mixture and 450 °C nitridation temperature with a duration of 15, 30, 60, 120 and 240 minutes separately. In other group, the nitridation process is on only one hour. Three different gas mixtures of %5, %10 and %25 N2 were used at 400, 450 and 500 °C. Improvement of some properties were observed. [ABSTRACT FROM AUTHOR]

In this study, AISI 430 ferritic stainless steel and AISI 304 austenitic stainless steel sheets with 3 mm thickness were joined by Tungsten Inert Gas (TIG), Metal Inert Gas (MIG) and shielded metal arc welding methods. Mechanical properties of the welded samples were investigated in terms of tensile strength, notch impact strength, microhardness and micro structure. The results of the tensile test indicated that fracture occurred at the HAZ of the ferritic stainless steel side in the all samples. The highest tensile strength in welded samples were obtained in the samples joined with TIG welding. According to the notch impact test, impact energy of the samples joined with TIG and MIG is higher than that of the samples joined with shielded metal arc welding. Microhardness test showed that the highest hardness was obtained in the HAZ at the AISI 430 stainless steel for all welding condition used in this work. According to microstructure investigation, it was observed that grain growth occurred in the HAZ of the AISI 430 ferritic stainless steel. [ABSTRACT FROM AUTHOR]

Under the construction of German Mine Hunter Consortium (Abeking&Rasmussen and Lürssen), Istanbul Shipyard/Pendik is building Aydin Class Mine Countermeasures (MCM) Vessels for Turkish Navy. Aydin Class Mine Countermeasures (MCM) Vessels distinct from the other world navies because of their hull made of austenitic stainless steel. Nowadays, German, Italian and Canadian navies use this type of steel for ship hulls. Austenitic stainless steel has many advantages, like resistant to the corrosion of sea water, high yield point and non-magnetic structure. But these metals are having also disadvantages, like poor heat conductivity and high thermal expansivity. These disadvantages create more distortions than normal steels in welding conditions. Fittings of welded structure are very important section in shipbuilding, so geometry of welded structure need to be accurate. For straightening of distortions, flame straightening method is widely using in shipbuilding industry. Nowadays for quality products it is necessary to reduce price. Straightening of distortions via flame straightening method is more time, manpower and material consuming. So improving of straightening of distortions will be beneficial for budget of government. The aim of this thesis is to show benefits of usage of Thermal Tensioning Technique as a method of straightening of distortions for Aydin Class Mine Countermeasures (MCM) Vessels which are built at the Istanbul Shipyard/Pendik. Straightening of distortions via Thermal Tensioning Technique is examined for ship building industry as a preventing method with many academic researches. The stiffened panel made of austenitic stainless steel is used in the experiment of the Strathclyde University/ Scotland. In specific condition under gas protection weld (MIG), thermal camera is used for distribution of heat, thermo couples are used for temperature measurement and laser appliance is used for distortion measurements. This paper focuses on the transient temperature fields created by the large heat inputs from arc welding which is the driving force for distortion in the plates. The use of a thermal imaging camera allows the thermal fields to be viewed on a whole-field basis. The use of a welding rig in this kind of investigation is essential as it allows parameters to be kept constant throughout. The moveable track is controlled by stepper motors such that the travel speed of the weld can be adjusted to a tenth of a millimeter per second. The torch is held static while the plate is pulled along at a constant speed by a series of pulleys and small stepper motors. The welding machine was connected to the computer and so all parameters could be entered via the computer so that all the variables could be controlled. The camera was held in place with scaffolding and the tripod for the camera fixed to a bracket that allowed movement in all directions. The CCD thermal imaging camera used here was the ThermaCam SC500 from FLIR systems. The camera is able to provide thermo graphic images in the infrared spectrum from 3 to 12μm. Following initial tests with austenitic stainless steel plates the amount of background radiation reflected from the plate to the camera was seen to be high. This led to the painting of the plates with a high emissivity, two-part zinc silicate primer made up in two parts. To verify thermal images thermocouples were also present at distances of 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100mm. The laser appliance is used for distortion measurements. All of austenitic stainless steel plates are scanned before welding and again after welding. The data was used to compare the distortion effects under different restraint conditions.… [ABSTRACT FROM AUTHOR]

Copyright of Teknoloji is the property of Engineering Science & Technology, an International Journal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)