Ramazan Kaçar

Mechanical Properties of Laser Welded 2205 Duplex Stainless Steel

Abstract Duplex stainless steel is widely used in the oil, chemical industry and to a lesser extent in the medical industry, because of the high mechanical properties, corrosion resistance and good weldability. In this study, AISI 2205 (22Cr5Ni3Mo) duplex stainless steel samples were joined using the CO2 laser beam welding method. In order to determine the mechanical properties of the welded joints, tensile tests were applied and the hardness of the welded sample was measured on the cross-section. The microstructure characterization of welded samples was also carried out using optical microscopy, scanning electron microscopy and X-ray diffraction analysis. Although, the mechanical properties of welded samples were found acceptable, the final microstructure of the welded metal and the heat affected zone (HAZ) were significantly affected by the ferrite phase due to the low heat input that caused high cooling rates, respectively.

The effect of CO2 laser beam welded AISI 316L austenitic stainless steel on the viability of fibroblast cells, in vitro

It has been determined by the literature research that there is no clinical study on the in vivo and in vitro interaction of the cells with the laser beam welded joints of AISI 316L biomaterial. It is used as a prosthesis and implant material and that has adequate mechanical properties and corrosion resistance characteristics. Therefore, the interaction of the CO2 laser beam welded samples and samples of the base metal of AISI 316L austenitic stainless steel with L929 fibroblast cells as an element of connective tissue under in vitro conditions has been studied. To study the effect of the base metal and the laser welded test specimens on the viability of the fibroblast cells that act as an element of connective tissues in the body, they were kept in DMEMF-12 medium for 7, 14, 28 days and 18 months. The viability study was experimentally studied using the MTT method for 7, 14, 28 days. In addition, the direct interaction of the fibroblast cells seeded on 6 different plates with the samples was examined with an inverted microscope. The MTT cell viability experiment was repeated on the cells that were in contact with the samples. The statistical relationship was analyzed using a Tukey test for the variance with the GraphPad statistics software. The data regarding metallic ion release were identified with the ICP-MS method after the laser welded and main material samples were kept in cell culture medium for 18 months. The cell viability of the laser welded sample has been detected to be higher than that of the base metal and the control based on 7th day data. However, the laser welded samples viability of the fibroblast cells has diminished by time during the test period of 14 and 28 days and base metal shows better viability when compared to the laser welded samples. On the other hand, the base metal and the laser welded sample show better cell viability effect when compared to the control group. According to the ICP-MS results of the main material and laser welded samples which were kept in the cell culture medium for 18 months, it was determined that the Fe, Ni and Cr ion concentration released to the cell culture medium from the laser welded test sample was less than that of the main material.

Effect of Quenching Rate and Pre-strain on the Strain Ageing Behaviors of 7075 Aluminum Alloys

The mechanical properties of aluminum alloys are strongly dependent on the thermo-mechanical process so, the strain ageing behavior of 7075 Al-alloy was investigated in this study. A set of test pieces was solution heat treated at 480 °C for 2 h, water quenched (SHTWQ) then pre-strained for 8% in tension. The test samples were aged at 140 °C for 0.5, 1, 2, 3, 4, 6, 8, 10, 12, 24, 48, 72 and 96 h in a furnace. The other set of test samples were solution heat treated at 480 °C for 2 h, quenched in sand (SHTSQ) then pre-strained for 8% in tension. They were also aged at 140 °C for same intervals. The effect of strain ageing, on the mechanical properties of Al-alloy, was investigated by mean of hardness, and tensile tests. The results shown that, the quenching rate after solution heat treatment, ageing time and temperature, as well as pre-strain, play a very important role in the precipitation-hardening associated with ageing process of the 7075 Al-alloy.

Optimization of welding parameters for DP600/TRIP800 dissimilar joints

Abstract The widespread application of resistance spot welding in automotive body assemblies has made it mandatory for automotive manufacturers to examine the quality of the welding. A variety of destructive and nondestructive tests are applied and the weld nugget size is examined for inspection for weld quality. Because of the wide variety of welding parameters used in the spot welding, a welding diagram which gives the optimum weldability range for the welded material is required and extensively used. Due to the different chemical, physical and mechanical properties of different materials in dissimilar joints, it is difficult to evaluate the quality of the weld. In this study, the DP600/TRIP800 dissimilar steel couple was joined using resistance spot welding by combining various welding parameters including welding current, welding time and electrode force. The tensile shear test was applied for determining relationship between welding parameters and mechanical properties of weldment. For quality inspection, the weld nugget size and microstructure of welded sample was examined metallographically and the welding diagram dedicated to the optimum weldability range was also developed for dissimilar joints.

HARDOKS400-AISI304 ÇELİK ÇİFTİNİN ELEKTRİK ARK VE MAG KAYNAĞI

Bu calismada asinmaya direncli hardoks celiginin, ostenitik paslanmaz celige elektrik ark kaynak (EAK) ve gaz alti ark kaynak (GMAK) yontemleri ile birlestirilebilirligi incelenmis, kaynak yontemi farkinin birlestirmenin mekanik ozelliklerine ve yapisina etkisi arastirilmistir. Standartlara uygun V kaynak agzi acilan HARDOKS 400–AISI 304 celik cifti EAK ve GMAK yontemleriyle cok pasolu olarak, yerde yatayda alin alina birlestirilmistir. Farkli cins celik birlestirmesinin mekaniksel ozellikleri; cekme, uc nokta egme ve darbe centik testi ile belirlenmistir. Ilave olarak birlestirmenin kesitinde sertlik olcumu ve mikroyapi incelemesi de gerceklestirilmistir. Elde edilen bulgulara gore; EAK yontemine gore GMAK yontemiyle birlestirilen numunelerin mekanik ozelliklerinin daha iyi oldugu tespit edilmistir.

Effect of static strain aging on the fatigue behavior of S275JRC steel

Abstract In this study, the effect of static strain aging on the fatigue behavior of a mild steel (S275JRC) was evaluated. For this purpose, the 5 % prestrained mild steel was aged at a temperature of 160 °C for different intervals. The aging behavior was determined primarily for the as-received (AR) as well as in the homogenization and normalizing heat treated (H+N heat treated) condition. The yield stresses before and after aging process as well as the hardness values of the aged steels were measured for the assessment of the strain aging progress. The dynamic mechanical behavior of strain aged samples was also determined by fatigue test under the dynamic loads. An increase in the yield strength due to strain aging and hardness induced improvement in fatigue strength of the steel were observed.

LAZER KAYNAĞI İLE BİRLEŞTİRİLEN AISI 2205 DUBLEKS PASLANMAZ ÇELİĞİN MEKANİK VE MİKROYAPI ÖZELLİKLERİNİN İNCELENMESİ

Bu calismada, AISI 2205 dubleks paslanmaz celik levhalar CO 2 lazer isini kaynak yontemiyle %50 Ar + %50 He gaz korumali ortamda, 4000W lazer gucuyle ve 90cm/dk kaynak hiziyla birlestirilmistir. Kaynakli birlestirmelerin mekanik ozelliklerini belirleyebilmek icin cekme ve centik darbe testleri uygulanmistir. Kaynakli baglantinin sertlik olcumu kaynak yonune dik kesitten gerceklestirilmistir. Mikroyapi karakteristikleri ise Optik mikroskop, Taramali Elektron Mikroskobu (SEM), Enerji Dagilimli X-Isini Spektroskopisi (EDS) ve XRD vasitasiyla incelenmistir. Sonuc olarak, CO 2 lazer kaynak yontemi ile birlestirilen dubleks paslanmaz celik kaynak metali ve isi tesiri altindaki bolgenin (ITAB) dusuk isi girdisine bagli yuksek soguma oranindan etkilenerek final yapisinin ferrit lehine degistigi tespit edilmistir. Kaynakli birlestirmenin mekanik ozellikleri kabul edilebilir degerlerde bulunmustur.

AISI 420 MARTENZİTİK PASLANMAZ ÇELİĞİN CO2 LAZER IŞINI KAYNAK YÖNTEMİYLE KAYNAK KABİLİYETİNİN ARAŞTIRILMASI

Bu calismada, temin edildigi ve isil islem uygulanmis sekliyle CO 2 lazer kaynak yontemiyle birlestirilen AISI 420 martenzitik paslanmaz celigin mekanik ve metalurjik ozellikleri arastirilmistir. Calisma sonucunda temin edildigi sekliyle birlestirilen numunelerin istenilen mekanik ozellikleri sergilemedigi belirlenmistir. Kaynak oncesi on tav ve kaynak sonrasi gerilme giderme isil islemi uygulanmis birlestirmelerin yapisindaki martenzitin temperlenmesi sonucu ozellikle ITAB ve kaynak metalinde mikrocatlak yayiniminin engellenmesi sonucunda istenilen mekanik ozellikler elde edilmistir.

Effect of Post Weld Heat Treatment Process on Microstructure and Mechanical Properties of Friction Welded Dissimilar Drill Pipe

In this study, N80-42CrMo4 dissimilar drill pipes were welded by a roto-friction welding machine. A set of welded samples were tested as-welded condition. Another set of welded samples were post weld heat treated (stress relief annealing) at the temperature of 600 °C, for 20 min. and then tested. The microstructures of the as-welded and stress relief annealed samples were examined by optical microscope and SEM. The properties of the all welded samples were determined by hardness measurement, tension and V notch-impact tests. The high hardness especially in the weld interface resulted in low toughness. As a conclusion, the stress relief annealing treatment caused a little decrease in yield strength and ultimate tensile strength, but increase in the elongation. The ductility of samples also increased after annealing treatment which is very important for static and dynamic loads.