5086-h32 alüminyum alaşımında kaynaklama parametrelerine sıcak çatlama hassasiyetinin mvt metodu ile belirlenmesi

Hot cracking is a serious problem that encounters during welding of aluminium-magnesium alloys. In the present study, solidification and liquation type of hot cracks in weld metal and the heat-affected zones of 5086-H32 aluminium alloy were investigated by using Modified Varestraint Test (MVT) with TIG-AC and TIG-DC welding. With determining the size, type and number of cracks, a relation was established between welding line energy and strain on the hot crack formation. This information was used to determine the hot crack safe parameter ranges. The hot cracking tendency as a function of applied parameters were discussed in the frame of temperature fields around the moving heat source. Moreover, the characteristic hot crack locations on the 5086-H32 MVT specimens were generalized. The results of the study indicated that the increase in line energy and strain increased the hot cracking tendency of the specified aluminium alloy. In the low line energy range, the main hot cracking mechanism is the solidification cracking which could be overcome by the use of a suitable filler material. At high line energy range, due to the increased amount of interdendritic liquid, the amount of solidification cracking decreases by healing mechanism. However, because of the enlarged-temperature-field around the weld zone, fraction of HAZ cracking increases. The comparison between the hot cracking tendencies in low and high line energies indicates that the low line energy ranges with low augmented strains resulted in hot crack safer parameters.Ph.D. - Doctoral Progra

Effect of Residual Stresses on the Structural Safety of the Butt Welded Structural Steels

Butt welded seams are widely used in steel constructions. The welding conditions, bevel geometry and the weld sequence are decided by considering the material thickness, welding process and the accessibility. Welding operation generates a residual stress state in the joint area depending on the geometry or path of the weld, initial temperature of the material, heat input, clamping conditions, cooling conditions, phase transformations, etc. Design of a product ignoring residual stresses always involves risks for distortion or early failure in the service. In this work, the construction safety measures and the loading safety was discussed based on the surface residual stress distribution in the butt welded joints

Alın Kaynaklı Yapısal Çeliklerdeki Kalıntı Dağılımının Konstrüksiyon Güvenliğine Etkisi

Plakalar arası alın dikişleri konstrüksiyon bağlantısı olarak başvurulan birleştirme türlerinden birisidir. Bu dikişler plaka kalınlığına, kaynak yöntemine ve ulaşılabilirliğe bağlı olarak farklı kaynak ağzı ve paso dizilimi ile kaynak yapılmaktadır. Gerçekleştirilen kaynak işlemi, kaynak dikişi boyunca geometri, ilk sıcaklık, ısı girdisi, tutma koşulları, soğuma koşulları vb faktörlere bağlı olarak bir kalıntı gerilme profili meydana getirmektedir. Bu bildiride MAG kaynağı uygulanmış çok pasolu bir plaka alın birleştirme işlemine ait kalıntı gerilme dağılımı incelenecektir. Takiben konstrüksiyon üzerinde alınması gereken önlemler ve konstrüksiyonun yüklenebilirliği üzerindeki kriterler tartışılacaktır

Hot Cracking Susceptibility of Twin Roll Cast Al-Mg Alloy Welds

The hot cracking susceptibility of two different Al-Mg alloys during welding at various applied strains was investigated. At each strain value, the amount of hot cracking susceptibility increased with increasing magnesium content. Thermal analysis results verified that hot cracking susceptibility indeed call be related to the solidification range. As suggested in the solidification range approach, the results of the present Study confirm that the extent of solidification and liquation cracking depend oil the magnitude of solidification range and the strain imposed during welding. The fracture surfaces of liquation and solidification cracks were investigated with EDS. Liquation crack surfaces were found to have high Mg content whereas solidification crack surfaces revealed iron rich phases. A quench test was designed to observe the effect of mid-plane segregation zone. It was observed that high segregation at the mid-section of the alloy having higher magnesium can increase the liquation cracking susceptibility during welding since it decreases the solidus temperature of the intergranullar liquid

Numerical and Experimental Determination of the Residual Stress State in Multipass Welded API 5L X70 Plates*

Residual stres s distributions in multipass welded API SL X70 steel plates were determined by numerical and experimental methods. SYSWELD finite element software was used for numerical simulations. Microstructure variations were also considered for calculation of residual stresses. The continuous cooling transformation diagram was obtained via JMatPro software. The results showed that residual stress distribution is sensitive to number of weld passes, and microstructure changes. The simulation results were compared with those obtained by Magnetic Barkhausen Noise measurements on the welded plates. Simulation and experimental results gave qualitatively similar tendencies for the variation of the residual stress state

Numerical and Experimental Determination of the Residual Stress State in Multipass Welded API 5L X70 Plates

Residual stress distributions in multipass welded API 5L X70 steel plates were determined by numerical and experimental methods. SYSWELD finite element software was used for numerical simulations. Microstructure variations were also considered for calculation of residual stresses. The continuous cooling transformation diagram was obtained via JMatPro software. The results showed that residual stress distribution is sensitive to number of weld passes, and microstructure changes. The simulation results were compared with those obtained by Magnetic Barkhausen Noise measurements on the welded plates. Simulation and experimental results gave qualitatively similar tendencies for the variation of the residual stress state

S235 Çeliğinin MAG Köşe Kaynağında Farklı Sabitleme Noktalarına Bağlı Gelişen Çarpılma Eğilimlerinin Sonlu Elemanlar Yöntemi ile Tahmin Edilmesi

Bu çalışmada, S235 yapı çeliği plakalarına uygulanan MAG köşe kaynağı işlemi esnasında kullanılan sabitleme sisteminin yapıda meydana gelen deformasyon eğilimi üzerindeki etkisi incelenmiş ve deformasyonun önceden tayin edilebilirliği tartışılmıştır. Uygulanan sabitleme düzeninin yapıda kapladığı hangi faktörlere bağlı olduğu anlaşılmaya çalışılmıştır. Farklı sabitleme sistemleri kullanılarak MAG kaynağına tabi tutulan S235 tipi çelik plakalarda meydana gelecek olan deformasyon, “Weld Planner” yazılımı kullanılarak sonlu elemanlar yöntemiyle bilgisayar ortamında hesaplanmış, elde edilen sonuçlar gerçek deformasyon değerleriyle karşılaştırılarak doğrulanmaya çalışılmıştır.In this study, effect of clamping system on the deformation tendency of MAG fillet welded S235 structural steel plates was isvestigated and the efficiency of the software based calculation method was discussed. Effects of size of the each clamping area, number and location of clamps were studied. The computer based calculatios were performed by using finite element based “Weld Planner” software. Simulated results were compared and validated by real weld experiments

Investigating the effects of subsequent weld passes on surface residual stresses in steel weld merits by Magnetic Barkhausen Noise technique

Variations of surface residual stresses with subsequent weld passes were investigated in API 5L X70 steel plates by the magnetic barkhausen noise (MBN) technique. The plates were welded by applying a number of different passes under fully clamped conditions. After each weld pass, the MBN signal and hardness distributions on the front and back surfaces of the plates were measured. A specific calibration procedure and setup were used for conversion of the MBN signals into elastic stress values. The results were analyzed by considering microstructure investigations and hardness measurements, and then the results were compared with the results of X-ray diffraction measurements. MBN measurement after appropriate calibration seems to be a good candidate for rapid nondestructive monitoring of the variation of surface residual stresses in welded components. Moreover, it might provide critical data for computer simulation and weld process design, leading to a higher performance and longer life in service by controlling the residual stress state

Effect of weld repair on microstructure and mechanical properties of API 5LX65 steel

Weld repair is a common technique to remove defects in the weldments. However, particularly in the high strength low alloy steels (HSLA), heat input during weld repair causes complex changes in the microstructure and mechanical properties. In this study, the influences of repeated heat input and thermal cycle upon repair weld on the microstructure and mechanical properties of the welded joints of API 5L X65 were investigated via optical microscopy, scanning electron microscopy; Charpy-V impact, Vickers hardness, and tension tests. The results were analyzed and evaluated for enhancement of strength and toughness of the repaired pipeline steels