A comprehensive study on the microstructure and mechanical properties of arc girth welded joints of spiral welded high strength API X70 steel pipe

In the paper, the effect of welding technology on the microstructure and mechanical properties of girth welded joints was presented. Metallographic examinations based on light microscopy and SEM were conducted on girth welded joints of API X70 steel pipe. Research has shown that microstructure of the heat-affected zone (HAZ) of MMA girth welded joints is not homogeneous and depends on the thermal history of each area during the welding process. Near the fusion line the zone is coarse, and further away there is a fine-grained zone. In the area of root passes the microstructure consists of recrystallized ferrite grains unlike to cap passes where the fine bainitic microstructure can be observed. In the case of MAG girth welded joints, the weld microstructure consists of primary austenite grains. The primary austenite boundaries serve as nucleation sites of ferrite. The microstructure of the HAZ varies continuously from a coarse—to fine-grained microstructure of the base material. The results of mechanical properties of girth welded joints are also presented. The hardness and strength of arc welded joints depend on welding filler materials as well as welding technology. The results of hardness distribution of MMA and MAG girth welded joints confirmed the results of microstructural evaluation

Starzenie naturalne złączy stopów aluminium Al-Zn-Mg-Cu wykonanych metodą zgrzewania tarciowego z mieszaniem materiału

The long term natural aging behavior of friction stir welded aluminum 7136-T76 and 7042 T6 extrusions was investigated. The microstructural characteristics and mechanical properties in the as-welded and six years naturally aged conditions were studied and correlated to a coupled thermal/material flow model of the joining process. Hardness profiles for the 7136 alloy taken along the mid-plane thickness of the workpiece displayed the characteristic W-shape. With natural aging, hardness recovery occurred on both sides of the weld, but the position of the hardness minima, particularly on the advancing side, shifted away from the weld centerline. The hardness profile for the 7042 alloy displayed U-shape in the as-welded condition and W-shape after natural aging. The hardness behavior upon natural aging correlated to the temperature profile developed during welding and the degree to which phase dissolution occurred in the regions adjacent to the stir zone.W artykule przedstawiono wyniki badań dotyczące długoterminowego starzenia naturalnego złączy stopów aluminium 7136-T76 i 7042-T6 wykonanych metodą zgrzewania tarciowego z mieszaniem materiału. Złącza w stanie po zgrzewaniu oraz po 6 latach starzenia naturalnego scharakteryzowano pod względem mikrostrukturalnym oraz mechanicznym. Wyniki badań skorelowano z modelem termicznym i modelem płynięcia materiału podczas zgrzewania. Profil twardości złącza stopu 7136 wykazuje charakterystyczny kształt litery „W”. Starzenie naturalne powoduje wzrost twardości, przy czym minimum twardości, szczególnie po stronie natarcia, odsuwa się od środka złącza. Profil twardości złącza stopu 7042 przyjmuje kształt litery „U” po zgrzewaniu i kształt litery „W” po starzeniu naturalnym. Takie zachowanie twardości po starzeniu naturalnym jest związane z temperaturą podczas procesu zgrzewania oraz stopniem, w jakim rozpuszczają się fazy w obszarach sąsiadujących ze strefą mieszania

Investigations of friction stir welds between 5083 and 7075 aluminum alloys using EBSD and X-ray techniques

Microstructure and texture of the friction stir welded 5083 and 7075 aluminum alloys were characterized by means of the electron backscatter diffraction and X-ray techniques. A complex vortex-like microstructure with distinctive bands of the both joint materials was found in the centre of the weld. The alternating bands filled roughly equiaxed dynamically recrystallized grain volumes. The grain size was slightly smaller in bands of the alloy 7075 than in bands of the alloy 5083. Grains in the thermomechanically affected zone were elongated, especially on the retreating side of the weld (7075 alloy). On the other hand, the grain shape in the heat affected zone was similar to that for the base material

Microstructural and Mechanical Characterization of Electron Beam Welded Joints of High Strength S960QL and Weldox 1300 Steel Grades

The paper shows the results of metallographic examination and mechanical properties of electron beam welded joints of quenched and tempered S960QL and Weldox 1300 steel grades. The aim of this study was to examine the feasibility of producing good quality electron beam welded joints without filler material. Metallographic examination revealed that the concentrated electron beam significantly affects the changes of microstructure in the weld and the adjacent heat affected zone (HAZ) in both steel grades. The microstructure of the welded joints is not homogeneous. The four zones, depending on the distance from the weld face, can be distinguished. Basically, the microstructure of the weld consists of a mixture of martensite and bainite. However, the microstructure of HAZ depends on the distance from the fusion line. It is composed of martensite near the fusion line and a mixture of bainite and ferrite in the vicinity of the base material. Significant differences in mechanical properties of the welded joints were observed. For a butt welded joint of the S960QL steel grade the strength is at the level of the strength of the base material (Rm = 1074 MPa). During the bending test the required angle of 180° was achieved. The impact strength at –40°C was 71,7 J/cm2 . In the case of the Weldox 1300 steel grade butt welded joints exhibit high mechanical properties (Rm = 1470 MPa), however, the plastic properties are on the lower level than for the base material

Erosive Wear of Inconel 625 Alloy Coatings Deposited by CMT Method

The article presents the investigation results concerning the determination of the characteristics of erosive wear caused by the impact of Al2O3 solid particles on the surface of Inconel 625 alloy after plastic working and the same material after weld cladding process using the CMT method. Erosion wear tests were performed at two temperatures: 20°C and 650°C. The erosion tests were conducted using the standard ASTM G76. A jet with a specified abrasive waight was directed to the surface of the tested material at an α impingement angle varied in the range of 30-90° at a velocity imparted to the abrasive by the medium, which was compressed air. The eroded surface was examined using a scanning electron microscope (SEM), while the depths of craters caused by the erosion tests were measured with an optical profilometer. The predominant mechanisms of the formation of mass losses during solid particle erosion were microcutting and microfissuring

Erosive Wear of Inconel 625 Alloy Coatings Deposited by CMT Method

The article presents the investigation results concerning the determination of the characteristics of erosive wear caused by the impact of Al2O3 solid particles on the surface of Inconel 625 alloy after plastic working and the same material after weld cladding process using the CMT method. Erosion wear tests were performed at two temperatures: 20°C and 650°C. The erosion tests were conducted using the standard ASTM G76. A jet with a specified abrasive waight was directed to the surface of the tested material at an α impingement angle varied in the range of 30-90° at a velocity imparted to the abrasive by the medium, which was compressed air. The eroded surface was examined using a scanning electron microscope (SEM), while the depths of craters caused by the erosion tests were measured with an optical profilometer. The predominant mechanisms of the formation of mass losses during solid particle erosion were microcutting and microfissuring

Microstructure of Friction Stir Welded Dissimilar Wrought 2017A and Cast AlSi9Mg Aluminum Alloys

Friction stir welding was applied to join dissimilar aluminum alloys: wrought 2017A and cast AlSi9Mg. The produced weldment was free from cracks and any discontinuities. The weld microstructure was composed of alternating bands of the welded alloys; however, the alloy that was placed on the advancing side (AlSi9Mg) dominated the weld center. The grain size within the particular bands was similar in both alloys. The hardness profile reflected the microstructure formed during welding. The weld microstructure as well as the shape of hardness profile across the weld were justified by numerical simulation of material flow during welding