Influence of pre-and post-weld heating on weldability of modified 9Cr-1Mo(V-Nb) steel pipe under shielded metal arc and tungsten inert gas welding processes P. K. Ghosh and U. SinghWelding of modified 9Cr-1Mo(V-Nb) steel pipes has been carried out via shielded metal arc (SMA) and tungsten inert gas (TIG) welding processes. The weld joints have been produced using different preheating temperatures, followed by post-weld heat treatment (PWHT) at various temperatures. The microstructures of the weld and of the heat affected zone (HAZ) of the weld joints have been studied under the optical microscope and correlated with the preheating and PWHT. The average hardness of the weld and different regions of the HAZ, and tensile properties of the weld joints have also been studied and correlated with the preheating and PWHT. The tensile properties of the SMA and TIG weld joints produced using preheating and PWHT at various temperatures are compared and correlated with their microstructures. It is noted that a comparatively high preheating temperature of the order of 573 K is beneficial, and PWHT is necessary to reduce the susceptibility to cold cracking of weld joints of the present steel. The PWHT at 1123 K enhances ductility to fracture, but decreases the tensile strength of the base material, causing fracture of both the SMA and TIG weld joints from this region close to the HAZ. The tensile properties of SMA welds are found to be superior to those of the TIG welds, especially for PWHT at temperatures up to 1023 K. STWJ/403Extruded modified 9Cr-1Mo(V-Nb) steel pipes of outer diameter and wall thickness of the order of 50 and 6 mm respectively were welded via SMA and TIG welding processes. For both welding processes the root pass was carried out via autogenous TIG welding. The pipes, in sections of length 105 mm, were welded after an edge preparation to form a weld groove as shown schematically in Fig. 1. Before welding the sections of pipe were precisely matched with no root gap and held by a tack weld, followed by thorough cleaning of the weld groove by wire brushing. The job was held horizontally in a centring chuck of a stepless rotating table and a suitable fixture was arranged

This paper reports the results of a systematic investigation of residual stresses as a function of welding speed in a set of Ti-6Al-4V friction stir welds. The investigation focuses on residual stress but links these data with microstructural information derived from micrographs and hardness measurements as well as mechanical testing results. Residual stresses were determined using energy dispersive synchrotron X-ray diffraction, which allows phase specific stresses to be distinguished. The data presented in this paper demonstrate that welds with high tensile properties can be obtained, which also have relatively low peak tensile residual stress values of y30% of the tensile strength. The data also show a clear correlation between heat input and the width of the residual stress profile. IntroductionTi-6Al-4V is an alpha-beta titanium alloy that offers a good combination of low density, high strength and excellent corrosion resistance, and has high biocompatibility. It is widely used in the aerospace sector, in high performance automotive parts, in chemical industries and in the manufacture of implantable medical devices and sensors, and accounts for more than 50% of all titanium alloy usage.While fusion welding techniques can be readily applied to Ti-6Al-4V alloys, their relatively poor thermal conductivity can cause problems through the effects of a high thermal gradient on residual stress, distortion and microstructural modification. Titanium alloys are also sensitive to the presence during welding of contaminants such as hydrogen, oxygen, iron, nitrogen and carbon, which can lead to porosity and hard inclusions. 1 Some difficulties are avoided by welding under inert gas shielded conditions and appropriate measures to avoid cross-contamination from steel manufacturing processes, e.g. a dedicated clean area for titanium.The development of solid state welding processes, such as friction stir welding (FSW), which are performed at reduced peak temperatures, offers the potential to reduce distortion and achieve lower residual stress values. Solid state stirring processes with their associated recrystallisation also lead to generally favourable microstructural modification, e.g. fine equiaxed grains in the weld nugget. The advantages of friction welding processes, in terms of weld preparation and post-weld dressing, microstructure and mechanical performance, have therefore led to significant interest in their application to certain high technology industrial sectors, e.g. transportation. [2][3][4][5] The focus of the present paper is to identify process parameters that give good tensile properties relative to parent plate values along with low levels of residual stress and hence which would give good static and dynamic performance in service. To this end, FS butt welds were made in 3 mm Ti-6Al-4V plate at five different tool travel speeds, ranging from 45 to 165 mm min 21 with a constant tool rotational speed of 550 rev min 21 , and the residual stresses were investigated non-destructively using synchrotron X-ray dif...

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Undoped nanostructured tin oxide (SnO(2)) arrays were prepared on oxidized Si substrates by nanosecond pulsed laser interference irradiation for hydrogen gas sensing applications. Scanning electron microscopy (SEM), in combination with Atomic Force Microscopy (AFM), showed that the SnO(2) surface consisted of periodic features of ∼130 nm width, ∼228 nm spacing, an average height of ∼8 nm along the periodicity and tens of microns length. The SnO(2) nanostructured arrays and precursor thin films were tested by cyclic exposure under dynamic conditions of hydrogen in the concentration range of 300-9000 ppm. The observed electrical response of SnO(2) towards hydrogen at low concentrations and room temperature drastically improved in the nanostructured array as compared to the thin film. The results suggest that this method to fabricate SnO(2) nanostructured arrays has the potential to produce nanodevices that have ultra-low detection limits, and fast response and recovery times, which are suited for practical hydrogen sensing applications.