Abstract: An experimental investigation on the strain rate sensitivity of die steel (D3) has been presented in this paper at different rates (0.001-2500s-1) of uni-axial compression. Quasi-static tests (0.001s-1) of the material are conducted on universal testing machine (UTM), whereas, the experiments at high strain rates are performed on split Hopkinson pressure bar (SHPB) apparatus. The effects of gauge length of the specimen on the material properties of the material are studied at different strain rates. The material parameters of existing Cowper-Symonds and Johnson-Cook material models are determined and the suitability of the models is examined.
Abstract: Micromachining has been gaining wide importance in today’s industrial and research applications. It represents techniques/ methods to achieve small features (less than 1mm) on varied parts and components. A microcontroller is widely used to control such processes to obtain the desired dimensional accuracy. It is programmed to guide the tool in a controlled path to provide required precision in an advanced manufacturing process. Microcontrollers are cheaper alternatives as compared to servo controllers. They can be coupled with developed experimental setups and further with computers to get micro machined aspects realized in the laboratory. In the current paper, a VMC-850X microprocessor with a 8085 based VMC 8501 control unit was used to machine microchannels on a special optical glass workpiece. Material removal (MR) and tool wear (TW) were measured as the response characteristic, while the variable process parameters were applied voltage, electrolyte concentration and tool speed. The obtained experimental results showed that all the parameters were significant. The applied voltage had 85.58% effect in MR and 66.71% effect in TW study. The FESEM micrograph could provide useful information on material removal mechanism.
Abstract: Abstract: In the present work the effect of different durations of Post Weld Heat Treatment soaking times (0.5,2,10,50 hours) are analyzed on the mechanical and microstructural properties of Cr-Mo alloy steel of ASTM A387 Gr-22,2.25% Cr-1%Mo alloy steel. These are used in high temperature services in steam generation applications, Oil and Gas industries, Thermal and Nuclear power plants etc. The work is focused on different regions of weldment like base metal, HAZ and weld metal to compare and analyze the results obtained in as-welded and different soaking times from hardness test, tensile testing and microstructural examination. Results showed that the hardness varies from weld centre line to base metal and peak hardness was found in the HAZ. The hardness is reduced to large extent when PWHT is done at 50 h. Microstructural changes were observed during different post weld heat treatments and their effect on mechanical properties and best suitable soaking times were reported.
Abstract: Laser beam welding offers various advantages over the other conventional weld processes. In fusion reactor, some critical components with high weld quality are proposed to be fabricated with Laser beam welding. The present paper reports the mechanical properties and micro structural characterization of 8 mm thick SS 316L samples fabricated with high power CO2 Laser welding system. The process parameters of 3.5 kW and speed of 600 mm/min with Argon shielding gas are used. The Laser welded samples are subjected to non destructive testing with X-ray radiography and ultrasonic tests. The welded samples tested have indicated good quality joints with full penetration and no significant porosity and cracks. Further, the samples are subjected to standard mechanical tests namely tensile properties test (UTS), bend test and Impact Fracture test. The Laser weld joints produced better tensile properties as compared to the base metal. In addition, Vickers hardness tests and optical microstructure are studied for the base metal (BM), Heat Affected Zone (HAZ) and weld zone(WZ).
Abstract: In the present paper, Haynes 214 plate of 7mm thick was welded by Gas tungsten arc welding (GTAW) in two passes. The welded plates were subjected to post-weld heat treatment such as direct aging (DA) and solution treatment + aging (STA). The aging cycle was optimized using hardness by generating isothermal aging curve. The weld tensile properties, hardness test, microscopic analysis and fractographic studies were carried out in as-welded condition and at two different post-weld heat treatment conditions. The results show a significant increase in both yield and tensile strength after post weld heat treatment.
Abstract: Bimetallic welds made between ferritic steels and austenitic stainless steels are conventionally fabricated using arc welding procedures such as Tungsten Inert Gas, Metal Inert Gas, Shielded Metal Arc Welding and Submerged Arc Welding. However friction welding provides a new and unique solid state approach for joining many similar and dissimilar materials, which may not be possible to join by other welding techniques available without adding any external filler metal. This approach is mostly used in joining of dissimilar materials. The reason for increased utility being the absence of any external filler material which may otherwise add to the heterogeneity of the weld structure. In this paper, the fabrication and effect of friction welding parameters on mechanical-micro structural changes of bimetallic weld joints has been discussed. An attempt has also been made to relate the effect of friction welding parameters on the peak temperature values taken near faying surface and micro hardness changes measured in various zones of weld.
Abstract: Ti3Al2.5V alloy is lean alpha plus beta titanium alloy having two phase microstructure at room temperature (RT) and has beta transus temperature (Tβ) about 9350C and Ti6Al4V-ELI (extra low interstitials) alloy has two phase structure at RT and has Tβ about 9750C. The samples were electron beam welded (EBW) after the optimization of weld parameters on bead-on plate of 6mm thickness of Ti6Al4V-ELI alloy. The samples were heat treated (solution treated, ST at 9100C for 20 minutes water quenched, WQ and aged at 5100C for 8 hours and air cooled, AC to RT). The specimens were tested to evaluate mechanical properties in as-welded, solution treated and aged conditions. The improvement in the tensile strength was 810 MPa to 897 MPa in as weld to ST conditions, and comparable in STA condition (887 MPa). The improvement in yield strength was 760 MPa to 782 MPa and 848 MPa in as-welded, ST and aged conditions respectively. While there is a decreasing trend in the ductility (%EL) of the joint in three conditions (as weld, ST and STA). In all the specimens evaluated at different heat treated conditions the failure location was within parent Ti3Al2.5V alloy (parent metal away from the weld interface) as confirmed through OM (optical microscopy).
Abstract: Joining of dissimilar metals leading to better material utilization with improved functionality encouraged the research thrust on various dissimilar material joining processes including laser brazing. This papers reports the development of laser brazing joints and their characterization for 3 mm thick Cu sheet with 3 mm thick AISI 316L stainless steel (SS) sheet in butt joint configuration using 63Ag-35.25Cu-1.75Ti active brazing foil as filler metal. Comprehensive experiments were carried out to identify the optimum processing parameters for controlled simultaneous heating of the filler metal and sh-7eets by laser beam resulting in melting of the filler metal without melting Cu and SS sheets. Using this methodology, a number of brazed joints were successfully prepared at different set of processing parameters. The brazed joints were subjected to various non-destructive (visual and dye-penetrant test) and destructive (microscopic examination, energy dispersive spectroscopy, four point bend testing etc.) characterization techniques. The results demonstrated that laser energy per unit length of 100 J/m is threshold limit for feasibility of brazing process for selected metal and thickness combination. Microscopic studies of transverse section of laser brazed joint showed full penetration across the thickness without the melting of parent metals. EDS studies showed the diffusion of filler material (Ag) more towards the Cu sheet as compared to that of SS sheet. Four point bend test showed that the alignment of laser beam-metal joint was critical for the brazing joint strength and improved joint strength was achieved when the beam was at the centre of the brazing joint. A maximum joint strength of 343.7 MPa was achieved for laser power of 550 W at scan speed of 3 mm/min.
Abstract: Weldment characteristics like bead width, bead height, penetration and weldment cross-sectional areas are the factors that contribute the weld quality. Submerged arc welding (SAW) is mostly used to join the heavy structures around the world because of its high deposition rate and good weld quality. The present investigation deals with single pass double side full penetration SAW butt joints with process parameters for minimizing the welding distortions. The plates were without having any edge preparation and welded from both the sides using full factorial design of experiments with process parameters such that full penetration was achieved. The shrinkage forces from both the sides of the joints acted in opposite direction to minimize distortions. The process was modelled using adaptive neuro – fuzzy inference system (ANFIS) technique to predict the effects of process parameters on weldment characteristics and angular distortion of SAW butt joint. The ANFIS model has been developed on the basis of full factorial experimental data. The validation of ANFIS model has been also done for a number of test cases.
Abstract: This paper deals with the development of submerged arc welding wires for longitudinal double submerged arc welded (LDSAW) line pipe weld through transmission electron microscopy (TEM). The experimental procedure in the paper describes the test coupons preparation for submerged arc welding (SAW) with various combinations of wire and flux with varying level of alloying element. Microstructural characterization by transmission electron microscopy has been carried out to establish the desired microstructure in the weld of LDSAW for manufacturing the API-5L X-120M line pipes. The TEM micrographs for shows the lath type ferrite and bainitic type ferrite with high dislocation density. The lath type ferrite and bainitic type ferrite with high dislocation density also have fine precipitates in the ferrite matrix having orientation relationship. The weld metal suitable for X-120M have the microstructure of mainly bainitic and martensitic with high dislocation density and coarse precipitates in the matrix. The bainitic and martensitic microstructure have excellent fracture toughness down to -20 °C at this strength level (X-120M).