Advanced Materials Research Vol. 1029

Abstract: Abstract. The main aim of this paper is to assess the quality of newly produced, alloyed flux-cored wire with increased thickness of the steel cover compared to traditional according to AWS A5.29 standard, alloyed with Ni and Mo, and designed for welding of fine-grained HSLA steel. Flux-cored wire was produced on a pilot production line that allows calibration of steel band of higher thickness and production of flux-cored wire. Quality assessment of the alloyed flux-cored wire was based on the analysis of the results of tests of mechanical properties and microstructure mainly of the weld metal. Variation of chemical composition and microstructure were analyzed along weld metal (for each welding pass) and heat affected zone (HAZ) using SEM and EDS. Based on the results of the quality assessment of flux-cored wire, the conclusions about the feasibility of industrial application of selected metallurgical grade of flux-cored wire designed for welding of fine-grain HSLA steel were presented.

Abstract: In this paper research elements regarding the effect of water pressure variation on cut surfaces quality are presented in the field of abrasive water jet cutting of materials hard to process by machining such as austenitic stainless steels, in this case with a thickness of 20 mm. Selection of the optimal cutting process based on technical and economic criteria takes into consideration the type and thickness of the targeted material and also the physical and geometrical quality requirements. The present paper contains experimental research results regarding abrasive water jet cutting of austenitic stainless steel EN 1.4306 (ASTM 304 L) at different values of water pressure. The abrasive material used is Garnet with particle granulation 80 Mesh. By making roughness measurements and hardness examinations of the cut surface an evaluation will be made of the surface quality defining the optimal pressure values.

Abstract: The wider implementation into automotive sector of new materials categorized as Advanced High Strength Steels (AHSS) in order to reduce costs and weight require the development of appropriate joining technologies. The paper presents the results of applying of a new hybid welding process, i.e. Pulsed LASER-(micro)TIG, for realizing overlap joints for Zn-coated AHSS materials. The statistical influence of main hybrid welding process parameters was investigated by means of factorial experimental design and weighted against the shear strength results of the realized joints. The influence of laser pulse peak power, the average welding TIG current and the joint gap was investigated for three types of Zn coated AHSS with different thicknesses. The results revealed that sane joints could be obtained with the new welding process and that the new process is fit to be applied for these materials. Each material did behave different in respect to the investigated process parameters and the results did reveal rather strong interaction between the influence factors (IF), however the joint gap does play an important role in respect to the maximum shear strength of the joint, which could be correlated to the specifics of the laser beam welding of Zn coated steels. The strong interaction between the studied IF imply further study of the new process by including other process parameters.

Abstract: In most of the engineering applications, such as mining, agriculture, metallurgy, the equipments fail due to abrasive wear. Hardfacing is one of the most economical and most widely used methods of improving surface characteristics of engineering equipments (wear, corrosion) without changing the bulk properties of the components.Fe-Cr-C hardfacing alloys are well known for their excellent performances under severe wear conditions. The wear behaviour of hardfacing alloys depends on their chemical composition, on the microstructure obtained after welding, of the welding technology, respectively the welding parameters which strongly influence, for example, the dilution with the base material or formation of precipitated hard phases.The aim of this study was to characterize the microstructure of Fe-Cr-C hardfacing alloys and to investigate their abrasive wear behaviour. The research has been carried out using four types of Fe-Cr-C hardfacing alloys (8 12, 16 and 20 % Cr). The alloys were deposited on the low-carbon steel S355 JR by manual arc welding method. The abrasion wear testing was carried out using the Taber Rotary Abraser Equipment. The microstructure characterization and surface analysis were performed using optical microscopy and HV 10 hardness tests.

Abstract: In this study the repair weld simulation of an austenitic steel pipe is performed to measure the residual stresses caused by the welding. The simulation consists of three work tasks. First the girth welding of the pipe is performed on simplified geometries to decrease the calculation time. The next work task is the simulation of the machining of the repair weld excavation, performed in one simulation step. The last task is the simulation of the repair welding. Residual stress measurements are performed on weld repair to provide validation of the simulation performed on the model.

Abstract: High density graphite and silicon carbide powder (alpha phase) were used to obtain joints by Spark Plasma Sintering (SPS) technique. The joining of C/SiC was performed both by direct bonding (DB) and with the aid of a ceramic powder mixture (SiC+5%wt.B₄C) as intermediary joining material. The joints were performed in vacuum at 1900°C under 30 MPa with a dwell time of 3 minutes. The interface structures of the obtained joints were characterized from the structural and mechanical point of view. XRD analysis of both joints have shown only the presence of crystalline phases of SiC and C while the crystalline phase of B₄C was not detected due to its low content (5 wt.%) with a higher degree of amorphization of 9.1% for the junction with interlayer than that of the corresponding junction obtained by DB (5.5%). Interface compositional analyses and SEM images have shown that the process of diffusion bonding was the mechanism both for joining by DB and with a SiC+5wt%B₄C interlayer. The Vickers microhardness and Young Modulus values measured by nanoindentation evidenciated a strong increase of HV values (11 – 14 GPa) at interface for the junction with SiC+B₄C intermediate layer and, as expected, the highest stiffness (180-197 GPa).

Abstract: Reinforced concrete is a material formed by pouring concrete over reinforcement steel bars and wires and sometimes by a polymer that turns by drying in a hard and rigid composite. Welding of steel reinforcement concrete is a relatively difficult operation and with a large amount of work, given by the large number of welds that are needed and when this work is make in site conditions. The most common method of steel reinforcement welding is manual welding with coated electrode. The major disadvantage of this process is low productivity in welding effects on execution time, and the cost of welding. An alternative to manual welding with coated electrode for steel reinforcement welding on site is the welding process with self-shielded tubular wires.The aim of this paper is to determine the mechanical properties of welded reinforcing steel PC 52 with self-shielded wires, using a vibroacustic technique. To validate this method, the results obtained by vibroacoustic signal processing are compared with those determined by the tensile stresses of the same samples.

Abstract: The aim of this paper is the development and validation of a vibroacustic technique to welding defects detection, especially for welded thin plate structures. In welded structures subjected to dynamic cyclic loads may appear and propagate fatigue cracks due to local structural damage. These cracks may initiate due to the technological parameters used in welding process, or due to environmental operating conditions. By the means of Finite Element Method (FEM), the natural frequencies and shape modes of welded stainless steel specimens are determined. The analysis is carried out in undamaged condition as well as damaged one, after artificially induced damages. The experimental measurement of the vibroacustic response is carried out by using a condenser microphone, which is suitable for high-fidelity acoustic measurements in the frequency range of 40 – 18.000 Hz. The vibration responses of the welded specimens, in free-free conditions, are carried out using algorithms based on Fast Fourier Transform and Prony’s series. The results are compared to modal parameters estimated using FE Analysis and with natural frequencies computed by Euler-Bernoulli theory.

Abstract: The performances, qualities and extraordinary development potential of the friction stir welding process (FSW) are well known in the world, both in the scientific and industrial areas. The innovative technical developments, based on the principle of the FSW process, conducted at ISIM Timisoara, as well as the results obtained so far have put the foundation for initiating a new method for bonding of materials, namely friction stir soldering. The principle of the new soldering process is based on important features of the FSW process. The paper presents the results of a program of experiments, which had as its main objective checking whether the new proposed soldering process is viable and applicable. Positive results were obtained by the soldering tests of copper (Cu99), brass (CuZn39Pb2) and steel (S235). Promoting this new environmentally friendly process of soldering is beneficial, because it complies with the current trends worldwide regarding both the environment and health.

Abstract: An experimental research regarding the effects of artificial ageing by UV exposure on the tensile properties of a plastic coated composite material with fabric inserts, used mainly in the production of truck covers is presented in this paper. For the purpose of artificial ageing, the authors designed and built at ISIM Timisoara an original equipment with high performance UV lamps, adjustable geometry and forced cooling system. Defects of different sized were created in the aged and not aged specimens in order to simulate potential imperfections that appear during the joining process of these materials. The influence of artificial ageing with 24h and 48h exposure and imperfection size is highlighted by comparative analysis of the results obtained from the tensile tests that were carried out on all specimens. The results are further compared to the tensile properties of aged and not aged welded specimens, obtained using high frequency current and hot air welding methods. The results show clear correlation between the imperfection size and the maximum tensile force and the elongation at break respectively. It is concluded however that further testing is necessary in the specially built equipment in order to properly describe the effect of accelerated artificial ageing by UV exposure on the tensile properties of plastic coated composite materials with fabric inserts.