Abstract: The influence of used work rolls profiling on the quality of hot rolled metal was studied. The defect non-flatness is the main reason for hot rolled metal rejection to second grade at the continuous hot rolling mill 1700 of ArcelorMittal Temirtau JSC. The most optimal among studied profiling is concave profiling with average cumulative value ΣΔ=1.71mm. This is evidenced by the least volume of hot rolled metal, rejected to the second grade due to non-flatness.There were mathematical models developed, forecasting the volume of metal, rolled with the defect non-flatness with definite cumulative profiling of work rolls.
Abstract: During the refurbishment of the hydroelectric generating set A6 on HPP Djerdap 1, for the state analysis and assessment of the level and causes of degradation of the structure of the vertical Kaplan turbine runner guide vane apparatus non-destructive tests and inspections, as well as destructive tests of base material and welded joints, have been carried out after 40 years of service. Results of non-destructive tests performed on welded joints are presented in this paper (magnetic particle and ultrasonic inspection), as well as results of destructive tests of the base material and welded joints (testing of tensile properties, impact testing, metallographic analyses of the structure). A large number of crack type line indications were detected by magnetic particle inspections, while the occurrence of partial penetration in roots of welded joints was detected by ultrasonic inspections, as well as lamellar tearing of the base material. Tensile properties of tested samples taken in longitudinal and transverse direction fulfilled the requirements of the standard with certain deviations, which does not stand for samples taken in z-direction with significantly lower values of contraction of the cross-section than minimum prescribed values, which proves that base material is not resistant to the occurrence of lamellar cracks. Metallographic tests performed on specimens taken from the base material in longitudinal and transverse direction showed that the microstructure is stripe-shaped and ferrite-pearlite with non-metallic inclusions of oxide, sulphide, silicate and aluminate type, while metallographic tests performed on specimens taken from welded joints showed that their microstructure is stripe-shaped and ferrite-pearlite with non-metallic inclusions of oxide type. A large number of micro-and macro-cracks were detected in the microstructure as well. Experimental tests enabled the determination of the causes of occurrence of lamellar tearing in base material and crack type defects in welded joints, while analytical calculation that refers to the stress state enabled integrity of welded structure of the upper ring of the turbine runner guide vane apparatus.
Abstract: Present heat exchangers should ensure very good heat transfer while having as small size, high durability and the optimum performance at low prices. Thus to achieve these goals is used as base material, aluminum in various forms, of which can be made the heat exchangers energetic efficient. Realization of aluminum heat exchangers can be properly with present requirements using the brazing joint elements. Brazing achieved joining with temperature for two base materials using a filler metal with a melting point above 450°C. A properly brazed joint is performed with a metallurgical connection between two or more metals, which is generally as strong as or stronger than the base metal used.
Abstract: Metal materials are subjected to innumerable time-dependent degradation mechanisms when operate in power, petrochemical and refinery plant. These materials are subjected to multiaxial stresses, creep, fatigue, corrosion and abrasion. As a result of service especially at high temperatures and high pressures, can lead to forming cracks, damages or failures. In situation of breakdown in such systems there is a need for weld repair on plant components and repair work can be expensive and time-consuming. Most weld repairs of low alloy steels require high-temperature post weld heat treatment (PWHT); but in certain repairs, however, this is not always possible. Expenses of the repair work could be reduced if the weld repairing is performed on site. Application of the nickel based filler metal can be alternative to performing PWHT. These repair welding procedures with Ni based filler metal could be categorized as cold repair welding. Purpose of presented investigation was to compare a repair welding technology with filler austenite material based on Ni and without application of the PWHT, with a classical repair welding procedure with preheating and PWHT and using a filler metal with chemical composition similar to parent metal. Properties comparison of the welded joints obtained by these two repair welding technologies was performed for the Cr-Mo steel (13CrMo4-5) by the metal arc welding procedure with covered electrode (MMA - 111). Weldability analysis by the analytical equations and technological tests for determination of the sensitivity to crack forming for cold and hot cracks by the CTS and Y tests, were performed for both repair welding technologies. Tensile tests, absorbed energies tests, banding tests and hardness measurements were performed on trial joins. Light optical microscopy (LOM) was applied for microstructure analysis. The fracture toughness for both technologies, were estimated by the calculated stress intensity factor KIc and dynamic stress intensity factor KId for weld metal and heat affected zone. All of the obtained results were analyzed and discussed. It was concluded that repair welding technology with Ni base filler material without PWHT, enables welded joints without the appearance of cracks, with a good mechanical properties, slightly higher hardness in the HAZ, but with lower expenses compared to standard repair welding technology. In applying this technology in emergency welding repairing on-site, on the equipment and industrial facilities with high security requirements, inspection using non destructive technique has to be frequently applied compared to standard procedures.
Abstract: Submerged arc welding is the most applicable and productive procedure when thick sections have to be welded. Nevertheless, the manufacturers of pressure vessels, pipelines, ships and offshore structures keep on looking for new and modern design solutions of equipments and technologies which should lead to increase of welding process productivity. For instance, the longitudinal welds of pipelines are, mostly, performed by submerged arc welding procedure with multiple arcs and/or multi-wires, such as twin, tandem or twin-tandem, in order to increase the process productivity. However, achievement of optimal mechanical properties of the welded joint should remain the most important quality criteria. It is well known that dependence of the mechanical and metallurgical changes on heat transfer plays a major role in obtaining of safe welded structures and preserving of their structural integrity. That is why the investigation of heat transfer induced by the welding process is required. Furthermore, setting of distance between thermal sources and its influence on the overlapping phenomenon of temperature fields should be explored when submerged double-arc welding procedure is applied. Three dimensional finite element model of butt welded joint - used for simulation of heat transfer in pipeline steel joint performed by submerged double-arc welding process - is developed and described in this paper. Numerical results and a comparative analysis related to the temperature distribution, thermal history, and temperature variation in cross section of the welded joint at different time steps are discussed. Finally, important conclusions regarding the influence of distance between thermal sources on thermal effects and temperature fields overlapping are drawn.
Abstract: In many countries, in the industrial practice, the hard layers deposition is used to increase the hardness of the components active zones. A viable solution to increase the imposed properties consists in the deposition of amorphous layers by thermal spraying. Ferroalloy powders were deposited by plasma jet thermal spraying on aluminium substrates in order to increase the hardness. By plasma jet thermal spraying of Fe-B, Fe-Ni-B and Fe-Cr-Mn-Mo-W-B-P-Si powders on aluminum supports, have been obtained hard layers having the thickness between 72 μm and 86 μm, and granular structures made from α solid solutions, fine particles of specific oxides and complex particles of Fe-B, Fe-B-Si, Fe-Cr, Fe-W-Mo and Fe-P. The measured hardness had the values between 383 and 391 HV1 for the deposited layers made from powders type Fe-B, the values between 410 and 420 HV1 for the deposited layers made from powders type Fe-Ni-B, and the values between 448 and 475 HV1 for the deposited layers made from powders type Fe-Cr-Mn-Mo-W-B-P-Si. No defects, such as cracks or microcracks, have been observed on the hard layers surfaces deposited by plasma jet thermal spraying.
Abstract: Thermal spraying is composed of a group of processes in order to obtain thin films, where fine powders, metallic or nonmetallic, will be deposited in molten or semi-molten state to form a coating layer with the properties required for use. Few layers of stainless steel on usual steel substrates were deposited through thermal spraying deposition in different conditions. As anchor layer a nickel thin film was used between substrate and external layer. The materials surface was analyzed through scanning electrons technique using a VegaTescan LMH II microscope. Thermal metal spraying in electric arc was performed at different working distances which influenced the surface roughness of the deposited layers. To highlight these issues, the parameter of roughness (Rz) and (Ra) measurements were made of the corresponding obtained surfaces. Due to the fact that macroscopically it was noted an increased roughness, it was necessary that the experimental investigations to be conducted on a Taylor-Hobson equipment, model FormTaly Surf 50 (AMTEK, USA).
Abstract: In the welding process of metals, two materials are joined by a filler material with low melting point (below 450 °C), also below the melting point of materials to be joined. The braze-welding filler material has a melting point over 450 °C to 1000 °C. Filler material is distributed between two surfaces of the joint by capillary action close, the blended material is applied on an electrode specially manufactured and intended operation. This paper proposes an analyze of the techniques, feathers, technology requirements, process gaseous, materials (standard data base) and conditions used in braze-welding processes. The secret of solder bonding and weld seems to be the opening that supposes to be small. Two methods are proposed and analyzed for welding process based on braze welding. Scanning electrons microscope and EDAX detector were used to characterize the weld line by micro-structural and chemical point of view. The microstructure analysis concentrated on the weld line area presents reduced dimensional variation and a modification of the materials surface smoothness. Chemical elements distribution exhibits an increase of carbon percentage on the weld line and a decrease of iron in the same time and area.
Abstract: With this article, the authors present a number of technological characteristics determined for a dual-phase steel with 0.09% C and 1.90% Mn. This steel was obtained through intercritical quenching: heating at 740, 780 and 820 °C, maintaining for 30 minutes and then cooling in water, oil, oil in magnetic field of direct current (DC) and oil in ultrasonic field. It was determined the degree of cold upsetting, the ultimate tensile strength of the resistance butt welded joints and the cutting property based on the study of cutting forces and surface roughness; it was analyzed the influence of heat treatment parameters (heating temperature, quenching medium) and ferrite-martensite structure on these characteristics.