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The effect of nitrogen concentration in the shielding gas on microstructure and mechanical properties of autogenously plasma arc welded lean duplex Allegheny Ludlum ATI 2003® material was studied. Six single-pass plasma arc butt welds were produced for the evaluation. One weld was performed using 100% argon shielding and backing gas, while the other five utilized varying additions of nitrogen in the shielding and backing gas, from 1 to 5%, with argon as the primary gas. 100% argon was used as the plasma orifice gas for all welds. The coupons were labeled 0 through 5, which correlated with the concentration of nitrogen. The heat input was consistent for each weld and was representative of a typical value for production plasma arc welding of lean duplex stainless steel. Mechanical testing and evaluation was completed in accordance with typical customer requirements and industry standards. Each weldment was tested mechanically and analyzed microstructurally to investigate any correlations with the nitrogen additions in the weld shielding gas. Mechanical tests consisted of transverse and longitudinal tensile testing per ASME 2010 Section II, Part A, SA-370, Charpy impact testing per ASME 2010 Section II, Part A, SA-370 at -40° C, and micro-hardness testing per ASTM E384 with a test force level of 500 grams-force (gf). The microstructural analysis included ferrite testing, utilizing both the Fischer® Ferritescope and PAXit® software, and optical microscopy with focus on austenite formation and morphology, precipitate formation, and grain size comparison. The mechanical tests from this study revealed that only specific coupons met the requirements provided in ASME Boiler and Pressure Vessel Code. The transverse tensile tests revealed that all the coupons met the minimum requirements for the tensile strength of 620 MPa (90 ksi). Conversely, the elongation for each of the coupons except coupon 5, with 5% nitrogen in the shielding gas, fell short of the 25% elongation minimum specified for the base material. Charpy impact tests disqualified coupons 0 through 2, which were unacceptable due to lateral expansions less than the minimum of 0.38 mm (.015 inches) per ASME Section VIII. Vickers micro-hardness testing was found to be optimum and below the ATI 2003® base metal requirement of 293 BHN per ASME Section II, Part A, SA-240. During ferrite testing, both using the Fischer® Ferritescope and the PAXit® software, it was determined that coupons 2 through 5 had optimum ferrite values of between 40 and 60%, for each the fusion zone, HAZ, and base metal. Conversely, Coupons 0 and 1 had values that fell outside this range. Neither secondary austenite precipitation nor formations of detrimental second phases were detected in any of the weld microstructures. In conclusion, 5 percent nitrogen added to the shielding gas had a beneficial effect on autogenously plasma arc welded ATI 2003® Lean Duplex Stainless Steel and resulted in optimum mechanical properties and microstructure of the weldment. Alternatively, autogenous plasma arc welding with 100% argon as the backing, shielding, and orifice gas resulted in unacceptable mechanical properties and an unbalanced ferrite-austenite ratio.
The objective of the research, through both an experimental and a modelling approach, was to determine the parameters controlling the nitrogen level in a weld. A second objective was to study the relationship between the weld microstructure and the corrosion properties. More particularly, the potential interest of microelectrode techniques has been investigated. TIG welding has been investigated through both an experimental and a modelling approach. TIG and A TIG tests have confirmed tnat it is necessary to add nitrogen in the shielding gas in order to prevent nitrogen loss during welding. For duplex stainless steel, 2.5 % nitrogen in the shielding gas is sufficient, whereas for high nitrogen content austenitic stainless steels higher levels are necessary. It has also been shown that, for a given grade, the nitrogen content increases when the penetration increases. Penetration depends on the material composition, with a beneficial effect of surface active elements (0, S, etc.). The model developed was based on the nitrogen exchange between the plasma, the weld pool and the shielding gas. It was first developed to describe nitrogen evolution during a stationary arc situation. The results were in good agreement with experiments. The model was then adapted to the case of welding with an active flux. An attempt was made to describe the traveling arc situation. However, some improvements are still necessary. Pitting corrosion tests have confirmed the influence of nitrogen content on the corrosion sensitivity of TIG welds. Microelectrode techniques have been used to characterise the local corrosion behaviour of welds. It has been shown that the scanning vibrating electrode technique was of limited utility to study corrosion resistance of highly alloyed stainless steels. More promising results have been obtained with microcapillary technique which make local electrochemical measurements possible. Finally, MIG tests have been performed in order to study the influence of the shielding gas composition on nitrogen content in the weld and also on the formation of porosities. For superduplex stainless steel, it has been demonstrated that nitrogen must be added in the gas to prevent nitrogen loss. It has also been shown that the number of porosities in the weld depends on the C02 content in the gas and not on the nitrogen content.
Control of Microstructures and Properties in Steel Arc Welds provides an overview of the most recent developments in welding metallurgy. Topics discussed include common welding processes, the thermal cycle during welding, defects that may occur during the welding process, the metallurgy of the material, metallurgical processes in the heat-affected zone and the fused metal, and the relationship between microstructures and mechanical properties. The book's final chapter presents examples of welded joints, illustrating how modern theories are capable of predicting the microstructure and properties of these joints. This book is an excellent resource for welding engineers, metallurgists, materials scientists, and others interested in the subject.
The rate of growth of stainless steel has outpaced that of other metals and alloys, and by 2010 may surpass aluminum as the second most widely used metal after carbon steel. The 2007 world production of stainless steel was approximately 30,000,000 tons and has nearly doubled in the last ten years. This growth is occurring at the same time that the production of stainless steel continues to become more consolidated. One result of this is a more widespread need to understand stainless steel with fewer resources to provide that information. The concurrent technical evolution in stainless steel and increasing volatility of raw material prices has made it more important for the engineers and designers who use stainless steel to make sound technical judgments about which stainless steels to use and how to use them.
The duplex stainless steels have been developed to provide a combination of tensile properties and resistance to pitting and stress corrosion cracking in comparison with the 300--series austenitic stainless steels. The optimum properties of duplex stainless steels are achieved when nearly equal proportions of aus-tenite and ferrite are present in the microstructure. Control of the ferrite/austenite balance in welds is not as straightforward as in the base metals since it depends on different welding parameters as well as type of welding process. This book is concerned with laser beam welding and its effect on size and microstructure of fusion zone then, on mechanical and corrosion properties of welded joints of the widely used 2205 duplex stainless steel plates. Results of laser welding process have been compared with that of tungsten inert gas (TIG) welding process. The results achieved in this investigation disclosed that laser welding parameters including laser power, welding speed, defocusing distance and type of shielding gas combinations play an important role in obtaining laser welded joint with acceptable fusion zone size and weld profile.
This book serves as a comprehensive resource on metals and materials selection for the petrochemical industrial sector. The petrochemical industry involves large scale investments, and to maintain profitability the plants are to be operated with minimum downtime and failure of equipment, which can also cause safety hazards. To achieve this objective proper selection of materials, corrosion control, and good engineering practices must be followed in both the design and the operation of plants. Engineers and professional of different disciplines involved in these activities are required to have some basic understanding of metallurgy and corrosion. This book is written with the objective of servings as a one-stop shop for these engineering professionals. The book first covers different metallic materials and their properties, metal forming processes, welding, and corrosion and corrosion control measures. This is followed by considerations in material selection and corrosion control in three major industrial sectors, oil & gas production, oil refinery, and fertilizers. The importance of pressure vessel codes as well as inspection and maintenance repair practices have also been highlighted. The book will be useful for technicians and entry level engineers in these industrial sectors. Additionally, the book may also be used as primary or secondary reading for graduate and professional coursework.
The revised edition of this important reference volume presents an expanded overview of the analytical and numerical approaches employed when exploring and developing modern laser materials processing techniques. The book shows how general principles can be used to obtain insight into laser processes, whether derived from fundamental physical theory or from direct observation of experimental results. The book gives readers an understanding of the strengths and limitations of simple numerical and analytical models that can then be used as the starting-point for more elaborate models of specific practical, theoretical or commercial value. Following an introduction to the mathematical formulation of some relevant classes of physical ideas, the core of the book consists of chapters addressing key applications in detail: cutting, keyhole welding, drilling, arc and hybrid laser-arc welding, hardening, cladding and forming. The second edition includes a new a chapter on glass cutting with lasers, as employed in the display industry. A further addition is a chapter on meta-modelling, whose purpose is to construct fast, simple and reliable models based on appropriate sources of information. It then makes it easy to explore data visually and is a convenient interactive tool for scientists to improve the quality of their models and for developers when designing their processes. As in the first edition, the book ends with an updated introduction to comprehensive numerical simulation. Although the book focuses on laser interactions with materials, many of the principles and methods explored can be applied to thermal modelling in a variety of different fields and at different power levels. It is aimed principally however at academic and industrial researchers and developers in the field of laser technology.
This report supplies information on joining processes applicable to titanium and its alloys in sheet metal applications, primarily related directly to airframe construction. Although the material presented here does not cover all titanium joining processes, and omits such processes as plasma-arc, submerged-arc, electroslag, flash, and high-frequency resistance welding, the data presented cover materials up to 2-inches thick in some cases and the report should be useful to anyone seeking titanium joining information. The joining processes covered fall into five categories: welding, brazing, metallurgical bonding (diffusion and deformation bonding), adhesive bonding, and mechanical fastening. The fusion welding processes that are discussed in detail include gas tungsten arc, gas metal arc, arc spot, and electron beam. The resistance processes give extended coverage are spot, roll spot, and seam welding. (Author).