Papers by Keyword: Duplex

Abstract: Numerical study of atmospheric ice accretion on circular cylinders in duplex configuration has been carried out at different operating and geometric conditions. Analyses showed a difference in ice accretion on both cylinders, as streamline accumulated ice shapes were observed along front cylinder and irregular ice shapes were found along rear cylinder. Results also showed a change in accreted ice load and ice shape along rear cylinder with the change in distance between both cylinders. Parametric study at different droplet sizes and temperatures showed a variation in ice accretion. This prelimenary research work provides a useful base for better understanding and further investigation of atmospheric ice accretion on circular overhead conductors in duplex configuration, installed in cold climate of high north regions.

Abstract: To strengthen the roof beams of a model duplex composite mold design process, for example, to explore the data in the IMAN UG design platform using three-dimensional solid steps, and introduces a three-dimensional solid design and development of applications for three-dimensional solid design in contemporary mold enterprise business without machining and assembly diagram programming situation.

Abstract: This lecture presents the authors personal views on the landmark events that have strongly affected the welding of stainless steels over their lifetime. Although 1913 is commonly recognized as the birth of stainless steels with the commercialization of the martensitic alloy of Harry Brearly and the austenitic alloy of Eduard Maurer and Benno Straus, the story can be considered to begin as long ago as 1797 with the discovery of chromium by Klaproth and Vauquelin, and the observation by Vauquelin in 1798 that chromium resists acids surprisingly well. From the 1870s onwards, corrosion resisting properties of iron-chromium alloys were known. One might mark the first iron-chromium-nickel constitution diagram of Maurer and Strauss in 1920 as a major landmark in the science of welding of stainless steels. Their diagram evolved until the outbreak of World War II in Europe in 1939, and nominally austenitic stainless steel weld metals, containing ferrite that provided crack resistance, were extensively employed for armor welding during the war, based on their diagram. Improved diagrams for use in weld filler metal design and dissimilar welding were developed by Schaeffler (1947-1949), DeLong (1956-1973) and the Welding Research Council (1988 and 1992). Until about 1970, there was a major cost difference between low carbon austenitic stainless steels and those austenitic stainless steels of 0.04% carbon and more because the low carbon grades had to be produced using expensive low carbon ferro-chromium. Welding caused heat affected zone sensitization of the higher carbon alloys, which meant that they had to be solution annealed and quenched to obtain good corrosion resistance. In 1955, Krivsky invented the argon-oxygen decarburization process for refining stainless steels, which allowed low carbon alloys to be produced using high carbon ferro-chromium. AOD became widely used by 1970 in the industrialized countries and the cost penalty for low carbon stainless steel grades virtually vanished, as did the need to anneal and quench stainless steel weldments. Widespread use of AOD refining of stainless steels brought with it an unexpected welding problem. Automatic welding procedures for orbital gas tungsten arc welding of stainless steel tubing for power plant construction had been in place for many years and provided 100% penetration welds consistently. However, during the 1970s, inconsistent penetration began to appear in such welds, and numerous researchers sought the cause. The 1982 publication of Heiple and Roper pinpointed the cause as a reversal of the surface tension gradient as a function of temperature on the weld pool surface when weld pool sulfur became very low. The AOD refining process was largely responsible for the very low sulfur base metals that resulted in incomplete penetration. The first duplex ferritic-austenitic stainless steel was developed in 1933 by Avesta in Sweden. Duplex stainless steels were long considered unweldable unless solution annealed, due to excessive ferrite in the weld heat-affected zone. However, in 1971, Joslyn Steel began introducing nitrogen into the AOD refining of stainless steels, and the duplex stainless steel producers noticed. Ogawa and Koseki in 1989 demonstrated the dramatic effect of nitrogen additions on enhanced weldability of duplex stainless steels, and these are widely welded today without the need to anneal. Although earlier commercial embodiments of small diameter gas-shielded flux cored stainless steel welding electrodes were produced, the 1982 patent of Godai and colleagues became the basis for widespread market acceptance of these electrodes from many producers. The key to the patent was addition of a small amount of bismuth oxide which resulted in very attractive slag detachment. Electrodes based on this patent quickly came to dominate the flux cored stainless steel market. Then a primary steam line, welded with these electrodes, ruptured unexpectedly in a Japanese power plant. Investigations published in 1997 by Nishimoto et al and Toyoda et al, among others, pinpointed the cause as about 200 ppm of bismuth retained in the weld metal which led to reheat cracking along grain boundaries where the Bi segregated. Bismuth-free electrode designs were quickly developed for high temperature service, while the bismuth-containing designs remain popular today for service not involving high temperatures.

Abstract: Stainless steels are used widely in many industries. A duplex microstructure offers a combination of advantages, including resistance to crevice and stress corrosion, reduced susceptibility to hot cracking in comparison with fully austenitic structures and excellent tensile strength. The paper discusses the effect of aging on the microstructure and corrosion resistance of X2CrNiMoN25-7-4 super duplex stainless steel. Low and predictable corrosion rate is an important parameter for steels operating in aggressive environments. Resistance to intergranular corrosion expressed by corrosion rate (mm/year) was determined in accordance with standard PN-EN ISO 3651-1. Metallographic studies were carried out to evaluate surface degradation and intergranular corrosion. The results support an evaluation of the impact that phase fraction changes caused by aging have on resistance to intergranular corrosion. The results of the corrosion analysis were used to develop mathematical models describing changes in corrosion rate over time for different phase fractions.

Abstract: By using biaxial gas-pressure forming method, it is possible to predict sheet metal forming behavior during hot forming process. The purpose of this study is to investigate the deformation behavior during equi-biaxial forming of a duplex stainless steel using conical and hemispherical dies. The present study constructs an analysis model to predict biaxial sheet forming behavior of duplex steel from results of tension tests. The results demonstrate that the developed technology to process design of high temperature gas-pressure forming by the finite element method can be applied to various types of components.

Abstract: This paper concerns the phase transformation induced by heat treatment and cold rolling in four duplex stainless steel. In 2205 and 2507 , during the isothermal heat treatments, chi-phase precipitates as small particles at the ferrite/austenite boundaries, followed by sigma precipitation. At the lowest temperature the formation kinetic of chi-phase is favoured, with the increasing of time and temperature a progressive transformation of chi to sigma occurs and the kinetic of sigma is favoured. During continuous cooling, the chi -phase appears at low cooling rates. In low Ni grades the grain boundaries precipitation of chromium nitrides were detected , but no sigma and chi. In 2101 the austenite transforms to martensite both after cold rolling and quenching

Abstract: This work presents mechanical properties and corrosion resistance of duplex stainless steels obtained through powder metallurgy starting from austenitic X2CrNiMo17-12-2 (AISI 316L), martensitic X6Cr13 (AISI 410L) powders by controlled addition of alloying elements in the proper quantity to obtain the chemical composition of the structure similar to biphasic one. In the mixes preparations the Schaffler’s diagram was taken into consideration. Prepared mixes of powders have been sintered in a vacuum furnace with argon backfilling. After sintering rapid cooling was applied using nitrogen. Produced duplex stainless steels have been studied by SEM with EDS and light optical microscopy (LOM) and X-rays analysis to determine obtained structures. Corrosion properties have been studied through electrochemical methods in 1M NaCl.

Abstract: Research activities on deformation and fracture characteristics of the Ti-Al intermetallics have assumed considerable significance in view of many potential applications as high temperature structural materials. These aspects are discussed in respect of two Ti-Al intermetallics with duplex and lamellar structures. The fracture toughness, crack growth resistance and fracture mechanisms are evaluated at room temperature. The differences in the behaviour of the alloys are explained in the light of microstructures as observed for the alloys.

Abstract: Interfacial strength distribution and thermal residual stresses in multi-layered or compositionally graded NiCrAlY/ZrO₂ coatings are analyzed. These coatings are fabricated by detonation gun spraying using mechanically alloyed, plasma-spheroidized composite powders. The problems in design of functionally graded materials (FGMs) are outlined and their modeling approaches are reviewed. Due to the concentrational or structural gradients in FGMs, the normal approximations and models, used for traditional composites, are not directly applicable to graded materials. The goal is to show the efficiency of the simplest models to provide the most accurate estimates of the properties and even to make simple elasto-plastic analysis of FGM components without vast computations by finite element methods with an arbitrary non-linear distribution of phases and corresponding properties is presented. Results showed that bonding strengths increased gradually with increase of the composition of metals in the FGM coatings. The FGM coating was more stable on the mechanical properties than normal duplex composites. And, the maximum compressive radial stress is found to be at or near the surface of the specimen where surface cracking may be generated. The maximum axial stress is at the edge of the specimen where spallation may occur. The maximum shear stress is also at or close to the edge.