Papers by Keyword: High Temperature Strength

Abstract: Magnesium alloys have spurred a strong interest in automobile and aerospace industries owing to their high specific strength and stiffness, with magnesium being the lightest structural metal. Alloying with rare earth improves tensile properties considerably. However, the availability of rare-earth elements is a concern. Therefore, attempts are being made to prepare alloys without rare-earth elements. One Mg-1Ca alloy was prepared with different amounts of Sn to study the impact on the high-temperature strength after dynamic recrystallization by hot rolling. Optical and electron microscopy analyzed the change in the microstructure. XRD and EDS were used to identify phases and composition of different microconstituent particles and high-temperature strength was measured at 250°C, 300°C, and 350 °C under 2 x 10^-4 s ^-1 strain rate and at 3000C, 3500C, 4000C, and 4500C temperature under 5 x 10 ^-4 s ^-1 strain rate. According to XRD investigation, the alloys essentially comprise the Ca-containing phase and Mg₂Sn particles. The Mg-1Ca-1Sn alloy exhibited maximum high-temperature strength at 250°C, attributed to the maximum amounts of MgCaSn particles. It was also found that dynamic recrystallization was accelerated by particle-stimulated nucleation and maximum refinement was found at 1% Sn-containing alloys.

Abstract: The final set of properties of the exhaust valve is formed in the course of the entire set of processes, the most important is the build-up of the valve chamfer which is subjected to constant high temperatures, gas flow and thermal cycling, therefore strict adherence to the whole complex of properties is necessary. In the study two materials were investigated: the deformable part of the base material (steel grade 40X10C2M (EN steel grade X40CrSiMo10)) and surfacing (alloy EP616A), used to manufacture the exhaust valve of the internal-combustion engine.The study was carried out at different stages of valve manufacturing: after electro-forging during the formation of a valve head from a rod, subsequent heat treatment (quenching + high tempering), after surfacing a ring with the heat-resistant alloy. The chemical composition of phases, inclusions, and sections of EP616A alloy around the shrink-hole were determined by the method of micro-X-ray analysis. The results indicate a shortage of visual inspection, and that conducting a selective destructive method does not ensure the full probability of detecting internal defects. It is advisable instead of destructive control to introduce ultrasonic flaw detection.

Abstract: Hot deformability and fracture of as-cast Fe-Cr-Mn-Ni stainless steel ingots with high nitrogen and high carbon contents were studied. Effective stress-strain curve indicates a decrease of the UTS from 510MPa to 90MPa with increase of temperatures from 600°C to 1200°C. Effective stress-strain curves exhibited typical work hardening until the final stage of fracture from 600°C up to 900°C. The fracture elongation decreased from 600°C with the increase of temperature up 850°C, but started to increase appreciably as the work softening becomes dominant in the stress-strain curves above 950°C, suggesting the increase of ductility above 950°C is associated with dynamic recrystallization. The high temperature deformability was enhanced above 1000°C by homogenization of the as-cast alloy due to the dissolution and redistribution of segregated particles, providing the homogeneous distribution of the nucleation site of dynamic recrystallization. . The presence of fatal crack at 1,250°C and the loss of hot ductility can be attributed to the partial melting in austenite grain boundaries at high temperatures.

Abstract: Ni-Cr-Co type Nickel-based super alloy Inconel 740H was studied. The effect of Nb, Al and Ti on the equilibrium of this alloy was analyzed by JMatPro software. The amount of Ti and Nb should be controlled by 1.50wt.%, and meanwhile, Al should be 1.0-2.0wt.%. If Mo and W were added the amount of Mo should be in the range of 1.0-2.0wt. %, and W should be about 1.0wt.%. Based on these results, three types of new alloys were designed, which contain Ni-Cr-Co-Mo type (1#), Ni-Cr-Co-W type (2#) and Ni-Cr-Co-Mo-W type (3#). Compared with the Ni-Cr-Co type Inconel 740H alloy, the room temperature strength, high temperature strength and high temperature durable performance of the three new alloys improved, which can provide the evidence and reference to optimize the chemical composition of Inconel 740H alloy, i.e., adding 1.50wt.% Mo and 1.0wt.% W individually or together.

Abstract: This research is to show the microstructure of fracture parts of structural steels by welding at the high temperature. Discontinuity of mechanical and chemical property at HAZ of welding parts is the cause of decreasing structure safety. Therefore, this study was determined the effect of the welding of steels through a high temperature tensile tests and fracture portion of the microstructure. The results showed that does not cause destruction until temperature reached 600°C.

Abstract: As a rapid deposition method, Electron Beam Physical Vapor Deposition (EBPVD) permits the fast fabrication of self-standing thick coatings with thickness in the range from several micrometers to hundreds of micrometers. In this paper, we present a new way to fabricate ferritic ODS alloy foil. By this method, 1.2 wt.% of yttria was successfully added to the ferritic base material. The base alloys are mainly composed of bcc structured Fe (Cr,Al) solid solution. The steady state creep rate of ferritic ODS is almost two magnitudes lower than that of FeCrAl alloy. Further thermo-mechanical treatment is expected to improve strength and ductility of both ODS and non-ODS material.

Abstract: The diffusion bonding of 316L stainless steel with Ni interlayer in the temperature range of 850-1050°C, under a uniaxial pressure 10 MPa for 60 min is investigated. The diffusion bonds have been evaluated light microscopy, SEM, X-ray diffraction and tensile test. The main result is that the introduction of the interlayer may reduce the room temperature strength but increase the high temperature strength. This is attributed to the transformation of Fe_0.64Ni_0.36 formed in bonding process into FeNi₃ at high temperature. Kirkendall voids are formed in the Ni interlayer near the interface where the specimen fractured. Fractographic study indicates that the fracture mode of the joints is strongly affected by the bonding and testing temperature. The fracture is a mixed mode of brittle and ductile fracture in high temperature tensile test, while it is brittle fracture at room temperature.

Abstract: This paper analyzes the adaptability of process of alloy structural steel 50Mn2V by simulating research. Through the high temperature tensile test、the multi-pass deformation test we study the deforming resistance characteristics of 50Mn2V steel, and carry on the contrast with high strength steels P20（3Cr2Mo）of a factory; Through thermo-plasticity test the high temperature thermoplastic of 50Mn2V steel is studied. The test result indicates a factory has ability to produce the high strength 50Mn2V steel completely with present equipment.

Abstract: The blast furnace coke plays four roles as exothermic agent, reducer, carburizer and framework. The former three roles can be played by other fuels, but the role as framework still can’t be played by other fuels by now. In order to ensure its skeleton role, it must be sure that the coke has enough high-temperature strength. This research uses KSJ decarbonizing electric furnace, drum-I and high temperature compressive testing machine to furthest simulate the coke’s actual actions in the blast furnace. The research indicates that comparing with the reactivity and strength index after reaction of coke GB4000-1996, the blast furnace coke’s high temperature compressive strength under a certain temperature and a certain carbon loss rate can give a more comprehensive evaluation of the quality of coke.

Abstract: Much attention has been paid to unidirectionally solidified ceramic composites as candidates for high-temperature structural materials. We have recently developed potential ceramic eutectics, which are named Melt Growth Composites (MGC). The Al₂O₃/GAP(GdAlO₃) binary MGC has a novel microstructure, in which continuous networks of single-crystal Al₂O₃ phases and single-crystal GAP phases interpenetrate without grain boundaries. Chain structure in the Al₂O₃/GAP binary system is formed due to the frequent branching of both phases resulted in the entangled structure. Therefore, the Al₂O₃/GAP binary MGC has excellent high-temperature characteristics in the air atmosphere at very high temperatures. In the paper, high temperature strength, thermal stability of microstructure and strength, and fracture toughness of the Al₂O₃/GAP binary MGC are reported.