Papers by Keyword: Grain Refinement

Abstract: By using Gleeble1500-D thermal simulation machine, Rare Earth(RE) adding Q345B steel of single-pass compression test were carried out. A study had been made of the effect of different deformed conditions in hot rolling process on Nd-modified Q345B steel recrystallization behavior and microstructure evolution.The result shows that RE steel Q345B of single compression test are consistent with the general experimental rule. Rare Earth additions significantly increased hot- deformed resistance at low temperature compression, however, it is not obvious at high temperature. The increased hot-deformed resistance and the degree of the retardation is more obvious for heavy RE Tb than light RE Nd.

Abstract: The role of Fe on the grain refinement of high purity aluminium (HPAl) was investigated after adding commercial Al-5Ti-1B grain refiner rod. Experimental results show that with a 0.08% Fe addition, the grain structure at chill zone of the HPAl sample changes from coarse to fine equiaxed grains. More importantly, the grain size observed at the centre of the HPAl sample decreased from 500±50µm to 206±30µm. The improvement has been attributed to the interfacial segregation and solute concentration of the Fe at the solid-liquid interface.

Abstract: The Fe-V-Nb-RE(Ce) alloy was rapidly solidified with melt-spin method, and the nano-sized ribbon was gained with the rolling wheel speed of 45m/s.The microstructure and the grain size of the Fe-V-Nb-RE(Ce) inoculants were performed by SEM and XRD respectively. Subsequently the microstructure of the steel modified by the Fe-V-Nb-Re(Ce) inoculants was also studied. The results show that the average grain size of the nano-scale Fe-V-Nb-RE(Ce) inoculants obtained is 26.1nm and a large mounts of nucleation sites in the steel exist in the form of (V, Nb)C and FeCeSi which effectively increases the nucleation rate and bring about the refinement of austenite grains.

Abstract: This study evaluated the microstructure and mechanical properties enhancement of cross roll rolled Ni-10Cr alloy, comparing with conventional rolled material. Cold rolling was carried out to 90% thickness reduction and subsequently annealed at 700 °C for 30 min to obtain the fully recrystallized microstructure. For annealed materials after rolling, to investigate the grain boundary characteristic distributions, electron back-scattering diffraction technique was introduced. Application of cross roll rolling on Ni-10Cr alloy contributed to the notable grain refinement, consequently, average grain size was refined from 135 μm in initial material to 4.2 μm in cross roll rolled material. These refined grain size led to an enhanced mechanical properties such as yield and tensile strengths. Furthermore, <111>//ND texture in CRR material was well developed than that of CR material, which contributed to the mechanical properties and formability enhancement.

Abstract: Aluminum and its alloys solidify in large grains columnar structure which tends to reduce their mechanical behaviour and surface quality. Therefore, they are industrially grain refined by titanium or titanium + boron. Furthermore, aluminum oxidizes in ordinary atmosphere which makes its weldability difficult and weak. Therefore, it is anticipated that the effect of addition of zirconium at a weight percentages of 0.1% (which proved to be an effective grain refiner on the weldability of aluminum grain refined by Ti) is worthwhile investigating. This formed the objective of this research work. In this paper, the effect of zirconium addition at a weight percentage of 0.1%, which corresponds to the peritctic limit on the aluminum-zirconium phase diagram, on the weldability of aluminum grain refined by Ti is investigated. Rolled sheets of commercially pure aluminum, Al grain refined Ti of 3 mm thickness were welded together using Gas Tungsten Arc Welding method (GTAW), formerly known as TIG. A constant air gap was maintained at a constant current level, 30 ampere AC, was used because it removes the oxides of the welding process under the same process parameters. Metallographic examination of weldments of the different combinations of aluminum and its microalloys at the heat affected zone, HAZ, and base metal was carried out and examined for width, porosity, cracks and microhardness. It was found that grain refining of commercially pure aluminum by Ti resulted in enhancement of its weldability. Similarly, addition of zirconium to Al grain refined by Ti resulted in further enhancement of the weldment. Photomicrographs of the HAZ regions are presented and discussed.

Abstract: Aluminum and its alloys are the second most commonly used metal for a variety of industrial applications. They normally solidify in coarse grain columnar structure which tends to reduce their mechanical behavior and surface quality. It was found that this large grain size structure can be refined by using titanium, Ti, or titanium plus boron, Ti+B, and using the latter resulted in reducing the amount of Ti to fifth its values although boron itself is not a grain refiner. This is why it is becoming customary in the aluminum foundry to add Ti or Ti+B to their melt before solidification. The available literature reveals that most of the work is directed towards the metallurgical aspects and little was directed on the mechanical aspects. To the best of the authors knowledge, no work was directed on the aspects of grain refiners on the formability of metals. In this paper, the effect of addition of Zr on the mechanical properties of commercially pure aluminum grain refined by Ti+B in the as cast and extruded conditions is investigated. Comparison between the addition of Zr alone or Zr+Ti+B is also investigated. It was found that addition of Ti+B either alone or in the presence of Zr resulted in grain refinement of aluminum both in the as cast and in the cold extruded conditions. The maximum reduction in grain size was 53.22% and 76.92%, respectively. Similarly, it was found that addition of Ti+B either alone or in the presence of Zr to Al resulted in improvement of its Vickers's hardness, However addition of Zr alone to Al resulted in decrease of its hardness in the as cast conditions but increase in the extruded condition .The maximum increase was in the case of adding both of them in the extruded condition being 94.59 %, (from Hv 37 to Hv72). Similarly the ultimate tensile strength, UTS, was improved at all additions except when Ti+B or Zr is added alone. On the whole it may be concluded that addition of Zr to Al grain refined by Ti+B resulted in enhancement of its grain size and improvement of its hardness, mechanical strength and ductility in the cold extruded conditions and resulted in slight decrease of its ductility when added in the as cast condition.

Abstract: The first results are presented of ESA MAXUS 8 sounding rocket benchmark experiment on γ-TiAl (Nb,B) intermetallics solidification, that was a part of the IMPRESS EU FP6 project. Having the aim to investigate the columnar and equiaxed primary microstructures formation at diffusion controlled melt growth, an experiment was designed applying the power-down directional solidification technique with fixing quench in automatic spaceborne furnace module TEM03-5M. Two related alloys were tested: one inoculated with boron grain refiner Ti-44Al-7.5Nb-2.7B (at.%); and the other Ti-45.5Al-8Nb (at.%) without grain refinement. The series of terrestrial reference processes has been performed accordingly in counter-gravity solidification direction. The numerical studies of heat-mass transfer, melt hydrodynamics and temporal solidification dynamics of these alloys have been implemented under the earth-and zero-gravity approximations using the GIGAN software package (IPPE). The comparison is performed of numerical model findings with the real microstructure and composition of samples, whose analyses were carried out by backscattered scanning electron microscopy (SEM) and X-ray microprobe (EDX) techniques. The convection-induced peritectic macrosegregation effect appearance and development in ground-based reference ingots is analytically observed and numerically studied. The achieved microstructure formation in space benchmarks is discussed.

Abstract: Rare earth (RE) has purification, denatured mixture and micro alloy function in steel. High Nb containing in steel can expend austenite non-recrystallization region, improve rolling temperature and lower equipment load. Effect of RE on dynamic recrystallization of low carbon high niobium steel is investigated by using thermal simulation experiment in this paper. Experimental results show that dynamic recrystallization does not occur in two test steel below 1000°C. RE elements can increase dynamic recovery beginning strains, refine and disperse M/A organization and change precipitates into small triangle shape.

Abstract: AISI 304L austenitic stainless steel was cold rolled to 90% with and no inter-pass cooling to produced 89% and 43% of deformation induced martensite respectively. The cold rolled specimens were annealed by isothermal and cyclic thermal process. The microstructures of the cold rolled and annealed specimens were studied by the electron microscope. The observed microstructural changes were correlated with the reversion mechanism of martensite to austenite and strain heterogeneity of the microstructure. The results indicated possibility of ultrafine austenite grain formation by cyclic thermal process for austenitic stainless steels those do not readily undergo deformation induced martensite. Keywords: Austenitic stainless steel, Grain refinement, Cyclic thermal process, Ultrafine grain

Abstract: Microstructure evolution during annealing of a Ni-20%Cr alloy subjected to high-pressure torsion (HPT) at ambient temperature was examined. It was shown that discontinuous static recrystallization (DSRX) occurs in non-uniform manner under subsequent annealing in the alloy strained to ε<4. The material strained to ε6 or higher exhibits continuous grain growth (GG) under subsequent annealing. It is attributed to the fact that HPT led to the formation of nanoscale grains with an average size of 50 nm. Increasing fraction of these grains with strain leads to transition from DSRX to continuous GG under subsequent annealing. It was found that the main feature of recrystallization behavior of the Ni-20%Cr alloy subjected to HPT is simultaneous occurrence of short-range ordering and recrystallization processes under annealing conditions. As a result, despite the formation of recrystallized structure with an average grain size of 340 nm after annealing at 600°C (0.52 T_m), the material exhibits very high microhardness of 3.6 GPa.