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Germany's gold
\"How were German's gold reserves created, and what role has gold played as a means of payment over time? ... The Deutsche Bundesbank's project to bring substantial gold holdings to Frankfurt am Main from storage locations in New York and Paris has generated a great deal of public interest over the past few years. This book is the first of its kind to provide a detailed account of how the gold in the Bundesbank's vaults came into being and how it has been used and stored over time. Splendid images of selected gold bars provide a beautiful backdrop to in-depth informtion on the properties of gold and how it is mined and processed\"--Back of dust jacket.
Book
Optimization Steel ingot Mould’ Riser Height Based on Solidification Simulation
Solidification process of 13.5t P91 steel ingot with different riser heights were simulated by software and predicted the distribution of shrinkage cavity. The simulation results showed the shrinkage cavity in the precedent ingots is much deeper. The simulation results is agreement well with experiment results. Therefore, the riser height was designed by solidifation simulation and verified by experiments and the results showed that optimized riser height can eliminate shrikage cavity and improve the quality of steel ingot.
Journal Article
Effect of Grain Refiner on Fracture Toughness of 7050 Ingot and Plate
In this paper, two types of grain refining alloys, Al-3Ti-0.15C and Al-5Ti-0.2B, were used to cast two types of 7050 rolling ingots. The effect of Al-3Ti-0.15C and Al-5Ti-0.2B grain refiners on fracture toughness in different directions for 7050 ingots after heat treatment and 7050-T7651 plates was investigated using optical electron microscopy (OEM) and scanning electron microscopy (SEM). Mechanical properties testing included both tensile and plane strain fracture toughness (KIC). The grain size was measured from the surface to the center of the 7050 ingots with two different grain refiners. The fracture surface was analyzed by SEM and energy dispersive spectrometer (EDS). The experiments showed the grain size from edge to center was reduced in 7050 ingots with both the TiC and TiB refiners, and the grain size was larger for ingots with the Al-3Ti-0.15C grain refiner at the same position. The tensile properties of 7050 ingots after heat treatment with Al-3Ti-0.15C grain refiner were 1–2 MPa lower than the ingot with the Al-5Ti-0.2B grain refiner. For the 7050-T7651 100 mm thick plate with the Al-3Ti-0.15C grain refiner, for the L direction, the tensile properties were lower by about 10~15 MPa; for the plate with the Al-3Ti-0.15C refiner than plate with Al-5Ti-0.2B refiner, for the LT direction, the tensile properties were lower by about 13–18 MPa; and for the ST direction, they were lower by about 8–10 MPa compared to that of Al-5Ti-0.2B refiner. The fracture toughness of the 7050-T7651 plate produced using the Al-3Ti-0.15C ingot was approximately 2–6 MPa · m higher than the plate produced from the Al-5Ti-0.2B ingot. Fractography of the failed fracture toughness specimens revealed that the path of crack propagation of the 7050 ingot after heat treatment produced from the Al-3Ti-0.15C grain refiner was more tortuous than in the ingot produced from the Al-5Ti-0.2B, which resulted in higher fracture toughness.
Journal Article
Experimental and Numerical Analysis of Thermal Fatigue of Grey Cast Iron Ingot Mould
This article presents the results of experimental studies and numerical calculations that were conducted to analyse the phenomena that occur during the operation of an ingot mould that is designed for casting steel ingots. The studies were conducted on an experimental stand in a foundry on an ingot mould that was designed to make ingots that weigh up to six tons; they consisted of determining the temperature of the ingot mould and measuring the displacements of its walls during filling with steel and cooling. These studies were used to create and verify a numerical model that was used to determine the temperatures, displacements, deformations, and stresses in ingot mould walls during the operating cycle using the FEM method. Microstructure studies of ingot cast iron that was subjected to thermal fatigue were also conducted on a laboratory stand; the temperature changes and test times were the same as those used under the normal operating conditions of the ingot mould. Cast iron samples were subjected to heating and cooling cycles within a range of 0 to 60 cycles; then, tensile tests were performed to determine their stress–strain curves. As a result of the conducted tests, a great influence was found of the number of cycles on decreases in the values of the modulus of elasticity and tensile strength—especially within a range of 0 to 10 cycles. A relationship was also found between the changes in these values and the image of the cast iron microstructure. Based on images of the cast iron microstructure after being subjected to different numbers of thermal fatigue cycles, the mechanism of the crack initiation and propagation was determined. The influence of the changes in the strength of the cast iron and the stress state that was determined by the FEM method on the durability of the tested type of ingot mould was analysed. The obtained research results will be useful for introducing design changes that are aimed at increasing the fatigue durability of ingot moulds.
Journal Article
Using the Radial Shear Rolling Method for Fast and Deep Processing Technology of a Steel Ingot Cast Structure
In advancing special materials, seamless integration into existing production chains is paramount. Beyond creating improved alloy compositions, precision in processing methods is crucial to preserve desired properties without drawbacks. The synergy between alloy formulation and processing techniques is pivotal for maximizing the benefits of innovative materials. By focusing on advanced deep processing technology for small ingots of modified 12% Cr stainless steel, this paper delves into the transformation of cast ingot steel structures using radial shear rolling (RSR) processing. Through a series of nine passes, rolling ingots from a 32 mm to a 13 mm diameter with a total elongation factor of 6.02, a notable shift occurred. This single-operation process effectuated a substantial change in sample structure, transitioning from a coarse-grained cast structure (0.5–1.5 mm) to an equiaxed fine-grained structure with peripheral grain sizes of 1–4 μm and an elongated rolling texture in the axial part of the bar. The complete transformation of the initial cast dendritic structure validates the implementation of the RSR method for the deep processing of ingots.
Journal Article
Long-distance settling simulation of equiaxed dendrite by a moving-frame algorithm: phase-field lattice Boltzmann study with parallel-GPU AMR
In large-ingot castings, the settling of equiaxed dendrites often results in distinct cone-shaped negative segregation in the lower region of the ingot. To accurately predict and control such macrosegregation, it is important to understand the kinetic behavior of equiaxed dendrites in the melt. The phase-field lattice Boltzmann (PF-LB) model is powerful for simulating dendrite growth with melt convection and solid motion. However, it is computationally expensive and represents only the short-distance motion of dendrites in three-dimensional (3D) simulations. For an efficient 3D evaluation of the effect of dendrite motion and rotation on growth behavior, we introduce the moving frame algorithm to PF-LB simulations. Here, the computational domain tracks the settling dendrite to express long-distance settling without restricting the domain size. The PF-LB simulations were accelerated by parallel computing using a combination of multiple GPUs and adaptive mesh refinement (AMR), also referred to as parallel GPU-AMR. The moving-frame algorithm was modified to adapt to AMR. From the simulation results, we demonstrate that the proposed method helps evaluate the effect of dendrite rotation on the settling and growth velocities of equiaxed dendrites in 3D.
Journal Article
Statistical Evaluation of Arc Dynamics Measured During an Industrial VAR Melt of IN718 Under Various Arc Gaps
An industrial scale experiment on the impacts of process variations on ingot quality of IN718 was carried out by monitoring the associated magnetic fields by VARmetric. The test performed monitored operational variations during the processing of the ingot when different arc gaps were maintained. A short, medium, long, and extra-long arc gap were chosen during the melt, the system was allowed to operate for approximately 2 hours at each arc gap before readjusting to the next arc gap. Magnetic field measurements were used to continuously determine the arc centroid position during the melt. A detailed analysis of the arc position measurements was conducted employing quantitative and statistical tools to assess the overall impact of process variations on the distribution of arcs. The arc rotation and spread were characterized for different arc gaps which clearly shows the transition from a diffuse to a constricted arc mode. A strong correlation was observed between the arc radius, rotations, and arc gap which may be able to be used to monitor arc gap size in lieu of drop shorts.
Journal Article
Forecasting Increase of Quality of Large-Sized Forgings Used for Stamping, Piercing, and Rolling of High-Duty Products
When utilizing current combined systems of manufacturing large-sized shaft forgings, there is a tendency towards using an integrated approach, which consists in optimizing the shape of forged ingots and methods of their forging, intensifying shear strains in the axial zone of the ingots during their plastic deformation, and eliminating asymmetry of external forces at various points along the cross section of the ingot being deformed. This paper presents the results of the comparative analysis of quality of shaft forgings when forging ingots with a three-beam symmetric and asymmetric cross-section, as well as with the traditional octahedral cross-section, are used for the manufacture of shaft forgings. It has been shown that the use of forging ingots with a three-beam symmetrical and asymmetrical cross section provided an increase of KCU by an average of 4.3% and 13.1%, and of density by 17.5% and 21.0%, respectively, in the absence and presence of inert gas (argon) blowdown of the melt in the casting ladle before casting it into ingot molds. Their use also contributes to an increase in the number of forgings, suitable for ultrasonic testing, according to the C/c class with a permissible equivalent discontinuity diameter of ≤ 3 mm.
Journal Article
Bulk synthesis of Ti28Zr40Al20Nb12 high entropy alloy: a critical evaluation of processing conditions
The bulk Ti
28
Zr
40
Al
20
Nb
12
refractory high entropy alloy (RHEA) ingot with total mass of 20 kg was produced by vacuum induction melting followed by mould casting. The bulk ingot shows dual-phase structure: the soft (Ti, Nb)-rich bcc matrix and the hard Al
3
Zr
5
-type hcp phase. The variation of cooling rate of the bulk ingot affects both microstructure and compression properties. Phase morphology changes from smaller grains at the edge to coarse grains at the center of the ingot. The total volume fraction of hcp phase at the edge is above 40%, which decreased to around 30% in the intermediate region and the center of the ingot. Whereas, the fraction of hcp phase inside the grains inversely increased to be larger than 10% at the center. Crushing destruction happened for all samples during compression. The compression strength for samples prepared from the edge of the ingot ranges from 640 to 944 MPa, which dramatically increases to over 1500 MPa for the intermediate regions. The highest strength of 1950 MPa was obtained in the specimen prepared from the center of the middle area of the ingot. When comparing the sample properties along the axial direction, it is found that the samples prepared from the bottom areas were of higher embrittlement than those from the top or middle areas due to larger cooling rate. The findings indicate that more efforts should be devoted to investigate the processing of bulk RHEAs ingot with respect to their potential application.
Journal Article
Reducing the risk of blowholes in heavy steel plates: causes to consider
The comprehensive metallographic analysis and statistical big-data analysis of blowhole appearance in heavy plate manufacturing gave no exact cause of defect formation but indicated differences in the chemical composition of defective and clean heavy plates and, above all, high content of residual elements. The rare BHs were found in the largest width ingot and on thinner plates that can be connected with the opening of blowholes after a thick layer of scale is removed after reheating. The non-metal inclusions in areola around blowholes have a higher silicon and manganese content, possibly forming by casting mixture particles entrapping and dissolved by liquid steel at pouring. The copper-enriched phases were found in the formed scale and on the interface between metal and scale, making them characteristic of hot-shortness defects that are difficult to differentiate from blowholes. The ways to eliminate the risk of blowhole formation and ensure the highest quality and efficiency of cast ingots are proposed.
Journal Article