International Journal of Metalcasting最新文献

Spherical sheet steel molds filled with gray iron melts of varying chemical compositions and metallurgical conditions were air-cooled until solid, followed directly by austempering to preserve the austenite grain structure. The castings were studied using a combination of cooling curves and quantitative metallography, in order to clarify control of the austenite grain structure and its impact on the local microstructure. A novel method utilizing fast Fourier transform provided visual overview of macroscopic trends in the scale of the flake graphite structure. Castings inoculated with Sr-containing ferrosilicon featured finer eutectic cell structure but coarser equiaxed structure of austenite, emphasizing that melt treatments applied to control the graphite structure may have unintended effects on the austenite grain structure. In most non-inoculated castings, the microstructure was banded, with alternating layers of coarse and fine flake graphite with distance from the casting surface. The extent of the columnar zone of austenite grains showed no correlation with the graphite structure nor the volume fraction of dendrites. The volume-to-surface ratio of dendrites was more uniform in the columnar zone, but increased toward the center in the equiaxed zone. The casting with the highest carbon equivalent (4.34), featured zones containing finer dendrites and graphite. These zones appear to be gaps in the early solidification structure which filled later by secondary dendritic growth from surrounding austenite. This highlights that high carbon equivalent may lead to poor dendrite coherency which can make the microstructure less uniform and less predictable.

This study investigates the effect of tempering temperature on the microstructure and wear resistance of high-alloy white cast iron (Ni-Hard 4) with 1.15% W and 0.5% B additions. Specimens were austenitized at 850 °C for 5 h, quenched in air, and tempered at temperatures between 250 and 650 °C for 4 h. Equilibrium and non-equilibrium thermodynamic calculations were performed using Thermo-Calc software. After the microstructural investigations, hardness testing was carried out. A pin-on-disk tribometer was used to conduct wear tests under dry sliding conditions. Microstructure and worn surfaces were examined using light and scanning electron microscopes. The results showed that increasing tempering temperature resulted in a higher volume fraction of carbides. It was found that tempering at 550 °C for four hours increases resistance to wear giving the lowest measured values of weight loss and wear rate. Accordingly, tempering allows the precipitation of fine carbides in the martensitic matrix which may increase wear resistance.

Chromite sands have been utilized to produce cores in foundries for many years. This investigation focuses on finer grades of chromite sand for core produced with shell technology. The specific shell cores produced result from the unique thermal characteristics of finer grades of chromite sand. The resulting castings demonstrate a high level of casting integrity.

Numerical simulation of the foundry process, aimed at reducing costs and production lead times, directly impacts the responsiveness and competitiveness of the foundries that employ it. Three experiments were conducted to establish the values of specific heat capacity (Cp), density (ρ), and thermal conductivity (λ) of green sand over a measurement range spanning from room temperature to over 800 °C. These experiments yielded representative data for the real properties of silico-clay sand, which were subsequently substituted for the generic properties provided in the NovaFlow&Solid® software database. It is worth noting that this study is not limited to a single software; the physical properties obtained can be transferred to other simulation software as well. A cooling simulation was conducted with the corrected physical properties of the sand, and the resulting curve better reflects reality than the one initially obtained with the original values. Having a more precise knowledge of the exact temperature of the metal at a given moment is crucial for predicting certain defects.

The semi-solid slurry preparation process, microstructure, and mechanical properties of truck coarse filter bracket were studied in this paper. The semi-solid aluminum alloy slurry with high solid fraction was prepared by the Slurry Enthalpy Equilibrium Device (SEED) method, and the optimum slurry preparation parameters were determined through the observation and analysis of the slurry microstructure as follows: pouring temperature 700 °C, rotation speed 180 r/min, and crucible temperature 400 °C. The average grain size and shape factor of the slurry prepared under these conditions are 50.448 μm and 0.799. Die casting trial production which used the best process parameters of slurry preparation and die casting was carried out. The results show that the die casting parts are completely filled with no obvious surface defects. It can be seen from the cutting experiment and X-ray non-destructive test that the internal structure is dense and uniform, and there are no obvious casting defects that were observed such as cracks and holes. The semi-solid die castings were strengthened by T6 heat treatment. The experimental results showed that the optimal heat treatment parameters were a solution temperature of 470 °C and time of 4 h, aging temperature of 175 °C and time of 12 h. Under these conditions, the microstructure morphology was improved significantly. The tensile strength and yield strength reached 342.1 MPa and 309.1 MPa, respectively, which were 38.9% and 95.3% higher than the semi-solid state, and the elongation was 4.5%.

In this paper, the effect of Si content on the microstructure and mechanical properties of the Al–1.2Mg–xSi–1.2Cu–0.6Mn cast alloy was investigated. The study aimed to explore the optimal addition of Si element to improve the comprehensive properties of alloys. The microstructure, phase composition and fracture morphology of the alloy were determined through OM, SEM, EBSD and XRD analysis. The Si content in the alloy ranged from 0.48 to 2.4 wt.%. With the increase of Si content, the number of strengthening phases increases, which improves the comprehensive properties of the alloy. When the Si content is 0.8 wt.%, the eutectic Mg₂Si transforms from rod-shaped to larger block shaped, and the formation of coarse Mg₂Si phase limits the elongation of the alloy. When the Si content is 2.4 wt.%, fine Al₂Cu phases are present in this alloy and coexist with Al(Fe,Mn)Si phases, while an increase in the Si content appears as partially accompanied by an incipient crystalline Si phase around the Al(Fe,Mn)Si phase. The alloy exhibits a maximum tensile strength, yield strength and elongation of 198.2 MPa, 101.2 MPa and 4.96%, respectively, with a hardness of 80.94 Hv. It consists of five alloy phases, mainly α-Al, Mg₂Si, Al(Fe, Mn)Si eutectic phase, Q-AlCuMgSi eutectic phase and the beginning crystalline silicon phase formed due to the increased Si content. The Si content can improve alloy strength, but there is some damage to the toughness of the alloy. Higher silicon alloy content results in the formation of fine Al₂Cu eutectic. This result makes it possible to achieve a higher level of strength with a reduced loss of ductility in the alloy.

To improve their performance, this research characterized the effects of Si on various attributes of high-Cr white cast irons. Hypoeutectic alloys of 15 and 25% Cr white irons were produced with Si levels varying of 0.4, 1 and 1.6%Si and poured into 3-inch (75-mm) Y-block sand molds. Various tests were used to determine the optimum hardening temperature and the kinetics of pearlite transformation. In addition, image analysis was performed to determine eutectic carbide fraction. Furthermore, energy-dispersive spectroscopy analysis was conducted to determine the distributions of the alloying elements among the various solidification constituents. Raising Cr from 15 to 25% caused the optimum hardening temperature to rise from 1680 to 1920 °F (915 to 1050 °C). In the 15% Cr series, an increase of 1.2% Si raised the optimum hardening temperature by 80 °F (50 °C), whereas, for the 25% Cr series, the optimum hardening temperature was unchanged. Peak hardness was significantly higher (by 50 HB) in the leaner Cr alloys and the peak hardness in both the 15% and 25% Cr alloys decreased slightly (by 20 HB) when the Si content was increased from 0.4 to 1.6%. However, the hardenability (the time to the onset of pearlite transformation) increased with increasing Si content. The influence of Si on % eutectic saturation was not clear. When analyzing carbide fraction, Si had a negligible effect in the 15%Cr series, but seemed to cause the 25%Cr series to develop less eutectic carbide, that is, become more hypoeutectic. Cr was richest in the eutectic carbides and leanest in the eutectic austenite matrix. Si was largely rejected from the eutectic carbides and richest in the eutectic austenite.

In the same way that a building needs a solid foundation to remain firm and stable, graphite requires proper nucleation sites to precipitate and grow in the right way. Phenomena that occur during solidification process will determine the nature of the nuclei (non-metallic inclusions), as the topology of the land will establish the quality of a construction. Their presence will define the nucleation potential of the melt, being highly influenced by a multitude of variables such as the base metal composition, the graphite spheroidization treatment, or the inoculation process. A good knowledge of the formation of these particles will help an excellent control of the formation of graphite. Silicates, oxides, sulfides, carbides, and nitrides were found acting as nuclei for graphite depending on the solidification conditions. The objective of this paper is to improve the understanding of the mechanisms that govern nucleation, verifying some theories already described by other researchers, but also developing some new ones. The direct relation between the type of nuclei and the processes that occur during the liquid–solid transformation was also demonstrated.