Next Issue
Previous Issue

Table of Contents

Metals, Volume 9, Issue 3 (March 2019)

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
Cover Story (view full-size image) This paper describes the synthesis of tungsten disulfide (WS2) powder by the sulfurization of [...] Read more.
View options order results:
result details:
Displaying articles 1-114
Export citation of selected articles as:
Open AccessArticle Prediction and Knowledge Mining of Outdoor Atmospheric Corrosion Rates of Low Alloy Steels Based on the Random Forests Approach
Metals 2019, 9(3), 383; https://doi.org/10.3390/met9030383
Received: 11 March 2019 / Revised: 19 March 2019 / Accepted: 23 March 2019 / Published: 26 March 2019
Viewed by 367 | PDF Full-text (6173 KB) | HTML Full-text | XML Full-text
Abstract
The objective of this paper is to develop an approach to forecast the outdoor atmospheric corrosion rate of low alloy steels and do corrosion-knowledge mining by using a Random Forests algorithm as a mining tool. We collected the corrosion data of 17 low [...] Read more.
The objective of this paper is to develop an approach to forecast the outdoor atmospheric corrosion rate of low alloy steels and do corrosion-knowledge mining by using a Random Forests algorithm as a mining tool. We collected the corrosion data of 17 low alloy steels under 6 atmospheric corrosion test stations in China over 16 years as the experimental datasets. Based on the datasets, a Random Forests model is established to implement the purpose of the corrosion rate prediction and data-mining. The results showed that the random forests can achieve the best generalization results compared to the commonly used machine learning methods such as the artificial neural network, support vector regression, and logistic regression. In addition, the results also showed that regarding the effect to the corrosion rate, environmental factors contributed more than chemical compositions in the low alloy steels, but as exposure time increases, the effect of the environmental factors will gradually become less. Furthermore, we give the effect changes of six environmental factors (Cl concentration, SO2 concentration, relative humidity, temperature, rainfall, and pH) on corrosion with exposure time increasing, and the results illustrated that pH had a significant contribution to the corrosion of the entire process. The paper also dealt with the problem of the corrosion rate forecast, especially for changing environmental factors situations, and obtained the qualitative and quantitative results of influences of each environmental factor on corrosion. Full article
Figures

Figure 1

Open AccessArticle Compositional Design of Soft Magnetic High Entropy Alloys by Minimizing Magnetostriction Coefficient in (Fe0.3Co0.5Ni0.2)100−x(Al1/3Si2/3)x System
Metals 2019, 9(3), 382; https://doi.org/10.3390/met9030382
Received: 31 January 2019 / Revised: 13 March 2019 / Accepted: 20 March 2019 / Published: 26 March 2019
Viewed by 310 | PDF Full-text (7764 KB) | HTML Full-text | XML Full-text
Abstract
Developing cost-effective soft magnetic alloys with excellent mechanical properties is very important to energy-saving industries. This study investigated the magnetic and mechanical properties of a series of (Fe0.3Co0.5Ni0.2)100−x(Al1/3Si2/3)x high-entropy alloys [...] Read more.
Developing cost-effective soft magnetic alloys with excellent mechanical properties is very important to energy-saving industries. This study investigated the magnetic and mechanical properties of a series of (Fe0.3Co0.5Ni0.2)100−x(Al1/3Si2/3)x high-entropy alloys (HEAs) (x = 0, 5, 10, 15, and 25) at room temperature. The Fe0.3Co0.5Ni0.2 base alloy composition was chosen since it has very the smallest saturation magnetostriction coefficient. It was found that the (Fe0.3Co0.5Ni0.2)95(Al1/3Si2/3)5 alloy maintains a simple face-centered cubic (FCC) solid solution structure in the states of as-cast, cold-rolled, and after annealing at 1000 °C. The alloy after annealing exhibits a tensile yield strength of 235 MPa, ultimate tensile strength of 572 MPa, an elongation of 38%, a saturation magnetization (Ms) of 1.49 T, and a coercivity of 96 A/m. The alloy not only demonstrates an optimal combination of soft magnetic and mechanical properties, it also shows advantages of easy fabrication and processing and high thermal stability over silicon steel and amorphous soft magnetic materials. Therefore, the alloy of (Fe0.3Co0.5Ni0.2)95(Al1/3Si2/3)5 holds good potential as next-generation soft magnets for wide-range industrial applications. Full article
(This article belongs to the Special Issue High Entropy Alloys: Challenges and Prospects)
Figures

Figure 1

Open AccessArticle Strategy to Enhance Magnetic Properties of Fe78Si9B13 Amorphous Powder Cores in the Industrial Condition
Metals 2019, 9(3), 381; https://doi.org/10.3390/met9030381
Received: 3 February 2019 / Revised: 22 March 2019 / Accepted: 23 March 2019 / Published: 26 March 2019
Viewed by 296 | PDF Full-text (16425 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the soft magnetic properties of Fe78Si9B13 amorphous magnetic powder cores (AMPCs) were enhanced by coordinately adjusting the technological parameters, including the particle size distribution, molding pressure, and coating agent content, in the industrial condition. The [...] Read more.
In this study, the soft magnetic properties of Fe78Si9B13 amorphous magnetic powder cores (AMPCs) were enhanced by coordinately adjusting the technological parameters, including the particle size distribution, molding pressure, and coating agent content, in the industrial condition. The results show that the optimized comprehensive soft magnetic properties of the Fe78Si9B13 AMPCs could be obtained under the following process conditions: (1) the distribution of particle size is 20 wt.% for 140–170 mesh, 70 wt.% for 170–270 mesh, and 10 wt.% for 270–400 mesh; (2) the molding pressure is in the range of 2.35–2.45 GPa; and (3) the additive amount of sodium silicate is 1.5 wt.%. After the collaborative optimization, the AMPCs’ compact density, ρ, the effective permeability, μe, and the residual effective permeability at the applied magnetizing field of 7.96 kA/m, μe@7.96 kA/m, increased from 5.61 g/cm3 to 5.86 g/cm3, from 58.13 to 77.01, and from 40.36 to 49.57, respectively. The attenuation ratio of the effective permeability, when in the frequency band of 20–100 kHz, was less than 0.85%. The core loss at the 50 kHz for the maximum magnetic flux density of 0.1 T reduced from 380.85 mW/cm3 to 335.23 mW/cm3. This work will encourage the further application of Fe-based AMPCs in the fields of electronics and telecommunication. Full article
(This article belongs to the Special Issue Metals Powders: Synthesis and Processing)
Figures

Figure 1

Open AccessArticle Research and Application of a Rolling Gap Prediction Model in Continuous Casting
Metals 2019, 9(3), 380; https://doi.org/10.3390/met9030380
Received: 6 March 2019 / Revised: 23 March 2019 / Accepted: 23 March 2019 / Published: 25 March 2019
Viewed by 385 | PDF Full-text (5107 KB) | HTML Full-text | XML Full-text
Abstract
Control of the roll gap of the caster segment is one of the key parameters for ensuring the quality of a slab in continuous casting. In order to improve the precision and timeliness of the roll gap value control, we proposed a rolling [...] Read more.
Control of the roll gap of the caster segment is one of the key parameters for ensuring the quality of a slab in continuous casting. In order to improve the precision and timeliness of the roll gap value control, we proposed a rolling gap value prediction (RGVP) method based on the continuous casting process parameters. The process parameters collected from the continuous casting production site were first dimension-reduced using principal component analysis (PCA); 15 process parameters were chosen for reduction. Second, a support vector machine (SVM) model using particle swarm optimization (PSO) was proposed to optimize the parameters and perform roll gap prediction. The experimental results and practical application of the models has indicated that the method proposed in this paper provides a new approach for the prediction of roll gap value. Full article
(This article belongs to the Special Issue Continuous Casting)
Figures

Figure 1

Open AccessArticle Effect of Laser Heat Treatment on the Microstructure and Properties of Alloy 800H
Metals 2019, 9(3), 379; https://doi.org/10.3390/met9030379
Received: 28 February 2019 / Revised: 21 March 2019 / Accepted: 22 March 2019 / Published: 25 March 2019
Viewed by 292 | PDF Full-text (5780 KB) | HTML Full-text | XML Full-text
Abstract
The effects of laser heat treatment on the microstructure and properties of alloy 800H were investigated. The fracture morphology, elemental changes, and phase composition of the specimens were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffractometry (XRD). The [...] Read more.
The effects of laser heat treatment on the microstructure and properties of alloy 800H were investigated. The fracture morphology, elemental changes, and phase composition of the specimens were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffractometry (XRD). The results show that the long-lasting life of the specimen after laser heat treatment increased by 28.6%, and the elongation after fracture increased by 20.7%. The macroscopic morphology of the fracture specimen exhibited obvious ductile fracture morphology, and the changes in the elemental content and grain size significantly affected the ductility and toughness of the alloy. This study has certain guiding significance for the optimization of the heat treatment process of this type of alloy. Full article
Figures

Figure 1

Open AccessCommunication Effects of Thermal Aging on the Low Cycle Fatigue Behaviors of Cast Duplex Stainless Steels
Metals 2019, 9(3), 378; https://doi.org/10.3390/met9030378
Received: 6 March 2019 / Revised: 21 March 2019 / Accepted: 22 March 2019 / Published: 25 March 2019
Viewed by 303 | PDF Full-text (4689 KB) | HTML Full-text | XML Full-text
Abstract
The low cycle fatigue (LCF) behaviors of cast duplex stainless steel (CDSS) thermally aged at different times were investigated under different strain amplitudes. The effects of thermal aging on the LCF lives of CDSS are closely related to the strain amplitude. At a [...] Read more.
The low cycle fatigue (LCF) behaviors of cast duplex stainless steel (CDSS) thermally aged at different times were investigated under different strain amplitudes. The effects of thermal aging on the LCF lives of CDSS are closely related to the strain amplitude. At a low strain amplitude, the fatigue life of the material increases significantly after thermal aging, while the LCF life decreases with an increasing aging time at a high strain amplitude. After thermal aging at 400 °C for 10,000 h, the fatigue fracture morphologies of CDSS change from fatigue fringes to mixture features including fatigue fringes in austenite and cleavage cracks in ferrite. Severe plastic deformation in ferrite of the aged CDSS under a high strain amplitude causes the cleavage cracking of ferrite. The premature failure of ferrite accelerates the propagation of fatigue crack and shortens the fatigue life at a high strain amplitude. Full article
Figures

Figure 1

Open AccessArticle Effect of Graphene and Carbon Nanotubes on the Thermal Conductivity of WC–Co Cemented Carbide
Metals 2019, 9(3), 377; https://doi.org/10.3390/met9030377
Received: 15 February 2019 / Revised: 19 March 2019 / Accepted: 20 March 2019 / Published: 24 March 2019
Viewed by 407 | PDF Full-text (5937 KB) | HTML Full-text | XML Full-text
Abstract
In recent years, it has been found that the service life of cemented carbide shield machine tools used in uneven soft and hard strata is substantially reduced in engineering practice. The study found that thermal stress is the main reason for the failure [...] Read more.
In recent years, it has been found that the service life of cemented carbide shield machine tools used in uneven soft and hard strata is substantially reduced in engineering practice. The study found that thermal stress is the main reason for the failure of cemented carbide shield tunneling tools when shield tunneling is carried out in uneven soft and hard soil. To maintain the hardness of cemented carbide, improving the thermal conductivity of the shield machine tool is of great importance for prolonging its service life and reducing engineering costs. In this study, graphene and carbon nanotubes were mixed with WC–Co powder and sintered by spark plasma sintering (SPS). The morphology was observed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The Rockwell hardness, bending strength, and thermal conductivity of the samples were tested. The results show that adding a small amount of graphene or carbon nanotubes could increase the bending strength of the cemented carbide by approximately 50%, while keeping the hardness of the cemented carbide constant. The thermal conductivity of the cemented carbide could be increased by 10% with the addition of 0.12 wt % graphene alone. Full article
(This article belongs to the Special Issue Design of Cemented Carbides and Cermet)
Figures

Figure 1

Open AccessArticle Simulation Approach for Cathodic Protection Prediction of Aluminum Fin-Tube Heat Exchanger Using Boundary Element Method
Metals 2019, 9(3), 376; https://doi.org/10.3390/met9030376
Received: 12 February 2019 / Revised: 12 March 2019 / Accepted: 20 March 2019 / Published: 23 March 2019
Viewed by 362 | PDF Full-text (2663 KB) | HTML Full-text | XML Full-text
Abstract
The multi-galvanic effect of an Al fin-tube heat exchanger was evaluated using polarization tests, numerical simulation, and the seawater acetic acid test (SWAAT). Determination of the polarization state using polarization curves was well correlated with numerical simulations using a high-conductivity electrolyte. However, the [...] Read more.
The multi-galvanic effect of an Al fin-tube heat exchanger was evaluated using polarization tests, numerical simulation, and the seawater acetic acid test (SWAAT). Determination of the polarization state using polarization curves was well correlated with numerical simulations using a high-conductivity electrolyte. However, the polarization results did not match those of the low-conductivity electrolyte due to the lower galvanic effect. Although the polarization state is changed by electrolyte conductivity, the total net current of the tube is decreased in the case of the anodic joint. From SWAAT results, the leakage time of Al fin-tube heat exchanger assembled by anodic joint was longer than the case with cathodic joint. Full article
(This article belongs to the Special Issue Corrosion and Protection of Metals)
Figures

Figure 1

Open AccessArticle Preparation Method of Spherical and Monocrystalline Aluminum Powder
Metals 2019, 9(3), 375; https://doi.org/10.3390/met9030375
Received: 5 March 2019 / Revised: 19 March 2019 / Accepted: 20 March 2019 / Published: 23 March 2019
Viewed by 376 | PDF Full-text (3004 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a new production method for a spherical and monocrystalline aluminum powder. Aluminum powder of irregular particle shapes was mixed with silica nanoparticles and heated to a temperature above the melting point of aluminum. Due to its molten state, high surface [...] Read more.
This paper presents a new production method for a spherical and monocrystalline aluminum powder. Aluminum powder of irregular particle shapes was mixed with silica nanoparticles and heated to a temperature above the melting point of aluminum. Due to its molten state, high surface tension, and poor wettability, the aluminum particles were transformed into liquid and spherical droplets separated by silica nanoparticles. The spherical shape was then retained when the aluminum particles solidified. The influence of the processing temperature on the particle shape, phase composition, and microstructure was investigated. Moreover, calorimetric, X-ray diffraction, grain size, and scanning electron microscopy with electron backscatter diffraction (SEM-EBSD) measurements of the particles’ microstructure are presented. It is proven that, by this means, a spherical and monocrystalline aluminum powder can be efficiently created directly from an air-atomized irregular powder. The observed phenomenon of particles becoming round is of great importance, especially when considering powder preparation for powder-based additive manufacturing processes. Full article
Figures

Graphical abstract

Open AccessArticle On the Development of Material Constitutive Model for 45CrNiMoVA Ultra-High-Strength Steel
Metals 2019, 9(3), 374; https://doi.org/10.3390/met9030374
Received: 28 February 2019 / Revised: 19 March 2019 / Accepted: 21 March 2019 / Published: 22 March 2019
Viewed by 316 | PDF Full-text (6277 KB) | HTML Full-text | XML Full-text
Abstract
For the implementation of simulations for large plastic deformation processes such as cutting and impact, the development of the constitutive models for describing accurately the dynamic plasticity and damage behaviors of materials plays a crucial role in the improvement of simulation accuracy. This [...] Read more.
For the implementation of simulations for large plastic deformation processes such as cutting and impact, the development of the constitutive models for describing accurately the dynamic plasticity and damage behaviors of materials plays a crucial role in the improvement of simulation accuracy. This paper focuses on the dynamic behaviors of 45CrNiMoVA ultra-high-strength torsion bar steel. According to investigation of the Split-Hopkinson pressure bar (SHPB) and Split-Hopkinson tensile bar (SHTB) tests at different strain rate and different temperatures, 45CrNiMoVA ultra-high-strength steel is characterized by strain hardening, strain-rate hardening and thermal softening effects. Based on the analysis on the mechanism of the experimental results and the limitation of classic Johnson-Cook (J-C) constitutive model, a modified J-C model by considering the phase transition at high temperature is established. The multi-objective optimization fitting method was used for fitting model parameters. Compared with the classic J-C constitutive model, the fitting accuracy of the modified J-C model significantly improved. In addition, finite element simulations for SHPB and SHTB based on the modified J-C model are conducted. The SHPB stress-strain curves and the fracture morphology of SHTB samples from simulations are in good agreement with those from tests. Full article
(This article belongs to the Special Issue Multiscale Modeling of Materials and Processes)
Figures

Figure 1

Open AccessArticle Quenching and Partitioning of Multiphase Aluminum-Added Steels
Metals 2019, 9(3), 373; https://doi.org/10.3390/met9030373
Received: 27 February 2019 / Revised: 18 March 2019 / Accepted: 19 March 2019 / Published: 22 March 2019
Viewed by 432 | PDF Full-text (4014 KB) | HTML Full-text | XML Full-text
Abstract
The quenching and partitioning response following intercritical annealing was investigated for three lean TRIP-type high-Al steel compositions. Depending on the intercritical austenite fraction following annealing, the steels assumed either a ferrite/martensite/retained austenite microstructure or a multiphase structure with ferritic, bainitic and martensitic constituents [...] Read more.
The quenching and partitioning response following intercritical annealing was investigated for three lean TRIP-type high-Al steel compositions. Depending on the intercritical austenite fraction following annealing, the steels assumed either a ferrite/martensite/retained austenite microstructure or a multiphase structure with ferritic, bainitic and martensitic constituents along with retained austenite. The amount of retained austenite was found to correlate with the initial quench temperature and, depending on the intercritical annealing condition prior to initial quenching, with the uniform and ultimate elongations measured in tensile testing. Full article
(This article belongs to the Special Issue Advances in Low-carbon and Stainless Steels)
Figures

Figure 1

Open AccessArticle Effects of Cerium on Weld Solidification Crack Sensitivity of 441 Ferritic Stainless Steel
Metals 2019, 9(3), 372; https://doi.org/10.3390/met9030372
Received: 26 February 2019 / Revised: 9 March 2019 / Accepted: 13 March 2019 / Published: 22 March 2019
Viewed by 300 | PDF Full-text (3385 KB) | HTML Full-text | XML Full-text
Abstract
The addition of rare earth element Ce in ferritic stainless steel can improve the high temperature performance to meet the service requirements of automobile exhaust systems at high temperatures. Automobile exhaust systems are generally applied as welded pipes, so it is necessary to [...] Read more.
The addition of rare earth element Ce in ferritic stainless steel can improve the high temperature performance to meet the service requirements of automobile exhaust systems at high temperatures. Automobile exhaust systems are generally applied as welded pipes, so it is necessary to study the effect of Ce on the weldability of ferritic stainless steel. In this study, the Trans-varestraint test method was used to test the solidification crack sensitivities of 441 and 441Ce ferritic stainless steel. The 441Ce steel, which has added Ce, showed poor resistance to weld solidification cracking. Using Thermo-Calc software, Ce was observed to expand the solidification temperature range of 441 ferritic stainless steel, increase the time for solid–liquid coexistence during solidification, and increase the sensitivity of solidification cracking. Further, from scanning electron microscopy and energy dispersive spectrometer analysis, the addition of Ce was found to reduce high temperature precipitation (Ti,Nb)(C,N), reduce or even eliminate the “pinning” effect during solidification, and increase solidification crack sensitivity of 441 ferritic stainless steel. Full article
(This article belongs to the Special Issue Characterization of Welded Joints)
Figures

Figure 1

Open AccessArticle On the Design of Innovative Heterogeneous Sheet Metal Tests Using a Shape Optimization Approach
Metals 2019, 9(3), 371; https://doi.org/10.3390/met9030371
Received: 15 February 2019 / Revised: 11 March 2019 / Accepted: 16 March 2019 / Published: 22 March 2019
Viewed by 331 | PDF Full-text (20784 KB) | HTML Full-text | XML Full-text
Abstract
The development of full-field measurement methods has enabled a new trend of heterogeneous mechanical tests. The inhomogeneous strain fields retrieved from these tests are being widely used in the calibration of constitutive models for sheet metals. However, today, there is no mechanical test [...] Read more.
The development of full-field measurement methods has enabled a new trend of heterogeneous mechanical tests. The inhomogeneous strain fields retrieved from these tests are being widely used in the calibration of constitutive models for sheet metals. However, today, there is no mechanical test able to characterize the material in a large range of strain states. The aim of this work is to present a heterogeneous mechanical test with an innovative tool/specimen shape, capable of producing rich heterogeneous strain paths and thus providing extensive information on material behavior. The proposed specimen is found using a shape optimization process where an index that evaluates the richness of strain information is used. In this work, the methodology and results are extended to non-specimen geometry dependence and to the non-dependence of the geometry parametrization through the use of the Ritz method for boundary value problems. Different curve models, such as splines, B-splines, and NURBS, are used, and C1 continuity throughout the specimen is guaranteed. Moreover, several deterministic and stochastic optimization methods are used in order to find the method or the combination of methods able to minimize the cost function effectively. Results demonstrated that the solution is dependent on the geometry definition, as well as on the optimization methodology. Nevertheless, the obtained solutions provided a wider spectrum of strain states than standard tests. Full article
(This article belongs to the Special Issue Constitutive Modelling for Metals)
Figures

Figure 1

Open AccessArticle The Influence of Mg-Based Inclusions on the Grain Boundary Mobility of Austenite in SS400 Steel
Metals 2019, 9(3), 370; https://doi.org/10.3390/met9030370
Received: 23 January 2019 / Revised: 14 March 2019 / Accepted: 20 March 2019 / Published: 22 March 2019
Viewed by 308 | PDF Full-text (4088 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the effects of the addition of Mg to the grain growth of austenite and the magnesium-based inclusions to mobility were investigated in SS400 steel at high temperatures. A high-temperature confocal scanning laser microscope (HT-CSLM) was employed to directly observe, in [...] Read more.
In this study, the effects of the addition of Mg to the grain growth of austenite and the magnesium-based inclusions to mobility were investigated in SS400 steel at high temperatures. A high-temperature confocal scanning laser microscope (HT-CSLM) was employed to directly observe, in situ, the grain structure of austenite under 25 torr Ar at high temperatures. The grain size distribution of austenite showed the log-normal distribution. The results of the grain growth curves using 3D surface fitting showed that the n and Q values of the growth equation parameters ranged from 0.2 to 0.26 and from 405 kJ/mole to 752 kJ/mole, respectively, when adding 5.6–22 ppm of Mg. Increasing the temperature from 1150 to 1250 °C for 20 min and increasing the addition of Mg by 5.6, 11, and 22 ppm resulted in increases in the grain boundary velocity. The effects of solute drag and Zener pinning on grain boundary mobility were also calculated in this study. Full article
Figures

Figure 1

Open AccessArticle Effect of Grain Size Distribution on Recrystallisation Kinetics in an Fe-30Ni Model Alloy
Metals 2019, 9(3), 369; https://doi.org/10.3390/met9030369
Received: 27 February 2019 / Revised: 20 March 2019 / Accepted: 21 March 2019 / Published: 22 March 2019
Viewed by 324 | PDF Full-text (3375 KB) | HTML Full-text | XML Full-text
Abstract
This paper discusses the role of grain size distribution on the recrystallisation rates and Avrami values for a Fe-30 wt. % Ni steel, which was used as a model alloy retaining an austenitic structure to room temperature. Cold deformation was used to provide [...] Read more.
This paper discusses the role of grain size distribution on the recrystallisation rates and Avrami values for a Fe-30 wt. % Ni steel, which was used as a model alloy retaining an austenitic structure to room temperature. Cold deformation was used to provide uniform macroscopic strain distributions (strains of 0.2 and 0.3), followed by recrystallisation during annealing at 850–950 °C. It was shown that the Avrami parameter was directly related to the grain size distribution, with a lower Avrami exponent being seen for a larger average and wider grain size distribution. A method to predict the Avrami exponent from the grain size distribution was proposed. In situ heating in an SEM with EBSD showed the recrystallisation kinetics to be affected by differences in stored energy and nucleation in the different grain sizes supporting the proposed relationship. Full article
Figures

Figure 1

Open AccessArticle Micromechanical Modelling of the Cyclic Deformation Behavior of Martensitic SAE 4150—A Comparison of Different Kinematic Hardening Models
Metals 2019, 9(3), 368; https://doi.org/10.3390/met9030368
Received: 15 February 2019 / Revised: 13 March 2019 / Accepted: 15 March 2019 / Published: 21 March 2019
Viewed by 356 | PDF Full-text (6171 KB) | HTML Full-text | XML Full-text
Abstract
A fundamental prerequisite for the micromechanical simulation of fatigue is the appropriate modelling of the effective cyclic properties of the considered material. Therefore, kinematic hardening formulations on the slip system level are of crucial importance due to their fundamental relevance in cyclic material [...] Read more.
A fundamental prerequisite for the micromechanical simulation of fatigue is the appropriate modelling of the effective cyclic properties of the considered material. Therefore, kinematic hardening formulations on the slip system level are of crucial importance due to their fundamental relevance in cyclic material modelling. The focus of this study is the comparison of three different kinematic hardening models (Armstrong Frederick, Chaboche, and Ohno–Wang). In this work, investigations are performed on the modelling and prediction of the cyclic stress-strain behavior of the martensitic high-strength steel SAE 4150 for two different total strain ratios (R ε = −1 and R ε = 0). In the first step, a three-dimensional martensitic microstructure model is developed by using multiscale Voronoi tessellations. Based on this martensitic representative volume element, micromechanical simulations are performed by a crystal plasticity finite element model. For the constitutive model calibration, a new multi-objective calibration procedure incorporating a sensitivity analysis as well as an evolutionary algorithm is presented. The numerical results of different kinematic hardening models are compared to experimental data with respect to the appropriate modelling of the Bauschinger effect and the mean stress relaxation behavior at R ε = 0. It is concluded that the Ohno–Wang model is superior to the Armstrong Frederick and Chaboche kinematic hardening model at R ε = −1 as well as at R ε = 0. Full article
Figures

Figure 1

Open AccessFeature PaperArticle Strain Hardening, Damage and Fracture Behavior of Al-Added High Mn TWIP Steels
Metals 2019, 9(3), 367; https://doi.org/10.3390/met9030367
Received: 15 February 2019 / Revised: 18 March 2019 / Accepted: 19 March 2019 / Published: 21 March 2019
Viewed by 339 | PDF Full-text (16356 KB) | HTML Full-text | XML Full-text
Abstract
The strain hardening and damage behavior of Al-added twinning induced plasticity (TWIP) steels were investigated. The study was focused on comparing two different alloying concepts by varying C and Mn contents with stacking fault energy (SFE) values of 24 mJ/m2 and 29 [...] Read more.
The strain hardening and damage behavior of Al-added twinning induced plasticity (TWIP) steels were investigated. The study was focused on comparing two different alloying concepts by varying C and Mn contents with stacking fault energy (SFE) values of 24 mJ/m 2 and 29 mJ/m 2 . The evolution of microstructure, deformation mechanisms and micro-cracks development with increasing deformation was analyzed. Al-addition has led to the decrease of C diffusivity and reduction in tendency for Mn-C short-range ordering resulting in the suppression of serrated flow caused due to dynamic strain aging (DSA) in an alloy with 0.3 wt.% C at room temperature and quasi-static testing, while DSA was delayed in an alloy with 0.6 wt.% C. However, an alloy with 0.6 wt.% C showing DSA effect exhibited enhanced strain hardening and ductility compared to an alloy with 0.3 wt.% C without DSA effect. Twinning was identified as the most predominant deformation mode in both the alloys, which occurred along with dislocation glide. Al-addition has increased SFE thereby delaying the nucleation of deformation twins and prolonged saturation of twinning, which resulted in micro-cracks initiation only just prior to necking or failure. The increased stress concentration caused by the interception of deformation twins or slip bands at grain boundaries (GB) has led to the development of micro-cracks mainly at GB and triple junctions. Deformation twins and slip bands played a vital role in assisting inter-granular crack initiation and propagation. Micro-cracks that developed at manganese sulfide and aluminum nitride inclusions showed no tendency for growth even after large deformation indicating the minimal detrimental effect on the tensile properties. Full article
(This article belongs to the Special Issue Physical Metallurgy of High Manganese Steels)
Figures

Figure 1

Open AccessFeature PaperArticle Optimizing the Conditions of Metal Solidification with Vibration
Metals 2019, 9(3), 366; https://doi.org/10.3390/met9030366
Received: 27 February 2019 / Revised: 18 March 2019 / Accepted: 20 March 2019 / Published: 21 March 2019
Viewed by 320 | PDF Full-text (3396 KB) | HTML Full-text | XML Full-text
Abstract
Vibration treatment of solidifying metals results in improvement in the ingot structure. There is a need to study this process not only because of the practical potential of vibration treatment but also due to the lack of understanding the process. An important practical [...] Read more.
Vibration treatment of solidifying metals results in improvement in the ingot structure. There is a need to study this process not only because of the practical potential of vibration treatment but also due to the lack of understanding the process. An important practical challenge is to find optimal conditions for liquid metal processing. In this paper, the authors consider a solidification process in the particular case of a cylindrical chill mold with vibration as a solution of the Stefan problem. An integral value of mechanical stresses in the melt during solidification is considered as an efficiency criterion of vibration treatment. A dependence of this value on the vibration frequency and amplitude is obtained through solving the Stefan problem numerically. The solution allows one to find the optimal vibration frequency and amplitude. We verified the numerical solution with experimental data obtained upon vibration treatment of aluminum melt under different conditions. The experimentally found optimal conditions for metal processing were similar to those proposed in theory, i.e., a vibration frequency of about 60 Hz and an amplitude of about 0.5 mm. Full article
(This article belongs to the Special Issue Casting and Forming of Advanced Aluminum Alloys)
Figures

Figure 1

Open AccessArticle Avrami Kinetic-Based Constitutive Relationship for Armco-Type Pure Iron in Hot Deformation
Metals 2019, 9(3), 365; https://doi.org/10.3390/met9030365
Received: 2 March 2019 / Revised: 15 March 2019 / Accepted: 16 March 2019 / Published: 21 March 2019
Viewed by 308 | PDF Full-text (7035 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The work presents a full mathematical description of the stress-strain compression curves in a wide range of strain rates and deformation temperatures for Armco-type pure iron. The constructed models are based on a dislocation structure evolution equation (in the case of dynamic recovery [...] Read more.
The work presents a full mathematical description of the stress-strain compression curves in a wide range of strain rates and deformation temperatures for Armco-type pure iron. The constructed models are based on a dislocation structure evolution equation (in the case of dynamic recovery (DRV)) and Avrami kinetic-based model (in the case of dynamic recrystallization (DRX)). The fractional softening model is modified as: X = ( σ 2 σ r 2 ) / ( σ d s 2 σ r 2 ) considering the strain hardening of un-recrystallized regions. The Avrami kinetic equation is modified and used to describe the DRX process considering the strain rate and temperature. The relations between the Avrami constant k , time exponent n , strain rate ε ˙ , temperature T and Z parameter are discussed. The yield stress σ y , saturation stress σ r s , steady stress σ d s and critical strain ε c are expressed as the functions of the Z parameter. A constitutive model is constructed based on the strain-hardening model, fractional softening model and modified Avrami kinetic equation. The DRV and DRX characters of Armco-type pure iron are clearly presented in these flow stress curves determined by the model. Full article
(This article belongs to the Special Issue Constitutive Modelling for Metals)
Figures

Figure 1

Open AccessArticle Comparison of Energy Consumption and CO2 Emission for Three Steel Production Routes—Integrated Steel Plant Equipped with Blast Furnace, Oxygen Blast Furnace or COREX
Metals 2019, 9(3), 364; https://doi.org/10.3390/met9030364
Received: 31 December 2018 / Revised: 27 February 2019 / Accepted: 20 March 2019 / Published: 21 March 2019
Viewed by 350 | PDF Full-text (3761 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
High CO2 emissions and energy consumption have greatly restricted the development of China’s iron and steel industry. Two alternative ironmaking processes, top gas recycling-oxygen blast furnace (TGR-OBF) and COREX®, can reduce CO2 emissions and coking coal consumption in the [...] Read more.
High CO2 emissions and energy consumption have greatly restricted the development of China’s iron and steel industry. Two alternative ironmaking processes, top gas recycling-oxygen blast furnace (TGR-OBF) and COREX®, can reduce CO2 emissions and coking coal consumption in the steel industry when compared with a conventional blast furnace (BF). To obtain parameters on the material flow of these processes, two static process models for TGR-OBF and COREX were established. Combining the operating data from the Jingtang steel plant with established static process models, this research presents a detailed analysis of the material flows, metallurgical gas generation and consumption, electricity consumption and generation, comprehensive energy consumption, and CO2 emissions of three integrated steel plants (ISP) equipped with the BF, TGR-OBF, and COREX, respectively. The results indicated that the energy consumption of an ISP with the TGR-OBF was 16% and 16.5% lower than that of a conventional ISP and an ISP with the COREX. Compared with a conventional ISP, the coking coal consumption in an ISP with the TGR-OBF and an ISP with the COREX were reduced by 39.7% and 100% respectively. With the International Energy Agency factor, the ISP with the TGR-OBF had the lowest net CO2 emissions, which were 10.8% and 35.0% lower than that of a conventional ISP and an ISP with the COREX. With the China Grid factor, the conventional ISP had the lowest net CO2 emissions—2.8% and 24.1% lower than that of an ISP with the TGR-OBF and an ISP with the COREX, respectively. Full article
(This article belongs to the Special Issue Ironmaking and Steelmaking)
Figures

Figure 1

Open AccessArticle High-Pressure Oxidative Leaching and Iodide Leaching Followed by Selective Precipitation for Recovery of Base and Precious Metals from Waste Printed Circuit Boards Ash
Metals 2019, 9(3), 363; https://doi.org/10.3390/met9030363
Received: 1 March 2019 / Revised: 16 March 2019 / Accepted: 18 March 2019 / Published: 20 March 2019
Viewed by 389 | PDF Full-text (3743 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This paper deals with the recovery of gold from waste printed circuit boards (WPCBs) ash by high-pressure oxidative leaching (HPOL) pre-treatment and iodide leaching followed by reduction precipitation. Base metals present in WPCB ash were removed via HPOL using a diluted sulfuric acid [...] Read more.
This paper deals with the recovery of gold from waste printed circuit boards (WPCBs) ash by high-pressure oxidative leaching (HPOL) pre-treatment and iodide leaching followed by reduction precipitation. Base metals present in WPCB ash were removed via HPOL using a diluted sulfuric acid solution at elevated temperatures. Effects of potassium iodide concentration, hydrogen peroxide concentration, sulfuric acid concentration, leaching temperature, and leaching time on gold extraction from pure gold chips with KI–H2O2–H2SO4 were investigated. The applicability of the optimized iodide leaching process for the extraction of gold from the leach residue obtained after HPOL were examined at different pulp densities ranging from 50 g/t to 200 g/t. Results show that the removal efficiency was 99% for Cu, 95.7% for Zn, 91% for Ni, 87.3% for Al, 82% for Co, and 70% for Fe under defined conditions. Under the optimal conditions, the percentage of gold extraction from the gold chips and the residue of WPCBs was 99% and 95%, respectively. About 99% of the gold was selectively precipitated from the pregnant leach solution by sequential precipitation with sodium hydroxide and L-ascorbic acid. Finally, more than 93% of gold recovery was achieved from WPCB ash by overall combined processes. Full article
(This article belongs to the Special Issue Leaching Kinetics of Valuable Metals)
Figures

Graphical abstract

Open AccessArticle Study on Intensification Behavior of Bismuth Ions on Gold Cyanide Leaching
Metals 2019, 9(3), 362; https://doi.org/10.3390/met9030362
Received: 16 February 2019 / Revised: 11 March 2019 / Accepted: 15 March 2019 / Published: 20 March 2019
Viewed by 327 | PDF Full-text (2704 KB) | HTML Full-text | XML Full-text
Abstract
Gold cyanide leaching is inefficient with conventional cyanidation. Bismuth ions can improve the efficiency of gold cyanidation by intensifying gold dissolution. The electrochemical behavior, structure information, and surface product of gold anodic dissolution were studied during the intensification of bismuth ions on gold [...] Read more.
Gold cyanide leaching is inefficient with conventional cyanidation. Bismuth ions can improve the efficiency of gold cyanidation by intensifying gold dissolution. The electrochemical behavior, structure information, and surface product of gold anodic dissolution were studied during the intensification of bismuth ions on gold cyanide leaching. The electrochemical analysis showed that the bismuth ions can not only improve anode current density, but also make gold dissolve at a lower potential, increase the corrosion current and intensify gold anodic dissolution. The microstructure analysis showed that bismuth ions intensified the cyanide corrosion of the gold surface, causing a large number of loose honeycombs, gullies, pits, and large holes on the gold surface. The XPS, FT-IR, and Raman analysis showed that there is weak information of C≡N in the spectrum of Bi intensification contrasting to that of conventional cyanidation. Cyanide compounds may be the insoluble AuCNads, which does not deposit on the surface of gold plate after Bi intensification cyanidation. The insoluble intermediate AuCNads is likely to react promptly with CN- to form soluble Au(CN ) 2 , making less insoluble AuCNads deposits on the gold surface. Therefore, bismuth ions can promote the dissolution of insoluble AuCNads, prevents its passivation film to cover around the gold plate, keeps cyanide good contact with gold, and finally accelerates the cyanide dissolution of gold. Full article
Figures

Figure 1

Open AccessArticle Characterization of Double Leached Waelz Oxide for Identification of Fluoride Mineral
Metals 2019, 9(3), 361; https://doi.org/10.3390/met9030361
Received: 22 February 2019 / Revised: 14 March 2019 / Accepted: 15 March 2019 / Published: 20 March 2019
Viewed by 387 | PDF Full-text (2150 KB) | HTML Full-text | XML Full-text
Abstract
Double leached Waelz oxide (DLWO), with 76% zinc, is a secondary zinc containing raw materials obtained by the treatment of electric arc furnace dust. The content of fluoride in DLWO is still too high for direct leaching, as fluoride has a detrimental effect [...] Read more.
Double leached Waelz oxide (DLWO), with 76% zinc, is a secondary zinc containing raw materials obtained by the treatment of electric arc furnace dust. The content of fluoride in DLWO is still too high for direct leaching, as fluoride has a detrimental effect on electrowinning for zinc production. Knowledge of the characteristics of DLWO, and especially on how a fluoride mineral might exist, can contribute to further improvement of the selective leaching for the removal of fluoride. In this study, DLWO was characterized using analytical techniques, such as inductively coupled plasma-optical emission spectroscopy (ICP-OES), 19F liquid-state nuclear magnetic resonance (19F LS NMR), X-ray powder diffraction analysis (XRD), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) and 19F solid-state nuclear magnetic resonance (19F SS NMR). This study showed that DLWO mainly consisted of zincite (ZnO), cerussite (PbCO3) and a spinel containing zinc, iron and manganese. The fluoride mineral identified was calcium fluoride (CaF2). In SEM analysis, fluorine was found in larger grains together with calcium and oxygen, which was possibly calcium carbonate. Full article
(This article belongs to the Special Issue Metal Removal and Recycling)
Figures

Figure 1

Open AccessArticle Influences of the Heating and Cooling Rates on the Dissolution and Precipitation Behavior of a Nickel-Based Single-Crystal Superalloy
Metals 2019, 9(3), 360; https://doi.org/10.3390/met9030360
Received: 19 February 2019 / Revised: 12 March 2019 / Accepted: 14 March 2019 / Published: 20 March 2019
Viewed by 349 | PDF Full-text (7974 KB) | HTML Full-text | XML Full-text
Abstract
The effects of the heating rate before solution treatment, and the cooling rate after solution treatment on the morphological distribution and evolution of the precipitation phase of nickel-based single crystal superalloy were studied. The dissolution, precipitation, and growth of the precipitation phase and [...] Read more.
The effects of the heating rate before solution treatment, and the cooling rate after solution treatment on the morphological distribution and evolution of the precipitation phase of nickel-based single crystal superalloy were studied. The dissolution, precipitation, and growth of the precipitation phase and the matrix phase during heat treatment were analyzed by the means of high-power scanning electron microscopy. The results show that the morphology of the precipitated phase has nothing to do with the distribution of the precipitated phase and the heating rate in the heating process, but the cooling rate in the cooling process affects the shape, size, and distribution of the precipitated phase. The faster the cooling rate, the smaller the precipitated phase is, the more irregular the shape is, the smaller the equivalent edge length is, and the smaller the channel width of the matrix phase is. Full article
Figures

Figure 1

Open AccessArticle Structural Stress Method to Evaluate Fatigue Properties of Similar and Dissimilar Self-Piercing Riveted Joints
Metals 2019, 9(3), 359; https://doi.org/10.3390/met9030359
Received: 31 January 2019 / Revised: 13 March 2019 / Accepted: 14 March 2019 / Published: 20 March 2019
Viewed by 313 | PDF Full-text (2149 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, we discuss the application of a simple Battelle structural stress model to evaluate the fatigue life of a self-piercing riveted (SPR) carbon-fiber-reinforced polymer (CFRP) composite to aluminum AA6111. The analytical model accounts for the forces and moments acting on the [...] Read more.
In this paper, we discuss the application of a simple Battelle structural stress model to evaluate the fatigue life of a self-piercing riveted (SPR) carbon-fiber-reinforced polymer (CFRP) composite to aluminum AA6111. The analytical model accounts for the forces and moments acting on the rivets to determine the structural stresses which were then plotted against the laboratory-generated fatigue life data. The master S-N curve determined in this study thus accounts for various factors such as the stacking configuration, rivet head height, and fatigue load ratios. The analytical model used in this study was able to collapse a large number of fatigue life data into one master S-N curve irrespective of stack-ups, rivet head height, and load ratios. Thus, the master S-N curve derived from the model can be used to predict the fatigue life of the SPR joints. Full article
Figures

Figure 1

Open AccessArticle The Effect of Different Annealing Temperatures on Recrystallization Microstructure and Texture of Clock-Rolled Tantalum Plates with Strong Texture Gradient
Metals 2019, 9(3), 358; https://doi.org/10.3390/met9030358
Received: 28 February 2019 / Revised: 18 March 2019 / Accepted: 18 March 2019 / Published: 20 March 2019
Viewed by 350 | PDF Full-text (7409 KB) | HTML Full-text | XML Full-text
Abstract
The texture and the bulk stored energy along the thickness direction were extremely inhomogeneous in the clock-rolled tantalum sheets with 70% reduction. Therefore, the effects of different annealing temperatures on the microstructure and texture distribution of tantalum plates through the thickness were investigated [...] Read more.
The texture and the bulk stored energy along the thickness direction were extremely inhomogeneous in the clock-rolled tantalum sheets with 70% reduction. Therefore, the effects of different annealing temperatures on the microstructure and texture distribution of tantalum plates through the thickness were investigated by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The results showed that the occurrence of strong {111} recrystallization texture in the center layer can be attributed to the subgrains nucleation mechanism when annealed at the low temperature. Many subgrains with {111} orientation appeared in the center layer, due to its high stored energy and preferential nucleation sites of the {111} deformed matrix, and rapidly grew into the effective nucleus, resulting in the large {111} grain size and strong {111} texture after complete recrystallization. Contrarily, at the high temperature, high-angle grain boundaries had sufficient driving force to generate migration, due to the lack of recovery, and the growth time of recrystallized nucleus was much shorter, contributing to relatively uniform recrystallization microstructure and texture distribution along the thickness. Full article
Figures

Figure 1

Open AccessFeature PaperArticle Hot Forming of Ultra-Fine-Grained Multiphase Steel Products Using Press Hardening Combined with Quenching and Partitioning Process
Metals 2019, 9(3), 357; https://doi.org/10.3390/met9030357
Received: 18 February 2019 / Revised: 16 March 2019 / Accepted: 18 March 2019 / Published: 20 March 2019
Viewed by 363 | PDF Full-text (4267 KB) | HTML Full-text | XML Full-text
Abstract
Hot forming combined with austempering and quenching and partitioning (QP) processes have been used to shape two cold rolled high silicon steel sheets into hat profiles. Thermal simulation on a Gleeble instrument was employed to optimize processing variables to achieve an optimum combination [...] Read more.
Hot forming combined with austempering and quenching and partitioning (QP) processes have been used to shape two cold rolled high silicon steel sheets into hat profiles. Thermal simulation on a Gleeble instrument was employed to optimize processing variables to achieve an optimum combination of strength and ductility in the final parts. Microstructures were characterized using optical and scanning electron microscopy and X-ray diffraction. Tensile strengths (Rm) of 1190 and 1350 MPa and elongations to fracture (A50mm) of 8.5 and 7.4%, were achieved for the two high-silicon steels having 0.15 and 0.26 wt % C, respectively. Preliminary results show that press hardening together with a QP heat treatment is an effective method of producing components with high strength and reasonable tensile ductility from low carbon containing steels that have the potential for carbide free bainite formation. The QP treatment resulted in faster austenite decomposition during partitioning in the steels in comparison with an austempering treatment. Full article
(This article belongs to the Special Issue Advances in Low-carbon and Stainless Steels)
Figures

Figure 1

Open AccessArticle High-Temperature Friction and Wear Properties of NiCr/hBN Self-Lubricating Composites
Metals 2019, 9(3), 356; https://doi.org/10.3390/met9030356
Received: 30 January 2019 / Revised: 10 March 2019 / Accepted: 14 March 2019 / Published: 20 March 2019
Viewed by 305 | PDF Full-text (5373 KB) | HTML Full-text | XML Full-text
Abstract
NiCr/hBN self-lubricating composites with hBN solid-lubricant contents of 8%, 9%, 10%, 11%, and 12% (mass fractions) were prepared by powder-metallurgy method. Their tribological properties at room temperature and 600, 700, and 800 °C were studied. SEM and XRD were performed to analyze their [...] Read more.
NiCr/hBN self-lubricating composites with hBN solid-lubricant contents of 8%, 9%, 10%, 11%, and 12% (mass fractions) were prepared by powder-metallurgy method. Their tribological properties at room temperature and 600, 700, and 800 °C were studied. SEM and XRD were performed to analyze their wear-surface morphology and abrasive-dust composition. Results indicate that the NiCr/hBN self-lubricating composites have favorable tribological properties at room temperature and 600 °C. The optimum comprehensive friction and wear performance are achieved at 10% hBN, and the main wear mechanism is abrasive wear. At 700 and 800 °C, the friction and wear properties of NiCr/hBN self-lubricating composites obviously decline. The wear surface experiences oxidation and the spinel oxides Cr2O3, NiCr2O4, and CrBO3 are formed. The main wear mechanism becomes combined scratching and glue form of adhesive wear, leading to greatly increased wear rate for the NiCr/hBN sel-lubricating composites. Full article
(This article belongs to the Special Issue Alloys for High-Temperature Applications)
Figures

Figure 1

Open AccessArticle Numerical and Experimental Investigation of the Heat Input Effect on the Mechanical Properties and Microstructure of Dissimilar Weld Joints of 690-MPa QT and TMCP Steel
Metals 2019, 9(3), 355; https://doi.org/10.3390/met9030355
Received: 12 February 2019 / Revised: 11 March 2019 / Accepted: 15 March 2019 / Published: 20 March 2019
Viewed by 362 | PDF Full-text (8815 KB) | HTML Full-text | XML Full-text
Abstract
The study evaluates numerically and experimentally the effect of welding heat input parameters on the microstructure and hardness of the heat-affected zone (HAZ) of quenched and tempered (QT) and thermo-mechanically controlled process (TMCP) 690-MPa high-strength steel. Numerical analyses and experimental comparisons were applied [...] Read more.
The study evaluates numerically and experimentally the effect of welding heat input parameters on the microstructure and hardness of the heat-affected zone (HAZ) of quenched and tempered (QT) and thermo-mechanically controlled process (TMCP) 690-MPa high-strength steel. Numerical analyses and experimental comparisons were applied using three heat input values (10, 14, and 17 kJ/cm) in order to predict the thermal fields during welding. Experimental analysis was carried out of the microstructure and microhardness behavior in different HAZ areas. The numerical values indicate that the maximum respective values of temperature measured in QT steel and TMCP steel were about 1300 and 1200 °C for a heat input of 10 kJ/cm, 1400 and 1300 °C for a heat input of 14 kJ/cm, and 1600 and 1450 °C for a heat input of 17 kJ/cm. The cooling times resulted, for a heat input of 10 kJ/cm, in numerical t8/5 (14.5 s) and experimental (18.84 s) increases in hardness in the coarse-grain heat-affected zone (CGHAZ) of the QT steel (317 HV0.1), due to the formation of bainite and lath martensite structures with grain growth. Decreased hardness in the CGHAZ of TMCP steel (240 HV0.1) was caused by primary recrystallization of the microstructure and the formation of more equilibrium products of austenite decomposition. Increasing the heat input (14 to 17 kJ/cm) led to numerical t8/5 (29 s) and experimental (36 s) decreases in hardness in the CGHAZ of QT steel (270 HV0.1) due to the full austenite (thermal weld cycle), and maintained the relative value of TMCP steel (235 HV0.1). Full article
Figures

Figure 1

Open AccessArticle Recovery of Platinum from Spent Petroleum Catalysts: Optimization Using Response Surface Methodology
Metals 2019, 9(3), 354; https://doi.org/10.3390/met9030354
Received: 14 February 2019 / Revised: 14 March 2019 / Accepted: 14 March 2019 / Published: 20 March 2019
Viewed by 400 | PDF Full-text (4590 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The global yield of platinum (Pt) recovery from spent catalysts is about 30%. Pt recovery from spent catalysts is one of the most significant methods to reduce its supply risk and meet future demand. The current hydro-leaching processes always involve extremely high acidity [...] Read more.
The global yield of platinum (Pt) recovery from spent catalysts is about 30%. Pt recovery from spent catalysts is one of the most significant methods to reduce its supply risk and meet future demand. The current hydro-leaching processes always involve extremely high acidity (c(H+) > 6.0 mol/L), causing serious environmental issues and consuming large amounts of reagents. This paper studied the recovery of Pt from spent petroleum catalysts in a mild leaching solution (c(H+) = 1.0−2.0 mol/L). The HCl and NaCl were used as leaching agents, while H2O2 was used for oxidation of Pt. The leaching factors, including solid/liquid ratio (S/L), acidity, leaching temperature, and H2O2 usage, were studied. The leaching efficiency of Pt was 95.7% under the conditions of S/L of 1:5 g/mL, HCl of 1.0 mol/L, NaCl of 5.0 mol/L, 10% H2O2/spent catalysts of 0.6 mL/g, and temperature of 90 °C for 2 h. The leaching kinetic of platinum fits best to the Avrami equation. The apparent activation energy for leaching platinum was 114.9 kJ/mol. Furthermore, the effects of the operating variables were assessed and optimized by employing a response surface methodology based on Box-Behnken Design. The result shows that HCl concentration had the greatest impact on the leaching efficiency as compared to the H2O2 concentration and S/L ratio. Pt leaching efficiency was increased to 98.1% at the optimized conditions of HCl of 1.45 mol/L, NaCl of 4.55 mol/L, 10% H2O2/spent catalysts of 0.66 mL/g, and S/L of 1:4.85. The purity of Pt is over 90% by the reduction of iron powder. Full article
Figures

Figure 1

Metals EISSN 2075-4701 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top