Wt Pct Research Articles

Effect of Prior Plastic Deformation on the α-Cr Precipitation in a Binary Ni-Cr Alloy

The effect of prior plastic deformation on the discontinuous precipitation in a supersaturated binary Ni-Cr alloy (42 wt pct Cr) was investigated. Solutionised samples were cold rolled to different extents of reduction (20, 50 and 70 pct) and then subjected to aging heat treatments in the temperature range of 923 K to 1123 K (650 °C to 850 °C) for different time periods, resulting in the precipitation of α-Cr in various morphologies. The α-Cr precipitates were in the form of lamellar discontinuous precipitation, acicular continuous precipitation along the deformation bands, globularization and equiaxed precipitation concurrently with matrix recrystallization. The volume fraction of each morphology varied according to the heat treatments. Overall, the prior plastic deformation had a retarding effect on the kinetics of discontinuous precipitation and accelerated the kinetics of continuous precipitation. The retardation of discontinuous precipitation was attributed to the loss of supersaturation of the matrix due to the other competing modes of precipitation supported by deformation. Plastic deformation prior to aging is shown to be a possible route for engineering the microstructure in this alloy.

High-Strength Al-Zn-Cu-Based Alloy Synthesized by High-Pressure Die-Casting Method

High-strength alloys of Al-xZn-3Cu (x = 20, 30, 40 wt pct) are developed for die-casting process. The maximum tensile strength of the developed alloy is 435 MPa, with a stain to fracture of ~ 4 pct. Microstructural investigation shows that the grain size of α-Al gradually decreases and the area of the Zn-rich region increases as the amount of Zn increases. Local symmetry investigation reveals that the major phase of α-Al contains very fine nanoprecipitations of Zn phase (<10 nm), with a very small amount of strain along {1 $$ \bar{1} $$ 0}. In addition, the Zn-rich region of the grain boundary has a very complex microstructure. This study discusses the effect of the microstructure of the developed Al alloys on the mechanical properties.

Effects of Ti and Al addition on the Formation and Evolution of Inclusions in Fe-17Cr-9Ni Austenite Stainless Steel

The effect of titanium and aluminum contents on the formation and evolution of inclusions were investigated in Fe-17Cr-9Ni austenite stainless steel at 1873 K. Homogeneous spherical FeOy-CrOz-MnO-SiO2 was the main inclusion before titanium and aluminum were added. Thermodynamic calculations indicated that when the Al content exceeds 0.0085 wt pct and Ti content exceeds 0.036 wt pct, spherical FeOy-CrOz-MnO-SiO2 inclusions can be reduced to irregularly shaped Al2O3 and TiOx inclusions, respectively. The formation of TiN on the surface of Al-Ti-O inclusions can prevent the reduction of Al-Ti-O by Al or Ti. Moreover, the different formation mechanisms of Al-Ti-O inclusions and TiN are discussed. When Ti was added to reduce Al2O3, the added Ti initially caused the formation of Al-Ti-O inclusions and then reacted with N in the molten steel to form TiN. On the other hand, in the case of the addition of Al to reduce TiOx, the formed reduction products were Al-Ti-O inclusions and Ti dissolved in molten steel, the latter being an important source of Ti in the later formed TiN. The TiN found in the experimental samples is more likely to be formed in molten steel at a temperature of 1873 K than during cooling.

Mechanism for Si Poisoning of Al-Ti-B Grain Refiners in Al Alloys

Al-5Ti-1B is the most widely used grain refiner for Al alloys. However, it is not effective for grain refining Al alloys containing more than 3 wt pct Si. This adverse effect of Si is referred to as Si poisoning. In spite of extensive experimental and theoretical investigations in the past decades, the exact mechanism for Si poisoning is still not clear. In this work, the state-of-the-art electron microscopy was performed to investigate the mechanism for Si poisoning. Our experimental results suggest that Si segregates preferably to the TiB2/Al-Si melt interface and the pre-existing Al3Ti 2-dimensional compound (2DC) layer on TiB2 surface dissolves into the Al-Si melt. Based on the experimental results, we have postulated a new mechanism for Si poisoning: interfacial segregation of Si leads to enrichment of Si at the TiB2/Al-Si melt interface, and this in turn makes the pre-existing Al3Ti 2DC on the TiB2 surface unstable and dissolve gradually in the melt, resulting in a loss of TiB2 nucleation potency and hence a decreased total number of potent TiB2 particles available for heterogeneous nucleation and grain initiation and consequently an increased grain size. This mechanism for Si poisoning can explain consistently the experimentally observed phenomenon reported in the literature.

Examination and Analysis of 2 Pct Mg-55 Pct Al-1.6 Pct Si-Zn Coating on Steel

The current study was conducted to examine the microstructure of the 2 pct Mg-55 pct Al-1.6 pct Si-Zn (wt pct) coating on steel in detail and analyse the formation mechanisms of various reaction products in the coating. The coating microstructure was comprised of an α-Al dendrite framework, and an interdendritic network, occupied by a number of solidification products, which were fine Al-Zn mixtures, Mg2Si, Si, MgZn2, and lamellar MgZn2/Zn mixtures. It was found that the Al-Zn mixtures observed in the interdendritic region were the decomposition products of the high Zn α-Al components of various eutectic reactions taking place during solidification. A method was developed to differentiate the Si and Mg2Si phases optically with colour contrasts. It was found that, when Si and Mg2Si formed, they occupied the entire interdendritic spaces at the locations where they formed. Judging from the Al-Mg-Si liquidus projection, the Mg2Si phase should form first during solidification, followed by the simultaneous formation of Mg2Si and Si. On the other hand, the MgZn2 phase formed into two different morphologies, with a large blocky shape and fine precipitates embedded in the lamellar Zn/MgZn2 mixtures, both surrounded by Al-Zn mixtures. It was observed that all eutectic reactions involved the formation of an α-Al component, which formed in a divorced manner via either growing on existing dendrite arms, or sometimes as isolated islands embedded in blocky MgZn2.

A Novel Approach to Determine Variable Solute Partition Coefficients

Proper characterization of solute segregation during the solidification of alloys using partition coefficients (k) is essential to understand and model solidification paths and associated microstructural evolution. Traditional methods to determine k assume a constant value over the course of solidification, which leads to improper descriptions of segregation for elements with variable partitioning behavior. In this study, a novel method to determine partition coefficients as a function of fraction solid using electron probe microanalysis point grid measurements is described. The proposed method, termed the mass balance analysis (MBA), was applied to a cast 90 wt pct Co-10 wt pct Cu alloy with well-documented segregation behavior. The resultant partition coefficients indicated that kCu decreased as a function of fraction solid, while kCo significantly increased in the terminal stage of solidification. The measured k values showed excellent agreement with those taken from the solidus and liquidus lines of Co-Cu binary phase diagram generated using Thermo-Calc. The MBA was also applied to a multicomponent austenitic commercial alloy. It showed a decrease in the partition coefficients for both Cr and Nb as a function of fraction solid and demonstrated the applicability of the MBA method to highly alloyed multicomponent systems.

Effects of Basicity and Al2O3 Content on the Chemistry of Phases in Iron Ore Sinter Containing ZnO

The effects of basicity and Al2O3 content on the chemistry of phases in iron ore sinter containing ZnO were investigated by Rietveld analysis of the X-ray diffraction (XRD) patterns. Bulk composition analysis was carried out using inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and wet-chemical analysis. The composition of each phase was investigated using a scanning electron microscope-energy dispersive X-ray analyzer (SEM-EDX). It was found that ZnO exists in the franklinite and the silicoferrite of calcium and aluminum (SFCA) phases. With increasing ZnO content, the phase fraction of the franklinite increased, while the fraction of SFCA slightly increased. When ZnO content was fixed at 1 wt pct and basicity increased, the fraction of franklinite decreased and that of SFCA increased. Here, the solubility of ZnO in the SFCA increased. As the Al2O3 content increased, the fraction of franklinite decreased and that of SFCA increased, while ZnO content in the SFCA did not change significantly.

Pandat™ Simulation of the Solidification Sequence and Microstructure Development of the 2 Pct Mg-55 Pct Al-1.6 Pct Si-Zn Coating on Steel

The current study uses the Pandat™ software developed by CompuTherm to simulate the solidification sequence of the 2 pct Mg-55 pct Al-1.6 pct Si-Zn (wt pct) coating on steel. Using the Scheil model approach, the solidification process of the coating alloy is revealed to proceed in the following sequence: (i) primary (Al) formation at T = 553.3 to 475 °C, (ii) Si formation at T = 475 to 437.9 °C, (iii) simultaneous Si and Mg2Si formation at T = 437.9 to 383.6 °C, (iv) MgZn2 formation at T = 383.6 to 336.9 °C, and finally (v) simultaneous formation of (Zn) and MgZn2 at T = 336.9 °C to complete the solidification process, with (Al) being an important participating component throughout, and Si a significant component at Stages (ii) and (iii) and becoming insignificant at Stages (iv) and (v). It is also revealed that the remaining liquid composition varies significantly throughout the solidification process, and therefore, different isopleths must be produced to illustrate the starting solidification reactions at different stages. The simulation results are then used to interpret the complex microstructures observed in the coating.

Preparation of Low-Carbon and Low-Sulfur Fe-Cr-Ni-Si Alloy by Using CaSO4-Containing Stainless Steel Pickling Sludge

Stainless steel pickling sludge is the precipitate from the neutralization process of stainless steel pickling liquor. Until now, many methods about the harmless treatments of pickling sludge have been developed, and among them the most effective one is to produce Fe-Cr-Ni alloy by carbothermic reduction process. However, the carbon and sulfur (harmful elements for steel) contents of the produced Fe-Cr-Ni alloy are difficult to be controlled, especially for the high-CaSO4 sludge. The current paper proposed a new method to produce the low-carbon and low-sulfur Fe-Cr-Ni-Si alloy by using the high-CaSO4 stainless steel pickling sludge. Firstly, the sludge was pre-reduced by carbon at 1100 °C. Then, the pre-reduced sludge was mixed with silicon powder and reacted at 1550 °C for the deep reduction, separation, and desulfurization. By the current method, the Fe-Cr-Ni-Si alloy with a carbon content of 0.513 wt pct and a sulfur content of 0.003 wt pct was produced. Meanwhile, the Fe, Cr, and Ni contents in alloys were 59.600, 15.440, and 13.570 wt pct, with recovery rates of 97.99, 97.61, and 98.65 pct, respectively. Such an alloy can be used as the alloy additive for stainless steel production.

Evaluation of the Effect of Rare Earth Alloying Additions on the Hot Tearing Susceptibility of Aluminum Alloy 7150 During Rapid Solidification

Additive manufacturing of the high-strength 7xxx Al alloy series is limited due to the susceptibility of these alloys to hot tearing. The objective of the current study is to determine the effect of rare earth (RE) element additions on the hot tearing susceptibility of Al alloy 7150 during rapid solidification conditions characteristic of additive manufacturing processes. Cast 7150-xRE (x = 0, 3, 6 wt pct) samples were remelted using a number of laser power-scan speed combinations. Cracks were observed in melt pools for 6 out of 12 processing conditions for 7150, but in all 12 conditions for the RE-containing alloys. Electron backscatter diffraction of the melt pool revealed the melt pool boundary grain size increased with RE additions, and cracks occurred along the grain boundaries. RE-containing intermetallics were observed on the crack surfaces, and were noted to possibly impede the interdendritic flow of eutectic liquids. A smaller amount of eutectic was observed in the thermal data for the RE alloys compared to 7150. Hot tearing indicators were useful in understanding the effect of RE additions when coupled with the experimental results. It is concluded that the addition of 3 to 6 wt pct RE elements increases hot tearing in 7150.

Formation Mechanism of In Situ Intergranular CaZrO3 Phases in Sintered Magnesia Refractories

Sintered magnesia refractories combined by in situ intergranular CaZrO3 phases were synthesized using natural MgO-containing natural minerals with CaO and SiO2 impurities and nano-sized ZrO2 additive. A homogenous distribution of intergranular CaZrO3, independent from the intergranular CaO-MgO-SiO2 phases, was formed in situ within the sintered magnesia aggregates by introducing 0.75 wt pct nano-sized ZrO2 into the magnesite. The formation mechanism of the in situ intergranular CaZrO3 phases was determined. The nano-sized ZrO2 was introduced and uniformly distributed at grain boundaries of the magnesia due to the micron-nano-sized particles composite system and wetting grinding process. Then the CaO in impurities were prior to SiO2 to react with the ZrO2 for generating CaZrO3 at the grain boundaries by increasing sintering temperature. Nevertheless, the nano-sized ZrO2 particles were encapsulated in the MgO crystallites with similar particle size decomposed from brucite and prevented from reacting with CaO impurities in magnesite. The mixing homogeneity of magnesite particles and ZrO2 particles and the direct contact between ZrO2 and CaO impurities in magnesite has a crucial effect on the formation of intergranular CaZrO3 phases. Furthermore, the intergranular CaZrO3 phases could enhance the bonding of magnesia grains and have great potential for improving the service performance of magnesia.

High Temperature Oxidation Study of Nano-Y2O3 Dispersed Ferritic Alloys Synthesized by Mechanical Alloying and Sintering

This study concerns mechanism and kinetics of isothermal oxidation of four Fe-Cr-Al-Ti ferritic alloys in the range 700 °C to 900 °C for up to 50 hours in air. These four alloys with nominal compositions of 83.0Fe-13.5Cr-2.0Al-0.5Ti (alloy A), 79.0Fe-17.5Cr-2.0Al-0.5Ti (alloy B), 75.0Fe-21.5Cr-2.0Al-0.5Ti (alloy C), and 71.0Fe-25.5Cr-2.0Al-0.5Ti (alloy D) each with 1.0 wt pct nano-Y2O3 dispersion were synthesized by mechanical alloying and sintering at 1000 °C by hot isostatic pressing, high pressure sintering, hydrostatic extrusion and pulse plasma sintering techniques. A detailed characterization of the phase aggregate, microstructure and micro-composition of the oxide scale was carried out by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, respectively. Oxidation kinetics appear to follow a parabolic rate with an activation energy of 135 to 234 kJ/mol, which depend on alloy composition (i.e., Cr content). Oxidation mostly occurred by counter-ionic diffusion of oxygen from air to the interior and cations (Cr+3 or Fe+3) from the bulk toward the surface. Alloy D sintered by hot isostatic pressing offered the highest resistance to oxidation.

Strain-Rate Dependence of the Martensitic Transformation Behavior in a 10 Pct Ni Multi-phase Steel Under Compression

The deformation-induced transformation of metastable austenite to martensite can contribute to improved performance of many steel alloys in a range of applications. For example, one class of Ni-containing steels that has undergone consecutive heat treatments of quenching (Q), lamellarization (L), and tempering (T) exhibits improved ballistic resistance and low-temperature impact toughness. To better understand the origin of this improvement, we tracked the volume fraction of austenite present in a QLT 10 wt pct Ni steel during compression at low and high strain rates ( $$\dot{\varepsilon }={0.001}\,{{\text{s}}^{-1}}$$ and $$\dot{\varepsilon }\simeq {2500}\,{{\text{s}}^{-1}}$$ , respectively) using ex situ vibrating sample magnetometry measurements and in situ time-resolved X-ray diffraction measurements. We observe that the austenite-to-martensite transformation occurs more readily during quasi-static loading than during dynamic loading, even at small values of applied strain, which is qualitatively different from the behavior of steels known to undergo a strain-induced martensitic transformation mechanism. We propose that the strain-rate dependence of transformation in the QLT 10 pct Ni steel is dominated by the transformation in small austenite particles, where stress-assisted martensitic transformation is likely to be the dominant mechanism. Indirect evidence for this hypothesis is provided by electron backscatter diffraction measurements of deformed specimens.

Microstructural Evolution in an Fe-10Ni-0.1C Steel During Heat Treatment and High Strain-Rate Deformation

The fine structure in an Fe-10Ni-1.0Mo-0.6Mn-0.6Cr-0.08V-0.1C (wt pct) steel in a multi-step heat-treated condition called ‘QLT’ is understood by tracking its evolution in each step using transmission electron microscopy (TEM) and atom probe tomography; further, the consequence of high strain-rate deformation on the site-specific change in the QLT microstructure is examined by microdiffraction and energy dispersive spectroscopy in the TEM. The QLT treatment results in two generations of austenite (arising from the L- and the T-step) with differing Ni content. The primary focus of this study is on the thermal and mechanical stability of the precipitated austenite and the influence of austenite chemistry and size on the stability. Kolsky bar compression experiments were conducted to isolate a situation where an adiabatic shear band propagated partway through the specimen. Examination of the microstructure in such a specimen showed both generations of austenite to be present far from the shear band, ahead of the shear band and adjacent to the shear band. The austenite immediately ahead of the shear band was fragmented. Within the shear band, evidence was found for deformation-induced transformation to martensite. These findings are discussed within the context of improved damage tolerance and ballistic resistance observed earlier in field tests.

Partial Roasting of High-Arsenic Copper Concentrates

The partial roasting of high-arsenic copper concentrates at 973 K/998 K (700 °C/725 °C) under controlled atmosphere can remove > 95 pct of the arsenic contained in the concentrates, leaving a calcine with 52 to 68 wt pct bornite, 10 to 13 wt pct chalcopyrite and 2 to 5 wt pct magnetite, with 8 to 24 wt pct remnant chalcocite. The mineralogic composition of the calcine obtained is consistent with the calculated mineralogic composition based on the chemical analysis of the calcine and the gaseous phase in equilibrium with the calcine. The formation of the new solid phases present in the calcine (bornite and chalcopyrite) should take place in the emulsion phase of the fluidized bed, while the oxidation of part of the gaseous sulfur generated by thermal decomposition of the sulfides present in the concentrate could occur in the evolving cloud and wake surrounding the air bubbles in the emulsion phase of the fluidized bed.

Processing and Properties of Medium-Mn TRIP Steel to Obtain a Two-Stage TRIP Behavior

Two medium-Mn steels of nominal composition 0.15C-2.0Si-10.5Mn-(0.75, 1.5) Al-0.04Nb-balFe (wt pct) were processed to produce sub-micron grain sizes of 0.65 and 0.80 μm. Mechanical testing was performed in three successive conditions: hot rolled, intercritically annealed, and cold rolled with subsequent intercritical annealing. Intercritical annealing was performed at 923 K for 20 hours. Electron-backscattered diffraction and X-ray diffraction were utilized to characterize the microstructure, consisting of α-ferrite, α-martensite, e-martensite, and γ-austenite. Microstructural constituents were tracked during tensile deformation and it was found that both steels exhibited two-stage TRIP with γ-austenite martensitically transforming first to e-martensite and as strain increased e-martensite transformed to α-martensite.

Hidden Phenomena During Transient Reaction Trajectories in Liquid Metals Processing

The transient trajectory taken for a system striving toward equilibration has consequences on the rate of processes and on the chemical and physical state of products in metallurgical processes. A case study approach to recent advancements in liquid steel processing is given. A combination of techniques and knowledge developed is given as a targeted showcase of the authors’ contributions to the understanding of liquid metal droplet reactions and their contribution to the large-scale production processes within the steel industry. Examples relevant to novel ironmaking technologies, oxygen steelmaking, ladle metallurgy, and continuous casting are discussed, showing the range of processes that benefit from greater understanding in this area. This article considers specifically the reaction of liquid ferrous droplets, immersed in molten oxides, involving key alloying components, including phosphorus, aluminum, and carbon. The studies use high-temperature–confocal scanning laser microscopy (HT-CSLM), X-ray computed tomography (XCT), phase-field modeling, and in situ limited angle X-ray imaging. These techniques have seen significant development over recent years, and the combination of these powerful tools reveals the occurrence of spontaneous emulsification driven by chemical reaction (in the case of oxygen/phosphorus/aluminum reactions) and gas-phase formation (in the case of decarburization) both internally and externally to a steel droplet. A key finding is that the interfacial area pertinent for the heterogenous reactions to occur changes considerably (by up to an order of magnitude) depending on the chemical driving force. Additional key findings include the shift between preferential internal and external gas nucleation during decarburization, an inflection point of behavior as to whether or not spontaneous emulsification will occur (within the study discussed, this is between 3 and 4 wt pct Al) and the pathway of perturbation growth through which spontaneous emulsification occurs, including the physical maxima a perturbation will grow to before breaking away from the parent droplet.

Effects of Titanium Addition on the Microstructural and Mechanical Property Evolution of FeCrB Alloys

Effects of Ti addition on the microstructural and mechanical property evolution of FeCrB alloys have been systematically studied through experiments and modeling. Microstructural analysis reveals that Ti addition can induce the formation of in situ nanoparticles which can be mainly divided into two categories based on their distribution types. The first are the interfacial ones accumulating on the boride surface to control their growth, while the second are the intragranular ones distributed in the matrix to reinforce the FeCrB alloys. Model predictions show that the nanoparticle-induced growth restriction is responsible for the microstructural refinement. The refined microstructure and reinforcing nanoparticles can lead to the enhanced mechanical properties of FeCrB alloys. When the Ti addition reaches 1.4 wt pct, the FeCrB alloy exhibits the most refined and homogeneous microstructure and thus the optimal performance with its microhardness, macrohardness, ultimate tensile strength, elongation, impact toughness, and the wear-resistant performance are increased by 31.9, 29.0, 39.7, 128.6, 27.3, and 350 pct, respectively, compared with the base alloy.

The influence of temperature and matte grade on gas-slag-matte-tridymite equilibria in the Cu-Fe-O-S-Si system at p (SO2) = 0.25 atm

ABSTRACT Experimental measurements have been made of the compositions of slag, matte and tridymite phases in chemical equilibrium in the Cu-Fe-O-S-Si system at 1300°C, p(SO2) = 0.25 atm and selected oxygen partial pressures. The high temperature equilibration experiments were conducted using silica substrates under controlled CO-CO2-SO2-Ar gas atmospheres. The resulting phases obtained from the equilibrations were retained at room temperature through rapid quenching of the samples. The condensed phase compositions from the equilibrium experiments were measured by Electron Probe X-ray Microanalysis (EPMA). The data obtained in the present study, combined with those from previous studies, have enabled the liquidus slag temperature to be accurately described as a function of Fe/SiO2 ratio at p(SO2) = 0.25 atm for temperatures between 1200 and 1300oC and mattes containing from ∼44 to ∼ 78 wt pct Cu.

Thermodynamic Stacking Fault Energy, Chemical Composition, and Microstructure Relationship in High-Manganese Steels

Stacking fault energy (SFE) is related to activating complex high strength and ductility mechanisms such as transformation-induced plasticity and twinning-induced plasticity effects. This type of energy can be estimated by many different methods and its importance is in its ability to predict microstructure and phase transformation behavior when the material is submitted to stress/strain. In order to study the SFE, chemical composition, and microstructure relationships, eleven different welding parameters were chosen to obtain a large range of dilution levels. A new tubular wire electrode of high-manganese steel (21 wt pct Mn) was used as the consumable and an SAE 1012 steel plate (0.6 wt pct Mn) as the base metal in a flux-cored arc welding process. These welding parameters were related to the phases formed and phase transformation behavior in the fusion zone. The SFE of the austenite phase was calculated using a thermodynamic model. The welding parameters produced SFE values in the range of − 5 to 7 mJ/m2. $$\epsilon $$ -martensite and austenite were observed in all samples, but $$\alpha $$ ′-martensite was only found in those that presented negative SFE values, i.e., those with lower Mn content. Chemical Gibbs Free energy was the component with the most influence on the SFE. Nanoindentation detected the phase transformations during hardness testing for the medium and low dilution levels used, while the high dilution levels presented the highest hardness and modulus of elasticity values, and the lowest elastic and plastic deformation values. The results provide an improved method to develop high-manganese steels with microstructure control through welding parameters.