Fine Inclusions Research Articles

Characterization of Archaeological Artefacts Using Methods Specific to Materials Science: The Case Study of Dacian Ceramics from 2nd c. BC to 1st c. AD.

Combined analysis methods such as optical microscopy (OM), cathodoluminescence (CL) microscopy, X-ray diffraction (XRD), and scanning electron microscopy–energy dispersive X-ray spectrometry (SEM–EDX) have made it possible to obtain the first physico-chemical data of Dacian potsherds, exhumed at the archeological site of Ocnița-Buridava, Romania; the samples were provided by the “Aurelian Sacerdoțeanu” County Museum Vâlcea, dating from the 2nd century BC to the 1st century AD. The mineralogical and petrographic analyses revealed two types of ceramic pastes, taking into account the granulometry of the inclusions and highlighting the choice of the potter for fabricating the ceramic either by wheel or by hand. All samples showed an abundance in quartz, mica (muscovite and biotite), and feldspars. These observations were confirmed by cathodoluminescence imagery, revealing heterogeneous pastes with varied granulometric distributions. The XRD patterns indicated the presence of the mineral phases, indicating a firing temperature below 900 °C. The wheel-made ceramics have a fine, compact matrix with very fine inclusions (<40 µm). On the other hand, the hand-made ceramics present a coarse matrix, with inclusions whose granulometry reaches approximately 2 mm. The difference between these two types of ceramics is also confirmed by the mineralogical and chemical analysis. The wheel-made potsherds are more abundant in MgO, Al2O3, and CaO contents.

Influence of the radial-shear rolling (RSR) process on the microstructure, electrical conductivity and mechanical properties of a Cu–Ni–Cr–Si alloy

The article describes a method for producing semi-finished products from a copper alloy of the Cu–Ni–Cr–Si system for electrical purposes through the radial-shear rolling (RSR). From the Cu–Ni–Cr–Si alloy by hot deformation, rods with a diameter of 20 mm were obtained, which were then heat treated with quenching and aging. A detailed analysis of the microstructure and properties (mechanical and electrical) of the obtained samples was carried out after RSR and after heat treatment (HT). After RSR, material hardening occurs due to shear deformations forming a gradient structure with grain sizes varying from 8.22 μm to 15.95 μm between the surface and the center of the rod. The microstructure and mechanical property analysis showed that after heat treatment, the alloy is thermally hardened due to the precipitation of Ni2Si and Cr3Si particles uniformly distributed in the sample volume in the form of fine inclusions with an average size of 0.56–0.65 μm. After heat treatment, the alloy enhanced its mechanical properties (ultimate tensile strength (UTS) ~ 700–750 MPa, yield strength (YS) ~ 557–606 MPa, and elongation between 17 and 22%) and its electrical conductivity of 45.17% IACS from the 30.52% IACS of the RSR material. The improved mechanical properties of the heat-treated material are due to the different strength contributions mainly coming from dislocations and precipitates. The electrical conductivity improvement after the heat treatment is related to the dislocation density reduction and the increase in grain boundary misorientation due to the recrystallization phenomenon giving rise to a lower number of boundaries but with a twinning character. Thus, the RSR method offers a new industrial alternative for the production of semi-finished products from a Cu–Ni–Cr–Si alloy in the form of rods with diameters ranging from 10 to 55 mm.

Effect of cold rolling and annealing temperature on structure, hardness and electrical conductivity of rapidly solidified alloy of Al–Cu–Mn–Zr system

The experimental heat resistant alloy Al-3.3Cu-2.5Mn-0.5Zr (wt. %) has been manufactured using the method of electromagnetic casting (EMC) providing solidification at an ultra-high rate (~104 °C/s). The microstructure, phase composition, mechanical and electrical properties of the alloy in as-cast state and after cold rolling followed by annealing has been extensively studied using both thermodynamic calculations and experimental analysis. The microstructure of the as-cast EMC rod consists of the fine Al2Cu phase inclusions and aluminum matrix where all Mn and Zr and most of Cu are dissolved. The annealing of cold rolled strip at 400 °C allows reaching the optimal combination of strength, electrical conductivity and thermal stability.

Modifying of microstructure and toughness in the weld metal prepared by welding wire containing nanosized titanium oxides

Abstract Titanium oxides are beneficial to the weld metal for their nucleation effect on acicular ferrite. The present study puts forward a new method to introduce fine titanium oxides into the weld metal by using welding wire containing nanosized titanium oxides. In the study, a special way was introduced and it was adopted to prepared solid welding wire containing nanosized titanium oxides. The W1 weld metal was obtained by using this welding wire after multi-layer multi-pass welding; as a contrast, the W2 weld metal was prepared by using conventional welding wire of similar composition under the same welding condition. Microstructures of the two weld metals were studied by OM and SEM; nanosized titanium oxides in the welding wire and inclusions in each weld metal were investigated by SEM and TEM. Toughness of the two weld metals was measured through instrumented impact test; fracture and crack behaviour was analyzed with SEM observation. Through microstructure characterization, it is concluded that nanosized titanium oxides in the welding wire are transitted into the W1 weld metal to form Ti3O5 inclusions and size of the inclusions is larger than the nanosized titanium oxides in the welding wire due to cluster of the titanium oxides in the weld metal. The inclusion size just locates in the size range that is favorable for acicular ferrite nucleation. Through comprehensive analysis of the instrumented impact test, fracture and secondary crack, it is revealed that W1 weld metal shows higher crack initiation energy, higher crack propagation energy and higher impact toughness compared with the W2 weld metal, which results from finer inclusions in the W1 weld metal prepared by the special way.

Effect of zirconium on inclusions and mechanical properties of China low activation martensitic steel

The effects of 0.01–0.11 wt.% Zr on the inclusions, microstructure, tensile properties, and impact toughness of the China low activation martensitic steel were investigated. Results showed that Zr exhibits good deoxidation and desulfurization abilities. The scanning electron microscope was used to examine the inclusions in the ingots. The main inclusions in the alloys were Zr–Ta–O, Zr–O, and Zr–O–S. However, some blocky Zr-rich inclusions appeared in Zr-2 and Zr-3 alloys. Typical martensitic structures were observed in the alloys, and average prior austenite grain sizes of 21.1, 15.7, and 14.8 µm were obtained for Zr-1, Zr-2, and Zr-3 steels, respectively. However, increasing Zr content of the steels deteriorated their mechanical property, owing to the blocky inclusions. The alloy with 0.01% Zr resulted in excellent mechanical properties due to the fine inclusions and the precipitation of Zr3V3C carbides. Values of 576 and 682 MPa were obtained for the yield strength and ultimate tensile strength of Zr-1 alloy, respectively. Furthermore, the ductile–brittle transition temperature of the alloy decreased to − 85 °C.

Magnetic Properties and Microstructure of Sm &lt;sub&gt;5&lt;/sub&gt;Fe &lt;sub&gt;17&lt;/sub&gt;-Based Composite Magnets

We have investigated synthesis, magnetic properties and microstructure of Sm5Fe17-based hard magnetic phase with a Sm20Fe70Ti10 composition. Ultrahigh coercivities, μ0Hc=7.18 T at room temperature and μ0Hc=8.86 T at 10 K, have been achieved. The room-temperature coercivity, determined from high-field pulse measurements, reaches 35% of the anisotropy field μ0Ha=20.7±0.8 T. Further, it is demonstrated that a coercivity of 2.18 T is maintained even at 500 K. The Curie temperature TC of Sm20Fe70Ti10 is 577 K and the calculated exchange stiffness parameter A is 7.72 pJ/m. Detailed transmission electron microscopy investigations show a two-phase microstructure consisting of the Sm5Fe17-based hard magnetic matrix phase with grain size below 200 nm and finer, below 100 nm, Fe2Ti grains. Majority of the Fe2Ti phase is located at the grain boundaries with some finer inclusions found also inside the 5:17 grains. Despite the high fraction of the Fe2Ti grains, nearly single-phase demagnetization loops are observed. In order to enhance Ms, the effect of Ti content on phase constitution, magnetic properties and microstructure was studied in detail. Ms increases and Hc decreases for the Ti-lean compositions.

Impact of microarc carburizing and boriding of steel on diffusion layer structure

Intensification of carburizing and boriding of steel parts is achieved by microarc surface alloying. For carburizing, the parts are immersed in coal powder followed by electric current passing. For boriding, a coating with diffusant is used. Acceleration of diffusion is achieved by action of microarc discharges on the steel surface. The aim of this work was to study the effect of diffusion parameters on thickness, structure, and phase composition of coatings. The samples were made of 20 steel. Surface current density was 0.45 – 0.53 A/cm2. Duration of the process was 2 – 8 min. At the beginning of heating, temperature of the samples increases, and then stabilizes at 930 – 1250 °C due to cessation of micro-formation during combustion of coal particles. After carburizing, a eutectoid mixture is formed on the surface, then, the zone with ferrite-perlite structure is located, which transfers into the original structure. The maximum layer thickness (60 – 390 microns) is reached after 6 – 7 min of heating and then does not increase due to a decrease in the carbon potential during combustion of coal particles. Similar relationship is obtained when boriding: the maximum layer thickness (60 – 340 microns) is reached after 6 – 7 min and then does not increase due to depletion of diffusant source in the coating. At current density of 0.45 A/cm2, the layer consists of a base (a dispersed ferrite-carbide mixture) containing fine inclusions of iron borides and boron carbide. At current densities of 0.49 and 0.53 A/cm2, the layer has heterogeneous structure, with areas of high-hard boride eutectic located at the base. At high current density, diffusion of carbon and boron along the grain boundaries forms Fe – C – B triple eutectic. At lower current density, surface temperature is lower than eutectic formation temperature, so heterogeneous coating structure is not formed. The work results make it possible to choose modes of microarc heating to obtain the required parameters of diffusion layer.

Влияние послесварочной термической обработки на ударную вязкость сварного соединения из стали Р91

Sheets from ferritic-martensitic steel P91 welded by the electric arc method and heat treated in three different modes, i.e., tempering (PWDT), normalizing with tempering (PWNT) and double austenitization (quenching + normalizing) with tempering (PWDNT), are studied It is shown that the PWDNT and PWNT treatments raise the impact toughness and lower the scattering of the microhardness The PWDNT produces a finer structure than the PWNT and raises the impact toughness to 135 J due to formation of a homogeneous structure of tempered lath martensite with numerous fine inclusions of M 23 C 6 and MX. The welded joints treated by PWDNT and PWNT fracture by a ductile mechanism under the impact tests

Studies on heap leaching of gold with the addition of sodium acetate as an intensifying reagent

One of the cheapest methods of extracting gold is heap leaching. However, the recovery of gold by this method is relatively low, compared with cyanidation of the crushed material, so the search for the ways to intensify leaching and increase gold recovery is an urgent task. Investigations on heap leaching of gold from the gold-bearing ore of the Sari Gunay deposit were conducted using a promising reagent sodium acetate to intensify the heap leaching process. The results of assay-gravimetric, chemical, mineralogical and granulometric analyses of oxidized ore are presented. The average gold content in the ore was 2.90 g/t. According to the electron probe analysis, gold in the ore is present in the form of fine (micron) inclusions in minerals and ore rocks. Comparative studies on heap leaching of gold from the crushed ore with a grain size of –20 + 0 mm with the addition of sodium acetate and without that were carried out. The degree of gold recovery with sodium acetate at a flow rate of 0.5 kg/t was 58.74%, that without sodium acetate was 54.69%, i.e. the addition of the reagent provides an increase in recovery of more than 4%. Leaching with the addition of the reagent also reduces sodium cyanide consumption from 0.65 to 0.59 kg/t. The research results have shown that sodium acetate can be used to intensify the process of heap leaching of gold when the ore size is –20+0 mm.

157 The effect of different inclusion levels of corn starch and fine ground corn with different conditioning temperatures or die thickness on pellet quality

Abstract The objective of this experiment was to determine the effect of different inclusion levels of corn starch and fine ground corn with different conditioning temperature or die thickness on pellet quality. Experiment 1, treatments were arranged in 3×2 factorial design of corn starch inclusion level (0, 5 and 10%) and die thickness (4mm×13mm and 4mm×22 mm). Experiment 2, treatments were arranged in 3×2 factorial design of fine ground corn inclusion level (0, 10 and 20) and conditioning temperature (80 and 85°C) with treatments pelleted using a 4mm×22mm die (5.6 L:D). In both experiments, treatments were pelleted using a model CL-5 CPM pellet mill (Crawfordsville, IN). The result of experiment 1 demonstrated that there was no interaction between corn starch inclusion level and die thickness on modified pellet durability index (PDI), (P=0.636). Increasing die thickness from 12.7 to 22.2 mm increased PDI from 43 to 70% (P&amp;lt; 0.001). There was a linear decrease (P&amp;lt; 0.001) in PDI as the corn starch inclusion level increased from 0 to 10% (64, 60, and 46%, respectively). The result of experiment 2 demonstrated that there was no interaction between fine ground corn inclusion level and conditioning temperature on PDI (P=0.541). The fine ground corn inclusion level did not impact PDI (P=0.298). Increasing conditioning temperature from 80 to 85°C increased PDI (P&amp;lt; 0.001) from 76 to 85%, respectively (P&amp;lt; 0.001). Based on the results, the use of pure corn starch was not an effective binding agent in the feed when the diet contains at least 60% ground corn. The ratio of small corn particles to large corn particles in the diet did not impact pellet quality when the diets were conditioned above 80°C for 35 sec and then pelleted with a 5.6 L:D die. Increasing die thickness and conditioning temperature improved pellet quality.

Spectroscopic Feature and Identification Application of the Impurity and Inclusion in Type IIa HPHT Synthetic Diamond

In recent years, China has become the largest producer of type Ⅱa colourless HPHT synthetic diamonds. And the identification of type Ⅱa HPHT synthetic diamond has become a challenging task. This research attempted to find the evidence of identification for type Ⅱa HPHT synthetic diamonds. Diamond samples from the high pressure and high temperature (HPHT) manufacturers in China (HH, J, Z) were collected, from which the inclusions and the distribution of impurities of 11 typical type Ⅱa diamond samples produced in the past three years were studied. Two main points of understanding were obtained: (1) When the fluorescent colour and image of type Ⅱa diamond under DiamondviewTM and other equipments can not give clear identification evidence, the conical, black thread-like or thin tubular inclusions, the distribution of fine point inclusions, shapeless cohenite, hematite, and magnetite inclusions can be used as the reference for determining the new HPHT synthetic diamonds. (2) Some samples have impurity defects which can be tested, and their emission peaks and distributions which are related to Ni and B can be used as the contributory characteristics for determining HPHT synthetic diamonds.

Investigation of Screw Failed During Installation

Material used for screw production was investigated due to its inconvenient properties which caused the screw breaking on threads or in the head during the installation. Chemical composition of analyzed material corresponded with standard STN 17153 according to technological drawing for specific product. The metallographic analysis showed that failure of screws happened due to improper microstructure resulting from unsuitable thermal treatment of material. Fine inclusions based on aluminum nitride (AlN) and chromium carbonitride (Cr(C,N)) were segregated along the ferritic grain boundaries. Coarse aluminum nitride inclusions (AlN) in ferritic matrix affected the character of present fracture surface characterized by cleavage facettes. The fracture was propagated step by step following the planes with the increased concentration of inclusions across the whole cross-section of the screw.

Precipitates in Compact Strip Production (CSP) Process Non-Oriented Electrical Steel

Nitrogen and Sulfur in non-oriented electrical steel would form precipitates, which would severely affect its magnetic properties. Precipitates in compact strip production (CSP) process non-oriented electrical steel were investigated using a transmission electron microscope (TEM) and scanning electron microscopy (SEM). The precipitation mechanism and influence on grain growth were analyzed experimentally and theoretically. The results showed that the main particles in steel were AlN, TiN, MnS, Cu2S, and fine oxide inclusions. The spherical or quasi-spherical of MnS and Cu2S were more liable to precipitate along grain boundaries. During the soaking process, the amount of MnS precipitated on the grain boundary was much larger than that of Cu2S. AlN and TiN in cubic shape precipitated inside grains or grain boundaries. Precipitates preferentially nucleated at grain boundaries, and TiN, MnS mainly precipitated during soaking. In the subsequent processes after soaking, AlN and Cu2S would precipitate unceasingly with the decrease in the average size. The distribution density, the volume fraction, and the average size of the precipitates in the annealed sheets were 9.08 × 1013/cm3, 0.06%, and 54.3 nm, respectively. Precipitates with the grain size of 30–500 nm hindered the grain growth, the grains with 100–300 nm played a major role in inhibiting the grain growth, and the grains with the grain size of 70–100 nm took the second place.

Influence of Manufacturing Conditions on Inclusion Characteristics and Mechanical Properties of FeCrNiMnCo Alloy

Three CoCrFeMnNi high-entropy alloys (HEAs) were produced by vacuum induction melting, induction melting under inert gas atmosphere, and melting under inert gas atmosphere followed by air exposure, respectively. The different manufacturing conditions for the three investigated alloys resulted in different levels and types of inclusions. The alloys melted under vacuum or inert gas contained Al2O3 inclusions formed by impurity Al, due to its high oxidation tendency. The molten alloy exposed in air showed an excessive oxidation. During oxidation of the molten alloy in air, impurity Al was initially oxidized, and fine MnCr2O4 inclusions were formed rather than pure Al2O3 inclusions. This difference was analyzed based on thermodynamic calculations. Specifically, the influence of impurity content on the inclusion characteristics was investigated for the three HEAs. Moreover, the inclusion characteristics were found to have an influence on mechanical properties of the alloys also. In air-exposed HEA, smaller inclusions were formed, resulting in a higher dislocation density at the matrix/inclusion interface and thus strengthening of the HEA. Thus, it is proposed that atmospheric conditions could be an important factor to control the inclusion characteristics and to form fine inclusion particles, which could improve the mechanical properties of HEAs.

Rapid detection of inclusion particles in recycled aluminum materials by laser-induced plasma optical emission spectrometry with scanning laser beam

This paper describes an analytical method to evaluate the kind and the number of inclusion particles on the surface of a recycled Al ingot using laser-induced breakdown spectrometry (LIBS) with scanning laser beam. The surface was observed with scanning electron microscope - energy dispersive X-ray spectrometry (SEM-EDX) as well as scanning LIBS in the same viewing positions, in which inclusion particles of Si and Fe compounds were found. By measuring the emission intensity of the Fe I 358.119-nm and Si I 288.160-nm lines, the lateral distribution of Si and Fe inclusion particles was estimated from 2D intensity maps of these emission lines. The lateral resolution of the scanning LIBS was about 100 μm, which was restricted by the size of an ablated crater and the surrounding area; therefore, it is difficult to evaluate the actual number of fine inclusion particles (one or more particles may be counted to be a single particle). Nevertheless, the scanning LIBS has an advantage that the analysis can be conducted easily and rapidly compared to conventional analytical methods for inclusions. In our LIBS apparatus, the analysis for a sample surface of 4.0 × 5.0 mm2 was finished in about 40 min. and the time would be reduced if the spectrum analysis is automated on a computer. Accordingly, it is expected that the scanning LIBS can be utilized to consult on the quality of recycled Al materials in the recycling sites.

The late Barremian ecosystem of Las Hoyas sustained by fishes and shrimps as inferred from coprofabrics

Las Hoyas, a locality of the La Huérguina Formation in the southwestern Iberia Basin (Cuenca province, Spain), is a well-known late Barremian Konservat-Lagerstätte highly rich in coprolites that have a wide variety of morphologies. Thin sections of twenty specimens were prepared from seven coprolite morphotypes. All of the examined coprolites exhibit a microcrystalline calcium phosphate groundmass lacking recrystallization and containing fine inclusions. Three different coprofabrics have been characterized and reflect the diet and digestive processes of the animal producers. The fish scale coprofabric is formed by ganoine scales likely attributed to Semionotiformes; the decapod cuticle coprofabric includes exoskeletal fragments which might be assigned to Atydae shrimps and Astacidae crayfish prey. A combination of decapod cuticles and fish scales can occasionally occur in the same coprolite. The third coprofabric contains few or no inclusions, and likely denotes the presence of coprolite producers with very efficient digestive systems. The exceptional preservation of the Las Hoyas coprolites reveals the trophic importance of small crustaceans with thin and delicate exoskeletons, a food resource that is not usually evident in coprolites. The number of coprofabrics relative to the number of possible fecal producers is low, and may reflect taphonomic biases. Nevertheless, the coprofabric contents demonstrate that decapods and fishes were important food resources in this Barremian ecosystem.

Fine elastic circular inclusion in the area of harmonic vibrations of an unlimited body under smooth contact

Fine elastic circular inclusion in the area of harmonic vibrations of an unlimited body under smooth contact The problem of the interaction of harmonic waves with a thin elastic circular inclusion, which is located in an elastic isotropic body (matrix), is solved. On both sides of the inclusion between it and the body (matrix), the conditions of smooth contact are realized. The solution method is based on representing the displacements in the matrix through discontinuous solutions of the Lamé equations for harmonic vibrations. This made it possible to reduce the problem to Fredholm integral equations of the second kind with respect to functions associated with jumps in normal stress and radial displacement to included ones. After the realization of the boundary conditions on the sides of the inclusion, a system of singular integral equations is obtained to determine these jumps. Keywords: elastic inclusions, cylindrical waves, matrix, stress intensity factor.

Trace element associations in magnetite and hydrothermal pyrite from the Geita Hill gold deposit, Tanzania

Gold mineralization in the Geita Hill deposit is associated with pyrite formed along microfracture networks and sulfidation fronts together with K-feldspar and biotite. The sulfidation fronts are best developed in magnetite-bearing ironstone. The gold is present mainly as electrum and gold tellurides along grain boundaries, and as inclusions in pyrite, quartz, biotite and K-feldspar. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of pyrite and magnetite grains reflect complex fluid-host rock interactions. Magnetite textures and chemistry change with alteration intensity, indicating the progression of the alteration front into the host rock. Pyrite textures are uniform across all rock types and reflect late-tectonic growth linked to multi-staged infiltration of hydrothermal fluids. Trace element distribution patterns in pyrite are locally complex and influenced by host rock chemistry.Gold distribution patterns in pyrite correlate closely with Te, Ag, Bi and Pb, indicating that gold occurs in micro- and nano-inclusions of telluride minerals. This is especially so for gold in quartz veins, whereas gold in ironstone and diorite also occurs as electrum with an average Au/Ag ratio of 0.41. As, Co and Ni in pyrite are lattice bound and occur in high concentrations in ironstone and diorite where they show characteristic growth zoning patterns. Pyrite in quartz veins has As, Co and Ni concentrations that are low and variable. Cr, Cu, Mo, Mn and Zn are present in all rock types in isolated inclusions in pyrite grains, whilst Pb, Bi and Sb occur in more dispersed patches of fine clustered inclusions. The Se content in pyrite is typical for Archean gold deposits, and reflects an average temperature of ~340 °C for the mineralizing fluid. The Co/Ni ratio of pyrite grains varies between 0 and 5.2 in ironstone and diorite, and most likely reflects the equilibration Co/Ni ratio of the host rock. The Co/Ni ratio of pyrite grains in quartz veins varies between 1 and 12, and is consistent with a magmatic-hydrothermal origin for the ore fluid. Trace element distribution patterns in magnetite and pyrite indicate that As, Ni, Co, Cr, Mn and Cu were mostly locally derived, and remobilised into the pyrite during sulfidation of the host rock. The concentrations of these elements are strongly lithologically controlled, and they are not consistently incorporated into the pyrite after initial stages of growth. Au, Ag, Te, Bi and Pb were externally derived, and closely correlate in all varieties of pyrite as well as strongly altered magnetite. The alteration footprint of the Geita Hill deposit is limited in extent, and does not involve As and Sb that are typically enriched in Archaean lode-gold systems. Instead, Te and Bi are most characteristic for the deposit and could be of use as path finder elements together with altered magnetite grains.

Effects of yttrium and zirconium additions on inclusions and mechanical properties of a reduced activation ferritic/martensitic steel

The effects of two alloying elements, i.e., yttrium (Y) and zirconium (Zr), on the inclusion, microstructure, tensile property and impact toughness of reduced activation ferritic/martensitic (RAFM) steel are analyzed. The size and number of particles were determined by optical microscopy, and the particle types were examined by scanning electron microscopy. The size of ~ 20% and ~ 85% of the inclusions lied in the range of 0.5–1.0 μm and 0.5–3.0 μm, respectively. In Y- and Y–Zr-containing specimens, the density of the fine inclusions, with a size less than 0.5 μm, was found to be 1.06 × 1017 and 9.82 × 1016 m−3, respectively. All specimens were normalized at 1323 K for 30 min and tempered at 923 and 1023 K for 90 min, resulting in the formation of tempered martensite with M23C6 carbides and MX precipitates. Zr-containing RAFM steel tempered at 923 K formed M23C6 carbides and nano-sized carbides with Zr, conferring superior strength balance and impact toughness. The yield strength of alloy reached 695 MPa, and a low ductile–brittle transition temperature of 238 K was maintained.

Influence of TiN Additions on the Microstructure of a Lightweight Fe–Mn–Al Steel

The potential of different inclusions to act as heterogeneous nucleation sites for primary austenite during solidification of a lightweight Fe–30Mn–5.5Al–1.5C–1.2Si steel was analyzed by thermodynamic calculations and experimental heats. Thermodynamic simulations and lattice disregistry calculations were utilized to predict the stability and nucleation potential of different inclusions. TiN was considered as the grain-refining addition because of the success of this inoculant in other austenitic steel castings. Addition of TiN was performed through the use of a pre-made master alloy containing a large volume fraction of fine TiN inclusions. Experimental castings were produced from cylindrical phenolic resin-bonded sand molds with a bottom chill to introduce directional solidification. Additions of 0.5 and 1.5% of the TiN containing master alloy, up to 0.29 wt% Ti addition to the melt, did not yield detectable grain refinement of the as-cast grain structure when compared to the steel castings without additions. Scanning electron microscopy revealed that the inclusions present in the resulting castings consisted mainly of Ti(C,N) with up to a 0.4% area fraction, and this suggests that the original TiN inclusions were at least partially dissolved. Thermodynamic modeling predicted the equilibrium stability of Ti4C2S2 at temperatures above 1440 °C. Although this phase was not observed experimentally, a nanoscale interface layer of Ti4C2S2 or sulfur adsorption on the surface of the Ti(C,N) inclusions may be responsible for poisoning of the nuclei.