MnS Particles Research Articles

Morphological approach to hot tearing during continuous casting of steels

In the present work, plant samples were used to introduce a detailed understanding of the formation of hot tear segregations and open hot tears in the continuous casting process of steels. A more detailed sequence in four stages was proposed for the formation of hot tear segregations as well as open hot tears. Results revealed that hot tear segregations form in two spherical and elongated morphologies. The spherical precipitate hot tear segregations are caused by MnS particles, while the elongated precipitate hot tear segregations include more segregating elements. In addition, the outcomes showed that the spherical precipitate hot tear segregations, in comparison with the elongated hot tear segregations, are more associated with the open hot tear formation.

Correlation Between MnS Precipitation, Sulfur Segregation Kinetics, and Hot Ductility in C-Mn Steel

In a C-Mn steel without Nb, the mechanism of hot ductility loss and recovery has been understood. The specimens were solution treated at 1673 K (1400 °C), subsequently cooled to 1273 K (1000 °C) at a rate of 1 or 20 K/s and finally held at the temperature. At a rate of 1 K/s, the segregation concentration of sulfur at prior austenite grain boundaries decreases gradually with holding time. At the rate of 20 K/s, the segregation concentration of sulfur shows a convex profile in a time versus segregation concentration plot. Such segregation behaviors of sulfur are deeply related to the MnS reaction during cooling to 1273 K (1000 °C) or holding at the temperature. The high-temperature intergranular fracture observed in this steel is due to the sulfur segregated at the grain boundaries. The recovery of hot ductility results from the combination between the decrease in sulfur segregation concentration governed by the MnS reaction and the overall decohesion at the interface of the MnS particles which act as a strong sink of the free sulfur tending to segregate to the grain boundaries.

Hot Ductility and Deformation Behavior of C-Mn/Nb-Microalloyed Steel Related to Cracking During Continuous Casting

Hot ductility studies have been performed on C-Mn and C-Mn-Nb steels with an approach to simulate the effect of cooling conditions experienced by steel in secondary cooling zone during continuous casting. Thermal oscillations prior to tensile straining deteriorate hot ductility of steel by deepening and widening the hot ductility trough. C-Mn steels are found to exhibit ductility troughs in three distinct zones whereas C-Mn-Nb steel shows drop in ductility only at low temperature in the vicinity of ferrite transformation temperatures. Start of ferrite transformation in steels causes yield ratio to increase while work hardening rates and strength coefficient decrease with decrease in test temperature in presence of thermal oscillation prior to tensile testing. Inhibition of recrystallization due to build-up of AlN particles along with the presence of MnS particles in structure and low work hardening rates causes embrittlement of steel in austenitic range. Alloying elements enhancing work hardening rates in austenitic range can be promoted to improve hot ductility. The presence of low melting phase saturated with impurities along the austenitic grain boundaries causes intergranular fracture at high temperature in C-Mn steels.

Incorporation of Y2O3 Particles into 410L Stainless Steel by a Powder Metallurgy Route

Addition of yttria to steels has been proposed for the fabrication of oxide-dispersion-strengthened materials for nuclear power applications. We have investigated materials prepared from 12 Cr martensitic stainless steel, AISI 410L, produced by powder metallurgy. Materials were produced with and without yttria addition, and two different sizes of yttria were used, 0.9 µm and 50 nm. Tensile and mini-creep tests were performed to determine mechanical properties. Optical microscopy, SEM, TEM, and EDX analysis were used to investigate the microstructures and deformation mechanisms and to obtain information about non-metallic inclusion particles. SiO2, MnS, and Y2Si2O7 inclusion particles were observed. An SiO2 and Y2O3 interaction was seen to have occurred during the ball milling, which impaired the final mechanical properties. Small-angle neutron scattering experiments showed that the matrix chemistry prevented effective dissolution of the yttria.

Study properties of nanocomposites prepared with new polyimides and reactive nanosilica by epoxide functionalization

In this article, new types of organosoluble polyimides, poly(carbazole‐quinoxaline‐imide)s (PCQI), were synthesized and used in preparation of nanocomposites with modified nanosilica (mNS). The synthesized polyimides bearing different solubilizing functional moieties were casted into thin films at room temperature. SiO2 nanoparticles were surface modified with γ‐glycidoxypropyltriethoxysilane (GPTES) to obtain mNS containing epoxide functional groups. The PCQI/mNS nanocomposites were prepared via cure reaction of epoxide groups and polymer functional units. The PCQIs and nanocomposites films were tested for different properties including thermal using TGA and DMTA, mechanical, thermomechanical, photophysical, solubility, water uptake, and metal ions adsorption. The strong chemical bonding between mNS particles and polymer matrix reduced solubility of nanocomposite and enhanced thermal stability in term of 10% weight loss temperature (T10%, from 509°C to 582°C) and tensile strength (from 110 MPa to 155 MPa). These polyimides and nanocomposites were also efficient chelating agents for removal of metal ions such as , Cr3+, Pb2+, Cd2+, and Hg2+ from aqueous solutions either individually or in the mixture and at different pH values. POLYM. COMPOS. 36:545–555, 2015. © 2014 Society of Plastics Engineers

Behaviors of Normal Grain Growth in Polycrystalline Fe–3%Si Alloys

The grain growth processes of model alloys Fe–3%Si–MnS and Fe–3%Si were investigated. The MnS particles did not completely inhibit normal grain growth but drastically reduced growth velocity. Activation enthalpy (57.72 kJ mol−1) and pre‐exponential factor (7.82 × 10−9 m2 s−1) for boundary migration obtained by statistical regressive calculations were significantly lower than those obtained by bicrystal investigations. The observations indicated that atoms should be pre‐activated before they jump over moving boundaries. Activation enthalpy and pre‐exponential factor decreased with increased pre‐activation energy. The predominant migrations of strongly curved boundaries and triple junctions during grain growth in polycrystals increased the pre‐activation energy, which differed from the simplified behaviors of boundary migration in bicrystals.

Activation Energy for Recrystallization in Fe-3wt.%Si Alloys with Different S Contents

The recrystallization behaviors of 60% rolled Fe-wt.3%Si and Fe- wt.3%Si-Mn-S alloys containing coarsen MnS particles were observed in temperature range 600°C~1000°C. The activation energy for recrystallization was determined according to an Arrhenius type of relationship. It was found that the activation energy in the temperature range 600°C~750°C was much higher than that in the temperature range 850°C~1000°C. Thermo-mechanical calculation indicates that there are hardly precipitation behaviors of MnS particles in 600°C~1000°C. Fe3C will precipitate below 650°C and Cottrell atmosphere will form just above 650°C, which induces dragging effect against the boundary migration during recrystallization and increase the activation energy. The activation energy determined was about 99kJ/mol or 217kJ/mol in Fe-3%Si alloy and 91kJ/mol or 220kJ/mol in Fe-3%Si-Mn-S alloy for the recrystallization in high temperature range of 850°C~1000°C or low temperature range of 600°C~750°C respectively.

An Investigation on the Effect of S and Al on the Austenite Growth Morphology in Gray Cast Iron, Using Thermal Analysis and Etching Technique

The austenite nucleation and growth morphology was investigated through experiments by inoculation with pure Al in a controlled environment using DTA furnace and H.F furnace. The austenite volume fraction and the dendrite growth orientations were affected by the addition of Al to the melt. Thermal analyses were performed to study the effect of sulfur content on austenite volume fraction and growth morphology using DSC. The possibility of austenite nucleation by MnS particles was analyzed. Different sulfur contents in the alloys were resulting in change in the latent heat of solidification and the rate of austenite formation. Austenite volume fraction was measured with four methods, colour etching, DSC thermal analysis, lever rule, and using LH calculated by Thermo-Calc data base, and a comparison was made among them.

Anomalies in segregation kinetics of solutes under tensile stress in heat resistant steel

In heat resistant steels, tensile stress accelerates the decomposition of preexisting smaller carbides and the growth of larger carbides. Consequently, the dissolved carbon is enriched in the matrix during the decomposition. Under the tensile stress, the massive diffusion of the enriched carbon results in more active segregation to the grain boundary/carbide interfaces for the growth of the larger carbides than the carbide-free grain boundaries. The segregation kinetics of carbon forms a convex profile during the growth process of carbides. A concave segregation profile of chromium corresponds to the convex profile of carbon. This is attributed to the diffusivity of chromium much lower than that of carbon which makes the chromium as the rate-controlling factor for the carbide growth. Due to the repulsive segregation behavior between carbon and phosphorus, the concave segregation profile of phosphorus results from the convex segregation profile of carbon formed during the active carbide growth. A convex segregation profile of sulfur is also formed owing to the formation reaction of MnS particles, but it is independent of the segregation behaviors of the other solutes.

Wear Evaluation on Ni3Al/MnS Composite Related to Metallurgical Processes

Iron alloyed Ni3 Al with composition of Ni-18. 8A1-10. 7Fe-0. 5Mn-0. 5Ti-0. 2B in atom percent (NAC alloy) showed attractive tribological properties under unlubrication condition at room temperature. The alloy was prepared by hot isostatic pressing (HIP) process. The wear properties were associated with its intrinsic deformation mechanism. Unfortunately, the single phase NAC-alloy worked inadequately with its counterpart disk, and also showed a poor machinability. In the present work, NAC-alloy matrix composite with 6% (volume percent) MnS particle addition was studied to improve its wear behaviors and performance on machining. Two metallurgical processes of HIP and vacuum casting were applied to produce the testing materials. Pin-on-disk (POD) measurements were carried out at room temperature. A commercial vermicular graphite cast iron was selected as a reference material. The counterpart disk was made of a grey cast iron as liner material in ship engines. The contact pressures of 2.83 MPa and 5.66 MPa were normally applied in the tests. The investigation indicated that MnS particle addition in the NAC-alloy composites functions as an effective solid lubricant, and improved wear properties and machinability of the materials. Obviously, as-cast NAC-alloy with in-situ formed MnS-phase was working more effectively with the counterpart, comparing to the HIPed NAC-alloy composite with MnS particles. At the high contact pressure of 5.66 MPa, the specific wear rate of the as-cast NAC-alloy composite was high. The phenomenon of the negative effect is mostly due to the brittle second NiAl phase as evidenced in the microstructure analysis.

Precipitation of AlN and MnS in Low Carbon Aluminium-Killed Steel

The precipitation kinetics of AlN and MnS in low carbon aluminium-killed steel was calculated. Transmission electron microscopy (TEM), energy disperse spectroscopy (EDS) and phase analyses have been used to investigate the morphology, compositions and particle size distribution of AlN and MnS precipitates in three positions of the coil. The particles of AlN and MnS precipitates in the ferrite region after coiling and distributes along and adjacent to the ferrite grain boundaries. The shapes of AlN are plate-like, the precipitates size is about 10 to 60 nm; the shapes of MnS are spherical, the precipitates size is about 200 to 600 nm. The precipitation behavior of AlN is sensitive to the isothermal temperature and holding time, the precipitation quantity and particle size distribution of AlN in different positions of coil are unequal.

Enhancement of Pearlite Nucleation by Deformation of Austenite Matrix in an Fe–12Mn–0.8C Alloy

AbstractThe effect of plastic deformation of austenite on the nucleation of pearlite was investigated using an Fe–12Mn–0.8C (mass%) alloy. Slight warm deformation of austenite prior to pearlite transformation effectively accelerates the intragranular nucleation of pearlite although intragranular pearlite is hardly formed without deformation. Formation of pearlite at annealing twin boundaries is promoted in the warm‐rolled specimens. Additionally MnS particles are activated as intragranular nucleation sites of pearlite. Cold rolling of austenite introduces many deformation twins in the alloy used. Subsequent isothermal transformation heat treatments result in nucleation of pearlite at intersections of the deformation twins. It is concluded that incoherent portions introduced by deformation onto the annealing or deformation twin boundaries are effective nucleation sites in the pearlite transformation.

Effect of the low temperature annealing on primary and secondary structures and magnetic properties of Fe-3% Si

The processing of 3% Si steel is characterized by the use of MnS particles as a normal grain growth inhibitor. Experiments were carried out to investigate the grain growth in this material during heat treatments at low temperature. Industrial decarburized samples were annealed in the range 825-845 °C and a detailed study of grain size and texture was made by EBSD measurements. The primary grain size and texture were related to the secondary structure obtained after high temperature final annealing. The heat treatments for grain growth led to an increase in the mean grain size by 1.2 to 3 times, depending on the stability of MnS particles distribution. The increase of the primary grain size increased the core loss and decreased the magnetic induction of the fully processed material.

In situ observation and thermodynamic calculation of MnS in 49MnVS3 non-quenched and tempered steel

Based on thermodynamics calculation, the results of the formation temperature of MnS inclusions of non-quenched and tempered steel during heating process were discussed. It is shown that while the solid fraction is 0.9, MnS inclusions began to precipitate in the flnal stage of solidiflcation. The solidiflcation process of 49MnVS3 non-quenched and tempered steel during heating has been observed in situ using a confocal scanning laser microscope (CSLM), which agrees well with the thermodynamics calculation. MnS particles were coarsening during heating process, which would reduce the pinning efiect on the austenite grain boundaries and bring about the sudden growth of some austenite grains in this stage. KEY WORDS Confocal laser scanning microscopy; 49MnVS3 non-quenched and tempered steel; In situ observation; Thermodynamic calculation

Hot ductility behavior of a low carbon advanced high strength steel (AHSS) microalloyed with boron

The current study analyses the influence of boron addition on the hot ductility of a low carbon advanced high strength NiCrVCu steel. For this purpose hot tensile tests were carried out at different temperatures (650, 750, 800, 900 and 1000 °C) at a constant true strain rate of 0.001 s −1. Experimental results showed a substantial improvement in hot ductility for the low carbon advanced high strength steel when microalloyed with boron compared with that without boron addition. Nevertheless, both steels showed poor ductility when tested at the lowest temperatures (650, 750 and 800 °C), and such behavior is associated to the precipitation of vanadium carbides/nitrides and inclusions, particularly MnS and CuS particles. The fracture mode of the low carbon advanced high strength steel microalloyed with boron seems to be more ductile than the steel without boron addition. Furthermore, the fracture surfaces of specimens tested at temperatures showing the highest ductility (900 and 1000 °C) indicate that the fracture mode is a result of ductile failure, while in the region of poor ductility the fracture mode is of the ductile–brittle type failure. It was shown that precipitates and/or inclusions coupled with voids play a meaningful role on the crack nucleation mechanism which in turn causes a hot ductility loss. Likewise, dynamic recrystallization (DRX) which always results in restoration of ductility only occurs in the range from 900 to 1000 °C. Results are discussed in terms of boron segregation towards austenitic grain boundaries and second phase particles precipitation during plastic deformation and cooling.

Effect of Solute Depleted Area on the Distribution of MnS in Fe-3%Si

Hot deformation was applied on Fe-3%Si by the Gleeble-1500 thermo-mechanical system, and the effect of solute depleted area around the primary MnS particles precipitated prior to hot deformation on the distribution of strain-induced MnS particles was investigated. The obtained results showed that the depleted area around primary MnS particles affects significantly the distribution of strain-induced MnS particles, and the involved parameters were discussed.

Research on Characteristics of Deposition Precipitation Process in Production of Low Carbon Aluminum-Killed Steel in FTSR Technology

Precipitation characteristics of second phase in low-carbon steel produced by FTSR technology have been researched by TEM and EDS in this article. And preliminary research of precipitation conditions of second phase particles in thermodynamics and dynamics have been took. The results indicate that: there’re second phase particles precipitated dispersively in hot rolled low-carbon steels by FTSR technology. These particles mainly contain particles of Al2O3, MnS and AlN, and the precipitate size is about tens to hundreds of nano. Thermodynamical analysis declares that most of the Al2O3 and all of the MnS, AlN particles are precipitated in solid state. That’s why the precipitation process is slowed down by the diffusion velocity of the elements in solid, and thinner particles are precipitated while the material is in solid state than in liquid state. Different from the traditional plate rolling production of Al-killed steel, the precipitation of AlN particles are mainly controlled by the continuous casting process in thin slab casting and rolling process, but almost no precipitation of AlN particles in the rolling process.

Effect of chemical composition and production parameters on nanostructured component formation and a set of properties for high-strength low-alloy structural steels

The effect of alloying system and production parameters for hot-rolled product and annealing on the mechanical properties of microalloyed steel cold-rolled product are studied. The possibility is demonstrated of a marked effect of the amount and size of MnS particles and nano-precipitates of microalloying element carbonitrides on strengthening by grain refinement and dispersion strengthening. Recommendations are developed for assimilating industrial production of high-strength cold-rolled material with a yield strength of 320–340 MPa.

Self Lubricating Composite Coatings Containing TiC–MnS or WC-MnS Compounds Prepared by the Plasma Transferred Arc (PTA) Technique

Composite coatings containing manganese sulphide as lubricating addition and enhanced with hard carbide particles (TiC, WC) were synthesized on a plain steel substrate using the plasma transferred arc technique. The coatings are well bonded to the substrate, have a thickness of about 1 mm, and are free of any visual defects. They consist mainly of a martensitic or ferritic matrix enhanced with titanium or tungsten carbides and a dispersion of MnS particles. The tribological properties of the composites are assessed using a pin-on-disk device. Both composites possess self lubricating properties, due to the formation of a thin layer of manganese sulphide on their wear tracks. The corresponding friction coefficients vary between 0.25 and 0.28, compared with 0.50–0.60 obtained from similar hard coatings without MnS addition. The wear rates are of the order of 10−5 mm3/m N and are two orders of magnitude lower than those obtained from the substrate material with MnS addition, but without the presence of hard enhancing particles. The wear regime is mild abrasion due to the combined action of both lubricating (MnS) and hard (TiC or WC) particles.

Influence of Temperature Evolution on Precipitation Behaviour of Second Phase Particles in Grain‐oriented Electrical Steels

AbstractA model concerning dynamic precipitation of second phase particles during hot deformation of conventional grain‐oriented electrical steels is proposed. The model involves the solid solubility of the elements forming MnS, the corresponding nucleation driving force, as well as the evolution of dislocation densities during hot deformation, which supplies sites for heterogeneous nucleation of MnS particles. The model describes the dynamic process in which temperature keeps decreasing and dislocation density keeps increasing. The influences of reheating temperature, initial rolling temperature, finishing temperature and deformation duration on the precipitation behaviour are involved. Calculations have been conducted based on the model, to simulate the precipitation behaviour of MnS particles during hot rolling of grain‐orientated electrical steels under different parameters. The results indicate that hot rolling is very important for dispersive precipitation of MnS particles. The increase of particle density is promoted by proper increase of reheating temperature or proper reduction of initial and finishing rolling temperature, in which the driving force and dislocation density are increased. The simulation results agree basically with the experimental observations in hot strip of a grain oriented electrical steel.