Precipitation Behavior Of MnS Research Articles

Study on microsegregation model and MnS precipitation behavior of continuous casting ultra-low sulfur steel slab

The central segregation of elements in continuous casting slab is an important factor affecting the properties of steel materials. S segregation exists in the form of MnS. It is found in production practice that despite the ultra-low sulfur content of [ S ] ≤ 10 ppm in steel, MnS will still precipitate if the central segregation of slab is not well controlled, and MnS is an important factor causing the unqualified flaw detection of high-grade thick plate products. There are few studies on the microsegregation of ultra-low sulfur steel continuous casting slab. In this paper, the microsegregation model of continuous casting slab is established, and the effect of phase transformation on element segregation is fully considered. The precipitation behavior of MnS and the microsegregation of S, P, C, and Mn elements during slab solidification are discussed. Taking X pipeline steel as the research object, the simulation calculation shows that the segregation degree of P, S, and C is higher than that of Mn. When the solid fraction fs is greater than 0.9, the inflection point of S segregation decreases and MnS is formed. The segregation ratios of P, S, and C (CL / C0) after complete solidification were 4.5, 4.1, and 5.5, respectively. The carbon content affects the degree of element segregation by affecting the local solidification time. With the increase of carbon content, the degree of element segregation at the end of liquid steel solidification decreases.

Effect of electropulsing treatment on the precipitation behavior of MnS in sulfur-containing microalloyed 49MnVS3 steel

An experimental investigation has been conducted with respect to the influence of electropulsing treatment (EPT) on the 2D and 3D morphologies, distribution, number and size of MnS precipitates in the high-sulfur micro-alloyed 49MnVS3 steel. After the application of electric current pulse with a peak pulsed voltage of 30 V, the microstructure was refined due to the increasing nucleation rate of particles in liquid steel. Moreover, compared with the untreated steel with spherical MnS randomly distributed in the matrix, the MnS precipitates moved directionally to aggregate on the bottom and top surfaces of the ingot in order to minimize the free energy of the system in case of EPT. For untreated steel samples, the number of MnS was 409 (bottom), 579 (middle) and 437 (top), while that of the treated samples were 226 (bottom), 38 (middle) and 224 (top) in the scanning area of 2.65 × 107 µm2 with ASPEX. The number of MnS with small size decreased while the large-size MnS increased with the application of EPT.

In Situ Observation of the MnS Precipitation Behavior in High-Sulfur Microalloyed Steel Under Different Cooling Rates

In situ observation of the precipitation behavior of MnS in a high-sulfur microalloyed steel has been conducted by means of a confocal laser scanning microscopy (CLSM) with cooling rates increased from 50 to 400 °C/min. Differential scanning calorimetry analysis and thermodynamic calculation were carried out prior to and following the CLSM experiments using scanning electron microscopy (SEM) and X-ray energy-dispersive spectrometer. The results suggested that the initial MnS precipitate temperature decreased from 1440.0 °C to 1429.6 °C and the final temperature reduced from 1413.7 °C to 1381.6 °C as the cooling rate increased from 50 to 400 °C/min in the CLSM test. Three typical MnS morphologies of small angular, globular and larger dendrite cluster MnS were observed in the melting surface. Furthermore, with an increase in the supersaturation of MnS and a significant reduction of the local solidification time when the cooling rate increased from 50 to 400 °C/min, the large clusters MnS at interdendritic regions became thinner and more small angular MnS precipitates formed at dendrite crystals.

MnS Precipitation Behavior in MnO–SiO<sub>2</sub> Inclusion in Fe–Mn–Si–O–S Alloy System at Solid-Liquid Coexistence Temperature

With the emerging significance of creating an acicular ferrite microstructure to provide an optimum set of properties in steel, MnS precipitation behavior on a MnO–SiO2 inclusion at the solid-liquid coexistence temperature was experimentally investigated and thermodynamically elucidated in this study. Using a direct method of forming inclusions, alloy samples with varying sulfur concentrations [Fe-1.1Mn-0.10Si-0.05O-S (initial mass%); 0.005 to 0.031 initial mass% S] were prepared by holding at the solid-liquid coexistence temperature for 1 hour.

Effect of Strain on Strain‐Induced Precipitation Behavior of MnS in 3% Si Steel

Hot compression tests of 3% Si steel with a true strain range of 0.02–0.92 at a strain rate of 1 s−1 and a temperature of 1173 K, based on the Gleeble‐1500 thermo–mechanical simulator, are conducted. The effect of strain on the strain‐induced precipitation behavior of MnS is investigated via cold field‐emission ultrahigh resolution scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The experimental results obtained indicate that the volume density of MnS precipitates increases, whereas the mean diameter of MnS precipitates decreases with the increase in strain during the transient deformation stage. However, during the steady deformation stage, these parameters remain nearly constant. The precipitation behavior of MnS during the transient deformation stage is attributed to the increase in dislocation density with the increase in strain. More dislocations create a larger number of nucleation sites, which, in turn, increase the nucleation rate. At the same time, a model about static recovery affecting the dislocation density in the matrix after deformation is also proposed to elucidate the mechanism of the evolution of MnS in the aging process.

Effect of Sulfur Content on the Composition of Inclusions and MnS Precipitation Behavior in Bearing Steel

MnS inclusions in bearing steel have long been considered to significantly affect the fatigue life of bearing steel. In this paper, the sizes of inclusions in bearing steel with different sulfur contents were analyzed and the precipitation behavior of MnS was calculated using thermodynamics. Furthermore, the positive role of MnS in bearing steel was discussed. Results showed that when the size of inclusions in bearing steel was increased, the proportion of MnS components in composite inclusions gradually decreased. When the sulfur content was increased, the shape of inclusions changed from a particle shape to a strip shape. With increasing MnS content, the inclusion ratio of Al2O3 was significantly reduced in the Al2O3–CaO–MgO–MnS quaternary inclusion system, particularly for MnS proportions greater than 20%. The content of sulfur in bearing steel significantly affects the precipitation temperature of MnS. When sulfur content increases from 0.001% to 0.007%, the precipitation temperature of MnS increases from 1493 K to 1633 K as the precipitation of MnS moves from the austenite solid phase to the liquid and solid phases, and the precipitation size of MnS inclusions significantly increases. The size of oxide inclusions should be controlled to improve MnS wrap oxide inclusions in steel. Based on these results, a composition control with high sulfur levels and low oxygen levels should be adopted to improve the fatigue performance of steel.

MnS Precipitation Behavior of High-Sulfur Microalloyed Steel Under Sub-rapid Solidification Process

A typical high-sulfur microalloyed steel was investigated by a sub-rapid solidification process for grain refinement of the as-cast microstructure. The size and distribution characteristics of the MnS precipitates were analyzed. The variations in the dendrite morphology and secondary dendrite arm spacing (SDAS) under different cooling rates have been studied, which strongly influence the precipitation behavior of MnS. The 3D-morphology of MnS precipitates was revealed by a novel saturated picric acid deep-etching method. Most MnS precipitates with a length smaller than 5 μm were columnar or equiaxed in the corresponding dendrite zones under sub-rapid solidification conditions at cooling rates of 261 to 2484 K/s. Furthermore, an area scan analysis of the precipitates showed the number of small MnS per square millimeter with lengths lower than 3 μm decrease from 200,537 to 110,067. The percentage of large MnS with a length over 5 μm increased from 2.6 to 6.2 pct as the solidification condition changed from sub-rapid to air cooling. In addition, the size of MnS precipitate was found to depend linearly on the SDAS.

Analysis of precipitation behavior of MnS in sulfur-bearing steel system with finite-difference segregation model

To further reveal the influence of micro-segregation on the precipitation behavior of MnS in sulfur-bearing steel system, a coupled model of micro-segregation and MnS precipitation was established by the finite-difference method based on various calculation domains and the solid diffusion degrees, and a new controlled diffusion equation with more stable convergence was also used. 49MnVS3 and 1215 steels were used to analyze the influence of calculation domain, segregation model and S content on the precipitation behavior of MnS. The calculation results were verified by a high-temperature confocal laser scanning microscope (HT-CLSM). The results show that the domain has little effect on the precipitation temperature, precipitation solid fraction and precipitation amount of MnS, but affects the precipitation location and segregation of the solutes. For low- and medium-sulfur steels, the temperatures calculated by the diffusion control growth (DCG) model and the Lever model were nearly identical, whereas the temperature calculated by the Scheil model was lower. However, for high-sulfur steels, the precipitation temperatures calculated by three segregation models were nearly same. The precipitation solid fraction is more reasonable to describe the precipitation behavior of MnS. The precipitation behavior of MnS, observed by the HT-CLSM, matches well with that in the DCG model.

Study of manganese sulfide precipitation in medium sulfur, non-quenched and tempered steel via experiments and thermodynamic calculation

In this study, the precipitation behavior of MnS was calculated during the solidification process of the medium sulfur, non-quenched and tempered 49 MnVS steel. And the precipitation process was directly observed by a high-temperature confocal laser scanning microscope (HT-CLSM) equipped with a gold-image furnace. Besides, the precipitated particles were proved to be MnS by using the Scanning Electron Microscope-Energy Dispersive spectroscopy (SEM-EDS) analysis. The modified thermodynamic calculation indicated that the MnS precipitated from the residual liquid steel when the product of manganese and sulfur concentrations exceeded the equilibrium value at 1417.0 °C. Meanwhile, the results calculated by FactSage software shown that the beginning precipitation temperature of MnS is about 1411.0 °C. The observation of HT-CLSM demonstrated that the primary solid on the free surface of the liquid steel was visualized at 1485.0 °C during the solidification process (cooled from 1520.0 °C to room temperature with a rate of −30 °C/min). Then, the MnS particles started to form at 1437.0 °C and rapidly grew up into shape on the solid-liquid boundary. And the precipitation of MnS continued to form in a large amount (90% of the total) in the next 10 degrees. The enrichment of Mn and S near the local melt surface may be conducive the MnS formation, which results a higher actual precipitation temperature than the calculated value.

3%Si鋼中のMnS，MnSeおよびAlNとの複合析出と粒成長抑制効果

The precipitation behavior of MnS, MnSe and AlN in 3% Si steel was investigated for understanding inhibition of grain growth under isothermal annealing. It became clear that the precipitation of AlN was greatly influenced by that of MnSe. The precipitates became fine when hot-rolled at low temperature, and therefore the grain size after the recrystallization annealing became small. Similarly, the grain size after the isothermal annealing became small when the precipitates became fine. When MnS or MnSe precipitates formed complex with AlN, Ostwald ripening was suppressed, as a result, grain growth was inhibited.

Challenges of the study on precipitation behaviors of MnS in oriented electrical steels

The studies of the thermo-mechanic principles and the kinetic analysis of MnS precipitation behavior in oriented electrical steels conducted in the last dozen years have been summarized. The problems and insufficiency in the fields concerning nucleation theory of MnS precipitation, the relationship between the precipitation and dynamic recrystallization of the matrix as well as the influence of high-energy boundary precipitation on the pinning effect of the boundary migration were discussed. Suggestions were proposed to modify researches concerning the initial position density for MnS nucleation, the mutual interaction between the precipitation and the dynamic recrystallization as well as the kinetic principles of precipitation nucleation on grain boundaries with different boundary energy, which would complete the related theory of MnS precipitation behaviors.

Morphology and Precipitation Kinetics of MnS in Low-Carbon Steel During Thin Slab Continuous Casting Process

The morphology of manganese sulfide formed during thin slab continuous casting process in low-carbon steel produced by compact strip production (CSP) technique was investigated. Using transmission electron microscopy analysis, it was seen that a majority of manganese sulfides precipitated at austenite grain boundaries, the morphologies of which were spherical or close to the spherical shape and the size of MnS precipitates ranged from 30 nm to 100 nm. A mathematical model of the manganese sulfide precipitation in this process was developed based on classical nucleation theory. Under the given conditions, the starting and finishing precipitation temperatures of MnS in the continuous casting thin slab of the studied low-carbon steel are 1 189 °C and 1 171 °C, respectively, and the average diameter of MnS precipitates is about 48 nm within this precipitation temperature range. The influences of chemical components and thermo-mechanical processing conditions on the precipitation behavior of MnS in the same process were also discussed.

MnS Precipitation Behavior in Re‐Sulfurized Steels with Intermediate Levels of Sulfur

This paper presents results on the quantification of MnS precipitation during solidification of steels with intermediate levels of sulfur (0.05%) using a Confocal Scanning Laser Microscope (CSLM) equipped with a gold image furnace. The precipitation of MnS was observed in the liquid pools remaining in between advancing dendrites at the end of solidification. It was observed that MnS precipitated during cooling on existing mixed‐oxide particles of AI, Si and Ca. The rate of precipitation was seen to accelerate at two distinct points, once when the steel was molten and once during solidification.

3%Si鋼のMnS析出挙動に及ぼす熱間変形温度とS量の影響

3%Si鋼のMnS析出挙動に及ぼす熱間変形温度とS量の影響

Precipitation behavior of MnS on oxide inclusions in Si/Mn deoxidized steel

The precipitation behavior of the MnS phase of MnO-SiO2 oxides in Si/Mn deoxidized steels was examined. MnS phase formation in the oxide phase was clearly identified, and the Mn content in both phases increased with isothermal holding at 1,200°C. With increased cooling rate, both the size of inclusions and the precipitation ratio of the MnS phase in the oxides decreased. More than 90% of MnO-SiO2 oxides contain MnS phases and MnS precipitation is accompanied by an Mn-depleted zone around the oxides. This zone was created not just around the MnS, but around the whole oxide inclusion. One can tentatively conclude that the majority of the MnS islands after isothermal holding are formed by the diffusion of Mn and S from the matrix into the inclusions.

Effect of Ti Addition on the Potency of MnS for Ferrite Nucleation in C-Mn-V Steels.

The variation of precipitation behavior of MnS has been thermodynamically calculated in V-bearing C-Mn steels by substituting Ti for V. The use of two different set of solubility data for Ti 4 C 2 S 2 and TiS reported in literatures leads to a completely reversed precipitation behavior of MnS. The result of experimental observations is in qualitative agreement with the calculated result using the solubility data of Liu and Jonas. The calculated result showed, contrary to the case of V-containing steel, that the precipitated amount of MnS in steels bearing Ti-only rather decreases with decreasing temperature and that this is due to the formation of Ti 4 C 2 S 2 Controlled cooling experiments with interrupted quenching technique showed that MnS directly acts as the nucleation site for ferrite and that its nucleation potency depends on the precipitation behavior of MnS. Namely, MnS rarely acts as a nucleation site for ferrite in steels where its precipitated amount decreases with decreasing temperature.

Solubility of MnS in Fe-Ni Alloys as Determined by In-situ Observation of Precipitation of MnS with a Confocal Scanning Laser Microscope.

Solubility of MnS in Fe-Ni alloys has been investigated by in-situ observation with a confocal scanning laser microscope of specimens with various Mn, S and Ni contents which were heated and cooled in an infrared image furnace. Precipitation behavior of MnS at the surface of the specimens on cooling was monitored on a CRT and was recorded on videotape. Most MnS precipitates are found to form on alumina inclusion particles and grow in triangular (pyramidal) or rod-like shape. From precipitation temperatures obtained by the in-situ observation, the equilibrium constant of the reaction MnS←→Mn+S is determined as logK=log[%Mn][%S] f SMn= –9420/T+3.67, at T=1329–1493K for Fe–42mass%Ni alloy. The K value for γ-Fe at 1438K is in good agreement with that by Turkdogan et al., and Ni is found to increase the solubility of MnS.

薄鋳片-簡略熱延プロセスにおける軟質冷延鋼板の析出制御

Although thin slab-direct hot rolling process is expected as a future process of steel sheet production, its metallurgy has not been investigated thoroughly. In this paper, the metallurgy of mild steel in thin slab-direct hot rolling process has been discussed with special attention to the precipitation behavior of MnS and its influence on the hot-cracking at the edge of hot bands and the mechanical properties of cold rolled low carbon steel sheets. The following results are obtained :1. The hot-cracking resistance and mechanical properties of cold rolled sheets produced through thin slab-direct hot rolling process are not inferior to those produced through a conventional process, if S content is reduced and/or proper heat treatment prior hot rolling is carried out.2. The experimental findings indicate that MnS precipitates under a condition of the local equilibrium at the MnS/γ interface.3. The hot-cracking is probably caused by the remelting reaction of austenite at grain boundaries occupied by sulfur. For explaining the experimental findings, not only the equilibrium but also the kinetics of the diffusional reaction must be considered for the remelting process.

Precipitation behavior of MnS during δ/γ transformation in Fe−Si alloys

The precipitation behavior of MnS after solidification was analyzed with low-carbon Fe−Si alloys. This system was chosen since it has a wide temperature range for the δ/γ transformation. Experimental results showed that the amount of MnS precipitates increased drastically between 1300°C and 1100°C, and MnS precipitates were segregated almost entirely in the δ phase. This result was interpreted quantitatively by a mathematical model, taking into account the diffusion and the redistribution of solute elements and also the solubility product limit of Mn and S in both phases. Mathematical analysis shows that the precipitation of MnS starts first in the γ phase, but its growth will be very limited because of slow diffusion of Mn in the γ phase. The effects of some factors such as cooling rate and Si content of alloys on the rate of precipitation were discussed, and the degree of contributions of diffusion of Mn and the redistribution of S were estimated.

Precipitation behavior of MnS and Ca-containing inclusions in Ca-added CC slab.

Distribution of Ca-oxide, Ca-sulfide and MnS in Ca-added CC slab was investigated by new X-ray microanalyzer (CMA). The good relation between the amount of MnS and ACR, ESSP which were proposed as the parameter indicating the degree of shape control was not found. It was observed that the formation of MnS was suppressed by Ca addition even in the slab whose oxygen content was too high to form CaS.On the other hand, calcium-aluminate inclusions were able to be divided into the following two types by the chemical composition: 1) Ca+O type; S enriched region thinly covered this type of oxides. 2) Ca+S type; S was enriched in the whole region of this type of oxides.Compare to the Ca+O type inclusions, Ca+S type inclusions were mainly observed in the segregated area in CC slabs.By the thermodynamic consideration, it was found that the desulfurization reaction by calcium-aluminate during solidification should be considered to clarify the shape controlling mechanism.