MnS Precipitation Research Articles

The Effect of Tellurium on the Formation of MnTe-MnS Composite Inclusions in Non-Quenched and Tempered Steel

Te is a seldom-used alloying element, which is mainly used in free-machining steel. The Te content in this kind of steel is relatively low, and only a small amount of MnTe is generated. In previous studies, the effect of Te on the formation of inclusions was not fully studied. In order to clarify the mechanism, different amounts of tellurium were added into 38MnVS6 steel to form a certain amount of MnTe. The MnTe wrapped the MnS, forming a composite inclusion. With the increase of Te content in the steel, the diameter of inclusion increased, while the aspect ratio of inclusion varied little. The aspect ratio of most inclusions was in the range of 1~3. Besides, the MnS in the MnTe-MnS composite inclusions gradually changed from one big particle to several small particles. The solidification of the steel, as well as the precipitation of MnS and MnTe, was the main factor that affecting the formation of the composite inclusion. The mechanism of the process was systematically expressed in the current study.

The Influence of Sulfur Content on the Carbothermal Reduction of SiMn Slag

This article examines the influence of sulfur content on the carbothermal reduction of MnO and SiO2 in SiMn slag by carbon black. The sulfur content in the synthetic slag is varied from 0 to 1.0 wt pct. Reduction experiments are carried out in a thermogravimetric (TG) furnace at 1873 K (1600 °C) under CO atmospheric pressure. The reduction rates are measured based on the weight loss data, and the samples are characterized by SEM/EDS and ICP-MS. The wetting property of slag on carbon black is also studied with the sessile drop technique. The reaction rate on the slag-metal interface is one order higher than on the slag-carbon interface. A small amount of sulfur (0.2 and 0.44 wt pct) accelerates the slag-metal reaction rate constant by 2.2 and 4.2 times, respectively. Therefore, small amounts of sulfur in slag significantly improve the reduction of MnO and SiO2. The MnS precipitation phenomenon during slag cooling is studied by FactSage simulation and experimental verification.

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.

Cross-Scale Modeling of MnS Precipitation for Steel Solidification

One of the advantages of numerical simulations over traditional experimental methodologies is that they can synchronize nucleation, growth and coarsening during solidification from the point of view of microstructural analysis. However, the computational cost and accuracy are bottlenecks restricting simulation approaches. Here, two cellular automaton (CA) modules with different grid dimensions are coupled to form a cross-scale model in order to simulate MnS precipitation, accompanied by the matrix growth of dendrites during the solidification of a Fe-C-Mn-S steel, where the matrix growth is computed through the CA module with large grids based on the solute conservation and the undercooling of thermal, constitutional, and curvature, and increments of solid fraction of MnS are solved in combination with the transient thermodynamic equilibrium on the locally re-meshed grids once the MnS precipitation is formed. We utilize the cross-scale mode to illustrate MnS evolution in a solidifying matrix and explain the reason why it coexists in three shapes. Further, we study the effects of the content of elements Mn and S on MnS precipitation based on two continuously cast steel objects, with the factor of concentration product fixed as a constant. A re-precipitation of MnS is observed during the solidification of a system with a high content of Mn and low content of S. Simultaneous computation using cross-scale modeling can effectively save on computational resources, and the simulation results agree well with the experimental cases, which confirm its reliable accuracy.

Effect of Al2O3–SiO2–MnO inclusions on precipitation of MnS in Si–Mn-killed 304 stainless steels

ABSTRACTLaboratory experiments and thermodynamic calculation were conducted to investigate the precipitation of MnS inclusions in Si–Mn-killed 304 stainless steels with various Al and S concentrations. Three types of MnS-contained inclusions were detected: MnS phase dissolved in the MnO–SiO2 inclusion, the Al2O3-rich core phase surrounded by a MnS out layer, and the individual MnS. In steel with less than 0.001% Al, the liquid SiO2–MnO-rich inclusions can hardly influence the precipitation of MnS inclusions during the cooling process of 304 stainless steels. With the increase of Al in steel, more solid Al2O3-rich inclusions are formed, which can act as nucleation agents for MnS inclusions and dramatically promote the precipitation of MnS inclusions during the cooling process of Si–Mn-killed 304 stainless steels.

Effects of M-EMS Magnetic Field Intensity on MnS Precipitate in Rail

The process contrast tests with M-EMS stirring intensity was carried out, MnS inclusion scanned and statistics with Aspex, make comparison among the different process for the same testing area after conversion and unified the results that about the length of single inclusion and ratio of inclusion area. Result shows possibility of big size pure MnS separate increased with the greater stirring intensity; besides, nucleation possibility of compound state MnS increased, formation of bigger size compound MnS was promoted at the same time. Conclude that add nucleating agent while smelting and choose 210Gs as the proper stirring intensity is helpful for MnS inclusion separate control, and improve the technological level of inclusion control in rail at last.

Numerical analysis of effect of the solutes on formation of MnS in non-tempered steel

ABSTRACTTo analyse the effects of solute elements on formation of MnS in the micro-alloyed non-tempered steel, a novel coupling model of micro-segregation and MnS precipitation during solidification was built using the finite-difference method. Non-tempered 49MnVS3 steel was used to detect the effects of concentrations of elements on the precipitation behaviour of MnS. The results show that with contents of Mn at 0.05∼2%, S at 0.001∼0.3%, Si at 0.3∼0.7%, P at 0.001∼0.05%, C at 0.05∼1.0%, the precipitation temperature of MnS raised from 1360 to 1432°C, 1397 to 1447°C, 1425 to 1418°C, 1425 to 1418°C, dropped from 1488 to 1358°C, and its precipitation solidification ratio dropped from 1 to 0.785, 1 to 0.51, 0.883 to 0.866, 0.88 to 0.86, 0.96 to 0.77, respectively; the observed temperature of MnS by HT-SM was 1427.2°C, close to the calculated temperature of 1420.6°C by the proposed the diffusion control growth model.

Effect of sulphur content on precipitates and properties of DH36 structural steel

ABSTRACTIn the current research, the influences of sulphur content on precipitates and properties were investigated through thermodynamic calculation and microstructural analysis. The results show that the precipitates of DH36 structural steel are mainly (Nb, Ti)C and Ti(C,N), the size of which ranged from 7 to 220 nm. Plenty of nanoscale MnS was observed by transmission electron microscopy using carbon film replicas with 0.002% S. This is because the temperatures of maximum nucleation rate and fastest precipitation of MnS are much less than soaking temperature when S content is 0.002%, which is the main reason for the formation of nanoscale MnS. What is more, the pinning effect of nanoscale MnS can also refine the grain size. Consequently, ultra-low content of sulphur can be used to optimise the properties of DH36 structural steel.

Effect of MnS precipitation on solute equilibrium partition coefficients in high sulfur steel during solidification

Abstract

The Relationship between MnS Precipitation and Induced Nucleation Effect of Mg-Bearing Inclusion

Abstract The relationship between MnS precipitation and induced nucleation effect of Mg-bearing inclusion has been explored through scanning electron microscope and energy dispersive spectrometer (EDS). Results indicate that MnS prefers to precipitate on Mg-bearing inclusions. Statistical analysis suggests that MgAl2O4 and MgO may coexist in inclusion. After etching, it is found that Mg-bearing inclusions can induce the nucleation of intragranular acicular ferrites. Based on EDS line analysis and comparison with Al-Mn-Si-O inclusion in non-Mg-treated sample, this effect can be explained by Mn-depletion zone (MDZ), which is due to the vacancy property and crystal structure of MgAl2O4. In the same sample, similar induced nucleation effect and MDZ are not observed around pure MnS. This comparison implies that the formation of MDZ may be independent of MnS precipitation.

Mechanism of MnS Precipitation on Al2O3–SiO2 Inclusions in Non-oriented Silicon Steel

This study investigates the mechanism of MnS precipitation on Al2O3–SiO2 inclusions during the solidification of non-oriented silicon steel, especially the influence of the phase structures and sizes of the oxides on the MnS precipitation, by scanning electron microscopy and transmission electron microscopy coupled with energy dispersive spectrometry. The investigation results show that MnS tends to nucleate on submicron-sized Al2O3–SiO2 inclusions formed by interdendritic segregation and that it covers the oxides completely. In addition, MnS can precipitate on micron-sized oxides and its precipitation behavior is governed by the phase structure of the oxides. The MnS embryo formed in a MnO-containing oxide can act as a substrate for MnS precipitation, thus permitting further growth via diffusion of solute atoms from the matrix. MnS also precipitates in a MnO-free oxide by the heterogeneous nucleation mechanism. Furthermore, MnS is less prone to precipitation in the Al2O3-rich regions of the Al2O3–SiO2 inclusions; this can be explained by the high lattice disregistry between MnS and Al2O3.

Precipitation Behaviors of TiN Inclusion in GCr15 Bearing Steel Billet

There are many types of non-metallic TiN-based inclusions observed in GCr15 bearing steel, including single-particle TiN, multi-particle polymerized TiN, and complex inclusions like TiN-MnS, TiN-MgO-MgAl2O4 (TiN-MgO-MA), and TiN-MgAl2O4-MnS (TiN-MA-MnS). Thermodynamic calculations suggest that single-particle TiN precipitates dominate the mushy zone of GCr15 bearing steel. Kinetic calculations regarding TiN growth suggest that the final size of the single-particle TiN ranges between 1 and 6 μm in the initial concentration range of [pct Ti] = 0.0060 to 0.0079 and [pct N] = 0.0049 to 0.0070, at 1620 to 1640 K and a local cooling rate of 0.5 to 10 K/s. The multi-particle polymerized TiN are formed by single TiN particles in three stages: single-particle TiN inclusions approach each other drawn by the cavity bridge force (CBF), local active angles consolidate, and neck region sintering occurs. Based on the thermodynamic calculations of TiN, MnS, and MgO precipitation, the formation behaviors of complex inclusions of TiN-MnS, TiN-MgO-MA, and TiN-MA-MnS were investigated.

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.

Co‐Precipitation Behavior of MnS and AlN in a Low‐Carbon Steel

In this work, the simultaneous precipitation of MnS and AlN particles in low‐carbon steel and their effect on hot ductility is investigated. On basis of a thermal treatment, which involves an intermediate cooling and reheating step, the authors show that the two compounds can precipitate in a symbiotic manner under conditions, where precipitation of isolated AlN will otherwise be suppressed. This co‐precipitation behavior is studied by transmission electron microscopy with energy dispersive X‐ray spectroscopy, as well as accompanying thermokinetic simulations with the software package MatCalc. The calculated evolution of the phase fractions, mean radii as well as number densities of the two compounds shows good agreement with the experimental observations and, thereby, supports our interpretation of the MnS–AlN co‐precipitation mechanism.

Modeling on solute enrichment and inclusion precipitation during the solidification process of high sulfur steel slab

Abstract

Effect of Cu Addition on Precipitation and Growth Behavior of MnS in Silicon Steel Sheets

The influence of Cu addition on MnS precipitation and growth behavior in Fe-2.88Si-0.1Mn-xCu (x = 0, 0.25) has been investigated. SEM observation clarified that Cu addition has no effect on the morphology of MnS or its growth rate at early stage. In contrast, Cu addition suppresses the growth rate at the Ostwald ripening stage. At the early stage of growth, a plateau region was observed both with and without Cu addition. Neither the conventional diffusion limited growth nor the Ostwald ripening theory adequately explains these observations. Using the Kampmann–Wagner Numerical (KWN) model, it was possible to successfully reproduce such behavior, including the plateau region. The interfacial energy between ferrite and the MnS was evaluated by the KWN-model, and good agreement was found with previously reported values. The suppression in the growth rate at the Ostwald ripening stage by Cu addition can be explained by a 15 pct reduction in the interfacial energy which possibly occurs due to the segregation of Cu at the interface between MnS and ferrite. This segregation was experimentally confirmed by STEM-EDX analysis.

The Relationship Between MnS Precipitation and the Induced Nucleation Effect of Ti-Bearing Inclusions

Abstract The relationship between MnS precipitation and the induced nucleation effect of Ti-bearing inclusions has been analyzed using SEM and EDS. In comparison with a non-treated sample, it can be seen that the Ti treatment leads to the oxide evolution from Al-Mn-Si-O to Ti-Al-Si-Mn-O. Moreover, it was found that sulfur congregates around both types of oxide, which is attributed to the MnS precipitation. As for pure MnS, its proportion in the total inclusion decreases when a Ti treatment is performed. EDS line analysis suggested that a Mn depletion zone (MDZ) occurs in the Fe matrix surrounding Ti-Al-Si-Mn-O. It does not occur surrounding Al-Mn-Si-O in the comparison sample. This difference leads to different microstructures. The intragranular acicular ferrites (IAFs) are only observed in the Ti-treated sample. Further analysis indicated that this microstructure is induced by Ti-Al-Si-Mn-O inclusions. In the same sample, the similar induced nucleation effect and a MDZ could not be found surrounding pure MnS. This comparison suggests that the formation of the MDZ may be independent of a MnS precipitation.

Effect of Mg Addition on Nucleation of Intra-granular Acicular Ferrite in Al-killed Low Carbon Steel

To verify the formation behaviors and mechanisms of intra-granular acicular ferrite (IAF) grains nucleated by Mg-Al-O in low carbon steel, the steels containing different Mg contents were refined in a vacuum induction furnace. The effect of Mg addition on the formation of IAF structure in Al-killed low carbon steel was investigated by optical microscope (OM) and scanning electron microscope with energy dispersive X-ray spectroscope (SEM-EDX). It reveals that the IAFs are only detected in Mg-added steels, and the volume fraction of IAF increases with the Mg concentration from 8×10−6 to 26×10−6. It shows that not only the MgO-Al2O3-MnS and MgO-Al2O3-P2O3 particles are the effective nucleation sites for IAF, but also the pure MgO · Al2O3 phase can promote the ferrite nucleation. A Mn-depletion zone (MDZ) is characterized adjacent to the MgO-Al2 O3-MnS, which is believed to be one of the possible mechanisms to explain the IAF nucleation. The MDZ around the MgO-Al2 O3-MnS inclusion would be induced by the MnS precipitation on the inclusion. It seems that the ability of Mg-containing inclusions to induce the nucleation of ferrite might be attributed to a new mechanism, i. e., the P-rich zone formed on a few Mg-Al-O inclusions might be another factor for promoting the IAF formation.

Crystallographic and morphological aspects of AlN precipitation in high Al, TRIP steels

The dendritic AlN associated with poor ductility on straightening during continuous casting is believed to always crystallise out in the hcp structure. The present paper shows that AlN precipitation can also be present as an fcc phase. Because AlN precipitation is sluggish and needs suitable nucleants like MnS to aid its precipitation, the crystal structure of AlN is dependent on the order in which the austenite and MnS precipitate out during solidification. When austenite forms first, as with the 1%Al transformation induced plasticity (TRIP) steel, MnS nucleants are not available and AlN is forced to precipitate at the austenite grain boundaries as fcc so encouraging intergranular failure. With the 1.5%Al TRIP steel, on solidification, MnS is present in abundance, giving rise to the conventional hcp AlN.

Coherent to incoherent transition of precipitates during rupture test in TP347H austenitic stainless steels

Precipitation of various particles and their growth during rupture test have been investigated in TP347H austenitic stainless steels using a transmission electron microscopy. Various precipitates of MnS, Nb-rich MC, and MnS+MC and MnS+M2P complexes are observed in the γ matrix after rupture test at 750 °C. The MnS particles formed independently in the γ matrix show a coherency or semi-coherency with the γ matrix. The Nb-rich MC carbides show also a coherency with the γ matrix. The Nb-rich MC carbides showing a semi-coherency with the MnS also form on the surface of the coherent or semi-coherent MnS particles, and they show a cube-cube orientation relationship with the MnS particles. The MnS+MC complex loses the initial coherency with the γ matrix, as the MC in the complex grows. The Nb-rich M2P precipitates formed on the surface of the MnS particles do not show an orientation relationship with the MnS particles or the γ matrix. The MnS particles in the MnS+M2P complex hold the initial coherency with the γ matrix. Effects of MnS precipitation followed by the formation of the complexes on rupture life of the TP347H austenitic stainless steels are discussed from the viewpoint of MnS precipitates acting as sinks of free sulfur segregating to the grain boundaries.