Sulfide Inclusions In Steel Research Articles

Study on the effect of rare earth Ce on the modification of sulfide inclusions in U71Mn heavy rail steel

In this paper, the directional modification behavior of rare earth Ce on sulfide inclusions in steel is studied by thermodynamic calculation and experiment methods, and the mechanism of directional modification of rare earth Ce on sulfide inclusions in U71Mn heavy rail steel is proved. The results show that U71Mn heavy rail steel contained more large-sized inclusions and their distribution is more concentrated without the addition of rare earth Ce element. After the addition of rare earth Ce element, the average size of sulfur-containing inclusions in the steel decrease from 5.22 μm to 1.85 μm, and the number density of sulfur-containing inclusions in the steel increase from 83.65 mm−2 to 217.68 mm−2, indicating that the number of sulfur-containing inclusions in the steel increases after the addition of Ce element, and more small-sized sulfur-containing inclusions will form in the steel. The addition of rare earth Ce element can effectively reduce the existence of large-sized inclusions in the steel and modify large-sized inclusions into small-sized inclusions.

Study on the effect of Al-La composite deoxidation on the modification behaviors of TiN and sulfide inclusions in 20CrMnTi gear steel

This article uses experimental and thermodynamic calculations to study the directional modification behavior of TiN and sulfides in 20CrMnTi steel before and after the addition of rare earth La element. The morphologies (SEM) and elemental distributions (EDS) of TiN and sulfide inclusions in steel are characterized using scanning electron microscopy, and the sizes of the inclusions are statistically analyzed. With the addition of rare earth La, the average sizes of TiN and sulfide inclusions in steel decrease, and the proportions of TiN and sulfide inclusions in all inclusions of the steel decrease. The results show that the addition of La element can promote the formation of LaAlO3 in steel, which can be used as the nucleation core of TiN and MnS inclusions in steel, and then form LaAlO3-TiN and LaAlO3-MnS-TiN composite inclusions, which are smaller in size and more uniform in distribution than TiN and sulfide in steel before La element is added. When La is added alone, the average size of TiN inclusion in steel is 2.2 μm. After the deoxidation of Al-La alloy, the average size of TiN inclusion in the steel is 1.9 μm. After Al-La composite deoxidation, the TiN containing inclusions in the steel will be transformed into smaller LaAlO3-TiN composite inclusions. When adding La alone, the average size of sulfide inclusions in the steel is 2.1 μm. When Al-La composite deoxygenation is used, the average size of sulfide inclusions in steel is 1.1 μm, indicating that the Al-La composite deoxygenation has a better improvement effect on sulfide inclusions in steel than the improvement effect of adding La alone.

Diffusion and precipitation of MnS at interface between Mn–Al–Si oxides and steel during solidification

Sulfide inclusions in steel occur mainly as pure manganese sulfide (MnS) and manganese oxysulfide. The high-temperature precipitation of MnS at the oxide–steel interface was studied by inserting Mn–Al–Si oxide rods with or without MnS into different molten metals and solidifying under different cooling conditions. No MnS precipitated at the oxide–metal interface if the oxide contained no MnS, even if the steel contained Mn and S. At very low cooling rate, MnS in steel cannot diffuse to the oxide–steel interface, irrespective of the sulfide capacity of the oxide. MnS precipitated at the oxide–steel interface originated mainly from the oxide; thus, MnS in oxysulfide inclusions originates from diffusion from the oxide phase, not from the steel. Dispersed pure MnS inclusions precipitated from steel during solidification. A Mn-depletion zone existed on the oxide side with width larger than most inclusion radii in cast steel. This demonstrates that most oxysulfide inclusions are not large enough to present as residual MnS in the oxide phase.

Effects of deoxidizing degree on the pitting corrosion behavior of carbon and manganese steels

Nine steels with different deoxidizing degrees and two comparative steels were selected. Their pitting initiation susceptibility was compared by means of potentiodynamic polarization tests in 3wt% NaCl solution. The pit propagation rate was evaluated in artificial sea water and 3wt% sea salt solution by simulating occluded corrosion cell (SOCC) test and hanging plate test, respectively. The composition of inclusions and corrosive feature were studied by scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), and optical microscopy (OM). The results indicate that sulfide inclusions in steel are the sites for pit nucleation. The sulphide inclusions vary in shape from short spindle-like to long strip-like with increasing deoxidizing degree. Under the same conditions, the lower the deoxidizing degree gets, the lower the pitting initiation susceptibility becomes, and the stronger the resistance to pit propagation exhibits. For steels with different deoxidizing degrees, their pitting initiation susceptibility is mainly influenced by thermodynamic stability, while the pit propagation rate is primarily subject to the characteristics of inclusions in steel.

Thermodynamic examination of inclusion modification and precipitation from calcium treatment to solidified steel

Calcium treatment is a well established method to transform oxide and sulphide inclusions in steel to less harmful inclusions which can have beneficial effects on properties. Transformation of solid alumina clusters to liquid calcium aluminates by calcium is a much used technique to avoid nozzle blocking in continuous casting of aluminium deoxidised steels. Calcium treatment is also a key method to improve machinability, which can be further improved by increased sulphur content. Resulphurised steels, however, tend to have casting problems due to deficient modification of oxides or formation of solid CaS inclusions which also have a tendency to clog the nozzle. In this study, the formation and transformation of liquid and solid inclusions containing oxidic and sulphidic components were examined by thermodynamic calculations. A quasichemical slag model was applied to calculate equilibrium oxide and sulphide inclusions in steel. Calculations were carried out over a wide temperature range to study the formation of species in the melt corresponding to ladle treatment conditions as well as casting. To examine inclusion behaviour during casting and solidification, the interdendritic solidification model, IDS, was coupled with thermodynamic equilibrium calculations. The results show the conditions in which liquid inclusions can be formed with calcium treatment. The calculations were performed at different temperatures and varying calcium, aluminium and sulphur contents. The effect of total oxygen content was also studied. The main components in liquid calcium aluminates were CaO and Al2O3 plus some SiO2 and CaS. The stability relations of different compounds alter as a function of temperature. An abrupt change occurs during solidification when the partition of the inclusion forming elements between the liquid and solid iron phases are taken into account.

Effect of tool materials on surface machined roughness and cutting force of low-carbon resulfurized free-machining steels.

This study examined the effects of ceramic tool materials on the surface roughness and cutting force when low-carbon resulfurized free-machining steels were plunge-machined. The Tool materials used for the study were 9 kinds in total; 7 kinds ceramics-TiN, TiC, HfO2, ZrN, Al2O3, ZrO2 and La2O3-and a high-speed steel (Fe3C) and a cemented carbide (WC+Co).(1) Surface roughness and cutting force are the smallest in the ZrO2 tool, increasing in the order of TiN, ZrN, Al2O3, TiC, HfO2, WC+Co, La2O3 and Fe3C tools.(2) ZrO2, TiN, ZrN and Al2O3 tend to adhere selectively to manganese sulfide inclusions in steels, resulting in the formation of MnS films over the rake face of tools. On the other hand, HfO2, WC+Co, Fe3C and La2O3 tend to adhere selectively to the ferrite phase, forming a kind of built-up edge, whereas TiC hardly to manganese sulfide inclusions and ferrite phase.(3) Surface roughness and cutting force decrease in proportion to the area percentage of MnS films formed over the rake face of tools, because the MnS films play a role as a lubricant.(4) Adhesion of manganese sulfide inclusions to tools may not only stem from physical properties such as surface roughness of the tools but also from chemical bonding.

部分安定化ジルコニアセラミック工具の性能

Surface roughness and tool wear was investigated when low-carbon resulfurized free machin-ing steel was cut by means of either plunge-machining or ordinary turning with a partially stabilized zirconia ceramic tool (PSZ). Moreover, the cutting performance of the PSZ tool was compared with that of some conventional tools. (1) Small amount of manganese sulfide inclu-sions in steel has trends toward to adhesion to the PSZ tool, resulting in the formation of MnS layer on the tool with a thickness of 2-3 μm. (2) The MnS layer seems to have a roll of a kind of lubricant, and restricts the formation of built-up edge and wearing the tool. (3) The perfor-mance of the PSZ tool is superior to both a high-speed steel tool and a sintered carbide tool with respect to surface roughness and tool wear.

Solubility of sulfur in steel 100Kh13M in the presence of manganese and silicon

1. Additions of silicon and manganese to steel 100Kh13M cause a considerable reduction of the sulfur content in the solution (by a factor of 1.5). 2. When steel 100Kh13M contains both manganese and silicon, the sulfur content of equilibrium with the exess phase decreases, and this causes an increase of the weight of the sulfide inclusions in the steel. 3. The most efficient way of reducing the amount of sulfide inclusions in steel 100Kh13M is to reduce the sulfur content to 0.002–0.003%.

Precipitation of titanium and zirconium sulfides during uni-directional solidification.

Morphologies, chemical compositions and distribution of sulfide inclusions in steel have been examined on uni-directionally solidified iron alloy containing about 0.1% sulfur and one of sulfide forming elements; Mn about 1%, Ti about 0.5 or 1%, and Zr about 0.1 or 0.3%.The results obtained are summarized as follows;(1) Almost all of titanium and zirconium sulfides are observed in an interdendritic space in the morphology of Type II. The number density and mean diameter of these sulfides are approximately same as those for MnS.(2) In titanium added alloys many sulfide colonies consisting of rod- and/or plate-like TiS are observed, whose area fraction amounts to 0.2.(3) Rod- and plate-like inclusions observed in zirconium dded alloys make solid solution with manganese sulfide to form (Zr, Mn)3S4(Zr/Mn molar ratio: 0.4-3.5) and approach to a spherical form in the existence of manganese with about 1%.(4) The supersaturation for these sulfides to precipitate in the solidification sequence has been evaluated by use of phosphorus content in the steel matrix adjacent to a given sulfide precipitate. The supersaturation for sulfide precipitation is evaluated as follows;MnS : 1.0-1.7, TiS : 1.0-1.7, Zr3S4: 3.0-10 where the equilibrium relations between sulfur and sulfide forming elements determined by authors, and solute enrichment during solidification are taken into account.

Determination of volume fraction of sulfide inclusions in steels

This paper examines the effectiveness of a metallographic method suggested by Whiteley [1] for quantitative evaluation of sulfide inclusions in steels using image analyzing computers such as the Quantimet 720. This metallographic method was proposed originally for identification of manganese sulfide inclusions. It involves rubbing a metallographically polished surface with a suitable cloth containing absorbed silver nitrate. The resultant reaction turns the manganese sulfides white in color. In the present work, sulfide inclusions were studied in six steels employing the above metallographic method and the Quantimet 720. In addition, elemental analyses of inclusions before and after silver nitrate treatment were carried out using an ORTEC energy dispersive system attached to a JEOL scanning electron microscope. The conclusions were that not only manganese sulfides, but sulfides of other compositions were also turned white by the above metallographic method, that inclusions other than sulfides were not affected by this surface treatment, and that the whitening of sulfides was due to a silver deposit on them. In addition, it was found that a linear relation exists between the volume fraction of sulfide inclusions and the sulfur content, the constant of proportionality being dependent on the sulfide composition.

A Contribution to the Mechanism of Hydrogen Entry Into Steels in Acid Environments

Abstract It is proposed that the dissolution of sulfide inclusions in steels, when exposed to acid media create an environment similar to those containing H2S, and as a result increased charging of hydrogen occurs. This mechanism can be used to partially explain the effect of several alloying elements (i.e., Mn, Ti, Cu) on hydrogen cracking and the variation of susceptibility to hydrogen with sulfide inclusion morphology. This mechanism lends itself easily to pickling and acid cleaning operations where hydrogen embrittlement of high strength steels has been a problem for years.

Influence of particle size on deformation characteristics of manganese sulphide inclusions in steel

AbstractThe influence of inclusion size on the deformation behaviour of Type III MnS inclusions in an experimental steel during hot rolling has been investigated using an image analysing computer. It has been shown that the deformation of inclusions of less than 5μm dia. is size dependent, with smaller inclusions being less deformed. Totally undeformed inclusions can be observed, but it has not been possible to determine or predict precisely the size below which inclusion deformation will not occur with normally encountered conditions of mechanical working. The relationship between the size effect and the inclusion/matrix interfacial energy is discussed. In view of the importance of the statistical method used in the analysis in relation to the results obtained, the techniques of quantitative metallography employed are outlined in an appendix.

Discussion of “sulfide inclusions in steel”

Discussion of “sulfide inclusions in steel”

Sulfide inclusions in steel

New data on the Fe−Mn−S phase diagram are presented. One conclusion drawn using these data is that the rod-like “Type II” sulfides in steel result from eutectic solidification, not monotectic solidification. Effects of oxygen, carbon, silicon, and other elements on morphology of sulfides is shown experimentally. Oxygen leads to formation of Type I inclusions. Carbon and silicon reduce the solubility of sulfur in the melt and lead to various types of faceted sulfides including a faceted homologue of the rod-like Type II eutectic, and the “divorced” eutectic, Type III.

Pitting and sulphide inclusions in steel

Pits are initiated at sulphide inclusions (usually MnS) in both carbon steels and stainless steels. In carbon steels, the attack starts in the matrix close to the sulphide inclusion which is more noble than the matrix. Some sulphides, termed “active”, initiate attack more easily than others, termed “inactive”. Active and inactive sulphides in carbon steels may be distinguished by a so-called micro-corrosion test (MCT). In stainless steels, the attack starts in the sulphide inclusion proper, which is less noble than the surrounding oxide film, and then spreads to the active metal below the sulphide inclusions. The propagation of a pit is, in principle, the same in both types of steel and depends upon the formation of a concentration cell in which the pit solution has a higher salt content, a higher acid content and a lower oxygen content than the surrounding bulk of the solution. The detrimental effect of S upon the corrosion properties of steels is counteracted by metals which form sulphides less soluble than FeS. These sparingly soluble sulphides may either be present in the steel (examples: TiS, CrS and VS) or form during the corrosion process (examples: the sulphides of W, Mo, Ni, Co, Zn, Cd, Sn, Pb, Cu, Ag, Bi and Hg). Of the latter metals, Cu is of particular importance.

Effect of the addition of rare earth elements and their oxides on the properties of some stainless steels

1. The addition of 0.1% misch metal improves the ductility of Kh18N10T steel at high temperatures. The addition of 0.15–0.25% misch metal decreases the number of nitride and carbonitride inclusions. 2. The addition of 0.05% misch metal improves the ductility of Kh17N13M2T steel somewhat at 1000°C. 3. The addition of 0.15% misch metal improves the ductility of Kh17N13M2T steel at 1000°C. The number of carbonitride inclusions decreases with increasing amounts of misch metal. 4. The addition of ferrocerium (0.05–0.30%), lanthanum (0.05–0.25%), cerium dioxide (0.05–0.4%), lanthanum oxide (0.05–8.4%), or praseodymium oxide (0.05–0.3%) does not improve the ductility of steel at high temperatures. 5. Rare earth elements do not affect the size of oxide and sulfide inclusions in steel.

鋼の熱間加工に伴う硫化物系介在相の挙動

鋼の熱間加工に伴う硫化物系介在相の挙動