Titanium Carbosulfide Research Articles

Study of craters formed on surface of AISI 321 stainless steel after high power ion-beam exposure

Surface topography and elemental composition of craters formed on the surface of AISI 321 stainless steel after processing with powerful pulsed flows of Cn+ and H+ ions (accelerating voltage: 250 keV, pulse duration: approximately 100 ns) are studied. Processing is performed using single-pulse fluences of 1 and 3 J/cm2, with the number of pulses ranging from 1 to 50. It is determined that the average size of the craters increases and the number of craters decreases with an increase in the number of impact pulses. The average size and number of craters are not dependent on the degree of preliminary deformation of the samples. Based on the applied processing parameters, it is established that titanium sulfide or titanium carbosulfide inclusions are the preferred crater sites. Furthermore, the crater structure is examined through electron backscatter diffraction analysis. The structure and phase composition of the craters formed on steel as a result of exposure to a pulsed ion beam do not differ from the structural-phase state of the crater-free regions.

Study of the Effect of Recrystallization Annealing Regimes in Continuous Operating Units on the State of If-Steel Solid Solution and Mechanical Properties

Laboratory simulation of recrystallization annealing in continuously operating units is performed for rolled IF-steels of nine different compositions of laboratory and industrial melting. It is established that by controlling parameters of low-temperature processing regimes in a CAU and CHGU, it is possible to improve ductility and formability of rolled IF-steels significantly. During annealing rolled products in a CHGU it is possible to reduce the intensity of aging processes and prevent a reduction in ductility and formability using a strip temperature at the exit of the accelerated cooling section (P6) of at least 540°C, as well as a strip temperature at the exit from the cooling section after the galvanizing bath (P10) of not more than 180°C. This is especially relevant for IF-steels with a low sulfur content, when the possibility of stabilizing carbon in the form of titanium carbosulfide is limited. During annealing in a CAU rolled products from fully stabilized IF steels are slightly sensitive to overageing temperature regime. With incomplete stabilization of carbon in IF-steels, due to a low titanium concentration, its removal from solid solution in the form of cementite precipitates and the improvement of ductility and formability of rolled products is possible when using an overageing regime of 420–330°С, and especially at 390–300°С. Removal of carbon from the solid solution may be prevented by a high phosphorus concentration (≈ 0.011 wt.%) in steel. In this case, complete stabilization of IF steel is necessary by increasing titanium and/or niobium concentration.

Investigation of the Conditions of Formation of Aluminum-Magnesium Spinel Inclusions in Low-Carbon Automotive Sheet Steels of 08Yu type and Ultralow-Carbon Automotive Sheet Steels of the if and IF-HS Types

We study the regularities of reduction of MgO from the lining and surface slag accompanied by the formation of adverse corrosion-active nonmetallic inclusions (CANI) based on aluminum-magnesium spinel in the course of treatment of the melts of 08Yu-type low-carbon steel and ultralow-carbon steels of the IF and IF-HS types with ten different compositions. It is shown that the amount of formed CANI regularly increases with the aluminum content of steel up to 0.05–0.06 wt.% and the MgO content of slag, especially over 12–14 wt.%. We proposed some efficient techniques aimed at guaranteeing the required purity of steel (from the viewpoint of these inclusions). For the first time, it is shown that the deposition of titanium sulfide and carbosulfide on the surfaces of aluminum-magnesium spinel inclusions increases their corrosive activity.

Structural Properties and Phase Stability of Primary Y Phase (Ti₂SC) in Ti-Stabilized Stainless Steel from Experiments and First Principles.

The morphology and microstructural evaluation of Y phases in AISI 321 (a Ti-stabilized stainless steel) were characterized after hot deformation. The electronic structure and phase stability of titanium carbosulfide were further discussed by first-principle calculations. It was found that Y phases, like curved strips or bones in AISI 321 stainless steel, mostly show a clustered distribution and are approximately arranged in parallel. The width of the Y phase is much less than the length, and the composition of the Y phase is close to that of Ti2SC. Y phases have exceptional thermal stability. The morphology of Y phases changed considerably after forging. During the first calculations, the Ti2SC with hexagonal structure does not spontaneously change into TiS and TiC; however Ti4S2C2 (Z = 2) can spontaneously change into the two phases. The Ti–S bonds are compressed in Ti4S2C2 cells, which leads to poor structural stability for Ti4S2C2. There is a covalent interaction between C/S and Ti, as well as an exchange of electrons between Ti and S/C atoms. Evidently, the mechanical stability of Ti4S2C2 is weak; however, Ti2SC shows high stability. Ti2SC, as a hard brittle phase, does not easily undergo plastic deformation.

Steel 08Kh18N10T-VO for Power Generation Equipment Components

For manufacturing billets for power generation equipment components with prolonged service life at elevated temperatures, especially pure steel 08Kh18N10T is required. The technology of melting steel grade 08Kh18N10T-VO with thorough vacuum decarburization makes it possible to prepare large forging ingots at 70°C above the liquidus temperature. A study of billet metal shows that titanium carbonitride and carbosulfide make up 85–100% of nonmetallic inclusions in steel grade 08Kh18N10T-VO. With sulphur content reduced from 0.006 to 0.0026%, the amount of carbosulfide decreases by a factor of seven. With a sulphur content of 0.0026% there is no extensive titanium carbosulfide (Ti4C2S2). The grain size in component workpieces corresponds to points 3–5 according to GOST 5639. Mechanical properties at 20 and 350°C are better than specified in technical documents.

Development of Al-killed/Ti stabilized steels

Several Al-killed/Ti-stabilized low carbon steels were developed in a Mexican steel industry with the aim of obtaining an interstitial free steel for automotive applications. The steelmaking route involved the use of 100% sponge iron which was feed into an electric arc furnace, vacuum degassed, ladle treated and continuously casted. The resulting slabs were then hot rolled at 1100 °C and coiled at 650 °C. Then, the steel plates were cold rolled at room temperature and sheets annealed at 700 °C. As-cast micro structure showed the presence of α-ferrite with titanium nitrides in matrix and grain boundaries while in the ashot rolled condition, elongated grains showed the presence of titanium nitrides, titanium sulfides and titanium carbosulfides. The annealed sheets showed, additionally to the other precipitates, the presence of titanium carbides. Microstructure, texture, the Lankford ratio and mechanical properties of fully recrystallized coils fulfilled the target properties established by the automobile industry.

Development of Precipitation Strengthened Steel with Adequate Stretch Flangeability

An experimental steel of the composition (in wt.%) 0.04C-0.81Mn-0.38Si-0.15Ti-0.01S-0.013P-0.043Al was hot rolled into 4 mm plates at three different temperatures of 1100, 1000, and 900 °C. The yield strengths of these plates were in the range of 434-484 MPa while the ultimate tensile strength varied from 508 to 586 MPa. Elongation values ranged from 13.0 to 17.8%. Hole expansion ratios (λ) varied from 23 to 30.7%. In particular, the plate rolled at 1000 °C showed a yield strength of 484 MPa, an ultimate tensile strength of 586 MPa, a total elongation of ~15%, and a hole expansion ratio of ~23%. Transmission electron microscopy showed the presence of fine precipitates of titanium carbosulfide (~10-50 nm). Therefore, maximum precipitation strengthening was obtained in the plate that was hot rolled into a thickness of 4 mm at 1000 °C.

The Effect of Inclusion Type on the Toughness of 4340 Steel

The fracture toughness of ultra high strength steels can be improved for a constant inclusion volume fraction by increasing the inclusion spacing or by making the inclusion particles more resistant to void nucleation. One can increase the inclusion spacing by adding rare earth elements to form large and widely spaced inclusions. One can make the sulfide particles more resistant to void nucleation by adding small amounts of titanium to form small, closely spaced particles of titanium carbosulfide (Ti2CS). The fine particles of Ti2CS particles are much more resistant to void nucleation than other sulfide types, and this increased resistance to void nucleation can result in significant improvements in toughness. In this work, we considered three heats of 4340 steel in which the sulfur has been gathered in different ways. In one heat the sulfur has been gathered as particles of MnS. In a second an addition of lanthanum has been made to getter the sulfur as particles of La2O2S. In the third heat an addition of titanium was made and the sulfur was gathered as particles of Ti2CS. All three heats had yield strengths of about 1430 MPa. The fracture toughness was 87 MPa√m, 99 MPa√m, and 108 MPa√m for the manganese modified heat, the lanthanum modified heat, and the titanium modified heat, respectively.

Effect of titanium modification on the fracture behavior of ultrahigh-strength low-alloy steel

The causes of instability of fracture toughness of ultrahigh-strength low-alloy medium-carbon steel 55KhN2MA-Sh are determined with the help of mechanical tests and scanning electron microscopy of fracture surfaces. It is shown that the fracture toughness changes due to a change in the concentration of titanium within the grade composition. When the concentration approaches the upper standardized limit, the ductility and the impact toughness of the specimens decrease due to excessive growth in the number of segregations of titanium carbosulfides.

The effects of titanium additions on AF1410 ultra-high-strength steel

The mechanical properties and microstructure of two heats of AF1410 steel were compared. The first heat, heat 811, contained a titanium addition of 0.02 wt pct, while the second heat, heat 91, contained no titanium, manganese, or other strong sulfide formers. The sulfur in heat 811 was gettered as titanium carbosulfide, while in heat 91 the sulfides were chromium sulfide. The toughness of heat 811 was found to be much enhanced compared to heat 91, with Charpy impact energies of 176 J and 79 J and KIC fracture toughness values of 235 MPa.m1/2 and 170 MPa.m1/2, respectively. This significant difference in fracture toughness is attributed to the fact that titanium carbosulfide particles are more resistant to void nucleation than the chromium sulfide particles, which appear to nucleate voids at the onset of plastic strain. In addition to altering the sulfide particle type, the titanium addition also results in the presence of undissolved MC carbides in the titanium-modified steel in addition to the M2C carbides found in heat 91. These carbides act as grain growth inhibitors, resulting in a finer prior austenite grain size and martensite packet size in heat 811.

New type of Pb-free Machinable Soft-Magnetic Stainless Steels with Dispersed Titanium Carbo-Sulfide

Although conventional free-cutting soft-magnetic stainless steel contains Pb to facilitate machining, the replacement and elimination of Pb is required from the standpoint of environmental protection. In this article, the authors report the development of new Pb-free machinable soft-magnetic stainless steels in which titanium carbo-sulfide is used as an inclusion. The microstructural evolution, magnetic properties, corrosion resistance, machinability and mechanical properties of these new free-cutting stainless steels are presented.

快削電磁ステンレス鋼の溶接性に及ぼすＴｉ炭硫化物の影響

Soft-magnetic stainless steels have been used for high precision equipment. Their good machinability is rendered by Pb and/or MnS dispersed in them. From the viewpoint of health, Pb is an undesirable element. And MnS deteriorates the corrosion resistance and cold formability. A titanium carbosulfide, Ti4C2S2, is thermodynamically more stable than MnS and it is considered to replace MnS. Effect of titanium carbosulfide on weldability of a soft-magnetic stainless steel has been investigated. Regarding a laser-welded joint of this steel plate and Type304 stainless steel plate, weld bead appearance and shape of penetration were equivalent to those of conventional stainless steel. There were no welding cracks in the weld bead, and there were few microporosities in the case of lower heat input than 0.225kJ/cm. Furthermore, welded joint was ruptured in base metal or HAZ of Type304 stainless steel plate in tensile test, so the mechanical property of welded joint was excellent.

Solubility of Titanium Carbosulfide in Austenite.

A titanium carbosulfide solubility product of log[Ti][C] 0.5 [S] 0.5 =-14 646/T+5.51 and a Gibbs free energy of formation for titanium carbosulfide of Δ°G Ti4C2S2 =-1 121.9+0.196T kJ/mol were calculated from dissolution temperature experiments using a series of titanium-modified secondary hardening ultra-high strength steels. The presence of other precipitates such as TiN, TiC and TiS could be neglected for this class of steels. The effect of the alloying additions on the activity of carbon and hence on the dissolution temperature of titanium carbosulfide was also found to not be significant for these steels. The experimentally determined solubility product and Gibbs free energy of formation are compared with previously published data for titanium carbosulfide.

チタン炭硫化物を分散させたフェライト系ステンレス鋼の被削性と耐食性

Free-cutting stainless steels have been widely used for high precision equipment. Their good machinability is rendered by Pb and/or MnS dispersed in them. From the viewpoint of health, Pb is an undesirable additive. And MnS deteriorates the corrosion resistance and some fabricabilities. A titanium carbosulfide, Ti4C2S2, is stable thermodynamically more than MnS and so it is a candidate to replace MnS.In order to disperse the sufficient carbosulfides, 0.55%Ti, 0.03%C and 0.2%S were added to a ferritic base steel, Type 430(16.5%Cr), with low O and N both less than 50ppm. The steel showed the good machinability in turning and drilling comparable to Type 430F(0.6%Mn, 0.2S) and besides the excellent corrosion resistance under salt spray superior to Type 430F. These results demonstrate that Ti4C2S2 is a promising dispersoid in free-cutting stainless steels to substitute for Pb and MnS.

The effects of thermomechanical processing on the precipitation in an industrial dual-phase steel microalloyed with titanium

Analytical transmission electron microscopy was employed to characterize the precipitation at each step of the fabrication process and thermomechanical treatment of an industrial dual-phase steel microalloyed with titanium. Theoretical thermodynamic calculations as well as experimental analysis showed that more than half of the titanium carbosulfide (Ti4C2S2) precipitates would dissolve during reheating at 1240 °C. Despite this dissolution at 1240 °C, the remaining titanium carbonitrides and carbosulfides were effective in pinning austenitic grain boundaries, keeping the austenitic grain size at around 40 µm (at 1240 °C). It is also shown that, during hot rolling, there exist three regions of titanium carbide precipitation. The first is defined by an increase of titanium carbide precipitation due to deformation. The second region is marked by the insignificant change in precipitation. The third region is indicated by another increase in precipitation due to the austenite-to-ferrite transformation. The experimental and theoretical results on the contribution of TiC precipitation to hardening of ferrite (Orowan mechanism) were in excellent agreement, showing that TiC precipitates have the most important effect on increasing the yield strength, overshadowing the austenitic grain-boundary pinning contributions by Ti(C,N) and Ti4C2S2 precipitates.

Advanced microscopy techniques resolving complex precipitates in steels

Scanning electron microscopy as well as analytical transmission electron microscopy techniques such as high resolution, electron diffraction, energy dispersive X-ray spectrometry (EDX), parallel electron energy loss spectroscopy (PEELS) and elemental mapping via a Gatan Imaging Filter (GIF) have been used to study complex precipitation in commercial dual phase steels microalloyed with titanium. Titanium nitrides, titanium carbosulfides, titanium carbonitrides and titanium carbides were characterized in this study. Both carbon extraction replicas and thin foils were used as sample preparation techniques. On both the microscopic and nanometric scales, it was found that a large amount of precipitation occurred heterogeneously on already existing inclusions/precipitates. CaS inclusions (1 to 2 μ m), already present in liquid steel, acted as nucleation sites for TiN precipitating upon the steel's solidification. In addition, TiC nucleated on existing smaller TiN (around 30 to 50 nm). Despite the complexity of such alloys, the statistical analysis conducted on the non-equilibrium samples were found to be in rather good agreement with the theoretical equilibrium calculations. Heterogeneous precipitation must have played a role in bringing these results closer together.

Thermal stability of transition metal carbosulfides prepared by combustion synthesis

Tantalum carbosulfide and its intercalated compounds are soft layered materials that can easily be prepared by combustion synthesis. Titanium carbosulfide is a hard, brittle material with exceptional chemical stability. The thermal stability of these compounds has been investigated by heat treatments in air and inert atmospheres, as well as by differential thermal analysis in atmospheric air. It was observed that the substitution of Nb for Ta in tantalum carbosulfide leads to more exothermic reactions in the combustion synthesis, and DTA measurements revealed a small improvement of the high temperature stability in oxidizing environments. Our results show that titanium carbosulfide is stable in air up to 580°C, whereas the richer in sulfur tantalum carbosulfide, stabilized by partial substitution of Nb, is stable up to 415°C and does not decompose in an inert atmosphere at temperatures as high as 1100°C.

Ti添加極低炭素鋼におけるTi系炭硫化物の析出挙動

Ti添加極低炭素鋼におけるTi系炭硫化物の析出挙動

Ab-Initio Calculations of the Electronic Structure and Properties of Titanium Carbosulfide

AbstractTitanium carbosulfide (Ti2CS) is frequently found as an inclusion phase in Ti - containing steels. It is of considerable interest because, whenever present in preference to the more common manganese sulfide (MnS), it significantly improves the toughness (a very desirable property) of the steel. Currently, to the best of our knowledge, there is no data, either computational or experimental, regarding the structural properties of Ti2CS. This data is needed to understand the influence of the Ti2CS inclusions on the toughness of the host material.In this paper, our results from the ab-initio calculations, using the LKKR-ASA (Layer Korringa Kohn Rostoker method in the Atomic Spheres Approximation) on the equilibrium ground state properties of bulk Ti2CS are presented and discussed. In particular, attention is focused upon (a) the Energy – Atomic Volume curve generated to calculate the equilibrium lattice constant and the bulk modulus, and (b) the density of states calculations. The application of these results to the subsequent study of an interface involving the carbosulfide and the host matrix is also illustrated.

Chemical twinning in the Ti4C2S2-TiS system

Titanium carbosulfide Ti4C2S2 (H phase, P63/mmc, a=0.321 nm and c= 1.120) are TiS (Rm, a=0.3417 nm and c = 2.65) are frequently found to coexist within composite particle in ultra-low carbon interstitial-free (IF) steels. This more suggest that a direct transformation from TiS to Ti4C2S2 may be a major stabilization of C at higher temperatures in these steels. The deduced orient between Ti4C2S2 and TiS is in agreement with a reported crystal structure mode transformation mechanism between these two phases appears to be strongly related structures.At the as-cast condition, most of the S- and C-rich particles in the studied IF step as pure M4C2S2 (M=Ti, Nb). After a re-heating treatment at 1300°C, M4C2S2 discharge and a new phase were observed. This new phase can be indexed as a trigonated with a=0.33 nm and c=5.3 nm (Figure 1). After a second re-heating treatment appeared at the center layer of the multi-phase particles (Figure 2). It should be noted that (i) some planar defects were observed inside the new phase and Ti4C2S2 carbon and 2a).