Modification Of Inclusions Research Articles

Development of fracture toughness of ultrahigh strength, medium carbon, low alloy steels for aerospace applications

Ultrahigh strength, low alloy, steels with a medium carbon (0·25–0·50 wt-%) content and various amounts of chromium, molybdenum, nickel, silicon, and vanadium have been needed for high performance aerospace parts. The steels can be successfully employed at yield strengths of ≥1400 MPa, but their commercial use is often limited in practice by their poor fracture toughness. The present review surveys studies carried out over about the past 10 years to improve the fracture toughness of ultrahigh strength, medium carbon, low alloy steels, and the present understanding of this property is outlined. Particular emphasis is placed on improving the fracture toughness by microstructural control via thermal and thermomechanical treatments, modification of sulphide inclusions, and new alloying design. The major metallurgical factors controlling the fracture toughness are discussed for each of these techniques.

Granite-hosted mineral deposits of the New Ross area, South Mountain Batholith, Nova Scotia, Canada: P, T and X constraints of fluids using fluid inclusion thermometry and decrepitate analysis

The 370 Ma peraluminous South Mountain Batholith (SMB) intrudes Meguma Supergroup metasedimentary rocks in Nova Scotia. The New Ross area of the SMB contains polymetallic mineralisation (Sn, W, U, Mo, Cu and Mn) in pegmatite, greisen and vein directly or indirectly associated with highly evolved fractions of the SMB. Eight mineral deposits from this area have several fluid inclusion types hosted by quartz: (1) monophase liquid (L); (2) monophase vapour (V); (3) aqueous, L-V (4) aqueous, L-rich + solids; (5) aqueous, L-rich + halite. Inclusions have irregular to equant shapes and are pseudo-secondary or secondary. The irregularity and variability of L:V ratios within fluid inclusion populations suggest post-entrapment modifications of inclusions (i.e. necking).Thermometric data indicate three distinct fluids in terms of salinity: (1) 19-25 wt. % equiv. NaCl (rarely 14-25 wt. % NaCl equiv.), (2) 29-43 wt. % equiv. NaCl, and (3) 0-9 wt. % equiv. NaCl. Temperatures of first melting and ice/hydrohalife melting indicate CaCl2 in solution. Proximity of the deposits to Meguma Supergroup metasedimentary rocks suggests that this Ca component may be externally derived. The majority of the low-salinity fluid population has the composition of meteoric water. Electron microprobe analyses of artificially decrepitated mounds identify Na, Ca and K as major solutes, with a continuum in terms of compositions. Other solute components in the mounds are Fe and Ba, and a variety of metals of unknown speciation also occur (Cu, Zn, Fe, Ni). Homogenisation temperatures (Th) range from c. 80°C to 370°C, but for inclusion assemblages the range is 10°C to 20°C. Given the 3 kbar depth of emplacement of the SMB, estimated entrapment temperatures are c. 200°C to 550°C. The fluid inclusion data appear to reflect: (1) trapping of mixed Na-K-Ca brines during isobaric cooling in pegmatite and greisen deposits as indicated by large ranges in Th; (2) formation of deposits at different ambient pressures (i.e. depth); and (3) mixing of fluids of different reservoirs (i.e. magmatic, metamorphic, meteoric).

Mobility and H 2 O loss from fluid inclusions in natural quartz crystals

Petrographic observations on quartz crystals from the Mole Granite (Australia) and other localities shed new light on the mechanisms of post-entrapment modification of fluid inclusions. These modifications include migration away from pseudosecondary trails, changes in fluid salinity and density, shape distortion and the formation of “sweat-haloes” around strongly deformed inclusions. Increases in fluid salinity, which usually are associated with inclusion migration, indicate water-losses of up to 50%. However, LA-ICP-MS-analysis of unmobilized and mobilized inclusions of the same trail reveals basically unchanged ratios of major – and trace element cations, with the exception of Li, which seems to be incorporated into the crystal lattice during migration. Despite the fact that all these modifications are closely related to deformation processes, they occur not only in mechanically deformed quartz, but also in free-standing crystals. In the latter samples, stress has been generated internally as a result of brazil-twinned growth and compositional zonation. These observations and their interpretation leads to a list of practical criteria that should help in differentiating between reliable and suspect fluid inclusions in other samples.

Dehydration melting and devolatilization during exhumation of high‐grade metapelites: the Tatra Mountains, Western Carpathians

Partial melting and retrogression related to Variscan tectonic exhumation have been recognized in the high‐grade metapelites of the Tatra Mountains, Western Carpathians. Staurolite and kyanite relics document an early stage of the prograde metamorphism at c. 600 °C and 9–10 kbar. An increase in temperature to >730 °C at 11–12 kbar resulted in partial melting and incipient migmatization in the stability field of kyanite. Further heating at decreasing pressure during the earliest stage of exhumation led to the dehydration‐melting of muscovite and biotite at >750–800 °C and 6–10 kbar, producing garnet‐bearing granite as leucosomes in migmatite. Subsequent cooling is documented by garnet resorption by biotite and sillimanite (a reversal of the prograde biotite dehydration‐melting reaction). This was followed by nearly isothermal decompression to c. 4–5 kbar producing cordierite and some melt due to biotite decomposition. Later nearly isobaric cooling led to cordierite pinitization and formation of orthoamphibole, chlorite and carbonates. Densities of primary, monophase CO2–N2 inclusions (0.69–1.06 g cm−3) from the migmatite leucosome are consistent with the near‐peak and retrograde conditions. Highly varying N2 contents (5–30 mol%) are thought to result from the nitrogen uptake in retrograde K‐bearing minerals, or dilution by CO2 liberated during interaction of melt‐derived water with metapelite graphite. The relatively high nitrogen content, not observed until now in migmatites, could have been inherited from the high‐pressure metamorphism stage. It is assumed that the water‐absent composition of fluid inclusions is not representative of the bulk water content (XH2O≤0.7), which was masked by mechanical separation of the CO2‐ and H2O‐dominated immiscible phases, and/or by post‐entrapment modifications of the fluid inclusions. Decompression and the final stage of exhumation were accomplished by top‐to‐the‐south thrusting as well as west–east (orogen‐parallel) extension. They were most probably related to regional uplift and gravitational collapse of thermally weakened Variscan crust.

Interpretation of post-entrapment fluid-inclusion re-equilibration at the Three Mile Hill, Marvel Loch and Griffins Find high-temperature lode-gold deposits, Yilgarn Craton, Western Australia

Fluid inclusions that are interpreted to be related to vein filling of quartz veins at the Three Mile Hill and Marvel Loch gold deposits in amphibolite-facies rocks, and the Griffins Find deposits in granulite-facies rocks in the Yilgarn Craton of Western Australia are dominantly low-salinity H 2O–CO 2±CH 4 mixtures or CO 2–CH 4 fluids. At each deposit, inclusions have a wide range of compositions with respect to both the aqueous:carbonic ratio and the CO 2:CH 4 ratio of the carbonic phase, and most fluids could not have been in equilibrium with the mineral assemblage in the vein and adjacent rock. Inclusion densities suggest a range of P–T conditions of entrapment, and are in general not consistent with the conditions of vein formation indicated by vein assemblages. Diffusional addition of H 2 into inclusions, diffusional loss of H 2O, and reduction of inclusion volume are possible during cooling and uplift along the inferred P–T path. The inclusion populations could have been derived from an originally uniform population of low-salinity, aqueous dominated H 2O–CO 2 inclusions by a combination of these processes. Inclusion modification as the cause of the complex inclusion populations is supported by relations of molar volume to composition, and, to an extent, by variations in fluid salinity. If inclusion re-equilibration is the cause of inclusion variability, it was of variable intensity within a single vein system, and within individual clusters of inclusions in some samples, and is suggested to have been a function of the local petrological and textural environment.

Electron spectrum of arsenic inclusions in gallium arsenide

Energy-band spectra are calculated for various modifications of coarse arsenic inclusions in gallium arsenide.

Microalloyed Forging Steels

Microalloyed forging steels have been developed to improve the competitiveness of wrought steel components, especially in the automotive sector, by achieving the desired properties in the as-forged condition, thus eliminating the need to subsequently heat treat, straighten and stress relieve the previously specified low alloy steels. Significant cost reductions are realised by adopting microalloyed steels. This paper reviews the metallurgical principles on which microalloyed forging steels are based, including the relationships between steel composition, thermomechanical processing, microstructure and the resulting properties, highlighting the various strengthening mechanisms that are invoked. The properties, characteristics and applications of the initial development grade, 49MnVS3, are described. Research and development then focussed on increasing the strength and/or the toughness of this steel to improve its appeal to the market, especially for safety critical applications. the various metallurgical options are described and discussed. Attention has also been placed on maximising the machinability of these steels by controlled additions of sulphur, the adoption of inclusion modification techniques and other free machining additives. The fatigue properties and toughness of microalloyed steel forgings have been demonstrated to be fit for purpose, but compared with heat treated low alloy steels their fracture toughness is lower, albeit still significantly superior to castings. A wide range of forged automotive applications had been successfully converted to air cooled microalloyed steels over the past 25 years, with a large proportion of crankshaft and connecting rods now being made by this route. Future challenges have been identified to further extend the attainable properties and to improve the combination of strength and toughness, to broaden the market applications and the product range to include bar and rod. The use of warm near net shape forming processes for microalloyed steel is also anticipated. Greater exploitation of computer aided modelling and design techniques is encouraged to facilitate rapid prototyping, in order to improve further the competitiveness of forged engineering steels.

Wear characteristics of TiC, Ti(C,N), TiN and Al 2O 3 coatings in the turning of conventional and Ca-treated steels

The wear characteristics of single layers of TiC, Ti(C,N), TiN and Al 2O 3 were investigated during turning of conventional and Ca-treated quenched and tempered Al-killed steels. The experimental coatings were deposited using chemical vapour deposition (CVD) or moderate temperature CVD (MTCVD) on cemented carbide substrates of a single composition and the coatings were of similar thicknesses (7 ± 1 μm). The wear mechanisms and layer formation were studied using scanning electron microscopy, optical microscopy and X-ray diffraction. Inclusion modification appeared to be an effective means of enhancing machinability and all experimental coatings exhibited about 20% better performance as a result of Ca-treatment. In particular, the crater wear of the experimental coatings — excluding Al 2O 3 — was clearly reduced. Comparative cutting tests revealed important differences between the coating materials. Wear mechanisms of the experimental coatings are discussed in detail.

Quantitative study of modification of sulphide inclusions by calcium and its effect on the impact toughness of a resulfurised alloy steel

In this paper, the mechanisms of the shape control of sulphide inclusions by calcium in a resulfurised alloy steel and the quantitative effect of the shape factor, the size and the quantity of sulphide inclusions on the transverse impact toughness are investigated. There are three different types of sulphide inclusions in the calcium‐treated resulfurised alloy steel, 58CrNiMnMoVSCa, namely elongated MnS, oval (Mn,Ca)S with and without any calcium aluminate nucleus. The proportion of the former is reduced while that of the two latter raised as the ratio of Ca/S in steel increases. The mechanisms of the shape control of sulphide inclusions by calcium are mainly due to its solid solution hardening effect. Besides, the calcium aluminate, existing as the nucleus of the oval (Mn,Ca)S, restricts the hot deformation of the sulphide inclusions and as a result, enhances further the shape control. Based on the solid solution effect of calcium on sulphide inclusions, the quantitative relationship between the shape factor Λ of sulphide inclusions and the ratio of Ca/S in steel at a hot forging reduction of 85 is developed. Finally, the quantitative relationship between the transverse impact toughness and the parameters of sulphide inclusions, namely the shape factor (Λ), the size (L) and the quantity (N) is also developed.

Ａｇ‐マトリックス複合体のち密化と微細構造変化に及ぼす第２相ＺｒＯ２の影響

Rigid inclusions retard the densification of matrices. This study deals with the effects of inclusion/matrix particle size ratio and surface modification of inclusions on the densification of Ag matrix. The surface of YSZ inclusions was modified by chemical roughening and/or electroless Ag-plating. The sintering behavior and microstructure development of Ag-matrix composites containing surface-modified YSZ with different inclusion/matrix particle size ratio were investigated. The densification of the matrix with higher inclusion content and/or smaller inclusion/matrix particle size ratio was suppressed more significantly, irrespective of the sinterability of matrix. The chemical surface roughening of inclusions resulted in an increase in the hindrance of densification of matrix. On the other hand, the electroless Ag-plating of inclusions relaxed the hindrance of the densification. The densification of matrix with high inclusion/matrix particle size ratio led to the formation of density variation in the matrix. Pores located around inclusion particles remained in the matrix with low inclusion/matrix particle size ratio. Channel structure of pores formed in the matrix, particularly when the particle sizes of matrix powder and inclusion powder were almost the same.

Thermodynamics and Kinetics of the Modification of Al2O3 Inclusions.

The use of thermodynamic data in describing calcium modification of aluminium oxide inclusions has been summarised and reviewed. The majority of the published Al-S equilibrium diagrams, based on the following reaction:3CaO+3S+2Al=3CaS+Al2O3, vary significantly due to different sources for thermodynamic data, especially for the activity of CaO and Al2O3. Using ThermoCalc, the activities of CaO and Al2O3 have been calculated and compared to the published data. Calculations in the present work pertaining to the molten range of the system are in good agreement with the most recently published experimental data of Fujisawa et al.Based on the assessed thermodynamic data and observed phenomena during calcium modification of inclusions in steel melts of moderate sulphur content, a model for alumina modification by calcium treatment has been developed. According to the model, the reactions progress by the following sequence until the activity of Al2O3 becomes so low that precipitation of CaS occurs:Al2O3⇒CA6⇒CA2⇒CA⇒CAx(liquid)

Inclusion Modification by Calcium Treatment.

A major objective of calcium treatment in steelmaking is to improve product performance through inclusion modification. To establish inclusion modification, shape and composition of inclusions were monitored using SEM during and after addition of calcium wire into 2 kg heats of steel under various conditions of Ca consumption and Ca addition pattern. A mathematical model of the kinetics considering the evaporation of calcium and the reaction between inclusions and melt was developed to thoroughly examine these phenomena in calcium treatment. The calculated results were compared with the observed ones which were obtained in experiments.(1) Shape and composition of inclusions changed from a spherical SiO2-MnO system to almost lumpy Al2O3 with the addition of aluminum, and to spherical CaO-Al2O3 including CaS after addition of CaSi.(2) The process and consumption of calcium were found to affect the change of CaO and CaS contents of inclusions.(3) A mathematical model was developed assuming that vaporization rate of calcium from the melt and rate of reaction between melt and inclusions can be described by equations of the first order reaction, and that the size and number of inclusions remain constant during treatment.(4) The calculated [Ca] and CaO, CaS contents of inclusions showed good agreement with observed ones regardless of the conditions of CaSi addition.

鋼中介在物の組成・形態変化に及ぼすCa処理条件の影響

A major objective of calcium treatment in steelmaking is to improve product performance through inclusion modification. In order to establish inclusion modification, shape and composition of inclusions were monitored using SEM during and after addition of calcium wire into 2kg heats of steel under the various conditions of Ca consumption, Ca addition pattern and flux composition. From experimental studies of calcium treatment, the mechanism of modification of calcium aluminate and formation of CaS and MgO in inclusions was discussed from the thermodynamic point of view. The results obtained are summarized as follows.(1) Calcium addition pattern affected composition variation of inclusions, although it had no effects on relation between [Ca] and (%CaO) in inclusions. Apparent equilibrium constant log (Kcao) was approximated to be -6.4 by thermodynamic calculation.(2) CaS in inclusions were observed under the conditions of high Ca consumption, high [S] and low (SiO2) in flux.(3) [Mg], increased by reduction of MgO in flux or crucible after Ca addition, reacted with calcium aluminate and formed MgO in inclusions. Critical condition for formation of MgO was represented with relation between [Ca] and [Mg].

Post‐entrapment modification of fluid inclusions due to overpressure: evidence from natural samples

Abstract Effects of post‐entrapment fluid‐inclusion modification are examined with reference to retrogression‐related quartz veins from the Caledonian, Øse Thrust, northern Norway. The inclusions occur in secondary trails, and contain high‐density hypersaline aqueous fluids. On morphological characteristics, they are subdivided into, Type A: elongate, ellipsoidal and/or irregular inclusions, and Type B: more equant, regular, and/or negative crystal form. With reference to previous research on post‐entrapment modification of inclusions in quartz it is proposed that Type A inclusions experienced little or no post‐entrapment modification, whereas Type B inclusions show features characteristic of post‐entrapment permanent inelastic stretching and/or leakage. This produces increased homogenization temperatures (Th), associated with increased inclusion volume and lowering of density, whilst maintaining constant salinity. The similarity of data for degree of fill and salinity between Type A and Type B inclusions indicates that Type B inclusions have primarily modified by stretch rather than leakage. However, the spread towards slightly larger volume of vapour in Type B inclusions suggests that some leakage has also occurred. Because stretched and/or partially leaked inclusions have increased Th, isochore projections significantly underestimate trapping pressure (Pt) relative to unmodified inclusions. Therefore, recognition of post‐entrapment inclusion modification due to overpressure is crucial to avoid misinterpretation of data, but has considerable potential for constraining the detail of P‐T trajectories of individual rocks. On this basis, rocks from the Øse Thrust zone, north Norway, are shown to have experienced rapid uplift on a ‘clockwise’P‐T‐t path during the final stages of Caledonian (Scandian) orogenesis.

Improvement of Low Temperature Mechanical Properties of Ultrahish-strength Low-alloy Steels

Ultrahigh-strength low-alloy steels with a medium carbon (0.25 to 0.50 mass%) content and various amounts of chromium, molybdenum, nickel, silicon, and vanadium have been needed for high-performance aerospace parts. The steels can be employed successfully at yield strengths of 1400 MPa or higher, but their commercial use is limited by their poor ductility and toughness at low ambient temperatures. Brittle fracture has to be given serious consideration at these levels. This review surveys improvement of the low temperature mechanical properties of ultrahigh-strength low-alloy steels. Particular emphasis is placed on improving the mechanical properties through mixed-structure control, thermomechanical treatments, and modification of non-metallic inclusions. The major microstructures controlling the mechanical properties are discussed for each of these techniques.

The influence of aluminium deoxidation and sulphur content on oxide modification and machinability of steel

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低合金超強力鋼の低温機械的性質の改善

Ultrahigh-strength low-alloy steels with a medium carbon (0.25 to 0.50 mass%) content and various amounts of chromium, molybdenum, nickel, silicon, and vanadium have been needed for high-performance aerospace parts. The steels can be employed successfully at yield strengths of 1400 MPa or higher, but their commercial use is limited by their poor ductility and toughness at low ambient temperatures. Brittle fracture has to be given serious consideration at these levels. This review surveys improvement of the low temperature mechanical properties of ultrahigh-strength low-alloy steels. Particular emphasis is placed on improving the mechanical properties through mixed-structure control, thermomechanical treatments, and modification of non-metallic inclusions. The major microstructures controlling the mechanical properties are discussed for each of these techniques.

Treatment of Steel with Alkaline-earth Elements.

To evaluate the potential benefits of strontium treatment of steel compared to calcium, steel-clad wires of calcium-silicon, calcium and strontium were fabricated. Lengths of these wires were injected to 35 kg heats of AISI 1045 steel. Samples for total calcium or strontium, oxygen, sulphur, and aluminum were taken as frequently as possible during and after the injection. The recoveries of the alkaline-earth elements in steel for the three wires were 8.3, 4.6 and 0.41%, respectively. There was virtually no inclusion modification with the strontium wire compared to the calcium-containing wires. It was found that the absorption rate of the alkaline-earth elements increased with the sulphur and oxygen contents of the steel. A mathematical model for this enhanced dissolution rate was developed which identifies the fundamental limitations of the alkaline-earth elements for steel treatment.

Fluid inclusions in granulite-facies metapelites of the Hercynian ancient lower crust of the Serre, Calabria, Southern Italy

Investigations of fluid inclusions in granulitefacies metapelites of southern Calabria enable characterization of the fluid composition of these lower crustal rocks, and constrain the petrologically deduced retrograde P-T path characterized by isothermal uplift prior to isobaric cooling in middle crustal levels. Fluid inclusions in cordierite, garnet and sillimanite have a CO2-rich composition. Inclusions in cordierite rarely contain minor amounts of N2 and H2O, and in garnets some CO2−CH4−N2 inclusions have been analyzed by Raman microprobe. Quartz reveals the most complex fluid melusion compositions (1) CO2-rich, (2) CO2−CH4−N2, (3) CH4−N2, (4) H2O−MgCl2−CaCl2−NaCl, (5) H2O−NaCl and (6) H2O−CO2. The earliest fluid inclusions after peak metamorphism are rich in CO2 with minor amounts of N2 and H2O. An early CO2−(H2O−N2) fluid composition has been confirmed by detection of CO2, H2O and N2 in the channels of the cordierite structure. Most of the early CO2-rich fluid inclusions were modified during the uplift from the lower to the middle crustal level, resulting in a density decrease with CO2 still dominant. The subsequent isobaric cooling led to further modifications of the fluid inclusions. High-density inclusions around implosion textures or scattered amongst lower-density ones must have formed during this cooling episode. Aqueous inclusions in quartz are mostly formed late and are consistent with trapping during retrograde rehydration.

Thermodynamic conditions for inclusions modification in calcium treated steel

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