Influence of temperature history on strain-induced austenite transformation in 304 stainless steel

Experimental investigations were undertaken to find temperature history effects on strain-induced austenite transformation in metastable 304 stainless steel. Interrupted static tension tests were performed at temperatures 0 and — 15°C. During the first stage of deformation specimens were deformed at temperature T₁. During the second stage temperature T₂ was applied. Cases T₁ > T₂ and T₁ < T₂ were examined. Final amounts of α’ martensite X_M were measured magnetically. A method for their summation of martensite amounts was sought for and a conclusion was obtained showing that the final amount of martensite can be calculated by the relationship X_M= f(ε)|T₂ where ε = ε_T1, + ε_T2 ±Δε. The corrective strain Δε depends on ε_T1. Its connection with true stress – true plastic strain curve at temperature T₁ is discussed in this investigation.     

Microstructure and properties of a C–Mn–Si–dual-phase steel

A study has been carried out on an Fe–0.11% C–1.58% Si–0.4% Mn-dual phase steel. The dual-phase microstructures and properties are significantly affected by both the intercritical temperature and cooling rate from (α + γ) field. Upon rapid cooling (water or oil quench) from the temperature range 735–820°C, the structure comprises ferrite + martensite. On the other hand, slow cooling (air cooling) from the temperature range 735–820°C produces microstructures containing ferrite + martensite + pearlite/bainite and more favourable mechanical properties as: σ_0,2 = 281–296 MPa, σ_UTS = 632–690 MPa, TE = 26–30% and continuous yielding behaviour.     

Direct charging of thin slabs of a Ti-microalloyed low carbon steel for cold forming

With a near-net-shape continuous-casting simulator and the hot deformation simulator Wumsi, laboratory simulation tests have been performed to determine the final microstructure and the mechanical properties of a Ti-microalloyed low carbon steel for cold forming, produced in the process of direct charging of thin slabs. For two initial specimen thicknesses (45 and 25mm) restricted values of total strain ?_∑ were available to improve the coarse as-cast microstructure. In a series of deformation schedules ?_∑ was divided systematically into two components: an austenite grain-refining strain ?_γ–GF (above the recrystallization-stop-temperature T_RS) and an austenite strengthening strain ?_γ–s (below T_RS). After hot deformation accelerated cooling with simulated coiling was employed. It was found that the direct charging process guarantees a more complete dissolution of Ti(C,N) and so an intensifying effect of Ti-microalloying in comparison to a conventional cold charging. Structure refinement by rolling performed predominantly in the temperature region of non-recrystallized austenite (increasing ?_γ–s) leads to better hot strip strength and improved low temperature toughness properties accompanied with a slight deterioration of uniform elongation.     

Phosphate and Sulphide Capacities of CaO–CaCl2–CaF2 Slags

Abstract

The phosphate capacity of CaO–CaCl₂–CaF₂ slags with X _CaO = 0.2 and X _CaCl2 + X _CaF2 = 0.8 was measured in the temperature range of 1175°C to 1350°C. The activity coefficient of PO_2.5 was calculated using phosphorus distribution data. The sulphide capacity was calculated from a correlation between phosphate and sulphide capacities.

It was observed that the phosphate capacity increased with increasing CaF₂ mole fraction and decreasing temperature. At 1200°C the log γ_PO2.5 decreased from ?9.7 in a CaO–CaCl₂ binary slag to about ?10.4 in a CaO–CaCl₂–CaF₂ ternary slag. The effect of temperature on log ?_PO2.5 was observed to be smaller than the experimental error. A linear relationship between phosphate and sulphide capacities and optical basicity was observed at different temperatures. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.

Résumé

La capacité an phosphate des scories du système CaO–CaCl₂–CaF₂, avec X _CaO = 0.2 et X _CaCl2 + X _CaF2 = 0.8, était mesurée a temperature de 1175°C à 1350°C. Le coefficient d'àctivité du PO_2.5 était calculée en utilisant des données de distribution du phosphore. La capacite au sulfate était obtenue par correlation entre la capacite an phosphore et celle an sulfate.

Il était observe gue la capacité au phosphore s'accraissait avec augmentation de la fraction moleculaire du CaF₂, ou avec diminution de temperature. La valeur du log γ_PO2.5 a 1200°C décraissait de 9,7, d'une scorie binaire CaO–CaCl₂, à ?10,4 environ, d'une scorie ternaire CaO–CaCl₂–CaF₂. L'influence de temperature sur log γ_PO2.5 était observee plus petite que L'erreur experimental. Une relation lin é aire entre les capacites aux phosphate et sulfate et ea basicite opticale était observee aux differentes temperatures. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.     

Elevated temperature fracture of RS/PM alloy 8009: part i. fracture mechanics behavior

Increasing temperature and decreasing loading rate degrade the plane strain initiation (K _ICifrom theJ integral) and growth (tearing modulus,T _R) fracture toughnesses of RS/PM 8009 (Al-8.5Fe-1.3V-1.7Si, wt pct).K _ICidecreases with increasing temperature from 25 ‡C to 175 ‡C (33 to 15 MPa√m for an extrusion and 28 to 11 MPa√m for hot cross-rolled plate) and further declines to 10 MPaVm at 316 ‡C without a minimum.T _Ris greater than zero at all temperatures and is minimized at 200 ‡C. A four order-of-magnitude decrease in loading rate, at 175 ‡C, results in a 2.5-fold decrease inK _ICiand a 5-fold reduction inT _R.K _ICiandT _Rare anisotropic for extruded 8009 but are isotropic for cross-rolled plate. Cross rolling does not improve the magnitude or adverse temperature dependence of toughness. Delamination occurs along oxide-decorated particle boundaries for extruded but not cross-rolled 8009. Delamination toughening plays no role in the temperature dependence ofK _ICi, however,T _Ris increased by this mechanism. Macroscopic work softening and flow localization do not occur for notch-root deformation; such uniaxial tensile phenomena may not be directly relevant to crack-tip fracture. Micromechanical modeling, employing temperature-dependent flow strength, modulus, and constrained fracture strain, reasonably predicts the temperature dependencies ofK _ICiandT _Rfor 8009. While E and σ_ys decrease with increasing temperature for all aluminum alloys, the strain to nucleate crack-tip damage dominates the fracture toughness of 8009 and decreases with increasing temperature for a range of constraint. Damage mechanisms for this novel behavior are evaluated in Part II. Formerly Graduate Student Department of Materials Science and Engineering, University of Virginia     

High temperature work softening yield point phenomena in polycrystalline aluminum

Work softening yield points have been studied in high purity polycrystalline aluminum tested in the temperature rangeT ₂ = 100°to 450°C at constant strain rate subsequent to prestraining in tension at a lower temperature (T1) = room temperature or 350° C) or higher strain rate. The yield drops increase with prestrain as well as with the difference between the flow stresses at the test and prestrain temperature. Reductions in the yield drop caused by annealing atT ₂ prior to testing indicate that the yield drops are the result of dynamic recovery. It is shown that dynamic recovery is accelerated by concurrent straining.     

Characteristic properties of combustion and structure formation in the Ti-Ta-C system

Macrokinetic characteristics of the combustion of mixtures in the (100% ? X)(Ti + 0.5C) + X(Ta + C) system with a variable mixing parameter X and initial temperature T ₀ of charge heating are considered. For compositions with X = 10 and 30%, an abrupt increase in the velocity U _c and temperature T _c of combustion as a result of passing two parallel chemical reactions of titanium and tantalum carbide formation is established. The U _c (T ₀) and T _c (T ₀) dependencies are linear for the mixture with X = 50%. By hardening the combustion wave, it is revealed that the primary structure formation in the combustion region starts from the selection of submicron grains of nonstoichiometric titanium carbide from the supersaturated titanium melt. In the investigated range of parameter X, synthetic products are single-phase and represent titanium-tantalum carbide. An increase in X results in a decrease in the size and microhardness of (Ti, Ta) C grains and a reduction of the relative density of compact synthetic products. The kinetics of high-temperature oxidation of alloys on the basis of carbide (Ti, Ta) C is studied. Ceramics produced at X = 10% are most heat-resistant.     

Thermodynamics of manganese distribution between liquid iron and the CaO–Al2O3–SiO2–FeO–MnO system

The thermodynamics of distribution of constituents between liquid iron and the CaO–Al₂O₃–SiO₂–FeO–MnO system at 1600°C was studied using electrochemical indication of the equilibrium partial pressure of oxygen in both phases. The results show that oxidation potential of the Fe(l)–CaO–Al₂O₃–SiO₂–FeO–MnO system, expressed in terms of log p(O₂), is directly proportional to log (x(MnO) · x(FeO)/w| Mn |). Manganese distribution coefficient, L'_mn, in intersection CaO/Al₂O₃ = 1 decreases with increasing slag basicity expressed in terms of activity a(CaO) or 1/γ(MnO). Experimentally determined equilibrium constant K_Mn/Fe is equal to 2.7 for 1600°C. The number of exchanged electrons between Fe-O-Mn-Si electrode and the slag approaches the theoretical value.     

Reduktionsgleichgewichte im System Fe–F2O3–CaO oberhalb 1050 °C

Umfangreiche Schrifttumsauswertung der Reduktionsgleichgewichte von Kalkferriten im System Eisen-Hämatit-Calciumoxid und Darstellung der Ergebnisse in Ig (pCO₂/PCO)-1/T-Diagrammen. Unter Verwendung neuester Daten über die Schmelzgleichgewichte des Systems Fe–Fe₂O₃–CaO Extrapolation auf die Reduktionsgleichgewichte des flüssigen Zustandes.     

Thermodynamics of Mn–Fe–C and Mn–Si–C system

The solubility of C in Mn melts with different contents of Si and Fe at 1400 and 1500°C was determined. With these data the interaction coefficients e^Si_C, e^Fe_C, e^C_C as well as γ^o_C were evaluated. The standard free energy of solution of C in liquid Mn based on 1 wt.% solution standard at 1400 and 1500°C were calculated, respectively. The solubility of C in liquid Mn formulated in relation to temperature was made as to the conformability of the present results with those given in the literature.     

Thermodynamics of molten Li-Sn alloys

The activity of Li in molten Li-Sn alloys was continuously varied and monitored electrochemically in cells of the type Al-LiAl/glass electrolyte/Sn/glass electrolyte/Al-LiAl. The temperature (320 to 380 °C) and compositional dependence of the Li activity coefficient, γ_Li, was found to follow a quadratic expression of the form In γ_Li = A + B(1 − X_Li)² up to 30 mole pct lithium. Further, the liquidus temperature, T_L, was found to follow TL(°C) = 642 X_Li + 188 for 0.20 X_Li 0.44 over the temperature range 320 to 470 °C. The partial and integral molar heats of solution were calculated and the results indicate that strong attractive forces exist between Sn and Li. These forces are strong enough to induce substantial ordering in the melt to an extent that the integral molar entropy of mixing at high Li contents (36 mole pct) is negative.     

Oxidation Behavior of a Pd<Subscript>43</Subscript>Cu<Subscript>27</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> Bulk Metallic Glass and Foam in Dry Air

The oxidation behavior of both Pd₄₃Cu₂₇Ni₁₀P₂₀ bulk metallic glass (Pd4-BMG) and its amorphous foam containing 45 pct porosity (Pd4-AF) was investigated over the temperature range of 343 K (70 °C) to 623 K (350 °C) in dry air. The results showed that virtually no oxidation occurred in the Pd4-BMG at T < 523 K (250 °C), revealing the alloy’s favorable oxidation resistance in this temperature range. In addition, the oxidation kinetics at T ≥ 523 K (250 °C) followed a parabolic-rate law, and the parabolic-rate constants (k _p values) generally increased with temperature. It was found that the oxidation k _p values of the Pd4-AF are slightly lower than those of the Pd4-BMG, indicating that the porous structure contributes to improving the overall oxidation resistance. The scale formed on the alloys was composed exclusively of CuO at T ≥ 548 K (275 °C), whose thickness gradually increased with increasing temperature. In addition, the amorphous structure remained unchanged at T ≤ 548 K (275 °C), while a triplex-phase structure developed after the oxidation at higher temperatures, consisting of Pd₂Ni₂P, Cu₃P, and Pd₃P.     

Thermodynamics of Mn–Ca–j and Mn–C–j system

Solubility experiments of Ca and C in Mn melts with different contents of third elements j at different temperatures were carried out in Mo-wire-heated furnace. With these data the first and second order activity interaction coefficients of j upon Ca and C, based on the same activity and the same concentration method and also In γ_Ca⁰ and In γ_C⁰, were evaluated. The solubility of Ca and C in liquid Mn formulated in relation to temperature was determined and the standard free energy of solution of Ca and C in liquid Mn based on 1 wt.% solution standard was evaluated, respectively.     

Influence of hot isostatic pressing on microstructure and mechanical behaviour of nanostructured Al alloy

Abstract

Aluminium alloy AA 5083 [Al–4·4Mg–0·7Mn–0·15Cr (wt-%)], powder was ball milled in liquid nitrogen via the cryomilling method to obtain a nanocrystalline (NC) structure. Samples of the powder were hot vacuum degassed to remove interstitial contaminants, then consolidated by hot isostatic pressing (HIPing) at six temperatures (from 0·46T_m to 0·89T_m), before being high strain rate forged (HSRF) to produce plate material. The microstructure was analysed at the different processing stages. The compressive properties of the as HIPed material, plus tensile properties of the final product were studied. Despite grain growth during HIPing, an ultrafine grain (UFG) structure was retained in the consolidated material, which consequently had increased strength over conventionally processed AA 5083. As the HIP temperature was increased, the density increased. Strength changes were minimal in compression and tension with varying HIP temperature, once near full density was attained at 275°C (～0·64T_M). Yield strength data indicate negligible variation in the grain size of the materials.     

Plastic deformation of quenched and tempered 52100 bearing steel in compression

The compressive flow stress and rate of work hardening of quenched and tempered AISI 52100 steel were measured for a variety of heat treatments. Both the flow stress and the work hardening index,n, increase with decreasing tempering temperature. Flow stresses increase initially with increasing austenitizing temperature,T _a, then decrease with a further increase inT _a as the amount of retained austenite increases.n tends to increase asT _a increases. In specimens temperared to eliminate retained austenite,n decreases to near zero as the strain increases. This behavior appears to be characteristic of tempered martensite. When less than 10 pct retained austenite is present,n still decreases with increasing strain, but witn n ore than about 15 pct retained austenite,n increases with strain. Heat treatments which refine the primary carbides increase the flow stress forT _a≤840°C. Since fine primary carbides lead to more retained austenite at a givenT _a, n tends to be greater when primary carbides are refined. For one heat treatment, the retained austenite content was measured by an X-ray method as a function of plastic strain. From changes in the relative intensities of austenite reflections, it was found that austenite crystals most favorably oriented for deformation in compression transform most readily to martensite on straining.     

Äquivalente Wirkung der Legierungselemente auf die konzentrations- und temperaturabhängige Wasserstofflöslichkeit in eisenreichen Drei- und Mehrstoffschmelzen

Darstellung der Schrifttumsergebnisse zur Konzentrations- und Temperaturabhängigkeit der Wasserstofflöslichkeit in eisenreichen Dreistoffschmelzen. Mathematische Beschreibung der konzentrations- und temperaturabhängigen spezifischen Aktivitätskoeffizienten . Äquivalente Wirkung der Legierungselemente X_i auf den log – Verlauf und auf die partiellen energetischen Größen. Auswertung von Mehrstoffschmelzen Fe–H–X₁–X₂–X_n nach dem Äquivalenzverfahren.     

Precipitation in Nb-Stabilized Ferritic Stainless Steel Investigated with <Emphasis Type="Italic">in-situ</Emphasis> and <Emphasis Type="Italic">ex-situ</Emphasis> Transmission Electron Microscopy

A Nb-stabilized Fe-15Cr-0.45Nb-0.010C-0.015N ferritic stainless steel is studied with transmission electron microscopy (TEM) to investigate the morphology and kinetics of precipitation. Nb_x(C,N)_y\hbox{Nb}_{x}\hbox{(C,N)}_y and MnS precipitates are present in the steel in the initial condition. Ex-situ TEM analysis is performed on samples heat treated at 973 K, 1073 K, 1173 K, and 1273 K (700 °C, 800 °C, 900 °C, and 1000 °C). Within this temperature range, both Fe₂Nb\hbox{Fe}_2\hbox{Nb} and Fe₃Nb₃X_x\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_{x} (with X = C or N) precipitates form. Fe₂\hbox{Fe}_2Nb is observed at 1073 K (800 °C).   Fe₃Nb₃X_x\;\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_{x} precipitates form at the grain boundaries between 973 K and 1273 K (700 °C and 1000 °C). Up to at least 1173 K (900 °C) their fraction increases with time and temperature, but at 1273 K (1000 °C) they lose stability with respect to Nb_x(C,N)_y.\hbox{Nb}_{x}\hbox{(C,N)}_{y}. With in-situ TEM, no phase transition is observed between room temperature and 1243 K (970 °C). At 1243 K (970 °C) the precipitation of Fe₃Nb₃X_x\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_{x} is observed in the neighborhood of a dissolving Nb₂\hbox{Nb}_2(C,N) precipitate. For sections of grain boundaries where no Nb_x(C,N)_y\hbox{Nb}_x\hbox{(C,N)}_y precipitates are present, Fe₃Nb₃X_x\hbox{Fe}_3\hbox{Nb}_3\hbox{X}_{x} does not form. It is concluded that the precipitation of Fe₃Nb₃X_x\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_x is directly related to the dissolution of Nb₂\hbox{Nb}_2(C,N) through the redistribution of C or N.     

Influence of strain-history on deformation-induced austenite transformation in 304 stainless steel sheet

In the present investigation experiments were carried out to find strain history effects on deformation-induced austenite transformation in a metastable stainless steel sheet. The aim of this work was to obtain information on a final amount of martensite formed during γ → α’ transformation under various strain paths. All tests were performed at room temperature and at 0°C. Relationships of volume fraction α’ martensite vs true plastic strain X_M = f(ε) are presented and analysed.     

Dephosphorization equilibria between pure molten iron and CaO-saturated FeOn–CaO–SiO2 and FeOn–CaO–Al2O3 slags

Metal-slag refining reactions have been investigated to determine dephosphorization equilibria in steelmaking using CaO-saturated slags, low in P₂O₅–content, based on the systems FeO_n–CaO–SiO₂ and FeO_n–CaO–Al₂O₃. Slag compositions have been optimized with respect to basicity and oxygen potential to achieve maximum partition ratios wt.%(P₂O₅)/wt.%[P] and minimum phosphorus contents in pure molten iron at 1550, 1600 and 1700°C. Both slag systems prove to be effective dephosphorizers. Optimal slag compositions are around 10 wt.% SiO₂ near the CaO–3CaO · SiO₂ double saturation in the case of FeO_n–CaO–SiO₂ slags and at Al₂O₃ contents tending to zero in the case of FeO_n–CaO–Al₂O₃ slags. Attempts were also made to present phosphate capacities C_PO4^3?, fractions of free oxygen ions x_O^2? and theoretical optical basicities Λ as a function of the FeO_n content of slags.     

Strain aging kinetics of vanadium or titanium strengthened high-strength low-alloy steels

The strain aging kinetics of two commercially available high-strength low-alloy (HSLA) steels were investigated. Strain aging was found to be caused by interstitial solutes and is thought to occur in two stages: Snoek rearrangement and “Cottrell atmosphere” formation. The latter phenomenon can be satisfactorily described by an Arrhenius relationship with an average activation energy of 34.5 kcal/mole. This high activation energy is believed to be the result of interactions between interstitial solutes and strain fields of the coherent precipitates which strengthen HSLA steels. Consequently, strain aging in HSLA steels is considerably slower than in plain carbon steel. A simple relationship was developed for predicting equivalent strain aging times in these steels. It was shown that the relationship: logt ₁/t ₂= 7500[1/T ₁ - 1/T ₂], whereT ₁ <T ₂ < 478 K can be used to predict the timet ₁ necessary at temperatureT ₁ for producing strain aging identical to that observed in a shorter time at a higher temperature.