Coercive force and strength of carbon steel

By statistical analysis, a formula describing the tabular relationship between the Brinell (HB) and Rockwell hardness (HRC) of carbon steel is derived. Likewise, a formula relating HRC to the alloy strength σ _u is found. The dependence of the coercive force H _c of carbon steel on σ _u is established on the basis of measurements of HRC and H _c and σ _u values calculated from the proposed formula. Results of assessing σ _u on the basis of H _c are presented for 30, 35, 45, U8, U10, and U12 steel.     

Monitoring the Physicomechanical Properties of 40X Steel on the Basis of the Limiting Magnetic Hysteresis Loop

The mechanical properties (strength σ_u, yield point σ_0.2, relative elongation ψ; and hardness HB and HRC) of 40X steel depend monotonically on the tempering temperature T_te after quenching and are closely correlated. Their relationships are described by linear regression equations. The corresponding correlation coefficients and computational errors are determined. The coercive force H_c of 40X steel is not clearly related to its physicomechanical properties over the whole range of T_te. However, magnetic analysis of the structure of 40X steel may be based on an algorithm that employs Hc and the ratio of the residual magnetization to the saturation magnetization. The results given by this algorithm depend uniquely on T_te over its practical range and are highly sensitive to change in the physicomechanical properties of 40X steel.     

Electron-microscopic study of the slip systems in an Mg-4.5% Al-1% Zn alloy

Samples of a hot-rolled Mg-4.5% Al-1% Zn alloy plate cut normal to the rolling direction are studied to determine the density of dislocations with different Burgers vectors after warm rolling at low total strains. In the experiment, 22 different grains and their orientations are studied in a JEM-1000 high-voltage transmission electron microscope at an accelerated voltage of 750 kV using the WB DF technique (g, ng, where n = 2, 3, …) for the observation of dislocations. The main method used for the analysis of the Burgers vector of the dislocations is the invisibility criterion gb = 0. In the samples, dislocations with Burgers vectors 〈a〉, [c], and 〈a + c〉 are found. The dislocation dissociation reaction of the 〈a + c〉 dislocation into the 〈a〉 and [c] dislocations has been found for the first time, and an assumption is made that all of the found [c] dislocations result from this reaction. The density of the basal and nonbasal 〈a〉 dislocations does not depend on the orientation of the grains. Rarely found [c] and 〈a + c〉 dislocations are in grains whose orientations are near the texture maximum in the {0002} pole figure.     

Microstructure and High Temperature Impression Creep Properties of Mg–3Ca–xZr (x = 0.3, 0.6, 0.9 wt%) Alloys

The current study has investigated the influence of zirconium (Zr) addition to Mg–3Ca–xZr (x = 0.3, 0.6, 0.9 wt%) alloys prepared using argon arc melting on the microstructure and impression properties at 448–498 K under constant stress of 380 MPa. Microstructural analysis of as-cast Mg–3Ca–xZr alloys showed grain refinement with Zr addition. The observed grain refinement was attributed to the growth restriction effect of Zr in hypoperitectic Mg–3Ca–0.3 wt% Zr alloys. Heterogeneous nucleation of α-Mg in properitectic Zr during solidification resulted in grain refinement of hyperperitectic Mg–3Ca–0.6 wt% Zr and Mg–3Ca–0.9 wt% Zr alloys. The hardness of Mg–3Ca–xZr alloys increased as the amount of Zr increased due to grain refinement and solid solution strengthening of α-Mg by Zr. Creep resistance of Mg–3Ca–xZr alloys increased with the addition of Zr due to solid solution strengthening of α-Mg by Zr. The calculated activation energy (Q_a) for Mg–3Ca samples (131.49 kJ/mol) was the highest among all alloy compositions. The Q_a values for 0.3, 0.6 and 0.9 wt% Zr containing Mg–3Ca alloys were 107.22, 118.18 and 115.24 kJ/mol, respectively.     

Theoretical Conversions of Different Hardness and Tensile Strength for Ductile Materials Based on Stress–Strain Curves

Based on the power-law stress–strain relation and equivalent energy principle, theoretical equations for converting between Brinell hardness (HB), Rockwell hardness (HR), and Vickers hardness (HV) were established. Combining the pre-existing relation between the tensile strength (σ _b ) and Hollomon parameters (K, N), theoretical conversions between hardness (HB/HR/HV) and tensile strength (σ _b ) were obtained as well. In addition, to confirm the pre-existing σ _b -(K, N) relation, a large number of uniaxial tensile tests were conducted in various ductile materials. Finally, to verify the theoretical conversions, plenty of statistical data listed in ASTM and ISO standards were adopted to test the robustness of the converting equations with various hardness and tensile strength. The results show that both hardness conversions and hardness-strength conversions calculated from the theoretical equations accord well with the standard data.     

Rare-earth metals (REMs) in nickel aluminide-based alloys: I. Physicochemical laws of interaction in the Ni-Al-REM and Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>-REM-AE (alloying element) systems

The data on the Ni-Al-R (R = REM Sc, Y, La, lanthanides) binary and ternary systems and the interactions of three rare-earth metals (yttrium, lanthanum, cerium) with the main alloying elements (Ti (Zr, Hf), Cr (Mo, W) that are introduced into Ni₃Al-based VKNA alloys are analyzed. The binary aluminides of REMs in the Ni-Al-R ternary systems are shown to be in equilibrium with neither NiAl nor Ni₃Al. The solid solution of aluminum in RNi₅, which penetrates deep into these ternary systems, is the most stable phase in equilibrium with Ni₃Al. In the NiAl (Ni₃Al)-AE-R systems, REM precipitation (segregation) on various defects and interfaces in nickel aluminides is likely to be the most probable, and REMs are thought to interact with the most active impurities in real alloys (C, O, N), since REMs have a large atomic radius and, thus, are virtually undissolved in nickel, aluminum, and nickel aluminides.     

Enthalpy of mixing of liquid Cu-Ti-Zr alloys

The enthalpy of mixing of liquid Cu-Ti-Zr ternary alloys is studied by high-temperature isoperibolic calorimetry at 1873 K along three ray sections characterized by the ratios x _Zr: x _Cu = 3: 7, x _Ti: x _Cu = 3: 7, and x _Zr: x _Ti = 1 at x _Cu = 1?0.4. The isotherm of the integral enthalpy of mixing of these melts is described in terms of the Redlich-Kister-Muggianu model. Along with the substantial contributions of binary copper-titanium and copper-zirconium interactions, the contribution of a ternary interaction to the enthalpy of mixing of liquid Cu-Ti-Zr alloys also exists. The first partial enthalpies of mixing of Ni, Al, Si, Sn, and Y with the melts are studied to determine the character of the interaction between the ternary Cu-Ti-Zr melts and metal additions that facilitate amorphization upon melt quenching. The introduction of these metals into the ternary melts is shown to increase their thermodynamic stability.     

Equilibrium crystallization and distribution coefficients of alloy components in ternary systems with continuous solid and liquid solutions

Features of equilibrium crystallization of alloys in a ternary system consisting of solid and liquid solutions of components A, B, and C with melting points related as t _C < t _A < t _B are investigated in detail. It is demonstrated that, in alloys of any composition, the distribution coefficients of components B and C are k _B > 1 and k _C < 1, respectively. For the component A, this characteristic, depending on the alloy composition, can be either larger or smaller than unity, and at temperature t _A , k _A = 1.     

Effect of magnetron sputtering conditions on the structure and magnetic properties of FeZrN films

Nanocrystalline Fe_{97 ? x} Zr₃N _x films produced by rf reactive magnetron sputtering onto rotating and stationary substrates are studied. X-ray diffraction analysis is used to study the structure of the as-sputtered and annealed (at 300–600°C) films. The maximum saturation induction B _s reached for the films under study is 1.8–1.9 T; the minimum coercive force H _c is 1.5–1.8 Oe. These magnetic properties are explained using the structural state of the films.     

Effects of Growth Rates and Compositions on Dendrite Arm Spacings in Directionally Solidified Al-Zn Alloys

Dendritic spacing can affect microsegregation profiles and also the formation of secondary phases within interdendritic regions, which influences the mechanical properties of cast structures. To understand dendritic spacings, it is important to understand the effects of growth rate and composition on primary dendrite arm spacing (λ ₁) and secondary dendrite arm spacing (λ ₂). In this study, aluminum alloys with concentrations of (1, 3, and 5 wt pct) Zn were directionally solidified upwards using a Bridgman-type directional solidification apparatus under a constant temperature gradient (10.3 K/mm), resulting in a wide range of growth rates (8.3–165.0 μm/s). Microstructural parameters, λ ₁ and λ ₂ were measured and expressed as functions of growth rate and composition using a linear regression analysis method. The values of λ ₁ and λ ₂ decreased with increasing growth rates. However, the values of λ ₁ increased with increasing concentration of Zn in the Al-Zn alloy, but the values of λ ₂ decreased systematically with an increased Zn concentration. In addition, a transition from a cellular to a dendritic structure was observed at a relatively low growth rate (16.5 μm/s) in this study of binary alloys. The experimental results were compared with predictive theoretical models as well as experimental works for dendritic spacing.     

Relation between the solidification rate of a binary alloy and the alloying-element distribution coefficient

The change in the rate of equilibrium and nonequilibrium (according to Petrov–Scheil) solidification in binary model and some real solid-solution alloys with a distribution coefficient 0.2–2.5 is comprehensively analyzed. A relation between the solidification rate, on the one hand, and growth restriction factor Q and supercooling parameter P, which are used to determine the grain sizes in as-cast alloys, is revealed.     

The Friction Stress of the Hall–Petch Relationship of Pure Mg and Solid Solutions of Al,Zn, and Gd

Temperature and solute concentration effects on the friction stress, σ_o, of cast (texture-free) polycrystals of pure Mg, and of Mg-Al, -Zn and -Gd binary solid solutions are discussed using phenomenological arguments. The temperature effects on the pure metal suggest that σ_o relates to the ratio between the CRSS of prism and basal slip, against early suggestions that it should only relate to the CRSS for basal slip. Solid solution softening upon prism slip accounts for the minima in σ_o at ~ 0.5 at. pct in Mg-Zn and Mg-Gd alloys. In the concentrated alloys, solute-specific hardening effects upon slip and twinning lead to diverging behaviors: in Mg-Al and Mg-Zn, σ_o remains below that of pure Mg. Strong short-range order by Gd leads to a steep monotonic increase, and to a value larger in compression than in tension due to the activation of {10-11} twinning at high concentrations. The negative σ_o of the dilute Mg-Zn alloys is an artifact created by the tension/compression asymmetry stemming from the polar character of {10-12} twinning.     

Effect of heat treatment on the superplasticity of magnesium alloys

A necessary microstructural condition for the manifestation of the effect of superplasticity in alloys is a small grain size (d < 10 μm). The ingots of commercial magnesium alloys have a very coarse cast structure with d > 100 μm. We have studied the regimes of heat treatment of such materials in AZ91, AE42, QE22, and ZRE1 alloys with a purpose of obtaining a fine-grained structure. The optimum temperature of overaging of quenched magnesium alloys lies between 300 and 350°C. After hot pressing of heat-treated alloys, the average grain size is 6.4 (AZ91), 6.2 (AE42), 1.2 (ZRE1), and 0.7 (QE22) μm. The best characteristics of superplasticity are manifested by the ZRE1 and QE22 alloys with a relative elongation of 750% and strain-rate sensitivity m = 0.75 at T = 420°C and strain rate \(\dot \varepsilon \) = 3 × 10^?4 s^?1. Under these conditions, the AZ91 and AE42 alloys have δ ≤ 260% and m = 0.45.     

Magnetic Hysteretic and Mechanical Properties of a 31Kh20K3M Alloy with an Increased Carbon Content

An Fe–31Cr–20Co–3Mo (31Kh20K3M) alloy containing 0.09 wt % C, which is almost twice as much as its maximum content according to GOST 24897–81, has been studied to verify the influence of the carbon content on the magnetic hysteretic properties of hard magnetic high-chromium Fe–Cr–Co alloys. The optimal heat treatment, including thermomagnetic treatment, results in the average values of residual magnetic induction B_r = 0.96 T and coercive force H_cB = 63 kA/m and the maximum energy product (BH)_max = 29 kJ/m³. Some heat treatment regimes give B_r = 1.03 T, H_cB = 72 kA/m, and (BH)_max = 31 kJ/m³. In addition, for isotropic alloy samples, the following average values are obtained: B_r = 0.71 T, HcB = 56 kA/m, and (BH)_max = 15 kJ/m³. These magnetic hysteretic properties of the 31Kh20K3M alloy with an increased carbon content are similar to those of a powder 30Kh21K3M alloy with the minimum carbon content.     

Influence of heat treatment on the residual magnetization of steel in partial magnetic hysteresis

A formula is derived for the residual magnetization M_r of steel after repeated magnetic hysteresis, on the basis of measurements of the saturation magnetization M_s, the coercive force H_cs, the residual magnetization M_rs for the limiting hysteresis loop, and the maximum magnetizing field strength H_m of the partial hysteresis loop. The influence of variation in the tempering temperature t_te of steel on M_r at different H_m is analyzed. The dependence M_r(t_te) is established for small and large H_m. It is established that the M_r results may effectively be used for nondestructive assessment of the tempering of moderate-carbon alloy steel.     

The Effect of Low Concentrations Nb and C on the Structure and High-Temperature Strength of Fe<Subscript>3</Subscript>Al Aluminide

The Fe₃Al iron aluminide alloyed by low concentrations of Nb and C (c _Nb, c _C) is studied. The influence of the c _Nb/c _C ratio on the structure and high-temperature yield strength of iron aluminide was investigated. The structure and phase composition were studied by scanning electron microscope equipped with EDS and EBSD. The strengthening mechanisms are detected as strengthening by incoherent precipitates of NbC and as a solid solution hardening by Nb atoms.     

Predicting the critical stress intensity in structural steels

A method is proposed for predicting the critical stress-intensity coefficient K _1c of structural steels (their crack resistance) on the basis of uniaxial tensile tests of standard samples. The derivation of this method relies on the concepts of mechanical stability and embrittlement when nonuniform force fields act on a metal. The strain-hardening index n of the metal at the critical transition temperatures from the plastic state to the quasi-brittle state (T _c or T ₀) and from the quasi-brittle state to the brittle state (T _k2) plays a key role here. The proposed method may prove effective in monitoring the crack resistance of steels certified in scientific and plant laboratories.     

Quasi-steady-state characteristics of solidification of alloys made from VT3-1 alloy during vacuum arc remelting

Numerical calculations are presented of the depth of a liquid pool, time of local solidification, and temperature gradient in the axial region of an ingot during vacuum arc remelting (VAR) of VT3-1 titanium alloy (Ti-6.5Al-2.5Mo-1.5Cr-0.5Fe-0.3Si) corresponding to quasi-equilibrium conditions. Calculations were carried out for ingots of diameters D = 400, 800, and 1200 mm in the ranges of mass melting rates \(\dot M\) = 0.5–12.0, 0.5–35.0, and 1.5–30.0 kg/min, respectively. It is found that the depth of the liquid pool (H, mm) linearly increases with increasing \(\dot M\) and is virtually independent of D in the conditions under consideration and, therefore, can be presented as a unique dependence H = 66.63 \(\dot M\) + 71.91. A finite depth of the liquid pool at a zero mass melting rate is associated with that the state \(\dot M\) = 0 corresponds to a finite current of the arc, which holds a part of metal in the liquid state. It is shown that the time of local solidification depending on \(\dot M\) has a minimum associated with various physical processes, which determine the kinetics of the solidification front at small and large solidification rates. In relative units, which correspond to a minimum, these dependences are identical for all considered diameters of the ingot. In addition, based on autoradiographic investigations of solidification of VT3-1 alloy under the VAR conditions, critical values of the temperature gradient (G) and velocity of motion of the crystallization front (v) along the ingot axis, which determine the passage from the column structure to the equiaxial one, are determined. Starting from these results, the plots v(G) are constructed, which turn out to be very useful in the development of remelting modes, excluding the appearance of some type of liquation process. It is revealed that at the specified ingot diameter, the dependence v(G) is decreasing and, at the specified temperature gradient, the velocity of motion of the solidification front decreases as D increases, which indicates an increase in D for the smelting of the ingots of highly-doped alloys.     

On the Nonequilibrium Interface Kinetics of Rapid Coupled Eutectic Growth

Nonequilibrium interface kinetics (NEIK) is expected to play an important role in coupled growth of eutectic alloys, when solidification velocity is high and intermetallic compound or topologically complex phases form in the crystallized product. In order to quantitatively evaluate the effect of NEIK on the rapid coupled eutectic growth, in this work, two nonequilibrium interface kinetic effects, i.e., atom attachment and solute trapping at the solid–liquid interface, were incorporated into the analyses of the coupled eutectic growth under the rapid solidification condition. First, a coupled growth model incorporating the preceding two nonequilibrium kinetic effects was derived. On this basis, an expression of kinetic undercooling (?T _k), which is used to characterize the NEIK, was defined. The calculations based on the as-derived couple growth model show good agreement with the reported experimental results achieved in rapidly solidified eutectic Al-Sm alloys consisting of a solid solution phase (α-Al) and an intermetallic compound phase (Al₁₁Sm₃). In terms of the definition of ?T _k defined in this work, the role of NEIK in the coupled growth of the Al-Sm eutectic system was analyzed. The results show that with increasing the coupled growth velocity, ?T _k increases continuously, and its ratio to the total undercooling reaches 0.32 at the maximum growth velocity for coupled eutectic growth. Parametric analyses on two key alloy parameters that influence ?T _k, i.e., interface kinetic parameter (μ _i ) and solute distribution coefficient (k _e ), indicate that both μ _i and k _e influence the NEIK significantly and the decrease of either these two parameters enhances the NEIK effect.     

Morphological Stability of <Emphasis Type="Italic">δ</Emphasis>-Ferrite/<Emphasis Type="Italic">γ</Emphasis> Interphase Boundary in Carbon Steel

The morphological changes of the δ-ferrite/γ interphase boundary have been observed in situ with a high-temperature confocal scanning laser microscope (HTCSLM) during δ/γ transformations (δ → γ and γ → δ) of Fe-0.06 wt pct C-0.6 wt pct Mn alloy, and a kinetic equation of morphological stability of δ-ferrite/γ interphase boundary has been established. Thereafter, the criterion expression for morphological stability of δ-ferrite/γ interphase boundary was established and discussed, and the critical migration speeds of δ-ferrite/γ interphase boundaries are calculated in Fe-C, Fe-Ni, and Fe-Cr alloys. The results indicate that the δ-ferrite/γ interphase boundary is very stable and nearly remains absolute planar all the time during γ → δ transformation in Fe-C alloy. The δ-ferrite/γ interphase boundary remains basically planar during δ → γ transformation when the migration speed is lower than 0.88 μm/s, and the interphase boundary will be unstable and exhibit a finger-like morphology when the migration speed is higher than 0.88 μm/s. The morphological stability of δ-ferrite/γ interphase boundary is primarily controlled by the interface energy and the solute concentration gradient at the front of the boundary. During the constant temperature phase transformation, an opposite temperature gradient on both sides of δ-ferrite/γ interphase boundary weakens the steady effect of the temperature gradient on the boundary. The theoretical analysis of the morphological stability of the δ-ferrite/γ interphase boundary is coincident with the observed experimental results utilizing the HTCSLM. There is a good agreement between the theoretical calculation of the critical moving velocities of δ-ferrite/γ interphase boundaries and the experimental results.