Volume 35, Issue 4 -

Hot corrosion of Inconel 625 in sodium chloride, potassium chloride, magnesium chloride, calcium chloride and their mixtures with different compositions is conducted at 900°C to investigate the effects of cations in chloride salts on corrosion behavior of the alloy. XRD, SEM/EDS were used to analyze the compositions, phases, and morphologies of the corrosion products. The results showed that Inconel 625 suffers more severe corrosion in alkaline earth metal chloride molten salts than alkaline metal chloride molten salts. For corrosion in mixture salts, the corrosion rate increased with increasing alkaline earth metal chloride salt content in the mixture. Cations in the chloride molten salts mainly affect the thermal and chemical properties of the salts such as vapor pressure and hydroscopicities, which can affect the basicity of the molten salt. Corrosion of Inconel 625 in alkaline earth metal chloride salts is accelerated with increasing basicity.

The minimum of oxygen content in the deoxidation equilibrium in liquid iron was thermodynamically analyzed in the present paper. Two criteria were developed to determine the existence of the minimum. The first criterion was 0≤xγMM+yγOM≤min(x/4.606[%M]ex2,(xeMM+yeOM)2/3.474x)$$0 \le x\gamma _{\rm{M}}^{\rm{M}} + y\gamma _{\rm{O}}^{\rm{M}} \le \min ({x \mathord{\left/{\vphantom {x {4.606[\% {\rm{M}}]_{{\rm{ex}}}^2}}} \right.\kern-\nulldelimiterspace} {4.606[\% {\rm{M}}]_{{\rm{ex}}}^2}},{{{{(xe_{\rm{M}}^{\rm{M}} + ye_{\rm{O}}^{\rm{M}})}^2}} \mathord{\left/{\vphantom {{{{(xe_{\rm{M}}^{\rm{M}} + ye_{\rm{O}}^{\rm{M}})}^2}} {3.474x}}} \right.\kern-\nulldelimiterspace} {3.474x}})$$ with xeMM+yeOM<0$$xe_{\rm{M}}^{\rm{M}} + ye_{\rm{O}}^{\rm{M}} \lt 0$$, or xγMM+yγOM<0$$x\gamma _{\rm{M}}^{\rm{M}} + y\gamma _{\rm{O}}^{\rm{M}}{\rm{\lt 0}}$$. And the second criterion was (xeMO+yeOO)+y/2.303[%O]ex>0$$(xe_{\rm{M}}^{\rm{O}} + ye_{\rm{O}}^{\rm{O}}) + {y \mathord{\left/{\vphantom {y {2.303{{[\% {\rm{O}}]}_{{\rm{ex}}}}}}} \right.\kern-\nulldelimiterspace} {2.303{{[\% {\rm{O}}]}_{{\rm{ex}}}}}} \gt 0$$. The criteria in terms of first-order activity interaction parameters were the special case of present thermodynamic analysis with neglecting the second-order activity interaction parameters. They were not fit for the case of xeMM+yeOM>0$$xe_{\rm{M}}^{\rm{M}} + ye_{\rm{O}}^{\rm{M}} \gt 0$$, in which case the criteria in terms of second-order activity interaction parameters should be taken into account to determine the existence of the minimum. The value 0.11 of eSiSi$$e_{{\rm{Si}}}^{{\rm{Si}}}$$ was smaller based on the existence of the minimum for the Fe-O-Si system. It was guaranteed that the minimum value of oxygen content on the deoxidation equilibrium curve existed at silicon content 20 mass%, when the value 0.32 of eSiSi$$e_{{\rm{Si}}}^{{\rm{Si}}}$$ was chosen, and the second-order activity interaction coefficients γSiSi$$\gamma _{{\rm{Si}}}^{{\rm{Si}}}$$ and γOSi$$\gamma _{\rm{O}}^{{\rm{Si}}}$$ satisfied the condition γSiSi+2γOSi=−1.54×10−3$$\gamma _{{\rm{Si}}}^{{\rm{Si}}} + 2\gamma _{\rm{O}}^{{\rm{Si}}} = - 1.54 \times {10^{- 3}}$$.

The oxidation behavior of Ti-5Al-2.5Sn and Ti-6Al-4V produced by hot isostatic pressing (HIP) has been studied at 650–850°C in air for 24 h. The oxidation kinetics of both alloys followed the parabolic law with good approximation, except for Ti-5Al-2.5Sn oxidized at 850°C. Multi-layered scales formed on both alloys at 750°C and 850°C. Ternary additions of Sn and V accounted for the different morphology of the scales formed on these two alloys. In addition, the oxidation behavior of HIP alloys is compared with that of the corresponding cast alloys and the scaling mechanism is discussed.

Combined influence of mean stress and stress amplitude on the cyclic life under elevated temperature (823–923 K) ratcheting of 316LN austenitic stainless steel is discussed. Constant life Haigh diagrams have been generated, using different combinations of stress amplitude and mean stress. In the plastic domain, the allowable stress was found to increase or decrease with mean stress depending on the temperature and combination of mean stress – stress amplitude employed. Strong influence of dynamic strain aging (DSA) was found at 823 K which affected the mode of deformation of the material in comparison with 923 K. Failure mode expressed through a fracture mechanism map was found to change from fatigue to necking depending on the test temperature as well as combinations of mean stress and stress amplitude. Occurrence of DSA at 823 K proved to be beneficial by way of extending the safe zone of operation to higher R -ratios in comparison with 923 K.

A mixture of Ti, Al, graphite and c-BN powders was used as raw material to fabricate Ti 2 AlC matrix-bonded c-BN composite using the self-propagating high-temperature synthesis (SHS) method. The effect of c-BN size and content on the fabrication of the composites was investigated. The results show that Ti 2 AlC matrix-bonded c-BN composites can be obtained by SHS. c-BN content and size evidently affected the phase composition and microstructure characteristic of the composites. At 10–30% c-BN (120/140 mesh) content, the product phases were Ti 2 AlC, Ti 3 AlC 2 , Al 3 Ti, TiN, TiC, AlN, graphite and TiB 2 . A dense transition layer with a thickness of about 10 µm showed the interface between c-BN and the matrix. However, Al peaks appeared, and the titanium aluminium carbide peak became weak in the samples containing 40% and 50% c-BN. c-BN was unequally enwrapped by one coating with a thickness of about 2 µm. The main product phases of the samples were Ti 2 AlC, Ti 3 AlC 2 , Al 3 Ti, TiN, TiC, AlN, graphite and TiB 2 in the products with different c-BN sizes. The addition of coarse c-BN particles (80/100, 120/140 and 170/200 mesh) yielded a transition layer with a thickness of approximately 10 µm on the interface and Ti 2 AlC main phase matrix. The finer the particle size, the greater the reaction activity. When c-BN was finer (20 μm), c-BN more easily reacted with Ti and Al to form TiN, AlN and TiB 2 . The synthesis of Ti 2 AlC was obviously inhibited.

In order to eliminate the flash, arc corrugation and concave in weld zone, level compensation friction stir welding (LCFSW) was put forward and successfully applied to weld 6061-T6 aluminum alloy with varied welding speed at a constant tool rotational speed of 1,800 rpm in the present study. The glossy joint with equal thickness of base material can be attained, and the shoulder affected zone (SAZ) was obviously reduced. The results of transverse tensile test indicate that the tensile strength and elongation reach the maximum values of 248 MPa and 7.1% when the welding speed is 600 mm/min. The microhardness of weld nugget (WN) is lower than that of base material. The tensile fracture position locates at the heat affected zone (HAZ) of the advancing side (AS), where the microhardness is the minimum. The fracture surface morphology represents the typical ductile fracture.

The thermo-viscoplastic behaviors of AISI 4140 steel are investigated over wide ranges of strain rate and deformation temperature by isothermal compression tests. Based on the experimental results, a unified viscoplastic constitutive model is proposed to describe the hot compressive deformation behaviors of the studied steel. In order to reasonably evaluate the work hardening behaviors, a strain hardening material constant ( h 0 ) is expressed as a function of deformation temperature and strain rate in the proposed constitutive model. Also, the sensitivity of initial value of internal variable s to the deformation temperature is discussed. Furthermore, it is found that the initial value of internal variable s can be expressed as a linear function of deformation temperature. Comparisons between the measured and predicted results confirm that the proposed constitutive model can give an accurate and precise estimate of the inelastic stress–strain relationships for the studied high-strength steel.

The present work describes the structural stability and electronic and mechanical properties of transition metal nitrides (TmNs: B1 cubic structure (cF8, Fm 3‾$$\overline 3 $$ m)) using first principles density functional theory (DFT) within generalized gradient approximation (GGA). The lattice constant of TmNs increases with increasing the atomic radii of the transition metals. Stability of the TmNs decreases from IVB to VIB groups due to increase in formation energy/atom. The bonding characteristics of these nitrides have been explained based on electronic density of states and charge density. All the TmNs satisfy Born stability criteria in terms of elastic constants except CrN and MoN that do not exist in equilibrium binary phase diagrams. The groups IVB and V–VIB nitrides are associated with brittle and ductile behaviour based on G/B ratios, respectively. The estimated melting temperatures of these nitrides exhibit reasonably good agreement with calculated with B than those of the C 11 for all nitrides.

Isothermal compression tests were conducted on A100 steel using a Gleeble 1500 thermal simulator at a temperature range of 900–1,200°C and strain rate range of 0.001–3 s −1 . Results show that the A100 steel has higher strength than the Aermet 100 steel at high temperatures. Constant values, such as A , α , and n , and activate energy Q were obtained through the regression processing of the stress–strain data curves under different strains. A set of constitutive equations for A100 steel was proposed by using an Arrhenius-type equation. The optimum processing craft ranges for A100 steel based on the analysis of the hot working diagram and deformation mechanism are as follows: temperature range of 1,000–1,100°C and strain rate range of 0.01–0.1 s −1 . The average grain size within this working range is 7–22.5 μm.

In this work, microwave energy is used for preparing a granular red mud (GRM) adsorbent made of red mud with different binders, such as starch, sodium silicate and cement. The effects of the preparation parameters, such as binder type, binder addition ratio, microwave heating temperature, microwave power and holding time, on the absorption property of GRM are investigated. The BET surface area, strength, pore structure, XRD and SEM of the GRM absorbent are analyzed. The results show that the microwave roasting has a good effect on pore-making of GRM, especially when using organic binder. Both the BET surface area and the strength of GRM obtained by microwave heating are significantly higher than that by conventional heating. The optimum conditions are obtained as follows: 6:100 (w/w) of starch to red mud ratio, microwave roasting with a power of 2.6 kW at 500℃ for holding time of 30 min. The BET surface area, pore volume and average pore diameter of GRM prepared at the optimum conditions are 15.58 m 2 /g, 0.0337 cm 3 /g and 3.1693 A 0 , respectively.

Zn 0.5 Ni 0.5- x Co x Fe 2- y La y O 4 ferrites (with x =0, 0.02 and y =0, 0.02) were prepared by an industrial method using the standard ceramic technique and sintered at 1,250°C in air. X-ray diffraction (XRD) was used to obtain the phase formation of the NiZn ferrites. The microstructure of ferrites was investigated by scanning electron microscopy (SEM). The XRD reveals that lattice parameter ( a ) is decreased and a secondary phase (LaFeO 3 ) is formed in the La–Co co-substituted NiZn ferrite sample, meanwhile, the grain size ( D ) of this sample decreased obviously by observing SEM photographs. Vibrating sample magnetometry (VSM), B-H analyzer, impedance analyzer and electrometer were carried out in order to characterize some properties of the ferrites. This investigation indicates that, La–Co co-substituted NiZn ferrite sample has higher power loss ( P cv ) than other samples at low frequency with an increase in coercive field ( H c ) and magnetocrystalline anisotropy ( K 1 ), a decrease in initial permeability ( μ i ) and saturation magnetization ( M s ). However, at high frequency, the power loss of La–Co co-substituted sample is low, which is attributed to high resistivity ( ρ ), small grain size ( D ), less number of Fe 2+ ions and low porosity ( P ).

In order to recycle the phosphorus in P-bearing converter slag and make it used as slag phosphate fertilizer, the effect of MgO and MnO in P-bearing steelmaking slag on phosphorus existence form, P 2 O 5 solubility and magnetic separation behavior were researched systematically. The results show that the phosphorus in slag is mainly in the form of n 2CaO · SiO 2 –3CaO · P 2 O 5 (for short n C 2 S–C 3 P) solid solution in the P-rich phase for CaO-SiO 2 -Fe t O-P 2 O 5 -X (X stands for MgO and MnO, respectively). And the increasing of MgO and MnO content has no influence on precipitation of n C 2 S–C 3 P solid solution in slag, MnO and MgO mainly enter into RO phase and base phase to form MnFe 2 O 4 and MgFe 2 O 4 , which has little effect on the P 2 O 5 content of P-rich phase, so which has little effect on the degree of phosphorus enrichment and phosphorus occurrence form of the P-bearing slag. And adding MgO and MnO into CaO-SiO 2 -P 2 O 5 -Fe 2 O 3 slag system can break the complex net structure formed by Si–O on certain degree, and also hinder the precipitation of β-Ca 3 (PO 4 ) 2 crystal with low citric acid solubility during the melting–cooling process. Therefore, adding appropriate MgO and MnO content into slag can improve the slag P 2 O 5 solubility, but the effect of different amounts of MgO and MnO on the P 2 O 5 solubility has little difference. Meanwhile, adding MgO and MnO into slag can improve the metallization of slag and magnetism of iron-rich phase, make the magnetic substances content increase and separation of phosphorus and iron incomplete, so it is adverse to phosphorus resources recovery from P-bearing slag by magnetic separation method. In order to recycle the phosphorus in P-bearing converter slag, the MgO and MnO content in the P-bearing slag should be controlled in the steelmaking process.

Effects of temperature and slag composition on dephosphorization in a 120 ton top-bottom combined blown converter steelmaking process by double slag method were studied. The slag properties were determined by scanning electron microscope- energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD). The results show that the transition oxidation temperature between dephosphorization and decarbonization T f is not the favorable temperature for the first deslagging. The optimum first deslagging temperature is confirmed to be approximately 1,673 K which is about 70 K higher than T f . High melting temperatures phases (such as 3CaO·SiO 2 ) in the slag with high basicity and MgO content are unfavorable to the dephosphorization. The optimum process condition for dephosphorization at the first deslagging in present work is approximately 1,673 K in temperature, 2.0 in slag basicity, 6 and 17 mass% in MgO and T.Fe content, 6 mass% ≤ MnO content.