High manganese steels show significant potential for industrial application due to their remarkable TRIP/TWIP effects at room temperature. The study on the TRIP behavior during warm deformation is important in controlling microstructures and properties of high manganese steels. In this paper, the microstructures, phase structures and reverse transformation of martensites to austenite in a high manganese steel which is composed of two types of martensites and austenite were investigated under warm deformation (100—500℃) by means of the determination of transformation temperature, calculation of phase diagram, microstructure observation, XRD analysis and EBSD orientation imaging technique. Results show that during compression above 300 ℃, TRIP effect disappeared and reverse transformation from martensite to austenite was enhanced. The transformation from bcc martensite to austenite was determined to be diffusive and no nucleation of austenite was needed. The warm deformation of austenite leads to the formation of coarse deormation twins and the mechanical stabilization of austenite, which suppressed the subsequent martensitic transformation during quenching. The austeniic grains in which reverse martensitic transformation completed at the latest, show mainly {110} and {100} orientations. In addition, hcp martensite could hardly edetected around bcc martensite, and the transformation of hcp martensite into austenite is regarded to be reversible and diffusionless.

In order to obtain the deformation grain structure for static recrystallization, an initial grain structure are produced by lattice deformation model; aiming at characteristics of different deformation regions and non–uniform distribution of the stored energy in deformed alloy, a multistate free energy (MSFE) function are proposed by introducing a weight factor for the stored energy and a characteristics state factor for different deformed regions. Based on these, the microstructure evolutions of static recrystallization for deformed Mg alloys are simulated by phase field model. The transformation dynamic curve of recrystallization, Avrami curve, and the regularity for stored energy releaing and distribution of grain size in recrytallization process are systematically analyzed. The dynamic regularity of statc recrystallization obtained by simulating is in good accord with the JMAK theory, and the Avramcurve by simulating can be regard as a linear with average slopes 2.45, 2.35, 2.19 and 2.15, respectively. The Avrami time index decreases with the true strain increasing. The stored energy releases faster, and the lasting time of static recrystallization process is shorter when the true strain is greater. Based on the established MSFE model, the simulation results here are in good agreement with the other theoretical results and experimntal results.

The tension process of single crystal Cu nano–rods with different cross section shapes were simulated by molecular dynamics at atomic scale. Based on centrosymmetry parameter method and combined with the dislocation nucleation theory, the effect of cross–section shape, cross–sectional area and slenderness ratio on the tensile mechanical properties of the nano–rods were analyzed, and the scale dependency of tensile mechanical properties of the single crystal Cu nano–rods has been revealed. The results show that after first yield, the nano–rods produce plastic deformation under the "dislocation nucleation–extended dislocation and sliding–lattice atom cross–slip" mechanism of the alternating cycle. The geometry of cross-section has negligible effects on the tensile initial plasticity of the nano–rods, while it shows apparent effects on the tensile mechanical properties. With the increase of cross–sectional area, two types of nano–rods have the phenomenon of early yield point, yield strength decreases and young’modulus increases. Compared with that of the square cross–sectional nano–rod, the variable rate of yield stess of the circular cross-sectional nano–rod is smaller while the variable rate of young’s modulus is lager. As the cross–sectional area increases to 500 nm², the young’s modulus of the two types of nano–rods become stable, and is close to the theoretical value of 84 GPa. Moreover, the slenderness ratio of the nano–rods has a slight effect on the tensile mechanical properties when the simulation size increased.

Cr8–type cold work die steels, such as Cr8Mo2SiV steel have been widely used in recent years due to high strength and high toughness, These steels have obvious secondary hardening effect. It has been widely reported that the secondary hardening mechanism of these die steels resulted from the combination of retained austenite and carbide precipitation. However, less attention has been paid on the secondary hardening of Cr8Mo2SiV steel. In order to investigate the secondary hardening mechanism of Cr8Mo2SiV steel, the hardness, retained austenite and precipitation of Cr8Mo2SiV steel were investigated in this paper by SEM, EDS, TEM and XRD analysis. Experimental results indicate that the secondary hardening peak of Cr8Mo2SiV steel which was quenched at 1030 ℃ appears at 520 ℃. Deep cryogenic treatment observably reduces the content of retained austenite, and thus increases the tempering hardness before secondary hardening peak and the secondary hardening peak shifted to low temperature by about 20 ℃. The tempered hardness of Cr8Mo2SiV steel decreased linearly wth the increase of soaking time when tempering at 520 ℃. The secondary hardening mechanism of Cr8Mo2SiV steel is the combination of the transformation of retained austenite and the earlstage of Mo₂C precipitation, and the role of transformation of retained austenite is more obvious. The early tage of Mo₂C–carbide precipitation is likely to be G.P. zone which ormed y [Mo–C] segregation group. As the tempering time extended, Mo₂C precipitated, and it ws dispersive and uniformly distributed.

In order to study the mechanism of mid–temperature thermal aging embrittlement in cast austenite stainless steel (CASS), the mechanical properties and microstructure were investigated of CASS which was aged at 400 ℃for 10⁴ h. The results show that, no change in the ferrite content (volume fraction) was detected. After long term aging, the magnetic permeability of the CASS declined, bt the nano–hardness of ferrite phases increased. The Charpy impact energy decreased rapidly and the impact fracture morphologies changed with aging time. Large number of α' particles precipitated homogeneously in the ferrite phases of the CASS aged for 10⁴ h. α′ precipittion produced by spinodal decomposition in ferrite was considered to the primary mechanism of thermal aging in CASS at mid-temperature. G phases were also observed n some positions of ferrite after long term aging.

Mg–10Gd–3Y–1.8Zn–0.5Zr (mass fraction, %) (GWZ1032K) alloys were fabricated by permanent mold casting and slow solidification with different cooling rates. The microstructures of the GWZ1032K alloys with different cooling rates were investigated by SEM, TEM and XRD. Two kinds of LPSO structure were observed, include lamellar 14H–LPSO structure in the grain interior and χ phase at the grain boundaries. Lamellar 14H–LPSO structure in α–Mg matrix propagated in the matrix with the decease of solidification rate, and filled the whole grain in the alloy solidified at 0.005 ℃/s. The second phase in the alloys also changed with deceasing the solidification rates, there are (Mg, Zn)₃RE compounds only when solidification rate is 5 ℃/s, (Mg, Zn)₃RE compounds and 14H–LPSO structured  phase when solidification rates are 0.5 and 0.1 ℃/s, and 14H–LPSO structured χ phase only when solidification rates are 0.01 and 0.005 ℃/s. It was detected that (Mg, Zn)₃RE compounds and χ phase existed simultaneously at the grain boundaries in the alloys at solidification rates of 0.5 ℃/s and 0.1℃/s, and the orientation relationship between them was determined to be [110] _χphase//[223]_(Mg,Zn)3RE and ∠g(001)_{χ phase} g(110) _{(Mg, Zn)3RE}=8.4°.

Mg–Al–Si alloys (AS series alloys) with a high content of silicon performed low ductility and strengths because of large amount of coarse Chinese scripts Mg₂Si particles distributed in the matrix. Trace elements, such as Ca, P, Sr and RE were selected to modify the morphology of Mg₂Si particles. Among these, Sr showed remarkable modification effect, however, the modification mechanism was not clarified yet. In this work, the effects of Sr on the morphology of Mg₂Si in Mg–9Al–1Si–0.3Zn (mass fraction, %) alloy and the mechanical properties were investigated, and the modification mechanism was explained by comparing Mg2Si morphologies. The Mg–9Al–1Si–0.3Zn alloy was composed of primary hopper Mg₂Si particles of 40 μm in size, coarse Chinese scripts Mg₂Si of 50—80 μm, island–like Mg₁₇Al₁₂ and the α–Mg matrix. 3D hopper crystals and Chinese scripts Mg₂Si particles were extracted by the electrochemical method. Both morphologies reveal the"corner effect"which leads to the preferential growth orientation of edges and corners of the octahedron Mg₂Si particle, respectively. When Sr was added into the alloy, the growth rates of both edges and corners of the Mg₂Si particles were depressed significantly due to the adsorption of Sr on the surface of Mg₂Si particles. When Sr addition went up to 0.32%, Mg₂Si phase was fully modified to small polygonal particles of 5—20 μm. Moreover, the grain size of the alloy decreased from 210 μm to 160 μm with Sr increasing, which is in accord with the GRF (growth restriction factor) mechanism. The increasing of mechanical properties is mainly attributed to the refinement of Mg₂Si phase.

In view of the numerical inverse identification of constitutive models, a forward numerical modelling of Gleeble tension tests is conducted. A coupled electrical–thermal–mechanical model is proposed for the resolution of electrical, energy and momentum conservation equations by means of finite element method. In momentum equation, the mixed rheological model in multi–phase region (e.g. δ–ferrite and γ austenite (δ+γ mixture)) is developed to consider the δ/γ phase transformation phenomenon for micro–alloyed low carbon steel at high temperature. Experimental and numerical results reveal that significant thermal gradients exist in specimen along longitudinal and radial directions. Such thermal gradients will lead to phase fraction gradient in specimen at high temperature, such as δ fraction gradient or liquid fraction gradient. All these gradients will contribute to the heterogeneous deformation of specimen and severe stress non–uniform distribution, which is the major difficulty for the identification of constitutive models, especially for the simple identification method based on nominal stress–strain. The proposed model can be viewed as an important achievement for further inverse identification methods, which should be used to identify constitutive parameters for steel at hgh temperature in the presence of thermal gradients.

By using thermo–mechanical simulator, OM and TEM, the dynamic recrystallization (DRX) and precipitation behaviors of a kind of low carbon V–microalloyed steel have been investigated at temperatures ranging from 900 to 1050℃ and strain rates from 0.01 to 10 s⁻¹. The activation energy (Q_def ) for hot deformation of this kind of V–microalloyed steel was calculated to be 341.97 kJ/mol by regression analysis, while the apparent stress exponent (n) was calculated to be 4.24. The equation describing the hot working process was also obtained. The critical strain for DRX was accurately determined based on the P–J method and high order polynomial fitting between strain hardening rate and true stress, and mathematical models of critical strain and peak strain versus Z parameter were deduced. The dynamic precipitation behavior of V(C, N) particles at low strain rate was further investigated. The results show that with increasing the strain, the average size of V(C, N) particles increases and the size distribution of the precipitates become wide. The calculations of the driving force for recrystallization and pinning force show that once the dynamic recrystallization take place, the dynamic precipitation could not prevent dynamic recrystallization from occurring.

Directional solidification experiments under heating temperatures of 1580℃ and 1650℃ were performed on Ti–47Al–2Cr–2Nb alloy in order to obtain the evolution of lamellar grains. From microstructural analysis in the mushy zone of directional solidified ingots, β phase was firstly solidified, then α phase was formed through peritectic reaction; α phase depended on the pre–existed β phase on which it nucleated, and only one of the 12 α orientation variants was selected during solid state β→ α transformations. As the average temperature gradient of the mushy zone was increased from 40 K/cm to 160 K/cm, the solidification interface morphologies were changed from columnar dendrite to celluar dendrite. Eliminating the influence of cutting plane to the γ–lamella orientation, it was shown that the columnar lamellar grains with an angle of approximately 74^? to growth direction gradually overgrew the ones with the angle of nearly 45^? to the growth direction at the withdrawal rate of 1 mm/min and temperature gradient of 40 K/cm. Increasing temperature gradient to 160 K/cm, the grains with the angle of about 74^? progressively rejected other with the angle of nearly 90^? to the growth direction. Calculation of the β dendrite preferred growth orientation indicated that  β dendrites tend to grow along the <110>_β orientation at the present solidification experiments. Increasing temperature gradient, the preferred growth tendency of dendrite became more drastically, other orientations, such as the <001>_β directional orientation, could rapidly be replaced.

High manganese steels containing 15%—30% (mass fractions) Mn and additions of (2%—4%)Si and (2%—4%)Al exhibit superior ductility and extraordinary strengthening behavior during plastic deformation, due to extensive twin formation under mechanical load (the so–called TWIP effect–twinning induced plasticity effect) or the ε–martensite and α′–martensite transformation (the so–called TRIP effect–transformation induced plasticity effect). In this paper, different heat treatments were carried out for high–manganese TRIP steels of Fe–15Mn–4Si–2Al and Fe–20Mn–4Si–2Al, and the uniaxial tensile tests were performed. The results show that increase of holding time at 1373 K can increase elongation and strength. Through the analysis of stress–strain curves, the relationship between mechanical properties and deformation mechanism was established. The dependence of phase compositions in high manganese TRIP steels on the heat treatment parameters has been studied by metallographic characterization and XRD pattern. The transformation routes of   γ→ ε→ α′ and γ → α′ were observed by TEM, which dominates the TRIP effects. Microstructural characterization of  ε–martensite and α′–martensite indicated that α′–martensite held the K–S orientation relationship with austenite, and the S–N (Shoji–Nishiyama) orientation relationship was observed between austenite and ε–martensite, whereas ε–martensite and α′–martensite held the Burgers orientation relationship. Deformation behavior of the two kinds of high Mn steels has been clarified through the relationship between work hardening rate of dσ/dε and true strain based on the true stress–true stain curves. It has been found that continuous transformation from austenite or ε–martensite to α′–martensite can take place during deformation, which increases the work–hardening rate to improve the TRIP effect.

Electrical resistance–temperature curves of 6082 aluminum alloy at various cooling rates during continuous cooling was obtained by in–situ resistance measurement. Phase transformation start and finish temperatures were ascertained by the slope change of resistance–temperature curves. Continuous cooling transformation (CCT) diagram for 6082 aluminum alloy was plotted. Microstructure evolution during cooling was examined by TEM observation to verify the validity of the CCT diagram. Applications of the CCT diagram were studied in this work. The results show that the CCT diagram obtained by in situ resistance measurement is credible. Resistance–temperature curves corresponding to different cooling rates depart from straight line to different directions. The phase transformation start and finish temperature decreases with the increase of cooling rates when the cooling rate is slow, but as the cooling rate increases to a certain rate the phase transformation start temperature increases suddenly and then decreases continously. Phase transformations mainly take place between 220 and 400 ℃. Critical cooling rate for preventing phase transformation is between 16—34 ℃/s. For plates 20 mm in thickness is proper to quench by 60 ℃ water. A step–quench process can be established by the tested CCT diagram to decrease quenching stress utmost and inhibit equilirium phase precipitation at the same time.

The Non–equilibrium molecular dynamics (NEMD) simulation method which is based on the linear response theory is applied to simulate the thermal conduction process of C, BN and SiC nanotubes. The three–body Tersoff potential is used to simulate the interactions among atoms. The effects of axial length, temperature and tensile strain on the axial thermal conductivity of the three kinds of nanotubes are investigated, and their thermal conductivities are compared and analyzed. The simulation results show that the axial thermal conductivity increases as the axial length increases, and exhibits a relationship k ∝ L^α that is in agreement with the solution of Boltzmann-Peierls phonon transport equation (B–P equation). It is found that the thermal conductivity of nanotube decreases with the increase of temperature. As the tensile strain increases, the thermal conductivity of nanotubes show an slight increase first, and then decreases. But, the corresponding tensile strains at which the tendency of thermal conductivity of the three nanotubes changes are different. Under the same conditions, the sequence of thermal conductivity from the biggest to the smallest is in the order of carbonanotues, boron nitride naotubes and carbon silicon nanotues.

With the development of marine industry, the corrosion of metal structures in marine sediment has received increasing attention. Marine sediment is a very complex marine corrosion environment. The corrosion of sulfate–reducing bacteria (SRB) in the marine sediment is thought as one of major corrosion factors. Sacrificial anodes are widely used for protection of steel structures in the marine environment due to their high theoretical current efficiency, low active potential and low cost. However, in the marine environment, the sacrificial anodes may be attacked by microbial activity, which leads to serious failure and energy loss. Some researchers have investigated the biocidal activity of sacrificial anode, but work about the influence of microbes on the performance of sacrificial anode has been rarely reported. In this paper, a comparative study of the corrosion behavior of Zn–Al–Cd sacrificial anode in marine sediment without and with SRB was carried out using electrochemical impedance spectroscopy (EIS), polarization curve (PC), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results of EIS and PC showed that the corrosion of the sample was enhanced sharply in the presence of SRB at the beginning, while the corrosion performance of the sample in marine sediment with and without SRB gradually became similar with each other due to the decreasing SRB populations. SEM images revealed that the damage of the sample in the SRB–containing medium was severer than that in the sterile medium. EDS analysis showed that the concentration of Al and Zn in the surface film of the sample with SRB was much lower than that for the sample without SRB, which suggests that the corrosion rate of the sacrificial anode is accelerated by SRB.

Welding technique is generally used in nuclear power plant for manufacturing and machining important components such as steam generator. The similar metal weld and dissimilar metal weld were commonly involved to connect and fixup tubings in steam generators. However, in recent years large amounts of cracking accidents have been observed in the welded joints. A concern has been raised about the integrity and reliability in the joint transition zone due to the high susceptibility of heat affected zone (HAZ) and fusion zone (FZ) to stress corrosion cracking (SCC). In this study, the similar metal and dissimilar metal joints were investigated and compared, focusing on the correlation between microstructure, residual strain and SCC behavior. The microstructures of transition zone in Ni–based Alloys 690 and 52 similar metal joint and Alloys 182 and A533B low alloy steel dissimilar metal joint were investigated comprehensively by SEM, EBSD, TEM. The residual strain distribution in the HAZ of 690–52 similar metal joint was quantitatively measured. The SCC behavior of 182–A533B dissimilar metal joint in high temperature oxygenated water were simulated by creviced bent beam specimen. The HAZ in the similar joint exhibits higher residual strain, sensitive microstructure and high susceptibility to SCC, therefoe, the HAZ region deserve more attention during the inspection and examination of components. The FZ othe dssimilar metal joint exhibits complicated microstructure and chemical composition. The type–II which parallels the fusion boundary (FB) and type–I linking the FB and type–II was typical in the FZ of the dissimilar weld. The SCC susceptibility and cracking growth rate are higher at type–II boundary in the FZ. The role of type–I boundary is to lead the crack growth to the FB. After reaching the FB, the crack growth is blunted by pitting. The FB plays a barrier role to the crack growth in the low alloy steel. The FZ in dissimilar metal joint is weak and high susceptible to SCC.

Stress corrosion crack growth rates of alloy 690 thermally treated (TT) after one–directionally (1D) cold–rolling along the longitudinal (L) direction and three–directionally (3D) cold–rolling were successfully measured by ACPD technique in deoxygenated water with different dissolved hydrogen contents (C_dH) at 340 ℃. The fracture mode is mainly intergranular mode in both two kinds of alloy 690TT. The crack growth rates in the T–L orientation are higher than those in the L–T orientation in 340 ℃deoxygenated environments. For 1D 25% alloy 690TT with T–L orientation, the measured average crack growth rate is 4.8×10⁻¹¹ m/s in 340℃ water with C_dH 30 μL/g, and the measured average crack growth rate is 1.1×10⁻¹⁰ m/s in 340 ℃ water with C_dH 10 μL/g. The mechanism of crack growth is internal oxidation mechanism.

The flow patterns were simulated by Hg in high speed continuous casting mold with electromagnetic brake. The velocity in mold and fluctuation of meniscus was measured by ultrasonic doppler velocity. The effect of the magnetic field on the fluid flow was analyzed. The influence of magnetic flux density and location on the flow discharged from the nozzle, the velocity in mold, the fluctuation and flow of the meniscus, and the washing intensity of flow were studied. The results showed that the flow discharged from the nozzle was suppressed, the flow in the upper eddy was strengthened, the flow in the lower eddy was weakened, and the fluctuation of free surface and the flow at the meniscus were improved. The magnetic field could not only damp flow, but also change the flow direction and redistribute the flux of liquid steel. When Bmax was higher than 0.29 T, it was beneficial to optimizing and controling the flow in the mold.