Piercing plug is a key deformation tool during manufacturing the seamless steel tubular product while oxidation is the most economical and practical method for the surface treatment of the piercing plug. The high-temperature oxidation behavior of piercing plug steel was investigated by employing the materials 20Cr2Ni3, 30Cr3NiMo2V and H13 under drop-feeding mixed H₂O-C₂H₅OH atmosphere. A two-stage surface treatment process of first oxidation and then reduction reaction was designed by adjusting the volume ratio of alcohol to water, and thus a two-layer oxide scale structure where the external layer mainly containing FeO was obtained subsequently. Morphology, chemical composition and phase constituents of the oxide scale were studied by using SEM, EDS and XRD, while the microstructure and hardness distribution of decarburization layer were studied by using OM and microhardness tester. The results show that the thickness of external oxide scale decreases with the increase of chromium equivalent, while the thickness of the inner oxide scale keeps basically unchanged. In the process of high temperature oxidation, the vacancy in oxide scale accumulates into micro holes, where the volatile substances and gases were concentrated to elevate the internal pressure high enough that makes the oxide scale "protrude" outwards. The mass transfer in oxidation process varied for different alloy elements. Ni and Mo cannot be oxidized in the specific atmosphere at 950 ℃ according to the oxidation thermodynamics, but exist in elemental form. The oxidation of C determines the microstructure and mechanical properties of the decarburization layer, where the hardness curves of 20Cr2Ni3 and 30Cr3NiMo2V exhibit a characteristic of "double-platform", while the hardness of H13 increases first slowly, then rapidly, and then gradually flattens out. Finally, the material selection for piercing plug steel is suggested from the viewpoint of engineering application.

Advanced duplex stainless steels (DSSs) in which Ni is mostly or completely replaced by Mn and N have been developed in recent years. Such Mn-N bearing DSSs can readily achieve exceptional room-temperature tensile properties through the transformation-induced plasticity (TRIP) effect of metastable austenite. During the processing of DSSs, solution treatment is a critical step that tailors the phase fraction and the overall properties. In particular, the phase chemistry can change due to different element partitioning between two constituents, resulting in a different TRIP kinetics, when DSS is solution treated at different temperature. In this work, the effect of solution temperature on tensile deformation behavior of a new Mn-N bearing DSS was studied. The mechanical properties and work-hardening characteristic of the steels solution treated at different solution temperature (1000~1200 ℃) were investigated by thermal modeling test, and the effects of solution temperature on the deformation substructure and fracture characteristics were analyzed by OM, SEM and EBSD. The results show that as the solution temperature increases, the yield strength and tensile strength of the steels decrease, while the elongation (uniform elongation and total elongation) increases firstly and then decreases. The steel solution treated at 1100 ℃ shows the optimum uniform elongation of 46.7%, and a better combination of ultimate tensile strength and ductility of approximately 44.6 GPa·%. The work-hardening rate of the steel shows a three-stage characteristic, namely it declines firstly and then increases and subsequently declines again as the strain increases. However, the increasing extent of the work-hardening rate decreases as the solution temperature increases. The strain-induced martensitic transformation (SIMT) of metastable austenite which causes the TRIP effect has two evolution mechanisms of γ→ε→α' and γ→α'. But SIMT can be suppressed when the solution temperature increases. The fracture surfaces of specimens solution treated at different temperatures show a quasi-cleavage mode, in which both ferrite and strain-induced martensite exhibit cleavage fracture while the residual austenite displays a dimple-mode fracture. Furthermore, the M_d30 which can characterize the stability of metastable austenite was calculated, which decreases from 81 ℃ to 38 ℃ as the solution temperature increases from 1000 ℃ to 1200 ℃, indicating that the TRIP effect gets weakening at a higher solution temperature, and the work-hardening and plasticity therefore decrease.

The difference of crystal structure and stacking fault energy (SFE) of two phases in duplex stainless steels (DSS) make different softening mechanism during hot deformation. Due to different austenite stability of Mn and Ni, the substitution of Mn for Ni will significantly affect dynamic recrystallization (DRX) behavior of compression deformation. The DRX behaviors of 23Cr-2.2Ni-6.3Mn-0.26N low nickel type DSS were studied in the deformation temperatures of 1073~1423 K and strain rates of 0.01~10 s^-1 by using a thermal simulator. The results showed that the deformation procedure of samples are mainly softened by dynamic recovery (DRV) of two phases at low temperature and high deformation strain rate, and mainly softened by austenite DRX at high temperature and low deformation strain rate. At the low strain rates of 0.01 and 0.1 s^-1, the grain size of austenite DRX increased with the increase of deformation temperature. The softening mechanism of samples are related to the Z parameter, and the deformation softening is mainly caused by austenite DRX under the condition of low Z value. Based on the thermal deformation equation, the apparent stress index of samples were calculated as 5.18, and the apparent activation energy of thermal deformation was calculated as 391.16 kJ/mol. The constitutive equation of the relationship between the peak flow stress and the Z parameter was established by hyperbolic sinusoidal model proposed by Sellars. The critical stress of DRX increases with increasing strain rate and decreasing deformation temperature, while the critical strain of DRX increases with the decrease of deformation temperature, and increases at first and then decreases with increasing strain rate (0.1~10 s^-1) at low deformation temperature. The relationship between the DRX critical stress (strain) and peak stress (strain), as well as DRX characteristic parameters and Z parameter correlation models, and the austenite phase DRX volume fraction models were determined. Moreover, the DRX volume fraction models predict that the increase of strain rate and the decrease of deformation temperature can delay occurrence of DRX.

Cl^- and SO₄^2- are most common aggressive ions containing in the seawater which may cause the localized corrosion of reinforcement structures. It is found that a protective passive film will form on the steel surface in the concrete pore solution. The localized breakdown of the passive film caused by the aggressive ions and the carbonation are the main reason for the localized corrosion initiation of reinforcements. In the previous studies, it is found that the performances of the SO₄^2- on the rebar corrosion were quite different in different pH value conditions and the test results did not unify. Therefore, the influence of pH value and the SO₄^2- on the corrosion behavior of Q235B carbon steel in the simulated pore solution was studied using anodic polarization, electrochemical impedance spectra (EIS), Mott-Schottky (M-S) and potentiostatic polarization methods. The anodic polarization curves indicate that when the pH value of the simulated pore solution was higher than 11, SO₄^2- had no damage to the passive film. However, once the pH value of the simulated pore solution decreased to 10, a small amount of SO₄^2- can lead to the breakdown of the passive film and induce pitting initiation. EIS and M-S measurement results suggest that the stability of the passive film would decrease with the decreasing of the solution pH. The concentration of the defect would increase in the passive film due to the pH decrease. The stability reduction and the increase of defect concentration both can lead to the passive film become fragile and more easily to be destroyed by SO₄^2-. Through the potentiostatic polarization test in conjunction with SEM observation, it is found that SO₄^2- can inhibit the growth of the passive film during the initial film formation period and lead to the appearance of metastable pitting corrosion under high pH value conditions. In the low pH value conditions, SO₄^2- could accumulate at the defect of the passive film and lead to stable pitting propagate on the steel surface.

With the extensive exploitation of ocean resources, the steels used in ocean engineering have been developed towards the trend of high strength-toughness and thick plates, which consequently causes welding problem and high risk of stress corrosion cracking (SCC). The heat-affected zone (HAZ) of high-strength low-alloy steel undergoes phase transformation during welding thermal cycle and it's generally considered to be most vulnerable to SCC. E690 steel, as a newly-developed high strength steel, is currently the leading kind of steel used in ocean platform for its excellent performance. However, there is few research about its SCC behavior in marine atmosphere, especially in SO₂-polluted atmosphere. Therefore, it's of great importance to investigate the SCC behavior and mechanism of simulated HAZ of E690 steel in this environment. However, the HAZ is a narrow zone including various microstructures; thus, the individual performance of different microstructures is inconvenient to study. In this work, various microstructures in HAZ, including coarse grained heat-affected zone (CGHAZ), fine grained heat-affected zone (FGHAZ) and intercritical heat-affected zone (ICHAZ), were simulated by heat treatment according to real HAZ microstructures of E690 steel. A comparative study of SCC behaviors of various HAZ microstructures in simulated SO₂-containing marine atmosphere was conducted by using U-bend specimen corrosion test under dry/wet cyclic condition. The results indicated that various HAZ microstructures have high susceptibility to SCC in this environment. The SCC susceptibility of CGHAZ and ICHAZ is very high with a high crack growth rate while that of FGHAZ and parent metal is relatively modest. SCC cracks were initiated after 5 d of cyclic corrosion test for U-bend specimen of various microstructures. The microcracks were initiated from the corrosion pits, which were induced by the galvanic corrosion between martensite-austenite (M-A) constituents and ferritic matrix.

TB9 titanium alloy has been widely used for aerospace due to it's superior low stiffness, corrosion resistance and workability. It has been reported that cold deformation can improve the comprehensive mechanical properties of titanium alloys. At the same time, the cold rotary-swaging deformation facilitates the production of small batches and the acquisition of special shape and size bars. However, current studies on the microstructure and properties of cold rotary-swaged titanium alloys are not systematic. So, the effects of cold deformation rate on the microstructure, texture evolution and mechanical property of TB9 alloy during cold rotary-swaging were investigated using OM, EBSD, XRD, TEM and tensile test. The results showed that the grain size of TB9 titanium was refined with the increase in diameter reduction. Meanwhile, with the deformation increases, the grains rotation along the swaging axis occurs, forming a preferred orientation, the textures change from initial {001}<110> and {001}<100> to α-fiber and γ-fiber {001}<110>, {112}<110> and {111}<110>. All of grains refinement, texture components and substructures contributed to the enhancement of strength after cold rotary-swaging. And the ductile kept on a high level after 70% cold working, which means the TB9 titanium has a great cold deformation ability.

In this work, the effect of pulsed magnetic treatment (PMT) on the microstructure of TC4 titanium alloy was investigated. TC4 titanium alloy is widely used in the manufacture of the blade of aviation engine. The microstructure of TC4 titanium alloy determines its property. PMT is a novel method used to modify the microstructures of alloys and has been explored in several papers recently. PMT has many advantages in the aspect of efficiency, energy-saving, non-deformation, etc. Therefore, the effect of PMT on the microstructures of TC4 titanium alloy was explored in this work. The variation of the dislocation density and the grain boundary angle of TC4 titanium alloy was observed after PMT. In the experiment, the magnetic induction density is 2 T, the pulse frequency is 5 Hz and the pulse number is 100. According to XRD tests, the dislocation density in TC4 alloy after PMT increased about 10.9%. KAM maps in EBSD test were used for evaluating the same area's dislocation density of the TC4 alloy before and after PMT. The dislocation distribution of TC4 titanium alloy changes notably: the in-grain dislocation density became more homogeneous and some local high-density areas disappeared, the distribution of dislocation near grain boundaries caused the angles of the grain boundaries altered and the fraction of low-angle grain boundaries decreased while the fraction of Σ11 grain boundaries (CSL grain boundary) increased. The motivation mechanism of the dislocation in TC4 titanium alloy under PMT was speculated based on the experimental results and some previous researches. The PMT may change the energy state of the electrons in pinning area of dislocations, which accelerates the electrons transformation from singlet state to triplet state and then increases the mobility of the vacancy or impurity atoms so that the dislocation de-pinning could occur under the original stress field and thus leads to dislocation movement and transformation of microstructure.

Pearlite is common microstructure in the carbon steel, which is widely applied in the railway steel and cold drawn steel where high wear resistance and strength are required. The pearlite colony is a circumscribed aggregate within which lamellae of cementite and ferrite phases have the same orientation. A cluster of wedge-shaped pearlite colonies will form the pearlite group nodules. The morphology of pearlite colonies will be influenced by the crystallography of pearlite. The common orientation relationship (OR) between pearlitic ferrite and pearlitic cementite is the Pitsch-Petch, Bagaryatsky, and Isaichev ORs. Combined with deep etching, SEM was used to investigate the morphology and crystallography of pearlite colonies and pearlite group nodules nucleated on the proeutectoid cementite in a Fe-1.29C-13.9Mn steel. The results showed that the initial morphology of the pearlite is irregular, but the pearlite possesses a parallel lamellar structure at the later stage of growth. Mutual ORs between phases of austenite, cementite, and ferrite in pearlite, proeutectoid grain boundary cementite, and Widmannstätten cementite were measured with the EBSD technique. Several reproducible ORs between cementite and ferrite lamellar have been observed, including the Pitsch-Petch, Bagaryatsky, and Isaichev ORs, without a particularly dominant OR. Since the two phases in the pearlite colonies have reproducible preferential OR, they are usually not independently nucleated, otherwise the independent nucleation of the cementite and ferrite inside the austenite has special crystallographic requirements for the mutual ORs between ferrite, cementite, and austenite. Thus, there will be a phase that nucleates first, which is called the "active nucleus". The active nucleus of pearlite has been carefully examined mainly according to the preferred OR between the pearlitic phases and existing phases. While the development of the pearlite crystallography is influenced by the active nucleus, no clear relationship was found between the ORs within the pearlite and active nucleus of the pearlite. The ORs between austenite and major pearlitic ferrite are near the K-S OR, but the ORs between austenite and the pearlitic cementite are various, depending on the preferred ORs between pearlitic ferrite and both austenite and pearlitic cementite. Widmannstätten cementite has never been seen to grow into pearlite. The measured data suggests that active nucleus of the pearlite colonies and pearlite group nodules nucleated on Widmannstätten cementite is ferrite. In some cases, grain boundary cementite was seen to grow as part of pearlite. Consequently, the grain boundary cementite is regarded as the active nucleus, though a preferred OR often coexists between pearlitic ferrite and either austenite or proeutectoid cementite. In other cases, the orientations of pearlitic cementite and grain-boundary cementite are discontinuous. For these cases, the ferrite is likely the active nucleus of pearlite. The orientation of pearlitic ferrite was seen to alter with the growth of pearlite, even causing the split of a single ferrite layer into two grain layers with a considerable misorientation. Significant distortion varying with the layers of pearlite was noticed in austenite near the pearlite growth front, indicating an evident strain field caused by the pearlite transformation. This requests a further investigation.

Duplex stainless steels (DSSs) are widely used for chemical industry, marine construction and power plants, due to the beneficial combination of ferrite and austenite properties: high strength with a desirable toughness and good corrosion resistance. The sympathetic nucleation (SN) of intragranular austenite precipitates has been frequently observed in DSS. This type of nucleation, which occurs in a considerable variety of steels and titanium alloys, has a great effect on the morphological arrangement of precipitates and hence the mechanical properties of metallic materials. Therefore, understanding the SN mechanism of austenite precipitates is essential to knowledge based material design of the microstructure in DSS. Three types of morphological arrangement, i.e., face-to-face, edge-to-edge and edge-to-face SN of austenite precipitates, have been identified in previous investigations on DSS. The adjacent grains of face-to-face and edge-to-edge sympathetically nucleated austenite have approximately the identical orientations, with a small-angle boundary between two austenite crystals. However, as regards to the edge-to-face SN, the lacking of crystallographic features of adjacent austenite precipitates obstructs the understanding of the mechanism for the edge-to-face SN. Moreover, it is usually difficult to distinguish between SN and hard impingement following nucleation at separate sites in conventional experimental observations. Thus, in the present work, the typical morphology of edge-to-face SN of austenite precipitates was directly observed at 725 ℃ in a DSS using in situ TEM. The orientation relationship (OR) between the sympathetically nucleated austenite precipitate and ferrite matrix is determined through analysis of Kikuchi lines. Since the long axes of austenite precipitates parallel to the invariant line are restricted in the thin TEM foil, there are only four types of austenite with different near N-W ORs and cystallographically inequivalent long axes. This work reveals that the ORs of sympathetically nucleated austenite grains belong to different Bain groups with those of the pre-formed austenites. The explanation for the OR selection is provided based on two factors favoring SN, namely the reduction of elastic interaction strain energy and the interfacial energy. The local stress generated by the semi-coherent pre-formed austenite was calculated by Eshelby inclusion method. The local stress field accompanying with the pre-formed austenite assists the subsequent nucleation and growth of sympathetically nucleated austenite. It shows that the elastic interaction energy for the sympathetically nucleated austenite of particular OR is negative. In addition, the pre-formed austenite and the sympathetically nucleated austenite grain are twin related. This indicates that the nucleation barrier associated with SN of austenite with selected OR is comparably lower than other candidates. Hence, the austenite precipitate with a specific OR is preferred during SN.

Refractory metal tungsten has wide applications in many fields such as aerospace, national defense, military and nuclear industry due to its excellent comprehensive mechanical properties. As the demand for high-performance materials in the new era is increasing, existing materials cannot meet the performance requirements under extreme conditions. The high pressure torsion (HPT) process can produce severe shear deformation and densify the material effectively, leading to ultrafine-grain structure with non-equilibrium grain boundaries and having a significant effect on improving the overall performance of pure tungsten materials. HPT process is used to prepare an ultrafine-grain material with excellent comprehensive performance, which can broaden the application field of refractory metal tungsten and promote the engineering application of high-performance materials. The HPT experiment was carried out on commercial pure tungsten at a relatively low temperature, and the microstructure evolution during HPT processing at various turning numbers has been investigated by means of EBSD, TEM and HRTEM. It was found that with the strain increasing, the grains were refined significantly, dislocation density and the ratio of non-equilibrium grain boundary increased obviously. Moreover, it was transparent that the low angle grain boundary transform into high angle grain boundary during HPT processing. At the same time, the dislocation structure moved to grain boundary gradually so that there was no obvious defect in fined grains. When the equivalent strain increased to 5.5, the deformation mode of grains transformed from intracrystalline sliding to grain boundary sliding, because the size of some grains was close to the mean free path of dislocation.

Aluminum and aluminum alloy are widely used in every field of modern life. It is especially important to understand the detailed mechanisms of aluminum atmospheric corrosion. Traditional studies only consider the role of oxygen reduction and focus on anions such as Cl^－, SO₄^2－ in the environment, ignoring the effects of cations such as Na⁺ on the atmospheric corrosion. However, recent studies have shown that the effect of Na element on the corrosion of aluminum can not be ignored. In this work, single-shot laser-induced breakdown spectroscopy (LIBS) was used to measure the aluminum atomic lines after corrosion for 35 d in the atmospheric environment, and combined with a three-dimensional tomography measurement, to study the depth profiling of Na on the aluminum surface. The results show that the Na element on the surface of the aluminum originates from the atmospheric environment, and Na is involved in the formation of corrosion product NaAlCO₃(OH)₂. The content of NaAlCO₃(OH)₂ decreases as the depth increases following an exponential power function. The content decrease of NaAlCO₃(OH)₂ in different depths can be transformed into the change of cathode area. Combined with the measured polarization curve of aluminum, the atmospheric corrosion model of aluminum including the presence of oxygen reduction and the change of cathode area was established using COMSOL software. The calculated corrosion depth is 6.155 μm, which is consistent with the depth of Na element measured by LIBS experiments. By studying the distribution of Na cations and corrosion products, a simulation model was established to reveal the influence on corrosion mechanism, which is of great significance for the study of early atmospheric corrosion of aluminum.

Fe-WC/metal double layer coatings containing Fe-C-Si super hard alloy (SHA) particles and tungsten carbide (WC) particles were fabricated on Al7075 substrates by resistance seam welding method to improve the wear resistance of aluminum alloys. The micro-structure and phase compositions of the Fe-WC/metal double layer coatings with different WC particle sizes (fine and coarse) were investigated by SEM and EPMA. Nano-hardness of different phases in the coatings were investigated by nano-indentation test. Finally, the friction behavior of the two kinds of Fe-WC /metal double layer coatings were contrasted by ball-on-disc test using WC and SUS 304 balls. The results show that the thicknesses of Fe-WC composite/metal double layer coatings were about 600 μm. The microstructure of the coatings was: WC/Fe composite (wear resistance layer)+Fe/Al composite (metal interlayer)+Al7075 substrate. When WC ball was used as the static counterpart, the wear mechanism of the coatings with fine and coarse WC particles were severe abrasive wear and brittle fracture with little abrasive wear, respectively. When SUS304 was used as the static counterpart, the coating with fine WC powder was demonstrated difficulty to be abraded due to the protection of the iron oxide adhesive layer, and the other proved a little brittle fracture. Moreover, the wear rate of both coatings using SUS304 ball was lower than that of WC ball in the ball-on-disc test.

GH3625 alloy is a wrought nickel-based superalloy mainly used in aeronautical, aerospace, chemical, nuclear, petrochemical and marine applications industry due to its good combination of mechanical properties and corrosion resistance on prolonged high-temperature exposure to aggressive environments. However, the cold deformation microstructure directly determines the microstructure of the alloy pipe, thereby affecting the performance of the alloy pipe. In this work, the microstructure evolution, grain boundary characteristics distribution, dislocation density, stress distribution and texture evolution of the hot-extruded GH3625 superalloy during cold deformation were investigated by EBSD technique. The results show that the degree of grain deformation increases and the grain morphology changes from flat to thin strip, with the increase of cold deformation. The rotation of the crystal makes the grain boundary perpendicular to the loading pressure axis. With the increase of cold deformation, the high angle grain boundaries (HAGBs) gradually changes to the low angle grain boundaries (LAGBs), and the proportion of twin grain boundary increases gradually. The average of local misorientation ({\bar{\theta }}_{\mathrm{L}}) increases with the increase of cold deformation, which can reflect the increase of dislocation density. With the increase of cold deformation, the uniformity of grain deformation gradually becomes better, and the stress concentration distribution gradually changes to the stress uniform distribution. With the cold deformation increases, the type of deformation texture remains basically unchanged, while the strength of the Copper texture {112}<111> with stable orientation is slightly reduced. Meanwhile, the Rotated-cube texture {001}<110> generated by inhomogeneous plastic deformation is reduced in strength. In addition, the formation of deformation twin results in a decrease in the strength of the Goss texture {110}<001> and the Brass-R texture {111}<112>.