Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： Hot rolled plate of a new low alloy steel Cu-Sb-Mo was prepared and then its corrosion performance was evaluated in solutions of sulfuric acid and hydrochloric acid respectively by means of weight loss tests and electrochemical measurements in comparison with two commercial steels 304 stainless steel and Q235B steel. Then the corroded steel was examined by EIS, SEM and XRD. The results indicate that the formed scale consisted of oxides and sulfides of the alloying elements (Cu, Sb and Mo) can inhibit both the anodic dissolution and cathodic hydrogen evolution reaction of the steel, decrease the corrosion current density and raise the charge transfer resistance of the steel, thereby the steel may be protected from further corrosion.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： The irradiation behavior of a China low activation martensitic (CLAM) steel was investigated by advanced transmission electron microscopy combined with nano- indentation measurement. The CLAM steel was irradiated by single-(D+), single-(He+) and sequential-(D+ plus He+ subsequently) ions respectively at room temperature. The nano- indentation hardness results show that all of the irradiated specimens exhibited obvious hardening. The irradiation hardening rate was obtained for each specimens by fitting the experimental data using the modified NGK model, in which D+ implanted samples had the lowest radiation hardening level while the one for He+ injection and D+ + He+ implanted samples were significant. The microstructure analysis indicates that the defect density gradually increased first and then decreased along the implantation depth direction. High-density irradiation induced defects were present at the vicinity of the implantation peak depth. Homogeneously distributed fine bubbles were observed in both single-(He+) and sequential-(D+ plus He+ subsequently) irradiated samples with the bubble appearance at shallower depth for the latter ones because of the synergistic effect. No bubbles were found in single-(D+ ) irradiated samples. The hardening rate of He+ implanted samples, in which both dislocation loops and helium bubbles occurred, is greater than D+ implanted samples. In D++He+ irradiated samples, certain defects occurred by D+ will recover when the samples are being irradiated by He+. Therefore, the hardening rate of D++He+ irradiated samples is not equivalent to the rate of D+ irradiated samples plus He+ irradiated samples. Irradiation hardening results from the synergistic reaction.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： Five ferrite/bainite (F/B) multi-phase steels with different volume fractions of bainite were obtained by TMCP process. The strain hardening behavior of high deformability pipeline steel with F/B multi-phase was studied by the analysis of longitudinal mechanical properties and modified C-J analysis. The relationships between volume fraction of bainite and stress ratio as well as yield ratio were analyzed, and relevant mechanisms were illustrated by modified C-J analysis. The results show that the stage of elastic deformation of high deformability pipeline steel mainly corresponds to stage I in modified C-J analysis, and the stage of plastic deformation consists of stage II and stage III; and the stage near yield point (0.5% strain) can go across stage I and stage II. However, the strain hardening capability of each stage is obviously different from each other, and the strain hardening behavior is closely related to the volume fraction of bainite in F/B multi-phase steel. The optimal matching between strength and plasticity of pipeline steel can be achieved by controlling the microstructure suitably. The stress ratio of Rt1.5/Rt0.5 is appropriate to describe the strain hardening capability near the yield point, and the stress ratios of Rt2/Rt1 and Rt5/Rt1 are appropriate to represent the strain hardening capability of plastic deformation stage in X70 grade pipeline steel. The stress ratio of Rt2/Rt1 is suitable to characterize the strain hardening capability of plastic deformation stage in X80 grade pipeline steel.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Microelement Hf added in Ni-based powder metallurgy (PM) superalloy can modify microstructure and improve mechanical properties, such as stress-rupture life, creep resistance and crack growth resistance, and also benefit to eliminate notch sensitivity. So systematically studying the effect of microelement Hf on PM superalloy microctructure will help to comprehend its corresponding mechanism. The effects of microelement Hf on the morphologies, chemical compositions and content of g' phase and MC carbide in FGH97 PM Superalloy were investigated by means of SEM and physiochemical phase analysis. The results showed that Hf facilitated the precipitations of g' phase and MC carbide, and changed chemical compositions of g' phase and MC carbide, the effect of Hf on the size and morphology of MC carbide was not obvious, while Hf greatly affected the size and morphology of g' phase and accelerated the splitting of g' phase from one instable cubic g' particle to stable octet of cubes. As Hf affected the lattice misfit of g'/g phase (d), modifying Hf content changed the critical splitting size of g' phase (Dc). The relationship between Dc and Hf content (w(Hf)) was found to be Dc=315.4+640.2w(Hf)-358.2[w(Hf)]2. With Hf content increased, the absolute value of d decreased and Dc increased. Cubic g' particle split into an octet of cubes when g' phase grew up to the critical splitting size.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： In order to obtain the optimal corrosion resistance, the characteristics of microstructure and alloy elements distribution of S32760 duplex stainless steel were studied after solid solution treatment at various temperatures from 1000 ℃ to 1300 ℃ by means of OM, EPMA, SEM, EDS and TEM. In addition, the pitting corrosion resistance was measured by the electrochemical workstation. The results show that the N atoms diffused into d phase from g phase during solution treatment when the temperature was higher than 1080 ℃. N atoms migrated back into g phase when the subsequent cooling was slow enough. However, Cr2N phase in situ precipitated during quenching because there was not enough time for the N atoms to diffuse back into g phase. Cr2N particles increased with the solution temperature increasing. Furthermore, s phase precipitated when the tested sheet was heat treated at or below 1040 ℃ due to the high content of N. Thus it is obvious that the solution temperature range of the S32750 duplex stainless steel is quite narrow, which is between 1040 ℃ and 1080 ℃, and it is confirmed that the optimal temperature is 1060 ℃. After treated at 1060 ℃ for 60 min, the Brinell hardness of S32760 steel is 249 HBW, pitting potential is up to 1068 mV and the passive current density is as low as 1.48×10-4 A/cm2.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： To find out the reason of poor secondary recrystallization behavior in thin-gauged grain-oriented steel, EBSD technique is applied to reveal the grain growth behavior of thin-gauged steel processed by HiB steel method under high cold-rolling reduction. Nitriding treatment with different times is conducted to ensure the occurrence of secondary recrystallization in thin-gauged grain-oriented steel and to determine the effect of nitrogen content. Attention is put on the influence of {114}<418> texture on the abnormal growth of Brass and Goss grains. Results show that, at initial stage of secondary recrystallization, {114}<418> grains in the surface region of sheets possess obvious growth advantage than the other oriented grains. If these grains in the surface region grew to the central layer of sheet and swallowed the nucleus of secondary recrystallization, abnormal growth could not occur. In contrast, reinforcing the inhibitors at surface region of sheet by nitriding treatment will avoid the excessive growth of surface grains and therefore improve magnetic properties of steel significantly. The {114}<418> grains are adverse to the abnormal growth of Brass-oriented and scattered Goss grains in way of island grains, but their effect on the abnormal growth of Goss grains is weaker.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Carburization in Ni-Cr-Fe-based alloys is an important phenomenon, especially in ethylene cracking tubes which serve at high temperatures under highly carburizing environment. In this work, the Cr35Ni45Nb tube subjected to service condition for 6 a was carburized by low-pressure vacuum carburizing (LPVC) at 1080 ℃. The carburization behaviors and corresponding mechanisms of phase evolution in the inner wall were comprehensively analyzed through SEM, XRD and EPMA. The results showed that oxidation behaviors of the tube at high temperature were consisted of external oxidation of Cr and internal oxidation of Si, resulting in formation of composite oxide scales. Depletion of Cr in the subsurface caused by surface Cr2O3 leaded to carbide dissolution and formation of carbide free zone and carburized zone. The critical concentration of Cr for carbide dissolution is about 19.0% (mass fraction). By comparing carburization behaviors of specimens whose oxide scales were retained or removed, the carburization resistance of the composite oxide scales in carburizing environment was systematically investigated. The results showed that the composite oxide scales formed previously acted as an effective barrier to carbon infiltration. However, the outermost Cr2O3 scale tended to be carbonized to form carbide scale to spall from the surface in the strongly reducing environment with low oxygen partial pressure, while the SiO2 kept stable all along due to its excellent thermodynamic stability. However, a certain amount of carbon was still capable to penetrate the alloy interior through gaps of the SiO2 scale due to its discontinuity. Therefore, continuity, density and high-temperature stability of the oxide scales were crucial for the alloy to achieve excellent anti-carburizing performance. Once the oxide layers were removed or carbonized adequately, inconceivable internal carburization occured widely. Large amounts of secondary carbides precipitated again in the previous carbide free zone due to high carbon activity. Widespread precipitations of graphite called metal dusting in the range of about 0.5 mm in depth occurred after long exposure of specimens to the carburizing environment. The carbon activity gradually decreased with increasing distance from the surface. The primary carbides within the deeper carburized region were transformed from M23C6 to M7C3 in situ, which were accompanied by precipitation of vermicular g phase in the primary carbides, phase transition from h to NbC and decomposition of intragranular secondary carbides. Severe coalescing and coarsening of carbides and metal dusting caused the serious degradation of microstructure, formation of macrocracks and final thinning of the Cr35Ni45Nb tube wall.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Based on the forced convection mixing (FCM) principle, a self-developed FCM semisolid slurry preparation device was successfully developed. Taking AZ91D magnesium alloy tensile parts for example, the rheodiecasting process that consists of slurry preparation, transportation and forming was achieved by combining with a diecasting machine. Microstructural characteristics of FCM rheo- diecasting parts in different processing parameters were investigated. Mechanical properties of AZ91D alloy parts in different processes were compared. Besides, the formation mechanism and solidification behavior of semisolid slurry were analyzed in FCM rheo- diecasting process. The results show that processing parameters have a great effect on the microstructures of parts, increasing rotation speed or decreasing barrel temperature appropriately is beneficial to optimizing the microstructure. The process not only can produce parts with fine, spherical and uniformly distributed primary a-Mg particles, but also is able to improve mechanical performance of parts significantly. Compared with traditional diecasting, the yield strength remains unchanged, but the ultimate strength and elongation are increased by 12.5% and 80.0%, respectively. Furthermore, compared with parts subjected to T4 and T6 heat treatment, the ultimate strength of the as-cast is the lowest, and the yield strength and elongation are between T4 and T6.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The Cu/Al dissimilar metal joint is a compound structure that can efficiently decrease manufacturing costs, reduce product weight, and integrate the advantages of both metals. For the excellent comprehensive properties, the Cu/Al dissimilar metal joint has broad application prospects in air conditioners, refrigerators, cables, electronic components, solar collectors, et al. Brazing is considered as a promising method to join the Cu/Al dissimilar metal for lower residual stress, lower costs, higher precision and better adaption to the structure of joint. Meanwhile, the Zn-Al filler metal is considered as the relatively ideal filler metal d ue to better property of the Cu/Zn-Al/Al joint. However, the influence of the composition of the Zn-Al filler metal on the interfacial structure near Cu substrate and property of the Cu/Al joint has not been investigated. In this work, the Cu/Al joints were brazed by Zn-15Al, Zn-22Al, Zn-28Al, Zn-37Al and Zn-45Al filler metals, respectively. The influences of the composition of Zn-Al filler metals on the interfacial structure near Cu substrate of the Cu/Al joints were investigated, and the relationships of the composition of the Zn-Al filler metals, the interfacial structure and the shear strength of the Cu/Al joints were described systematically. It was found that the interfacial structure of the Cu/Zn-15Al/Al brazed joint was Cu/Al4.2Cu3.2Zn0.7. For thinner Al4.2Cu3.2Zn0.7 layer (2~3 μm), the shear strength of the joint was higher (66.3 MPa). With the increase of Al content of the filler metal, the thickness of Al4.2Cu3.2Zn0.7 layer at the interface was increased for Cu/Zn-22Al/Al joint, even some CuAl2 phase can be found nearby the Al4.2Cu3.2Zn0.7 layer of Cu/Zn-28Al/Al joint, and the shear strength of the Cu/Al joints were decreased correspondingly. When the Cu/Al joint was brazed by the Zn-37Al filler metal, the interfacial structure near Cu substrate was transformed into Cu/Al4.2Cu3.2Zn0.7/CuAl2. For higher brittleness of CuAl2 layer, the shear strength of the joint was decreased obviously (34.5 MPa). Finally, the interfacial structure of the Cu/Zn-45Al/Al joint was transformed into Cu/CuAl2, the interfacial structure lead to the lower shear strength of the joint, which is only 31.6 MPa.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Different numbers of columnar grains in a Fe-3%Si electrical steel slabs with their major axes being parallel to the rolling direction were used for cold rolling and recrystallization annealing. The evolution of the texture of columnar grains was followed by EBSD technique. The results show that, in the case of single columnar grain with cube orientation, cube texture is adverse to be retained in condition of primary cold rolling with high reduction and recrystallization annealing, while strong cube texture can form after secondary cold rolling with low reduction and recrystallization annealing. But the cube texture hinders strongly the abnormal growth of Goss grains. For the sample containing two columnar grains with Goss and cube orientation, the initial Goss orientation rotates to {111}<112> orientation quickly and cube texture is retained effectively during cold rolling by high reduction. The interaction between the Goss and cube columnar grains is not strong. For the multi-columnar grains with different orientations, the grain boundaries between columnar grains promote g- texture and weaken the cube texture, which is in favor of abnormal growth of Goss grains.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Based on our earlier preliminary work, a model was developed for prediction of the critical grain size where the plasticity would be decreased as the grain refined. In the model the effect of grain size on the fracture strength was combined. The prediction of the model exhibited that in the range of grain size of 10 mm to 0.2 mm as an example, the total elongation of the steels would be firstly increased. But when the grain size was refined to 2.5 mm and below, the total elongation of the steels was not increased but decreased sharply, which was good agreement with the experimental results published recently. Present work illustrated that the dominant mechanism of the elongation decreased in the ultra-fine grain size materials is due to increase in resistance force of grain boundaries on the dislocation sources resulting in the difficulty of activation of dislocation movements. Its expression would be the decrease of the plastic strain in macro-level.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Hafnium (Hf) is one of the most important microelements in powder metallurgy (P/M) superalloy. Hf modifies the microstructure and drastically improves mechanical properties in P/M superalloy. The effect of Hf in a nickel-based P/M superalloy was systematically studied by means of FEG-SEM, TEM, AES, EDS and physical and chemical phase analysis. Hf mainly distributes at interdendritic region of the solidification powder in form of solid solution, which is helpful to reduce prior particle boundary (PPB). Hf facilitates morphology of γ′ phase to be unstable and enhances the large cubic γ′ phase to split into smaller ones, so the γ′ phase turns into a stable state with a lower energy faster. Hf is mainly distributed in γ′ phase and MC carbides, which changes the distribution of element between the γ′ phase, MC and g solid solution, which is beneficial to eliminate notch sensitivity and improves overall mechanical properties of the alloy.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Low carbon and low alloy steels require good combination of strength and ductility to ensure safety and stability of structures. Heat treatment in intercritical area can not only produce multi-phase microstructure, but also lead to the redistribution of alloying elements in different phases. Multi-step intercritical heat treatment is favorable to obtain retained austenite that is stabilized by repeated enrichment of alloying elements in reversed austenite and nanometer-sized precipitate that are primarily formed during tempering. Excellent mechanical properties are contributed by transformation-induced-plasticity effect of retained austenite and precipitation hardening effect of nanometer-size precipitates. In this work, the microstructural evolution and relative mechanical properties were investigated in a low carbon low alloy steel processed by a three-step heat treatment, namely, intercritical annealing, intercritical tempering and tempering. The microstructure was a typical dual-phase microstructure consisting of intercritical ferrite and bainite/martensite after intercritical annealing, and primarily comprised of intercritical ferrite, tempered bainite/martensite and retained austenite after intercritical tempering. Retained austenite with volume fraction of 29% distributed at the ferrite/bainite (martensite) boundaries and betweent bainitic/martensitic laths. Retained austenite was stabilized by enrichment of C, Mn, Ni and Cu in reversed austenite during the reversion transformation process. NbC precipitates with average size of 10 nm was formed in ferrite matrix and bainite/martensite, while Cu-containing particles in size range of 10~30 nm precipitated in ferrite and retained austenite during intercritical tempering and tempering process. The morphology of NbC precipitates was spherical, elliptical and irregular, and copper precipitates were spherical. With the combination of transformation- induced- plasticity (TRIP) effect of retained austenite and precipitation hardening, the steel possessed outstanding mechanical properties: yield strength > 700 MPa, tensile strength > 900 MPa, uniform elongation > 20%, and total elongation > 30%.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The elimination of the segregation improves the thermo plasticity of superalloy ingot during the homogenization process, but coarser grain structure and high-temperature oxidation caused in further homogenization have an adverse impact on the thermo plasticity. The inheritance of coarse grain structure in the followed hot working process increases the tendency of cogging crack and makes the grain refining harder, leading to a lower yield of the final workpiece. The microstructure characteristics and their hot deformation behaviors of GH4740H, GH4738, GH3625 and 690 alloys under different homogenizations were investigated by means of microstructure analysis methods and crack propagation testing. The experimental results show that the reasonable homogenization processing needs to take into account the segregation elimination arising thermo plasticity addition, more to consider grain coarsing and severe oxidation leading to decrease plasticity. Based on the residue dendrites can provide more recrystalazation nucleation sites, the partial homogenization possessing probably exists rationality. This research work provides an exploratory study for the improvement of the homogenization-cogging process of superalloy.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Effect of cyclic heat treatment on microstructure and mechanical properties of a Ti-V microalloyed steel was investigated. Therefore, the metallographic microstructure of the steels after heat treatment for each cycle was succesively examined and the relevant grain size was statistically determined; the cyclically heat-treated steels were also examined by means of SEM and TEM in order to reveal the microstructural evolution and the variations of average size and composition of precipitates in the steels with the increasing cycle number; while their tensile strength and toughness were measured. The results show that with the increasing cycle number, the average grain size of the steels decreases continuously. For mechanical properties, Rm has the same regularity due to the increase of mean size of the complex carbide with cycle numbers, while the AKU initially increases and thereafter decreases as a result of the joint influence of the average grain size and the proportion of proeutectoid ferrite.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Effect of annealing treatment in a temperature range of 850-1050℃ on the evolution of microstructure involved with austenite, ferrite and carbides etc., as well as the mechanical properties and fracture behavior was studied for a cold rolled Fe-Mn-Al-C low density steel. The results show that the experimental steel annealed at 850℃ exhibits a complex microstructure consisted of austenite, banded dferrite, a-ferrite and small amount of carbides; there also existed intercrystalline network of ferrite and carbides which resulted in higher strength and poor plasticity, thus the steel becomes susceptible to cleavage fracture; the steel annealed at 900-1050℃ consisted of recrystallized austenite as matrix, in which the volume fraction of a- ferrite decreased with the increasing temperature, while the band like d- ferrite was crushed into islets and distributed in the matrix discontinuously; as the growth of d-ferrite was more obvious than that of austenite, larger volume fraction of ferrite did occur, which resulted in high intensity of X-ray diffraction peaks of ferrite; the microstructure evolution during annealing lead to decrease of tensile strength and increase of total elongation with the increasing temperature; the experimental steel annealed at 1000℃ exhibits excellent combination of strength and ductility: i.e. tensile strength 1003.1 MPa, total elongation 41.28% and product of strength with ductility 41.4 GPa·%. Therefore, to acquire the optimal combination of strength and ductility, the cold-rolled Fe-Mn-Al-C steel should be annealed at temperatures above 950℃ . Furthermore, the measured density of 6.55 g·cm- 3 ensures this kind of ultra- high strength steel a remarkable weight reduction effect of 16.6%.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：通过腐蚀磨损试验研究了下贝氏体球墨铸铁材料的腐蚀磨粒磨损行为，分析了影响腐蚀磨损失重率的主要因素。采用SEM和TEM对磨损表面特性进行了分析；根据磨损表层纵剖面的显微硬度研究了材料表层在腐蚀磨损过程中的形变硬化效应；结合下贝氏体球墨铸铁的电化学行为研究了载荷对耐腐蚀性能的影响。结果表明：下贝氏体球墨铸铁的腐蚀磨损机理为化学腐蚀失重和犁沟式磨粒磨损。载荷的提高对表面粗糙度、材料表面与磨粒之间的摩擦力以及磨粒压入材料表面的深度有显著的影响，从而导致磨粒磨损失重率显著上升；并且，较高的载荷作用下，材料表面出现分层组织和条带状石墨，形成局部微型原电池，促使腐蚀速率提高，同时分层组织的疲劳断裂也将促使失重率进一步提升；不过，载荷的增加使得基体中残留奥氏体内部出现大量位错的缠结，促进材料表面硬化，这在一定程度上提高了材料的耐磨性能。当载荷从10 N增至200 N时，腐蚀磨损失重率从0.16 g/(cm2?h)增至0.42 g/(cm2?h）；当粗糙度Ra值由0.12 μm增大到5.2 μm时，腐蚀电流从0.56 mA上升至5.62 mA。另外，下贝氏体球墨铸铁的腐蚀磨损失重曲线可分为三个阶段，分别为磨损初期的点接触加速磨损阶段、磨损中期的面接触稳定磨损阶段、磨损后期的疲劳磨损失稳阶段。
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