Effects of Solution Annealing Temperature on the Galvanic Corrosion Behavior of the Super Duplex Stainless Steels

This study investigated the active dissolution of super duplex stainless steel (SDSS) at various solution annealing temperatures. The active dissolutions of the α-phase and γ-phase were compared, and the effects of the surface area ratio on the active dissolutions of both phases were investigated. There were two peaks in the active-passive transition region in the potentiodynamic test in the modified green-death solution. The two peaks changed as the solution annealing temperature was increased from 1050 to 1150 °C. The solution annealing temperature difference affected the critical anodic current densities. This provides useful information for determining the appropriate solution annealing temperature in the modified green-death solution for SDSS.     

氧化时间对微弧氧化膜电接触微动磨损行为的影响

目的研究不同氧化时间的铝合金表面微弧氧化涂层在电接触条件下的微动磨损行为,并探讨其磨损机理。方法通过控制氧化时间(10、20、30、40、50、60、70 min),在铝合金表面制备不同表面状态的微弧氧化涂层,并利用四线接触法研究其在电接触条件下接触电阻的变化,通过分析摩擦系数、F-D曲线、磨损形貌、三维轮廓及磨痕化学成分来揭示其微动磨损机理。结果电接触微动磨损下,氧化不同时间形成的微弧氧化涂层在相同电接触微动磨损条件下的耐磨性存在明显差异,进而影响其电接触行为。氧化10 min时,涂层磨损最严重,磨损区域的涂层迅速失效,从而导致铝合金基体外露,接触电阻骤降至零;氧化50 min时,涂层厚度最大,具有良好的耐磨性,缓减了接触电阻的衰减,接触电阻曲线在衰减过程中受到磨斑表面裂纹的影响而产生波动。结论氧化时间会影响微弧氧化膜表面形貌、粗糙度以及厚度,对其在电接触条件下的微动磨损行为影响较大。     

Grain-Size Effects on the High-Temperature Oxidation Behaviour of Chromium Steels

Oxidation of two low-Cr (Cr content 1.5 wt% and 2.25 wt%) and three high-Cr (Cr content 9 wt%, 12 wt% and 18 wt%) boiler steels was investigated at temperatures between 550 °C and 830 °C in laboratory air. Thermogravimetry (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were applied for evaluation of the oxidation kinetics, oxides phase identification and scale structure analysis. Particular attention was paid to the phenomenon of inward oxidation and its relationship with the Cr content of the steels under investigation. The results showed that the inward oxidation of the Cr steels is governed by grain boundary diffusion. Two different Cr-depending tendencies concerning the effect of alloy grain size on the inward oxidation were observed. For low-Cr steels (less than 2.25 wt% Cr), an increase in the grain size improved the oxidation resistance, while steels with high Cr content (18 wt% Cr) can form a thin and protective chromia scale on the surface more easily at finer grain size. In the latter case an increase in grain size deteriorates the oxidation resistance by the formation of a thicker scale composed of both an outer and an inner Fe-oxide-based layer.     

Oxidation After Breakdown of the Chromium-Rich Scale on Stainless Steels at High Temperature: Internal Oxidation

Breakaway oxidation of alloy 304L at 600 °C was studied in four environments (O₂ + H₂O + KCl, O₂ + H₂O + SO₂ + KCl, H₂ + H₂O + Ar, O₂ + K₂CO₃) for up to 168 h. The resulting scales were investigated by FIB/SEM, SEM/EDX, STEM/EELS, STEM/EDS and oxidation was elucidated by thermodynamic calculations (Thermo-Calc). The initial thin protective scale broke down in all cases. After breakaway, the scale consisted of two layers, i.e. an inward growing spinel/reaction zone and an outward growing iron-rich layer. The general features and microstructure of the scales after breakaway were similar in all environments and were explained in terms of: (1) Different diffusivities of Cr³⁺ and Fe²⁺ in the spinel oxide. (2) The appearance of a miscibility gap in the FeCr and FeCrNi spinel oxides. (3) The equilibrium composition of the spinel (at low pO₂ Ni is not present in the spinel).     

High Temperature Oxidation of Hot-Dip Aluminized T92 Steels

The T92 steel plate was hot-dip aluminized, and oxidized in order to characterize the high-temperature oxidation behavior of hot-dip aluminized T92 steel. The coating consisted of Al-rich topcoat with scattered Al₃Fe grains, Al₃Fe-rich upper alloy layer with scattered (Al, Al₅Fe₂, AlFe)-grains, and Al₅Fe₂–rich lower alloy layer with scattered (Al₅Fe₂, AlFe)-grains. Oxidation at 800 °C for 20 h formed (α-Al₂O₃ scale)/(AlFe layer)/(AlFe₃ layer)/(α-Fe(Al) layer), while oxidation at 900 °C for 20 h formed (α-Al₂O₃ scale plus some Fe₂O₃)/(AlFe layer)/(AlFe₃ layer)/(α-Fe(Al) layer) from the surface. During oxidation, outward migration of all substrate elements, inward diffusion of oxygen, and back and forth diffusion of Al occurred according to concentration gradients. Also, diffusion transformed and broadened AlFe and AlFe₃ layers dissolved with some oxygen and substrate alloying elements. Hot-dip aluminizing improved the high-temperature oxidation resistance of T92 steel through preferential oxidation of Al at the surface.     

CoCrNiAlY涂层制备工艺对组织形态及高温氧化行为的影响

为了研究CoCrNiAlY涂层微观组织结构对高温氧化行为和剥落行为的影响规律,采用激光熔覆技术和等离子喷涂工艺在718高温合金表面制备CoCrNiAlY涂层,观察其微观组织形态。利用XRD和SEM对1150 ℃高温氧化试验样品进行氧化层物相分析和形貌观察。结果表明,激光熔覆制备的CoCrNiAlY涂层中形成了胞状亚结构的等轴晶凝固组织,相对于等离子喷涂制备的CoCrNiAlY涂层结构更致密,具有更优异的抗高温氧化性能。在高温氧化过程中,等离子喷涂CoCrNiAlY涂层生成了以Cr₂O₃结构为主的复合氧化膜。激光熔覆CoCrNiAlY涂层生成Al₂O₃结构的单一氧化膜,而且熔覆层中原位形成的Y₂O₃钉扎作用能有效提高氧化膜的抗剥落性。文中系统分析讨论了两种不同工艺制备的组织形态对高温氧化膜形成机制的影响,激光熔覆涂层在高温下主要是以界面扩散方式形成致密的Al₂O₃膜,等离子喷涂涂层在高温下以界面反应的方式快速形成Cr₂O₃复合氧化膜。     

结合相对SiC基复相材料高温氧化行为的影响

利用X-射线衍射仪、扫描电镜和热重分析仪等手段,在1100～1500℃研究了Sialon结合SiC复相材料的高温抗氧化行为。结果表明:随氧化温度升高,由于氧化致密层的形成,试样氧化增重速率降低,出现氧化钝化现象;Sialon结合SiC复相材料高温抗氧化性能优于Si3N4结合SiC复相材料;高温氧化使得SiC质复相材料常温抗压强度比氧化前提高;随氧化温度升高,Sialon结合SiC复相材料的氧化膜表面形成较多气泡和开口空洞,使耐压强度呈下降趋势;Si3N4结合SiC复相材料随氧化温度升高,耐压强度降低,这是由于冷却过程方石英化伴生的网状裂纹密度增大。     

Role of the Austenite-Ferrite Transformation Start Temperature on the High-Temperature Ductility of Electrical Steels

The austenite to ferrite transformation start temperature was measured in two low-C, Si-Al grain non-oriented electrical steels using in situ x-ray diffraction and the direct comparison method with the (111)^γ and (110)^α diffracted intensities. It was shown that increasing Al content from 0.2 to 0.6 wt.% in a 0.06 wt.% C, 0.6 wt.% Si and 0.5 wt.% Mn steel increases the Ae₃ temperature from 928 to 955 °C. The results are supported by microstructural observations of isothermally transformed samples and used to discuss the loss of ductility during high temperature deformation (e.g. hot rolling) of this type of materials.     

Effect of Intergranular Precipitation on the Internal Oxidation Behavior of Cr–Mn–N Austenitic Stainless Steels

The effect of intergranular precipitation on the internal oxidation behavior of Cr–Mn–N austenitic steels at 1000 °C in dry air atmosphere was investigated using scanning electron microscope, transmission electron microscope, and X-ray diffraction analysis. The results show that intergranular M23C6 carbide morphologies play an important role on the internal oxidation behavior of Cr–Mn–N steels. During the period of the oxidation, both discontinuous chain-shaped and continuous film-shaped intergranular M23C6 carbides precipitated along the grain boundaries. Internal oxides of silica preferentially intruded into the matrix along grain boundaries with discontinuous M23C6 carbide particles, while silica was obviously restricted at the interfaces between the external scale and matrix on the occasion of continuous film-shaped M23C6 carbides. It is seemed that reasonable microstructure could improve the oxidation resistance of Cr–Mn–N steels.     

晶粒细化对Cr-25Nb合金高温氧化行为的影响

采用电弧熔铸和机械合金化+热压烧结技术制备晶粒尺寸相差较大的Cr-25Nb合金,研究其在950及1200 ℃空气中的氧化行为。结果表明,熔铸态及机械合金化Cr-25Nb合金氧化后均没有发生Cr的单一外氧化,而形成了以Cr2O3为外层、NbCrO4为内层的双层氧化膜结构;机械合金化Cr-25Nb合金在950及1200 ℃的氧化速度均小于熔铸态合金,特别是在1200 ℃氧化100 h后,熔铸态Cr-25Nb合金的氧化增重是机械合金化合金的2倍多。这主要是因为晶粒细化促进了氧化膜内应力的释放,提高了氧化膜与基体的粘附性     

Evaluation of Thermocyclic Oxidation Behavior of HVOF-Sprayed NiCrFeSiB Coatings on Boiler Tube Steels

High velocity oxy-fuel (HVOF) spray process has grown into a well-accepted industrial technology for obtaining coatings resistant to significant surface degradation processes. In the present study, HVOF process was used to deposit Ni-based hardfacing NiCrFeSiB alloy powder on kinds of boiler tube steels designated as SA210 grade-A1, SA213-T11, and SA213-T22. The microstructures and several properties of the as-sprayed coatings have been investigated. Thermocyclic oxidation studies were performed in static air at 900 °C. NiCrFeSiB-coated steels showed slow oxidation kinetics and considerably lower weight gains than that of uncoated steels. The superior performance of NiCrFeSiB coatings can be attributed to continuous and protective thin oxide scale of amorphous SiO₂ and Cr₂O₃ formed on the surface of the oxidized coatings. The combined technique of x-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, and electron probe microanalysis are used to characterize reaction products of the oxidized surfaces.     

Internal Oxidation Thermodynamics and Isothermal Oxidation Behavior of AgSnO2 Electrical Contact Materials

研究了Ag-Sn合金内氧化热力学与恒温氧化行为。热力学计算结果表明,Ag-Sn合金内氧化在热力学上是可行的,并绘制了合金氧化热力学区位图。经氧化实验获得Ag-Sn合金恒温氧化行为曲线。Ag-Sn合金快速氧化的温度区间为550℃至800℃。随内氧化温度的升高,合金的氧化更为彻底并逐步趋于平稳。实验所得AgSnO2材料中,SnO2颗粒弥散分布于Ag基体中。在内氧化过程中,氧的扩散使合金内部发生氧化,并生成呈网状排布的氧化物。     

Oxidation of Heat-Resistant Chromium Steels and Chromium-Nickel Steels

Abstract

Short- and long-term tests of heat-resistance were carried out on Cr20, Cr18Ni9, Cr24 and Cr24Ni20 steels. The long-term tests revealed increased oxidation connected with depletion of alloying elements near the metal surface. This may affect estimates of the life of components made from these steels based on short-term tests. Cyclic heating and cooling had a favourable effect on the oxidation rate with Cr24 steel and an adverse effect with Cr24Ni20 steel.     

Pd-Ni-Al涂层的高温长期氧化行为

利用TGA，XRD，SEM／EDS等方法，研究了Pd改性铝化物涂层在900—1100℃的长期高温氧化行为．结果表明，在900-1100℃下，与简单铝化物涂层相比，β-(Ni，Pd)Al涂层具有较好的抗高温氧化性能．添加改性元素Pd加速了涂层表面的θ-Al2O3向α—Al2O3转变，有利于形成致密的保护膜；另外，Pd还促进了合金基体中Ti元素向涂层的表面以及氧化膜中扩散．     

Influence of Oxidation Temperature and Cr Content on the Adhesion and Microstructure of Scale on Low Cr Steels

Descalability of steels during hot rolling processes is essential in order to maintain the surface quality of steel products, because the remaining scale can be impressed into the steel, producing surface defects. Therefore, a quantitative evaluation of scale adhesion at high temperature is needed in order to find suitable heating conditions for hot rolling processes that promote the formation of scale that easily detach. Round bar shape specimens of low Cr steels were oxidized in a fuel combustion environment, and then compressed at high temperature to detach the scale. The area fraction of the remaining scale was evaluated by image analysis. Under a thick outer oxide scale, a thin continuous inner oxide layer, which consisted of Cr and Si oxides, strongly adhered to the substrate, resulting in poor descalability. On the other hand, if this inner scale changed into a discontinuous layer with a porous FeO layer beneath, the descalability improved. It was found that scales with greater descalability formed on steels containing less Cr and for oxidation at higher temperatures.     

Microstructural Effects on Fracture Behavior of Ferritic and Martensitic Structural Steels

The effect of microstructure on fracture behavior of 1Cr-0.5Mo and 9Cr-1Mo structural steels was evaluated. 1Cr-0.5Mo steel is used in steam pipes and superheater tubes of power stations. Its microstructure is typically comprised of bainite in a pre-eutectoid ferrite matrix with an average grain size of 10 μm. 9Cr-1Mo steel was developed for applications in steam power stations and as a candidate structural material for first-wall and blanket components of future fusion reactors. Its microstructure consisted of a fully martensitic structure with a prior austenite grain size of 25 μm. The fracture properties were measured using instrumented impact testing at temperatures between ?196 and 300 °C. The total impact fracture energy, the crack initiation and propagation energy, the dynamic yield strength, the brittleness temperature, and the cleavage fracture stress were measured. The bainitic-ferritic alloy steel exhibited much higher resistance to ductile fracture at high test temperatures, while its resistance to brittle fracture at low test temperatures was reduced compared to that of the fully martensitic alloy steel. The results were discussed in terms of the chemical composition and microstructure of the two steel types.     

La元素对MoSi2涂层的宽温域氧化行为影响

采用包渗法在稀土 La₂O₃ 掺杂钼合金基体上制备 MoSi₂ 涂层,并就 La 元素对 MoSi₂ 涂层宽温域氧化行为的影响机制进行了系统研究。 结果表明:钼镧合金基 MoSi2 涂层组织结构较为致密,主要物相为 MoSi₂ 相。 不同温度下 La 元素对 MoSi₂ 涂层的抗氧化性能的影响不同,1600 ℃高温静态氧化条件下,La 元素的存在促进了涂层与基体的化学反应,加剧了 MoSi₂ 抗氧化主体层的消耗速度,使得 MoSi₂ 涂层的高温抗氧化性能有所下降;800 ℃ 中温静态氧化条件下, La 元素对 MoSi₂ 涂层抗氧化性能影响不明显;500 ℃低温静态氧化条件下,La 元素的加入加速了涂层中 Si 元素的扩散, 使得涂层表面能较快形成一层致密的氧化层,“Pest”效应得到抑制,从而显著提升涂层的低温抗氧化性能。     

晶粒尺寸对耐热钢在高温水蒸汽中的氧化行为的影响

从氧化动力学、氧化膜相组成及微观结构方面,研究了晶粒尺寸对18Cr-8Ni耐热钢在700 ℃下的高温水蒸汽中氧化行为的影响。结果表明：晶粒细化提高了耐热钢的抗水蒸汽氧化性能,降低了其氧化增重,推迟了失稳氧化的发生;晶粒细化改变了耐热钢氧化膜的微观结构,减小了“弹坑”区的尺寸且促进了“弹坑”区与合金界面上富Cr氧化物层的形成;晶粒细化对耐热钢抗水蒸汽氧化性能的改善主要归因于其对氧化物的形核和Cr向氧化膜/合金界面扩散的促进作用。     

Determination of Physico-Mechanical Properties and High Temperature Behavior of Stressed Reinforcing Steels

Protection of Metals and Physical Chemistry of Surfaces - This study experimentally investigated the effect of fire-induced high temperature on different grades of stressed steels. The steel in the...     

Zr-xNb-yCr合金在模拟失水事故下的高温蒸汽氧化行为

锆合金在失水事故（Loss of Coolant Accident, LOCA）下的高温蒸汽氧化行为是需要重点关注的问题之一。本文熔炼了Zr-xNb（x=0.5、1.0、1.5,wt.%）合金和Zr-1Nb-yCr（y=0.05、0.2）合金并制备成板状样品。采用同步热分析仪研究了5种锆合金在模拟LOCA工况下900~1200 ℃蒸汽中的氧化行为,利用金相显微镜观察分析了氧化样品横截面的显微组织,使用显微硬度仪研究了氧化前后样品的显微硬度。结果显示：在900~1100 ℃蒸汽中氧化时,Zr-xNb合金的抗高温蒸汽氧化性能不随Nb含量变化呈单一变化规律,且随温度升高发生变化,添加Cr使Zr-1Nb合金的抗高温蒸汽氧化性能变差,且影响复杂,不随Cr含量的增加呈单一变化规律;在1200 ℃蒸汽中氧化时,添加Nb和Cr对锆合金的抗高温蒸汽氧化性能影响不大;5种合金的氧化动力学规律随温度升高发生变化,总体由抛物线→直线规律转变,还会发生多次转折。从O在Zr基体中的固溶含量以及Zr基体α?β和氧化膜单斜(m)?四方（t）相变的角度探讨了Nb和Cr影响锆合金高温蒸汽氧化行为的机理。