Understanding of tribocorrosion and corrosion characteristics of304L stainless steel in hot concentrated nitric acid solution

Spent fuel reprocessing plays a pivotal role in achieving efficient recycling of nuclear fuel.Among thedifferent forms of failure encountered in spent fuel reprocessing,tribocorrosion stands out as a critical concern.Herein,the tribocorrosion behavior,as well as the corrosion behavior,of 304L stainless steel(SS)in high-temperatureconcentrated nitric acid was investigated.The results indicated that 304L SS formed a thin(1.54 nm)and stable passivefilm on the surface,imparting high resistance to nitric acid corrosion.Meanwhile,it was found that the synergistic effectbetween corrosion and wear accounted for a high total tribocorrosion weight loss of over 85%,implying the dominantrole of the synergistic effect in the tribocorrosion process.Furthermore,the wear of 304L SS in deionized water revealedboth abrasive and adhesive wear characterizations,whereas the tribocorrosion in nitric acid only exhibited abrasive wearfeature.Eventually,the tribocorrosion and corrosion models of 304L SS in hot concentrated nitric acid were proposedbased on the comprehensive experimental findings.

Influence of flash trap profiles on joint properties of friction welded CP-Ti tube to 304L stainless steel tube plate using external tool

Titanium tube and stainless steel tube plate were welded by an innovative friction welding of tube to tube plate using an external tool (FWTPET). Copper was used as an interlayer for joining the dissimilar materials and also to minimize the effect of intermetallics formed at the joint interface. The process parameters that govern FWTPET process are plunge rate, rotational speed, plunge depth, axial load and flash trap profile. Among them, the flash trap profile of the tube has a significant influence on the joint integrity. Various flash trap profiles like vertical slots, holes, zig-zag holes, and petals were made on the titanium tube welded to the stainless steel tube plate. Macroscopic and microscopic studies reveal defect-free joints. The presence of copper interlayer and intermetallics was evident from X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies. The microhardness survey was presented across and along the interface. A novel test procedure called “plunge shear test” was developed to evaluate the joint properties of the welded joints. The highest shear fracture load of 31.58 kN was observed on the sample having petals as flash trap profile. The sheared surfaces were further characterized using SEM for fractography.

Effect of current intensity on radiological properties of joined 304L stainless steels for photon interaction

Radiological properties, such as the linear attenuation coefficient(μ), mass attenuation coefficient(μ/ρ), half-value layer(HVL), tenth-value layer(TVL), mean free path(MFP), and effective atomic number(Z_(eff)), of 304 L stainless steels have been investigated with respect to photon interactions to determine the influence of current intensity at different gamma-ray energies.^(137)Cs and ^(60)Co radioactive point sources were used to irradiate 304 L stainless steels joined at 45–70-A weld currents for the transmission of the gamma rays at photon energies of661.0, 1173.2, and 1332.5 ke V. The μ, μ/ρ, HVL, TVL,MFP, and Z_(eff) of the steels were measured at the mentioned energies, and theoretical values for pure 304 L stainless steel were calculated for comparison. The minimum differences(%) in Z_(eff) between pure steel and steel joined at a weld current of 60 A were observed for relevant photon energies; the minimum difference between the theoretical value for pure 304 L and the experimental value for joined steel was 4.76%, and that between the experimental value for pure 304 L and the experimental value for joined steel was 2.60% at 1332.5 ke V. Moreover, the MFPs of the joined steels were compared with that of pure 304 L, and steel joined at 60 A, which had the minimum MFP, was compared with some radiation-shielding concretes in terms of MFP at the same gamma-ray energies.

Microstructure, tensile properties and mechanical anisotropy of selective laser melted 304L stainless steel

The microstructure and mechanical properties of 304 L stainless steel fabricated by selective laser melting are investigated in this study.With the optimized laser processing parameters,a relative density of 99.9%is achieved with fine austenite grains and nanoscale cellular subgrains in size of approximately 0.5μm.The presence ofδ-ferrite andσphase precipitates is identified by the x-ray diffraction and transmission electron microscopy.Moreover,the microstructure is identified as an austenite matrix with about 4%δ-ferrite and a trace amount ofσphase by using electron backscattered diffraction analysis.These smallσphase particles are mainly distributed along austenite grain boundaries.Furthermore,the presence of nanoscale cellular subgrains contributes to the good tensile strength and ductility of the selective laser melted 304 L,along with precipitate strengthening and strain hardening.Tensile property anisotropy is also identified in this 304 L,which is attributed to the microstructure difference on vertical and horizontal planes.

Effect of Heat Treatment on the Microstructure,Mechanical Properties and Corrosion Resistance of Selective Laser Melted 304L Stainless Steel

The influence of heat treatment holding temperatures from 600 to 1300℃ on the microstructure,mechanical properties and corrosion resistance in selective laser melted(SLMed)304L stainless steel is investigated in this work.The results reveal that there is no remarkable microstructure change after holding at 600℃ for 2 h,while recrystallization leads to a slight decrease in grain size in the temperature range of 700–900℃.The heat treatment at temperatures from 1000 to 1300℃ for 2 h obviously affects the morphology of grains in SLMed 304L stainless steel.Combining effects of grain coarsening,delta-ferrite(δ)phases reduction and residual stress release during heat treatment lead to the reduction of yield strength and an increasing elongation.The elongation of the samples heat treated at 800℃ for 2 h is,however,significantly decreased due to the increase in the amount of sigma(σ)phase.A remarkable increase in the amount ofδferrite results in an increase in yield strength but a decrease in ductility after heat treatment at 1300℃ for 2 h.The corrosion resistance of the samples heat treated at 1300℃ is significantly improved due to the substantial reduction of brittle phase(σ).There is no obvious effect of the presence ofδferrite on corrosion behavior.

Dissolution and repair of passive film on Cu-bearing 304L stainless steels immersed in H_2SO_4 solution

The antibacterial Cu-bearing 304 L stainless steel is a new kind of structural and functional integrated metal material. In this work, evolution behavior of passive film of different heat treated Cu-bearing 304 L stainless steel immersed in 0.5 M H2SO4 solution was investigated by using electrochemical measurements, atomic force microscopy（AFM） observation and X-ray photoelectron spectroscopy（XPS） analysis.The results show that the solution and aging treated samples have the similar polarization behaviors. The passive film impedance experiences an initial decrease within 7 days followed by a subsequent increase,while the defect density of passive film presents the opposite trend. Meanwhile, the evolution of surface morphology and the estimated thickness of the passive film confirm that it experiences initial dissolution and follow-up repair. Furthermore, the Cr^3＋ content in passive film undergoes sequential reduction to increase, however the variation tendency of Cu^2＋ content is just opposite, indicating that the content variation of Cr and Cu in passive film reflects the competitive process of film dissolution and repair. In addition, compared with solution treated samples, aged samples have a bigger icorrvalue and the rougher passive film. This indicates that the passive film of solution treated steel is more compact and stable.

Extrusion process of 304L H-shaped stainless steel used in passive residual heat removal heat exchanger

304L H-shaped stainless steel is used as the support frame of the passive residual heat removal heat exchanger(PRHR HX) in a nuclear fission reactor. The extrusion process is adopted to manufacture the 304L H-shaped stainless steel. Finite element method simulation is herein used to analyze metal flow characteristics, optimize the extrusion die, and predict the extrusion force at different temperatures and speeds. A Φ400-mm container and Φ388-mm forging billet are selected, and the 304L H-shaped stainless steel is successfully manufactured using a Germany SMS 60 MN horizontal extruder. The mechanical properties and microstructure of the manufactured 304L H-shaped stainless steel meet the requirements of the PRHR HX, and the surfaces of the product pass the dye penetration test. The H-shaped stainless steels are used in Haiyang nuclear power plant in Shandong Province.

Study on Factors Effecting Weld Pool Geometry of Pulsed Current Micro Plasma Arc Welded AISI 304L Austenitic Stainless Steel Sheets Using Statistical Approach

Pulsed current Micro Plasma Arc Welding is used to joint thin sheets of AISI 304L sheets, which are used in manufacturing of metallic bellows and diaphragms. In this article the effects of pulsing current parameters on weld pool geometry namely front width, back width, front height and back height of pulsed current micro plasma arc welded AISI 304L stainless steel sheets was analyzed. Four factors, five levels, central composite design was used to develop mathematical models, incorporating pulsed current parameters and weld pool geometry. The mathematical models have been developed by Response Surface Method. The adequacy of the models was checked by ANOVA technique. Variation of output responses with input process variables are discussed. By using the developed mathematical models, weld pool geometry parameters can be predicted.

超细晶层状结构304L不锈钢摩擦学行为研究

用MS-T3000型多功能摩擦磨损试验机评估了超细晶层状结构304L不锈钢在空气和PAO4润滑条件下的摩擦学性能,以传统粗晶态304L不锈钢为对比材料,分析磨损前后的材料结构、成分及磨痕表面形貌,揭示磨损机制。结果表明:在空气湿度为75%时,粗晶态304L不锈钢与超细晶层状结构304L不锈钢的平均摩擦因数分别约为0.44和0.33,粗晶态304L不锈钢表面发生严重的黏着磨损和氧化磨损,超细晶层状结构304L不锈钢表面发生较缓和的黏着磨损和微氧化磨损。在PAO4润滑条件下,粗晶态和超细晶层状结构304L不锈钢的摩擦因数和磨损率都显著降低,粗晶态样品为典型的微切削磨损机制,超细晶层状结构样品为更微弱的微切削磨损机制。

选区激光熔化成形304L不锈钢氦泡长大与辐照硬化行为

采用350 keV He+离子束在300℃下对沉积态和固溶态选区激光熔化成形(Selective laser melting,SLM)304L不锈钢进行辐照,辐照剂量为5×10^(16)ions/cm^(2),随后进行600℃保温1 h退火处理。利用透射电子显微镜(TEM)、正电子湮灭和纳米压痕仪研究氦泡的长大与材料硬化行为。系统对比了沉积态和固溶态两种状态的SLM 304L样品,结果表明:600℃退火处理时,沉积态SLM 304L不锈钢表现出优异的抗氦泡粗化能力,主要是由于沉积态样品中高密度位错和纳米析出物-基体界面等作为缺陷阱,有效抑制氦泡生长。此外,沉积态样品比固溶态样品具有更高的抗辐照硬化性能,退火处理后两者的硬化率分别为19%和51%。Orowan模型的计算表明,氦泡粗化程度的差异是造成两种状态下SLM 304L不锈钢硬化率不同的主要原因。

304L不锈钢在贫胺液换热器上的耐蚀性研究

国内多数天然气净化装置在设计时,会选用碳钢材质的胺液换热器,但在实际运行中经常会遇到腐蚀损伤问题。因此,越来越多的企业开始应用不锈钢材质管束的换热器。通过试验研究了304L不锈钢在高含硫含氯胺液的碱性环境中的点蚀和应力腐蚀开裂敏感性,验证了该材质在某气田贫胺液换热器运行工况条件下的适用性及安全性,为合理控制高含硫酸性气田换热设备材料的使用成本提供了有效依据。

打印方向对增材制造304L不锈钢微观结构及力学性能的影响

增材制造技术已被广泛应用于航空工业、汽车工业等各个领域。本文利用选择性激光熔融(Selective Laser Melting;SLM)技术加工得到304L不锈钢材料,并对其微观结构和力学性能进行研究。试验中,利用光学显微镜(OM)和电子背散射衍射仪(EBSD)对材料的不同截面进行微观观察;同时对水平打印试样和竖直打印试样进行单轴拉伸试验。试验结果表明,SLM技术加工得到的304L不锈钢的微观结构具有各向异性,垂直于打印方向和平行于打印方向的微观形貌具有显著的差异,同时材料内部存在较大的残余变形。

弯曲变形304L不锈钢在高温碱盐环境中的腐蚀行为研究

为探究弯曲变形不锈钢复合管在锅炉碱盐环境中的腐蚀行为及性能变化规律,通过对材料组织、结构及腐蚀产物形貌、组成等分析,研究了304L不锈钢在300℃含硫碱盐环境中的腐蚀行为,并重点分析了弯曲变形对304L不锈钢腐蚀性能的影响。结果表明:304L不锈钢在碱盐环境中试验48 h后表面腐蚀较轻微,腐蚀不均匀,腐蚀产物主要为Fe_(2)O_(3)、FeCr_(2)O_(4)和FeOOH,主要为元素铁和铬优先发生腐蚀;弯曲变形304L不锈钢腐蚀速率较大,腐蚀产物较厚,主要是弯曲变形使304L不锈钢小晶粒变形明显,位错和孪晶增加所致。

酸性停堆温度对模拟压水堆一回路环境中304L不锈钢表面氧化膜的影响

以压水堆一回路系统构件常用材料304L不锈钢为研究对象,采用高温高压循环回路模拟现场工艺在材料表面制备氧化膜,在此基础上开展了两种温度的酸性停堆工艺试验,并对比分析了酸性停堆温度对材料表面氧化膜的形貌、元素组成和物相结构的影响。结果表明:经预处理1000 h后,304L不锈钢表面形成了双层氧化膜结构,外层氧化膜为镍铁尖晶石Ni_(x)Cr_(y)Fe_(3-x-y)O_(4),内层氧化膜为富铬尖晶石Ni_(x)Fe_(y)Cr_(3-x-y)O_(4),其厚度均小于0.1μm;经170℃酸性停堆工艺处理480 h后,304L不锈钢内外层氧化膜均发生了显著的溶解,内层氧化膜的溶解导致氧化膜与金属基体的界面模糊;经60℃酸性停堆工艺处理480 h后,304L不锈钢表面尖晶石氧化物并未发生显著溶解,表面分布少量大颗粒状尖晶石氧化物,氧化膜与金属基体的界面较为清晰。

304L不锈钢碱液管线腐蚀原因分析及预防

针对某项目304L不锈钢碱液管线在投用一周后发生腐蚀泄露的问题,采用金相显微镜和能谱仪等仪器,对已腐蚀不锈钢碱液管线进行一系列理化试验分析,得出造成碱液管线泄露的主要原因,并提出了相应的预防措施。

石油化工304L不锈钢压力容器腐蚀机理研究

本文选择石油化工行业常用的304L不锈钢材料作为研究对象,在应变速率为1.5×10-6/s、不同腐蚀介质NaOH溶液浓度和腐蚀温度条件下进行试验,观察应力腐蚀变化规律和断口特征。结果表明:在高温和高浓度腐蚀介质的作用下,304L不锈钢压力容器的腐蚀倾向更为明显,断裂特征由韧性转为脆性。因此,在实际应用中需加强对304L不锈钢压力容器的腐蚀防护和监测,以确保其安全运行。

304L不锈钢在高温水中的应力腐蚀裂纹扩展

敏化的304L不锈钢紧凑拉伸试样在288℃的含氧循环水中发生应力腐蚀(SCC)后,沿试样横截面将裂纹尖端区制成透射电镜(TEM)试样,用高分辨分析型TEM观察裂尖,测量微区成分.结果表明,在不连续的SCC裂纹周围及裂尖前方存在几百纳米宽的氧化物区,成分为Cr2O3,Fe3O4或其混合物.在氧化物中存在大量的纳米级浅裂纹,在裂尖应力集中作用下,氧化物中首先形成不连续的微裂纹,它们长大并和主裂纹连接就导致SCC裂纹的不连续形核及扩展.

Q235-304L电偶对在Na_2S溶液中的电偶腐蚀行为研究

用电化学法和浸泡法研究了Q235-304L电偶对在3种不同浓度的Na2S溶液中的电偶腐蚀行为,用SEM观察试样的表面形貌.结果表明:在3种溶液中Q235钢的阳极过程均为混合控制,而304L的阴阳极过程均为电化学控制;偶接后Q235钢表面阳极金属的溶解过程与阴极过程同时进行,其阳极溶解电流大于电偶电流值;电偶腐蚀效应随阴阳极面积比的增大而增大;随着S2-浓度的升高,电偶对中Q235钢的腐蚀速率减小,电偶腐蚀效应也随之降低.

Cl^-对304L不锈钢从点蚀到应力腐蚀转变行为的影响

普查了国内某海滨核电站核燃料厂房(K厂房)不锈钢管道的腐蚀情况和Cl-浓度,发现K厂房不锈钢管道存在普遍的腐蚀问题,腐蚀主要发生在弯管和焊缝部位,以点蚀为主,K厂房大气中Cl-含量是现场大气环境中的18倍左右。采用自行设计的装置预制点蚀坑,用恒载荷法研究了溶液中304L不锈钢由点蚀扩展为应力腐蚀的行为过程;结果表明,304L不锈钢发生应力腐蚀门槛应力在80%Rp0.2左右,1级椭圆形点蚀坑扩展为SCC的Cl-临界浓度在5～10mg/L之间。根据现场调查和试验结果推断,K厂房奥氏体不锈钢管道在含有氯离子的大气中应力腐蚀开裂(SCC)过程可分为两个阶段,先是金属表面钝化膜被破坏而发生点蚀,以后以蚀坑底部的敏感点为裂纹源,扩展为SCC。

pH值对Q235碳钢与304L不锈钢在典型含硫环境中电偶腐蚀行为的影响

采用电化学法和浸泡法研究了Q235碳钢与304L不锈钢在典型含硫环境中的电偶腐蚀行为。采用SEM观察试样表面形貌。结果表明：在实验体系中304L的阴阳极过程均为电化学活化步骤控制；在pH为4和7的实验溶液中,Q235钢的阴阳极过程均受电化学活化控制；而在pH=13.3的实验溶液中,Q235阴极过程受电化学过程控制,阳极过程受离子扩散控制。在三种实验溶液中的电偶腐蚀效应随阴阳极面积比的增大而增大,但电偶电流随阴阳极面积比的变化并不呈现出对数正比规律。随着溶液pH值的升高,Q235钢的电偶腐蚀速率明显减小,但电偶腐蚀效应变化不明显。