合金元素对316 LN 不锈钢的力学性能和点蚀性能的影响

研究了N、Cr、Mo和Ni四种合金元素含量的变化对核电主管道用固溶态316LN不锈钢的晶粒尺寸以及常规力学性能和点蚀性能的影响.随着N含量的升高,316LN的晶粒明显细化,其在固溶处理过程中晶粒长大趋势也减小. N含量的升高可改善316LN的力学性能和耐点蚀性能,但是当N质量分数达到0.20%时,其耐点蚀性能又开始变差.晶粒细化对316LN强度的影响远小于N含量对316LN强度的影响. Cr及Ni含量对316LN的晶粒尺寸及抗拉强度、屈服强度等力学性能影响不大;Cr含量增加可轻微改善316LN的抗点蚀能力,Ni元素对316LN的耐点蚀性能影响不大,但可增大钝态的腐蚀速度从而不利于钝化膜的稳定.随Mo含量增加,316LN的晶粒尺寸略有减小,强度增大,延伸率显著降低,耐点蚀能力改善.     

Q125级ERW用石油套管钢力学性能及CO2腐蚀行为

设计研发一种低碳的Q125级ERW用石油套管用钢。运用SEM和TEM分析实验钢的强化机制,并采用高温高压反应釜对实验钢的CO2腐蚀行为进行研究。实验结果表明:实验钢的晶粒粒径10～15μm,晶区的长度约为2μm,马氏体板条束宽度约150 nm,这些均为实验钢具有较好的强韧性配合提供条件;直径约为50 nm的圆形(Nb,Ti)(C,N)析出物,通过钉扎晶界阻止γ晶粒的粗化过程,可有效阻止奥氏体晶粒的长大;直径约20 nm的椭圆形(Nb,Ti)C以及纳米级圆形NbC析出物,可起到钉扎位错的作用,阻止位错移动,可很大程度地提高强度;实验钢腐蚀速率随着温度的增加先增大后减小,在90℃时平均腐蚀速率和点蚀速率均达到最大值;在60℃时,点蚀速率与平均腐蚀速率相差程度最大。     

304不锈钢在模拟压水堆一回路水中高温电化学腐蚀行为

通过模拟压水堆一回路水环境,研究了氯离子浓度和溶解氧对304不锈钢高温电化学腐蚀行为的影响.动电位极化曲线结果表明,氯离子浓度主要影响高电位下的二次钝化效应,低电位下影响效果不明显,结合X射线光电子能谱对氧化膜元素成分的分析发现二次钝化效应与氧化膜中Fe/Cr元素含量比密切相关.电化学阻抗谱和扫描电镜结果表明,随着氯离子浓度增加,氧化膜阻抗逐渐降低,表面外层氧化物颗粒和间隙逐渐增大,耐腐蚀性能降低.随着溶解氧含量的升高,304自腐蚀电位逐渐升高,钝化电流密度降低,钝化区间缩小,表面氧化膜阻抗逐渐增加.     

一种核级316LN钢的相图计算与微合金化设计

用热力学方法计算了一种核级316LN钢及其在Nb、V微合金化条件下的伪二元平衡相图,研究了不同温度下钢的平衡相组成。结果表明,316LN钢中的主要析出相为Cr2N、M23C6、和相,Nb微合金化316LN钢中会形成含C的MX,有望提高材料的力学性能和耐晶间应力腐蚀性能,V微合金化316LN钢中会形成VN,但对稳定C的作用不大。     

Effects of chloride ion concentration and pH values on the corrosion behavior of Cr12Ni3Co12Mo4W ultra-high-strength martensitic stainless steel

The effects of Cl- ion concentration and pH values on the corrosion behavior of Cr12Ni3Co12Mo4W ultra-high-strength martensitic stainless steel (UHSMSS) were investigated by a series of electrochemical tests combined with observations by stereology microscopy and scanning electron microscopy. A critical Cl- ion concentration was found to exist (approximately 0.1wt%), above which pitting occurred. The pitting potential decreased with increasing Cl- ion concentration. A UHSMSS specimen tempered at 600°C exhibited a better pitting corrosion resistance than the one tempered at 400°C. The corrosion current density and passive current density of the UHSMSS tempered at 600°C decreased with increasing pH values of the corrosion solution. The pits developed a shallower dish geometry with increasing polarization potential. A lacy cover on the pits of the UHSMSS tempered at 400°C accelerated pitting, whereas corrosion products deposited in the pits of the UHSMSS tempered at 600°C hindered pitting.     

超纯奥氏体不锈钢00Cr25Ni22Mo2N非敏化态晶间腐蚀与磷(硅)的晶界偏聚

运用金相、电子显微镜观察及表面分析技术,研究了超纯奥氏体不锈钢00Cr25Ni22Mo2N制造的汽提管在尿素生产环境下的腐蚀形态和机理。结果表明:该钢种在生产条件下产生非敏化态晶间腐蚀。其特征是腐蚀介质不仅沿晶界向钢的内部渗入,而且同时向晶界的两侧扩展,因而在管断面上观察到的晶间腐蚀路径较宽,但深度较浅并呈现漏斗形貌。电子显微镜观察、二次离子质谱、俄歇能谱分析及计算表明,这种材料晶界不贫铬、无第二相沉淀,但有磷(硅)的高度偏聚。晶界区磷的含量(约25％)比晶内高约三个数量级。作者认为,磷的晶界偏聚造成的与晶内在腐蚀电解质溶液中的电位差,是这种超纯奥氏体不锈钢非敏化态晶间腐蚀的原因。     

时效处理对2024 Al合金晶间腐蚀性能的影响

对轧制态2024Al合金进行了495℃固溶处理和190℃不同时间的人工时效处理,采用光学显微镜、场发射扫描电镜、X射线能谱、电化学技术和加速腐蚀试验研究了2024Al合金的晶间腐蚀性能、腐蚀形貌和显微组织.加速实验结果表明,虽然2024Al合金易发生晶间腐蚀,但峰时效处理可明显提高合金的晶间腐蚀抗力.动电位极化曲线和电化学阻抗谱实验也获得了相似的结果.时效态2024Al合金腐蚀模式为局部晶间腐蚀和点蚀.点蚀由晶内第二相颗粒与基体Al间的电偶腐蚀引起,晶间腐蚀由晶界析出相与其周围的贫Cu区间以及基体Al与贫Cu区间的电偶腐蚀引起.     

Pitting corrosion resistance of a novel duplex alloy steel in alkali-activated slag extract in the presence of chloride ions

In this study, two types of reinforcing steels (conventional low-carbon steel and a novel duplex alloy steel with Cr and Mo) were exposed to chloride-contaminated extract solutions (ordinary Portland cement (OPC) extract and alkali-activated slag (AAS) extract) to investigate their pitting corrosion resistance. The results confirm that the pitting corrosion resistance of the alloy steel is much higher than that of the low-carbon steel in both extract solutions with various NaCl concentrations. Moreover, for each type of steel, the AAS extract contributes to a higher pitting corrosion resistance compared with the OPC extract in the presence of chloride ions, likely because of the formation of flocculent precipitates on the steel surface.     

Precipitation behaviors of X80 acicular ferrite pipeline steel

The precipitation behaviors of X80 acicular ferrite pipeline steel were investigated by using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The results show that dendritic precipitates in the as-cast steel slabs precipitate mainly in grain boundaries, and these dendritic precipitates dissolve and re-precipitate to two kinds of carbonitrides: Ti- and Nb-rich (Ti, Nb)(C, N) carbonitrides during reheating. Four types of precipitates mainly exist in the hot rolled plate: Ti-rich carbonitrides resulted from the dendritic carbonitrides undissolved during the reheating process; Ti-rich carbonitrides re-precipitated along austenite grain boundaries during the reheating process; NbC carbides mainly heterogeneously nucleated on the small pre-existing Nb-rich carbonitrides in the hot rolling process; and NbC carbides precipitated on dislocations during hot rolling.     

固溶后降温预析出对7A55铝合金力学及腐蚀性能的影响

采用硬度测试、电导率测试及透射电镜研究固溶后降温预析出处理对7A55铝合金板材力学和腐蚀性能的影响。研究结果表明:随着预析出处理温度降低,基体析出相粗化且密度变小,导致合金时效后硬度和强度降低;晶界析出的平衡相由连续链状分布逐渐变为不连续分布,连续网状的腐蚀通道转变为断续的腐蚀点,7A55铝合金抗晶间腐蚀和剥落腐蚀性能提高。     

连续退火工艺对B250P钢组织性能的影响

对含磷高强B250P钢板的连续退火工艺进行了模拟实验,通过光学金相、透射电子显微技术及拉伸实验,研究了连退工艺中加热速度、退火温度、保温时间及冷却速度对B250P钢微观组织及力学性能的影响.结果表明,B250P钢晶粒尺寸随着加热速度的增加、退火温度的升高及冷却速度的增大而增大;随着保温时间的增加,晶粒尺寸呈现出先减小后增大的趋势.退火过程中B250P钢析出相主要为纳米级的NbC和TiC,具有钉扎位错和大角度晶界及细化晶粒的作用.B250P钢的r值随着加热速度的升高而增大,随着冷却速度的增加而减小;提高退火温度和保温时间,r值先增大后减小.     

Influence of chromium on the initial corrosion behavior of low alloy steels in the CO2-O2-H2S-SO2 wet-dry corrosion environment of cargo oil tankers

The influence of Cr on the initial corrosion behavior of low-alloy steels exposed to a CO2–O2–H2S–SO2wet–dry corrosion envi-ronment was investigated using weight-loss measurements, scanning electron microscopy, N2 adsorption tests, X-ray diffraction analysis, and electrochemical impedance spectroscopy. The results show that the corrosion rate increases with increasing Cr content in samples subjected to corrosion for 21 d. However, the rust grain size decreases, its specific surface area increases, and it becomes more compact and denser with increasing Cr content, which indicates the enhanced protectivity of the rust. The results of charge transfer resistance (Rct) calculations indicate that higher Cr contents can accelerate the corrosion during the first 7 d and promote the formation of the enhanced protective inner rust after 14 d; the formed protective inner rust is responsible for the greater corrosion resistance during long-term exposure.     

低碳Nb--Ti二元微合金钢析出过程的演变

建立规则溶液亚点阵模型计算了不同温度(1073～1523 K)下低碳Nb--Ti二元微合金钢(Nb质量分数为0.023%,Ti质量分数为0.012%)中碳氮化物析出相的平衡摩尔分数、化学驱动力和各组元摩尔分数,对微合金钢中析出粒子演变规律进行研究,并利用透射电镜观察及能谱分析验证这种析出模式.计算结果表明,1523 K下析出粒子化学式组成为(Nb0.15Ti0.85)(C0.16N0.84),由富Ti的析出物逐渐过渡至Nb--Ti均匀析出,析出粒子演变顺序为(Nb0.15Ti0.85)(C0.16N0.84)、(NbxTi1-x)(CyN1-y)和(Nb0.5Ti0.5)(C0.56N0.44),与实验结果符合较好.随着温度降低,Ti/Nb质量比逐渐减小,得到的TiC比NbC更难溶.对均匀形核及位错处形核的临界核心尺寸和相对形核速率进行计算,得到最大形核率即可获得最细小第二相尺寸的温度.     

304 L不锈钢焊缝在混凝土模拟孔隙液中的点蚀行为

采用动电位极化曲线、电化学阻抗谱、Mott-Schottky曲线等电化学方法研究了以308 L为焊丝的304 L不锈钢焊接接头在不同氯离子含量的混凝土模拟孔隙液中腐蚀行为和电化学规律。随Cl-增加,304 L不锈钢焊接接头的三个区域(母材、焊缝和热影响区)在混凝土模拟孔隙液中的自腐蚀电位、点蚀电位及电荷转移电阻降低,钝化膜中载流子密度和焊接接头的点蚀坑数量增加。在同浓度的腐蚀溶液中,308 L的焊缝区域耐蚀性最佳,热影响区次之,304 L基体表现出低的电荷转移电阻和高的掺杂浓度使得母材的耐蚀性最差。     

NaCl溶液中20Cr9Ni5Co14不锈钢电化学腐蚀行为

采用电化学极化技术(动电位极化技术、线性极化技术和循环极化技术)和交流阻抗技术研究了不同条件下20Cr9Ni5Co14超高强度不锈钢的电化学腐蚀行为,并采用扫描电镜对极化后腐蚀形貌进行了表征.结果表明,20Cr9Ni5Co14钢在3.5%(质量分数)Na Cl溶液中出现钝化.随着Na Cl浓度的升高,钝化现象消失,而自腐蚀电流密度从8.223×10-7A/cm2减小至1.129×10-7A/cm2;随着p H值的降低,20Cr9Ni5Co14钢的致钝电位和过钝化电位增加.在p H值高于3时,腐蚀产物膜具有良好的耐腐蚀性能而导致反应步骤成为控制步骤.而当p H值降低到2时,腐蚀产物溶解速度很快,金属界面发生腐蚀速率很大,浓差极化成为了控制步骤.对腐蚀形貌研究表明,20Cr9Ni5Co14钢在极化过程中出现点腐蚀,导致了材料的耐腐蚀性能下降.     

低频电磁场频率对半连铸高强Al合金组织结构的影响

利用光学显微镜和透射电镜研究了在低频电磁场作用下,电磁场频率对半连铸直径100mm铝合金铸锭显微组织结构的影响·结果表明:与常规铸锭相比,当电流为100A,频率为15Hz时,晶粒尺寸有所减小,并且等轴晶数目增多·当频率增到25Hz时,晶粒细化最明显·随频率继续增大,晶粒尺寸又有所增大;在电流为100A,电磁场频率为25Hz时,晶内位错密度较高,沉淀相尺寸较小,析出相主要为颗粒状的η′,η相和小片状的T相,此时晶界两侧无析出带宽度为100nm左右;当电磁场频率为15Hz时,晶内沉淀相尺寸有所增大,析出相主要为片状和长板条状的η相、片状的T相和颗粒状的η′相,晶界两侧无析出带宽度增到300nm左右...     

Damage mechanism at different transpassive potentials of solution-annealed 316 and 316l stainless steels

Electrochemical impedance spectroscopy (EIS), anodic polarization and scanning electron microscopy techniques were used to investigate the damage mechanism in the transpassive potential region of AISI 316 and AISI 316L solution-annealed stainless steels (SS) with different degrees of sensitization. Depending on the DC potential applied during EIS tests, the AC responses in the transpassive region included three different regions:the first one associated with anodic dissolution of the passive layer, the second one contributed to the dissolution at the area near grain boundaries, and the last one attributed to pitting corrosion. In addition, the fitting results to experimental data showed that as the DC bias during the EIS test increases the charge transfer resistance (R_ct) decreases. Moreover, the R_ct values decreased as the sensitization temperature increases but the AISI 316L SS samples exhibited a higher resistance to intergranular corrosion than 316 SS samples.     

Damage mechanism at different transpassive potentials of solution-annealed316 and 3161 stainless steels

Electrochemical impedance spectroscopy(EIS),anodic polarization and scanning electron microscopy techniques were used to investigate the damage mechanism in the transpassive potential region of AISI 316 and AISI 316 L solution-annealed stainless steels(SS)with different degrees of sensitization.Depending on the DC potential applied during EIS tests,the AC responses in the transpassive region included three different regions:the first one associated with anodic dissolution of the passive layer,the second one contributed to the dissolution at the area near grain boundaries,and the last one attributed to pitting corrosion.In addition,the fitting results to experimental data showed that as the DC bias during the EIS test increases the charge transfer resistance(R_(ct)) decreases.Moreover,the R_(ct) values decreased as the sensitization temperature increases but the AISI 316 L SS samples exhibited a higher resistance to intergranular corrosion than 316 SS samples.     

X80管线钢中氮化物和碳化物析出热力学分析

基于规则熔体理论和平衡反应基础,对连铸工序X80管线钢中碳化物、氮化物析出进行热力学分析,研究Ti、Nb及Al的碳化物、氮化物析出规律。结果表明,固液两相区,TiC0.005N0.995和TiN分别在1785K和1784K时开始析出;奥氏体相区,碳化物、氮化物析出先后顺序为NbC0.64N0.36、NbC、NbN、AlN、TiC,相应析出温度为1457、1404、1354、1267、1226K;γ→α相变过程中,TiC发生相间析出,Nb主要以NbC形式析出,AlN析出量较少。     

基于氯离子时变扩散钢筋混凝土锈胀裂缝时变可靠度研究

基于氯离子Fick扩散定理和法拉第定律,通过研发的四电极传感器体系获得含氯离子混凝土模拟液中腐蚀电流密度规律以及混凝土中氯离子时变扩散系数,建立氯离子时变扩散钢筋腐蚀速率模型;在此基础上基于弹性断裂力学和坑蚀模型,建立坑蚀锈胀裂缝时变可靠度模型,采用Monte Carlo方法求得钢筋混凝土锈胀裂缝时变可靠度.研究表明,基于研发的MnO2参比电极四电极传感器体系平均腐蚀电流密度随氯离子浓度增加而线性增加,随时间增加趋于恒定.采用考虑氯离子时变扩散钢筋腐蚀电流在服役期间钢筋腐蚀电流密度减小.坑蚀锈胀裂缝开始时间在第10~15年;随保护层厚度和钢筋直径增加以及表面氯离子浓度减小,钢筋混凝土坑蚀裂缝宽度减小.研究结果对氯离子诱发的钢筋混凝土坑蚀腐蚀裂可靠度预测具有重要的参考价值.