Deformation Mechanism of Bimodal Structured 2205 Duplex Stainless Steel in Two Yield Stages

A kind of micro/nanostructured 2205 duplex stainless steel(DSS)with uniform distribution of nanocrystals was prepared via aluminothermic reaction method.The analysis of stress-strain curve showed that the fracture strength and elongation of the specimen were 946 MPa and 24.7%,respectively.At present,the research on microstructure of bimodal 2205 DSS at room temperature(RT)mainly depended on scanning electron microscope(SEM)observation after loading experiments.The test result indicates that there are two different yield stages in stress-strain curve of specimen during tensile process.The microstructure of duplex bimodal structured stainless steel consists of two pairs of soft hard regions and phases.By studying deformation mechanism of bimodal structured stainless steel,the interaction between soft phase and hard phase are discussed.The principle of composition design and microstructure control of typical duplex stainless steel is obtained,which provides an important research basis for designing of advanced duplex stainless steel.

Effect of Temperature and Cl^- Concentration on Pitting of 2205 Duplex Stainless Steel

The electrochemical behaviors of 2205 duplex stainless steel in NaCl solution with different temperatures and concentrations were studied by gravimetric tests, potentiodynamic polarization, electrochemical impedance spectroscopy and scanning electron microscopy. The experinental results show that temperature and chloride concentration have a great influence on the pitting resistance of 2205 duplex stainless steels. They not only effect the corrosion rate of pitting, but also change the shape of the pits. When NaCl solution was in low concentration and temperature below the critical pitting temperature, pits were very small and scattered with hemisphere-like shape. On the contrary, the pits of 2205 duplex stainless steel were large and sometimes had a lacy cover when the NaCl concentration was higher and the temperature was 70℃.

Lamella Multiple Grained Structure Making 2205 Duplex Stainless Steel with Superior Strength and Ductility

We demonstrate a 2205 duplex stainless steel(DSS)synthesized by aluminothermic reaction and followed two-step rolling which had a superior yield strength of 863 MPa,ultimate tensile strength of1103 MPa and an elongation of 21%at room temperature.The phase,grain size and distribution of the steel were characterized by optical microscope,X-ray diffraction,electron back-scatter diffraction and transmission electron microscope.The results show that the steel consists of lamellar ferrite and austenitic phase with multiple grain size distribution from nanoscale to microscale.The high strength is attributed to strengthening of high back stress arising from laminated dual-phase heterogeneous ultrafine grained structure and distribution.The high ductility originates from back-stress hardening and dislocation hardening.

Effects of Sulphate-reducing Bacteria on Corrosion Behaviour of 2205 Duplex Stainless Steel

The effects of sulphate-reducing bacteria （SRB） on the 2205 duplex stainless steel in the sea water and oil industry environments were studied by electrochemical impedance spectroscopy （EIS）, potentiodynamic polarization and microorganism analysis. The results showed that the detected SRB was the non-spore bacillus of about 0.8μm×（1.8--2.2）μm in size and the content of S was about 7. 59% in the corrosion products. SRB contributed to the corrosion evolution which caused the corrosion failure of 2205 duplex stainless steel pipe in the liquid hydrocarbon cooler. During the corrosion process, the produced H2S could significantly influence the anodic process and finally accelerate the corrosion. SEM observation indicated that the distribution of SRB on the surface of 2205 duplex stainless steel was nonuniform. X ray photoelectron spectroscopy analysis revealed that the surface film was composed of Cr2O3, MoO3 , FeS, FeS2, Fe（OH）2 and FeO after immersing the sample in the SRB medium for 14 d.

Effect of dissolved oxygen on electrochemical corrosion behavior of 2205 duplex stainless steel in hot concentrated seawater

The corrosion behavior of 2205 duplex stainless steel was investigated in hot concentrated seawater with different dissolved oxygen(DO) concentration by electrochemical measurement techniques and surface analysis methods. DO obviously enhances the cathodic reaction process, the formation of passive film and polarization resistance. With increasing the DO concentration from 0.34 to 3.06 mg L^(-1), the relative contents of Fe_(2)O_(3) and Cr_(2)O_(3) and the Cr-enrichment gradually enlarge in the passive film. The higher DO concentrations result in lower defect densities and thicker of space charge layers in the passive films,whichmayeffectively inhibit the intrusion of aggressive chloride ions. The increment inDOconcentration clearly increases the pitting potential, but decreases the repassivation potential. It may weaken both the occurrence and repassviation tendencies of stable pitting corrosion.

Quantitative micro-electrochemical study of duplex stainless steel 2205 in 3.5wt%NaCl solution

Duplex stainless steels(DSSs)are suffering from various localized corrosion attacks such as pitting,selective dissolution,crevice corrosion during their service period.It is of great value to quantitatively analyze and grasp the micro-electrochemical corrosion behavior and related mechanism for DSSs on the micrometer or even smaller scales.In this work,scanning Kelvin probe force microscopy(SKPFM)and energy dispersive spectroscopy(EDS)measurements were performed to reveal the difference between the austenite phase and ferrite phase in microregion of DSS 2205.Then traditional electrochemical impedance spectroscopy(EIS)and potentiodynamic polarization(PDP)tests were employed for micro-electrochemical characterization of DSS 2205 with different proportion phases inϕ40 andϕ10μm micro holes.Both of them can only be utilized for qualitative or semi-quantitative micro-electrochemical characterization of DSS 2205.Coulostatic perturbation method was employed for quantitative micro-electrochemical characterization of DSS 2205.What is more,the applicable conditions of coulostatic perturbation were analyzed in depth by establishing a detailed electrochemical interface circuit.A series of microregion coulostatic perturbations for DSS 2205 with different proportion phases inϕ10μm micro holes showed that as the austenite proportion increases,the corresponding polarization resistance of microregion increases linearly.

热处理对2205双相不锈钢显微组织及性能的影响

采用光学显微镜、显微硬度计和电化学工作站等研究了2205双相不锈钢经不同温度保温不同时间后的显微组织及性能,并分析了其经不同工艺热处理后的γ和α两相比例和析出相的变化。结果表明:2205双相不锈钢初始状态下α和γ相含量分别为41.2%和58.8%。保温时间相同时,随着热处理温度的升高,γ相含量减少,σ相含量先增加后减少,硬度增加,腐蚀电位先降低后增加。保温温度相同时,随着保温时间的延长(0.5~2 h),γ相和σ相含量增加,γ相含量增幅为2.43%~3.87%,σ相含量增幅为0.05%~0.08%,晶粒有长大趋势,硬度逐渐降低,腐蚀电位总体呈降低趋势。当加热温度为950和1000℃时,硬度随保温时间增加而降低的幅度较明显。σ相含量及α/γ比例增加是造成2205双相不锈钢耐腐蚀性能下降的主要原因。

热效应所致析出相对2205双相不锈钢耐蚀性的影响

研究不同热效应下2205双相不锈钢的析出相类型和特点,通过测试固溶态和不同热效应下2205双相钢的动电位极化曲线、电化学阻抗谱以及动电位扫描后试样表面形貌的观察,研究析出相对其耐腐蚀性能的影响。结果表明:固溶态材料的耐腐蚀性能及再钝化性能最好;而在850℃时效后,由于χ和σ相析出含量增多,在过电位下会由点蚀转变为选择性腐蚀,导致材料的耐腐蚀性能下降最严重;900℃时效后,2205双相不锈钢中的析出相含量降低,其耐腐蚀性能的下降有所缓解。

稀土元素对2205双相不锈钢500℃离子渗氮动力学的影响

对2205双相不锈钢在NH3中500℃有无稀土等离子体渗氮动力学(8,16,24 h)进行了对比研究.含稀土(La)渗氮8 h时,有效硬化层(78.3μm)、化合物层(58.3μm)、扩散层(20.0μm)增厚率都是最高的,分别为33.8%,17.8%,122.2%.试样渗氮24 h后,表面硬度最高为1866.7 HV_(0.025),渗氮层最高硬度为1782 HV_(0.025),是芯部硬度(365 HV_(0.025))的4.9倍.稀土等离子体渗氮后,γ′-Fe_(4)N衍射峰变高,峰值变强,稀土的加入减少了ε-Fe_(2-3)N相的析出.相较于无稀土等离子体渗氮,加入稀土后的扩散系数K提高了22.8%,达到了1.51×10^(-13) m^(2)·s^(-1).

焊接热输入量和保护气体成分对S32205双相不锈钢低温冲击韧性的影响

采用等离子弧焊(PAW)+钨极惰性气体保护焊(GTAW)对2205双相不锈钢进行焊接,研究了在GTAW焊接过程中,热输入量和保护气体这两个要素对材料焊接部位低温冲击韧性的影响,并通过金相和SEM等对微观组织结构进行分析研究。结果表明,采用GTAW焊接时,热输入量会影响晶粒组织中铁素体/奥氏体相比例和奥氏体形态,当热输入量为1.76 kJ/cm时,焊接部位的低温冲击性能(-46℃)最佳;在保护气体中添加N_(2),会影响奥氏体和铁素体比例以及氮化物(CrN/Cr_(2)N)析出相在铁素体中的析出数量,并且导致微气孔形成,当N_(2)添加量为1%左右时,焊接部位的低温冲击性能最佳。

2205双相不锈钢疲劳损伤声发射研究

2205双相不锈钢以其强度高、耐腐蚀、耐高温等优点成为桥梁结构的新兴材料,但其在疲劳荷载下的损伤问题对整体结构安全性能影响很大。为了明确2205双相不锈钢材料在疲劳荷载下的损伤发展情况,本文对3组相同矩形截面试件进行了三种不同应力比的拉伸疲劳损伤试验,同时进行声发射信号采集,通过声发射经历图分析探讨了声发射振铃计数及能量与试件裂缝发展程度的关系,并且采用裕度指标对试验过程进行了评估。结果表明,随着应力比的增大,声发射特征参数的循环周次有了一定的增长,且试件损伤进程放缓;同时裕度评价指标的变化范围逐渐减小,说明该指标可以较好地表征试件的疲劳损伤发展情况。基于试验和分析结果建立声发射累计振铃计数-疲劳裂纹长度的疲劳损伤模型,通过该模型得出的计算裂纹与实际裂纹发展趋势较为吻合。故本文研究成果可为2205双相不锈钢材料疲劳损伤检测和评估提供依据。

2205双相不锈钢单相的制备及其在氢氟酸溶液中的腐蚀行为

在2 mol·L^(-1)H_(2)SO_(4)+0.5 mol·L^(-1)HCl溶液中,通过恒电位极化方法,以2205双相不锈钢为测试材料,制备了奥氏体和铁素体两个单相。通过动电位极化和电化学阻抗方法,考查了铁素体单相和奥氏体单相在5%(体积分数)HF酸溶液中的电化学腐蚀行为。结果表明:2205双相不锈钢,铁素体相比奥氏体相表现出更高的自腐蚀电位,腐蚀趋势更小;同时表现出更低的维钝电流密度和更宽的钝化电位区间,2205双相不锈钢中的铁素体表现出比奥氏体更好的抗腐蚀性能,这主要是因为铁素体表面形成的钝化膜更为稳定,从而表现出更好的抗腐蚀性能。

基于小冲孔试验的2205双相不锈钢焊接接头的应力腐蚀开裂行为

在含有H^(+)的混合海水溶液中采用小冲孔应力腐蚀试验方法对2205双相不锈钢焊接接头不同区域的应力腐蚀开裂敏感性进行了研究。基于小冲孔试验的载荷-位移曲线建立了应力腐蚀开裂敏感性系数计算方法,并依托小冲孔试样毫微取样的优势对比了母材区、热影响区和焊缝区应力腐蚀敏感性的差异。从宏观断口与微观断口两方面分析了断裂机理。结果表明:焊缝区的应力腐蚀开裂敏感性均高于母材区和热影响区,焊缝区在海洋环境中更易发生应力腐蚀开裂。小冲孔应力腐蚀试验方法是一种评价焊接接头不同区域应力腐蚀开裂现象的有效方法。

固溶处理对不同环境介质中2205双相不锈钢摩擦磨损行为的影响

对2205双相不锈钢施加不同的固溶温度进行热处理,研究其在不同环境介质中的摩擦磨损性能。通过对磨损表面的观察,分析了不同环境介质与固溶温度对2205双相不锈钢磨损机制、磨损体积与摩擦系数的影响。研究结果表明,在干摩擦条件下,磨损机制包括黏着、磨粒和疲劳磨损,磨损体积与固溶温度呈正相关,即随着固溶温度的升高,磨损体积也增加。最大磨损体积出现在1120℃,而最小磨损体积出现在1000℃,表明了最轻的表面损伤和最佳的耐磨性。在3.5%NaCl溶液和去离子水中实现最小磨损体积的最佳固溶温度分别是1000℃和1160℃。在去离子水中,磨损机制包括黏着、轻微磨粒和疲劳磨损。在NaCl溶液中,主要的磨损机制是黏着磨损和腐蚀磨损,并伴随轻微的磨粒磨损和疲劳磨损。

固溶处理对2205双相不锈钢组织和冲击韧性的影响

本文采用光学显微镜(OM)、扫描电子显微镜(SEM)、冲击试验机等方法,研究了2205双相不锈钢热轧板在1000~1100℃固溶处理的组织特征和冲击韧性变化。结果表明:在1000℃~1100℃温度区间,白色岛状的奥氏体分布在黑色铁素体基体上。随固溶温度升高,铁素体含量逐渐增加。-40℃~20℃冲击试验结果表明,随固溶温度升高,冲击韧性逐渐提高,固溶温度为1100℃时4个温度下的冲击功都大于100J,SEM冲击断口形貌呈现出明显的韧性断裂特征。

冷轧对2205双相不锈钢在人工海水中耐蚀性的影响

为了明确冷轧后2205双相不锈钢在人工海水中腐蚀性能的变化,对2205双相不锈钢采用不同压下率(PCRR=20%~80%)冷轧,对试样进行金相观察和硬度测量,利用动电位极化曲线和电化学阻抗谱研究了冷轧2205不锈钢在人工海水(3.5%NaCl溶液)中的耐蚀性能。结果发现:2205不锈钢的硬度和耐蚀性随PCRR的增加均呈现非单调性变化:PCRR=0~40%时,试样的耐蚀性和硬度随压下率的增加而增强,自腐蚀电位从-309 mV增至-269 mV,PCRR=40%~80%时,试样的耐蚀性随压下率的增加而降低,自腐蚀电位从-269 mV减小至-322 mV;压下率为40%时试样的耐蚀性最高,压下率为60%时试样的布氏硬度最大,约为374 HBW。适当冷轧引起高密度位错和组织细化,对提高2205双相不锈钢的耐蚀性提高有利,但压下率过大易引起σ相析出,对耐蚀性不利。

退火温度对2205双相不锈钢氢脆性能的影响

研究了1000℃和1150℃退火5 min状态下2205双相不锈钢的微观组织和氢脆性能。结果表明:随退火温度增加,晶粒尺寸增加,铁素体含量增加,氢脆敏感性也随之增加。充氢导致2205双相不锈钢屈服强度升高、抗拉强度降低,同时断口出现脆性区域,该区域的厚度随退火温度增加而增加。受氢影响脆性区域的断裂模式为解理断裂加准解理断裂的混合断裂模式,退火温度会对该区域的断裂模式产生影响。

2205双相不锈钢高N焊材焊接接头耐蚀性能分析

选用高N焊材焊接2205双相不锈钢,分析焊接接头在6%,10%,17%不同浓度不同温度的FeCl_(3)溶液中的腐蚀情况。结果表明:焊缝试样和母材试样表面都发生了不同程度的腐蚀,随着FeCl_(3)溶液浓度的升高,无论是焊缝还是母材其腐蚀速率都随之增加,50℃下的腐蚀速率要高于20℃下的腐蚀速率。在6%和10%浓度的腐蚀介质中,母材表面的蚀孔数量明显多于焊缝。在17%的腐蚀介质中,腐蚀程度明显比浓度为6%和10%的要深。17%浓度下焊缝表面产生腐蚀的部位要比母材的多,通过选用高N焊材,获得组织合理的焊接接头,焊缝的耐腐蚀性能满足标准要求且和母材接近。

2205双相不锈钢在旋转压力过滤机中的应用

文章针对PTA氧化单元物料特性,选用2205双相不锈钢作为CTA旋转压力过滤机的主体材料,通过2205双相不锈钢材料的特性、焊接接头热处理以及残余应力测试研究,对2205双相不锈钢在旋转压力过滤机中应用可靠性进行分析,确保旋转压力过滤机安全稳定运行。

基于响应曲面法优化2205双相不锈钢层等离子弧熔覆工艺

采用等离子弧熔覆技术在Q345钢表面制备2205双相不锈钢层,采用响应曲面法研究了熔覆速度(3~7 mm·s^(-1))、熔覆电流(83~117 A)和送丝速度(43~77 mm·s^(-1))及其交互作用对熔覆层稀释率与宽高比的影响,得到优化的等离子弧熔覆工艺。结果表明:为获得稀释率低的熔覆层,需采用小熔覆电流和高送丝速度,为获得宽高比大的熔覆层,需采用大熔覆电流和低送丝速度,熔覆速度对稀释率和宽高比的影响均小;预测得到优化工艺参数为熔覆电流99 A、熔覆速度6 mm·s^(-1)、送丝速度50 mm·s^(-1),熔覆层的稀释率和宽高比分别为14.8%和4.36,与试验值的相对误差分别为2.9%和2.3%,说明采用响应曲面法建立的二次数学模型可靠。优化工艺下制备的熔覆层成型较好。