2205双相不锈钢高周疲劳诱发的相变行为

目前,对2205双相不锈钢(2205DSS)在疲劳载荷下的相结构演变还缺乏报道。对2205DSS双相不锈钢进行了高周疲劳试验,采用面积统计法测定了铁素体、奥氏体及其两相比,研究了应力幅值和循环周次对铁素体高周疲劳的影响,分析了疲劳诱发的相变机理,探讨了高周疲劳对2205DSS相变行为的影响。结果表明:随着应力幅值和循环周次的增加,2205DSS双相不锈钢中奥氏体逐渐减少,铁素体及其与奥氏体的比逐渐增加;两相具有不协调变形能力,循环载荷在相界处产生局部应力集中以及累积应变能增加,是促进碳原子发生上坡扩散并诱发界面向奥氏体方向移动的原因。     

低碳马氏体/贝氏体复合组织的疲劳裂纹萌生行为

本文用四点弯曲加载法测定了２０ＣｒＭｎＭｏ钢矩形缺口试样的条件疲劳裂纹萌生寿命,并用微观分析研究了疲劳裂纹的萌生行为。试验结果表明,通过短时等温处理,在低碳马氏体组织中引入２０～３０％贝氏体,可显著提高缺口试样的疲劳萌生寿命。复合组织中的贝氏体虽易于滑移变形引发裂纹,但在存在较大应力集中条件下（ｋｔ≥２）,因可同时形成较多的非扩展裂纹,能有效缓和应力集中,从而有利于延长扩展裂纹的形成寿命。     

AM355不锈钢在酸性溶液中的腐蚀电化学行为

结合腐蚀形貌,通过极化曲线、交流阻抗谱(EIS)和莫特肖特基(MS)曲线的测定,分析了溶液pH值对AM355不锈钢腐蚀电化学行为的影响。结果表明:随溶液pH值的减小,腐蚀电位正移,腐蚀电流密度增大,致钝电位发生了正移,致钝电流密度、维钝电流密度增大。钝化膜由铬氧化物和铁氧化物组成,酸性增加使得铁氧化物施主浓度增大,钝化膜表面吸附氢离子电荷密度增加。钝化膜的厚度及其电阻随pH值的减小而减小,钝化膜更容易被破坏,酸性达到一定程度,钝化膜局部区域优先腐蚀。溶液pH值减小,AM355在溶液中保持自钝化性能降低,材料的腐蚀速率增加。     

低周疲劳下16MnR微孔的裂纹萌生与扩展

采用宏观与微观结合的方法,在疲劳试验机上进行疲劳试验,在光学显微下观察裂纹的起裂与扩展.研究了压力容器用钢16MnR在低周疲劳下微孔(40～200μm)的裂纹萌生与扩展规律.研究表明裂纹的萌生机制:滑移带启裂和疏松带启裂,前者由剪应力起主要作用,后者由正应力起主要作用.而滑移带的局部性和裂纹开叉是低周疲劳下微裂纹的两大典型现象.微观缺陷尺寸、应力水平对疲劳寿命有显著影响,当应力水平较低时,微孔尺寸对寿命的影响明显.而当应力水平较高时(超过屈服极限),孔径对寿命的影响不敏感.在同一应力水平下,微缺陷尺寸存在临界值dt,当d＞dt时,疲劳寿命下降很多.     

加载载荷对ADB610钢疲劳裂纹扩展性能的影响研究

针对ADB610新型低碳贝氏体钢,采取紧凑拉伸试样、恒幅加载方式,在应力比为0.1时进行3种不同加载载荷下多试样的疲劳裂纹扩展试验,并测出裂纹扩展长度a和循环寿命N的a-N试验数据。然后采取七点递增多项式法对a-N试验数据拟合计算疲劳裂纹扩展速率。结果表明,加载载荷较小时,ADB610钢循环寿命较长;在疲劳裂纹扩展的初始阶段,加载载荷小的疲劳裂纹扩展速率相对较慢,但随着疲劳裂纹逐渐扩展,加载载荷小的疲劳裂纹扩展速率反而更大一些。     

第一代单晶高温合金中温高应力幅下的疲劳裂纹萌生行为

通过应力控制的疲劳实验探究第一代镍基单晶高温合金DD413在中温(760℃)高应力幅下的疲劳裂纹萌生行为,并使用扫描电子显微镜观察和表征了疲劳样品的断口形貌和纵截面的显微组织.结果 表明:在高应力幅条件下,疲劳裂纹主要萌生于表面开裂的块状碳化物和次表面开裂的骨架状碳化物.在疲劳过程中,氧化和循环加载的共同作用使样品表面...     

2205双相不锈钢在NaCl溶液中的疲劳裂纹扩展行为

为提高2205双相不锈钢的使用安全性,采用光学显微镜和力学性能测试等方法,研究了2205双相不锈钢在NaCl溶液中的疲劳裂纹扩展行为。结果表明:与空气中相比,2205双相不锈钢在NaCl溶液中的疲劳裂纹扩展门槛值有降低的趋势,近门槛区的裂纹扩展速率有所提高,并且裂纹扩展由近门槛区向稳态扩展区转变的临界ΔK提高;在稳态扩展阶段,NaCl溶液使裂纹扩展速率显著提高,导致疲劳寿命显著降低;当NaCl浓度在0.5%~26.6%范围内时,随着浓度的增大,稳态扩展阶段的Pairs方程参数m值呈增大趋势,C值呈减小趋势;NaCl溶液中力学和环境因素的交互作用,加速了疲劳裂纹扩展,材料一旦进入稳态扩展就更容易进入高速扩展区并最终发生断裂。     

相界面对核电Z3CN20-09M不锈钢裂纹萌生和扩展的影响

为研究国产核级主管道不锈钢Z3CN20-09M中奥氏体/铁素体相界面在裂纹萌生与扩展过程中的作用,通过扫描电镜原位拉伸技术对核级主管道不锈钢在拉伸过程中的组织形变、微裂纹的萌生与扩展进行原位观察,对断口进行了分析.研究表明,在拉伸过程中,微裂纹优先在杂质颗粒和相界位置萌生.当铁素体/奥氏体界面垂直于拉伸方向时,裂纹倾向于沿相界萌生,并沿相界扩展;当铁素体/奥氏体界面平行于拉伸方向时,微裂纹在相界开裂,并垂直于界面扩展,主裂纹发生偏折,界面在裂纹扩展过程中起阻碍作用.     

AlSi10Mg(Cu)铸铝合金的热疲劳裂纹萌生及早期扩展行为

微观观察AlSi10Mg(Cu)铸铝合金在热疲劳裂纹的萌生和早期扩展过程,重点研究共晶硅粒子对热疲劳裂纹行为的影响。结果表明:热疲劳裂纹萌生于脱粘共晶硅粒子与铝基体间的开裂界面,原因是共晶硅粒子与铝基体的热膨胀系数不同,引起热循环过程中两相热应变不协调,从而在两相界面处产生循环应力而引起疲劳破坏。热疲劳裂纹的扩展在长度和宽度上同时进行,具有良好塑性的铝枝晶对疲劳裂纹的扩展起阻碍作用。对热疲劳过程中共晶硅粒子周围应力场的模拟分析进一步解释了实验现象。     

P92钢蠕变-疲劳交互作用下的裂纹扩展行为EI北大核心CSCD

在630℃下,对P92钢进行应力控制下的蠕变-疲劳交互作用实验,研究P92钢高温蠕变-疲劳交互作用下的裂纹扩展行为,并结合断口形貌分析蠕变-疲劳裂纹扩展的机理以及a-N曲线的转折点含义。结果表明:P92钢在蠕变-疲劳交互作用下的断裂属于蠕变韧性断裂,应该用(C_t)_(avg)作为裂纹扩展的断裂参量;P92钢在蠕变-疲劳交互条件下,试样的断口主要表现为蠕变孔洞以及微裂纹。此外,发现a-lg(N_i/N_f)曲线以及(da-dN)-N曲线中的拐点,分别对应蠕变-疲劳裂纹萌生区向扩展区转变周次以及扩展区向瞬断区转变的周次。     

Effects of annealing and quenching on fatigue behaviour in type 444 ferritic stainless steel

In order to understand the effects of annealing and quenching on fatigue behaviour in type 444 stainless steel, fully reversed axial fatigue tests have been performed using smooth specimens of heat‐treated materials in laboratory air and 3%NaCl aqueous solution. Three materials subjected to different heat treatments, annealing at 960 and 1000 °C, and water‐cooling at 960 °C, were prepared. In laboratory air, the fatigue limit of the annealed specimens was lower than that of the as‐received specimen and decreased with increasing annealing temperature. The subsequent grain coarsening from the heat treatments was primarily responsible for the lower fatigue strength in the annealed specimens. The fatigue strength of the water‐cooled specimen was lower than that of the corresponding annealed specimen. In the annealed specimens, cracks were generated within ferritic grains, while in the water‐cooled specimen, at or near grain boundaries. In 3%NaCl solution, the fatigue strengths of all specimens decreased compared with those in laboratory air. Only in the water‐cooled specimens, crack initiation at grain boundary and intergranular crack growth were observed, indicating the most sensitive to corrosion environment.     

高温高压下超级13Cr不锈钢抗CO2腐蚀性能

为了推进超级13Cr不锈钢在油气田中的应用,用高温高压釜系统模拟了油气田腐蚀环境,研究了超级13Cr不锈钢在动静态环境中高温高压下的CO2腐蚀行为,利用扫描电镜、能谱仪和X射线衍射仪等对超级130r不锈钢表面腐蚀产物的形貌及成分进行了分析。结果表明：动态腐蚀时超级13Cr不锈钢的腐蚀速率随温度的升高而增大,150℃时最大,此后腐蚀速率随温度的升高而下降;静态腐蚀速率随温度的升高呈上升趋势;动态腐蚀速率高于静态的,动静态平均腐蚀速率均较小,属于轻度或中度腐蚀,在油气田的安全使用范围之内;动静态腐蚀时超级13Cr不锈钢表面均生成均匀、致密的钝化膜层,表现为均匀腐蚀,腐蚀产物成分为不锈钢基本成分,未发现CO2腐蚀产物,超级13Cr不锈钢具有良好的抗高温高压CO2腐蚀性能。     

Methods for the Evaluation of Corrosion Fatigue of Steels and Alloys

We study the process of corrosion-fatigue damage of stainless steels and alloys in the early stages of fracture and propose analytic relationships between the corrosion-fatigue strength of passivated steels and electrochemical parameters in the stage of crack initiation.     

Growth behaviour of small surface fatigue cracks in AISI 304 stainless steel

A series of axial tensile fatigue tests (R = 0.1) was carried out to investigate the initiation and the growth behaviours of very small surface fatigue cracks under two different surface conditions (viz. smooth and pitted surfaces) of AISI 304 stainless steel at room temperature. This paper deals with both of the two approaches regarding the analysis of fatigue: the approach based on the concept of fracture mechanics and low cycle fatigue. In particular, both the initiation and growth of cracks and the coalescence of small cracks by fatigue in the specimen have been investigated by the methods of surface replicas and photomicrographs. Quantitative information such as the initiation period, growth and coalescence behaviours of small cracks, and crack growth properties were systematically obtained. The results show that the accurate determination of these parameters is critical for the application of fracture mechanics to fatigue life assessment.     

The effects of saline aqueous corrosion on fatigue crack growth rates in 316 grade stainless steels

A study of fatigue crack propagation rates of 316 grade stainless steels in air and in an aqueous saline environment was carried out in an attempt to assess the fatigue properties encountered when such materials are used as surgical implants. The effects of variables such as temperature, pH, oxygenation level, bulk electrode potential, mean stress, frequency and stress waveform on the Paris crack growth law parameters were determined. Corrosion fatigue effects were observed in the aqueous saline environment, and a mechanism to describe this effect is proposed.     

直流电压降法应力腐蚀裂纹扩展速率在线测定试验系统

介绍了应用直流电压降方法(DCPD)在线测量高温高压水环境中不锈钢应力腐蚀裂纹扩展的原理与试验系统,并采用商用301不锈钢对试验方法的准确性与系统的可靠性进行了验证。试验系统包括水化学回路、加热控制系统、动态加载系统与数据采集系统。在320℃,15.5MPa的去离子水中通过改变溶解氧含量和添加SO42-,Cl-等条件下完成了验证性试验。对材料的裂纹长度-时间曲线和断口形貌分析表明,该试验系统能够稳定而准确地在线测量应力腐蚀裂纹扩展速率。     

几种高强度钢腐蚀疲劳裂纹扩展行为的研究

本文研究了ＧＣ－４,３０ＣｒＭｎＳｉＮｉ２Ａ和３００Ｍ超高强钢的腐蚀疲劳裂纹扩展行为。考虑了环境,热处理制度,应力比和频率对裂纹扩展的影响。研究结果表明：腐蚀环境和热处理制度对疲劳裂纹扩展有显著影响。在侵蚀性环境中随频率降低,裂纹扩展大幅度上升,随应力比提高,环境影响加剧。利用扫描电镜对试样断口形貌进行了分析,并讨论了高强钢的腐蚀疲劳机理。