Behavior of 316L stainless steel containing corrosion pits under cyclic loading

The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits.     

Evaluation of Monkman-Grant parameters for type 316LN and modified 9Cr-Mo stainless steels

The Monkman-Grant (M-G) and its modified parameters were evaluated for type 316LN and modified 9Cr-Mo stainless steels prepared with minor element variations. Several sets of creep data for the two alloy systems were obtained by constant-load creep tests in 550-650°C temperature range. The M-G parameters,m, m’,C, andC’ were proposed and discussed for the two alloy systems. Them value of the M-G relation was 0.90 in type 316LN steel and 0.84 in modified 9Cr-Mo steel. Them’, value of the modified relation was 0.94 in type 316LN steel and 0.89 in 9Cr-Mo steel. Although creep fracture modes and creep properties between type 316LN and modified 9Cr-Mo steels showed a basic difference, the M-G and its modified relations demonstrated linearity quite well. Them’ of modified relation almost overlapped regardless of the creep testing conditions and chemical variations in the two alloy systems, and the parameterm’ was closer to unity than that of the M-G relation.     

Corrosion Behavior of 316LN and 316 Stainless Steels During Long-term Exposure to Aerated 0.5 M NaCl Using Electrochemical Noise Technique

In the present work 316LN as well as 316 stainless steel (SS) coupons each of dimensions (0.025 × 0.018 × 0.006 m³) in well-polished condition were used as two nominal electrodes which were immersed in the aerated solution of 0.5 M NaCl. Correlated current and potential electrochemical noise (EN) signals were collected at 1 Hz sampling frequency for 1 h daily over a period of 30 days. The detrended EN data were used to calculate the noise resistance (R _N) as well as the spectral noise resistance at zero frequency (R _SN^o) values and other statistical parameters. To study the nature of pits and distribution of their diameters as well as depths, extensive observations of the pitted and the blank specimens were carried out using Confocal Laser Scanning Microscopy (CLSM). The current and the potential records of the two alloys showed distinct differences in their corrosion behavior. It was observed that within less than 4 h of immersion, 316SS showed signals indicative of unstable pitting and onset of stable pitting was noticed after 48 h of exposure. However, until about 24 h, 316LN showed just the random signals and unstable pitting was observed after 28 h. The signals clearly indicated continuous growth of the stable pits in 316SS as against the repassivation of the unstable pits in 316LN after 7 days exposure. It was observed that R _N values showed a continuous decrease in the case of 316SS, but were quite stable in the case of 316LN over the exposure period. Concurrent to these observations it was observed that 316SS specimen was extensively pitted. The frequency distributions of pit diameters as well pit depths were observed to be highest at 10-20 μm and 5-10 μm, respectively. However, pits with as large as 70-80 μm diameter and as deep as 20-25 μm too were observed. No pits were observed in case of 316LN even after 30 days of exposure, an observation that corroborates well with the stable R _N values. Thus, in the present investigation, the long-term tests using EN technique coupled with CLSM studies conclusively prove that many unstable pits initiated in 316SS turn into stable ones resulting in insidious localized corrosion attack whereas the unstable pits initiated in 316LN get passivated in the simulated coastal environment.     

316L不锈钢在硫酸盐还原菌与铁氧化菌溶液中的腐蚀及电化学行为

1 INTRODUCTION Type 316L stainless steel has good corrosion re- sistance and has been used increasingly for cooling water service in the chemical, petrochemical and power utility industries. However stainless steel is susceptible to localized corrosion by chloride ions and reduced sulfur compounds[1]. The presence of micro- organisms on a metal surface often leads to highly localized damages in the concentration of the electro- lyte constituents, pH and oxygen levels[2]. These mi- croorg…     

316L尿素级不锈钢高压管道施工技术

以日产 10 5 0t尿素装置的施工为例 ,对 316L尿素级不锈钢高压管道的焊接、安装、检验、水冲洗和试压等施工艺进行了系统性的介绍。     

超低碳不锈钢管-管板的焊接工艺试验与应用

超低碳不锈钢316L管-管板的焊接采用手工钨极氩弧焊,对316L不锈钢的焊接性进行了分析和研究,通过工艺试验,证明了焊接工艺的可靠性,并在不锈钢浓H2SO4冷却器阳极保护(管壳式)设备的焊接中取得了满意的效果.     

回用水对冷却水系统316L不锈钢的腐蚀

城市污水回用作循环冷却水系统,讨论了NH3-N、COD、Cl-、SO42-等因素对316L不锈钢耐腐蚀性的影响。极化曲线表明:当NH3-N的质量浓度超过18 mg/L时,NH3-N促进了不锈钢的点蚀;COD对316L不锈钢的点蚀并无多大的影响;Cl-促进点蚀,而SO42-的质量浓度小于300 mg/L时,SO42-对其点蚀有缓蚀作用。     

类激光熔覆Stellite合金沉积层的组织及磨损性能

为了进一步提高316不锈钢的表面性能,采用类激光熔覆技术在316不锈钢表面制备了Stellite合金沉积层.利用扫描电子显微镜、能谱仪、X射线衍射仪、显微硬度计与销盘磨损试验机,研究了Stellite合金沉积层的微观组织、化学成分、显微硬度及摩擦磨损性能.结果表明,Stellite合金沉积层主要由γ-Co和M_(23)C_6相组成.沉积层组织依附于316不锈钢基体的界面呈外延生长,由界面至表面依次呈平面晶、柱状晶和胞状树枝晶形态,且越靠近表面组织越细小.Stellite合金沉积层的最高硬度可达650 HV.在摩擦磨损过程中摩擦系数随着法向载荷的增大而减小,磨损机制主要为黏着磨损、磨粒磨损和氧化磨损.     

316LN钢高温塑性及其断口特征

利用Gleeble-1500D热力模拟试验机,对316LN钢进行温度为950~1200℃,应变速率分别为0.005、0.05、0.5和1s-1的热力模拟试验。借助扫描电镜(SEM)对断口进行观察,研究316LN钢的高温塑性及高温断裂机制。结果表明:316LN钢高温断裂为韧性断裂,随着温度和应变速率的增加,韧窝尺寸增大,深度增加,塑性增加。同时,采用回归方法构建了断裂应变、塑性指标(延伸率和断面收缩率)分别与变形条件(温度和应变速率)的关系模型,应用这些模型可以计算一定条件下316LN钢的断裂应变、延伸率和断面收缩率,对制定316LN钢的锻造工艺有一定的指导作用。