Metallurgical Analysis to Evaluate Cracking in a 316L Grade Stainless Steel Spiral Heat Exchanger

A spiral heat exchanger (SHE) constructed of Grade 316L stainless steel developed a leak after 8 years of service as a condenser on a distillation tower. Examination of the SHE identified the leak as being located on the cooling water side in the heat affected zone (HAZ) of a weld joining two plates. Cooling water deposits were observed in a V-shaped corner formed by the weld. A metallurgical examination identified the presence of transgranular cracks at the HAZ on the cooling water side. Analysis of the cooling water revealed the presence of chlorides. Based on the metallurgical analysis and the presence of chlorides, it was determined that the cracks and resulting leak were the result of chloride stress corrosion cracking.     

Metallurgical and Mechanical Properties of Underwater Laser Welds of Stainless Steel

In this paper, the microstructures and mechanical properties of underwater laser welds of Type 304 stainless steelwere investigated,JISY308L type filler wire was used as filler wire during welding.A gas-shielding nozzle was used toform a local dry cavity surrounding the welding zone.The main results are summarized as follows:(1)The shieldingcondition of the local dry cavity severely affects the oxyoxygen content of the weld,the worst shielding condition leading     

Metallurgical Analysis on a Cracked Super Duplex Stainless Steel Flange

A flange-to-pipe weldment in a seawater-intake-return-line suffered from cracking on its flange portion after in service for 4 months. The flange was fabricated from S32750 super duplex stainless steel. The cracked flange was investigated by visual inspection and fractographic examination on the crack surface, metallographic examination, hardness measurement, and chemical composition analysis of the flange-to-pipe weldment. The results of laboratory analysis showed that the flange had cracked in a brittle manner resulting from the presence of large amount of sigma phase in the flange material. Formation of such brittle second phase precipitates in the flange material was due to improper heat treatment.     

Use of Metallurgical Analysis to Pinpoint a Brake Problem and the Cause of a Bus Fire

The incident of concern involves a tour bus that caught fire. The fire took place while the bus was traveling at highway speeds. Bus fires can be catastrophic, consuming the entire vehicle and threatening the lives of passengers. In this case, the fire was detected soon enough to allow the bus to be evacuated. Further, the fire was extinguished in sufficient time to allow the origin of the fire to be traced by burn patterns to the brake assembly at the passenger’s side rear axle. With the origin established, it remained consequential to determine the cause. It was here that metallurgical analysis came into play. Two competing theories as to the cause were presented. One theory was that heat generated by a dragging brake ignited the adjacent tire. The dragging brake, in turn, would have been the result of a leak in the air line servicing the brake. The second theory was that an underinflated tire had overheated and ignited. To prove if either theory was correct, the brake drum was subjected to metallurgical examination. It so happened that the changes in microstructure of the drum material as a function of location and of temperature exposure verified that the dragging brake theory was correct. It is also important to realize that a correct and well-documented analysis provided knowledge as to the cause of the fire and is one step in preventing another such fire. This article was published in Materials Science & Technology 2007 Conference and Exhibition: Exploring Structure, Processing, and Applications Across Multiple Materials Systems (Detroit, MI), September 17–20, 2007, What We Can Learn from Failure Analysis Symposium, ASM International, Materials Park, OH, 2007.     

Mechanical and Metallurgical Studies in Double Shielded GMAW of Dissimilar Stainless Steels

In the present work, a simple arrangement is made to provide double layer shielding gas supply in addition to primary shielding during gas metal arc welding (GMAW) of two dissimilar stainless steels, i.e., AISI 316 and duplex 2205. Influences of double layer shielding in addition to five more process parameters like welding current, voltage, material of the electrode wire, the type of primary shielding gas, and flow rate on joint tensile strength and fusion zone microhardness are studied. An experimental design technique is used to design the experimental conditions and the results are analyzed to observe the influences of each process parameter and their interactions. The tensile strength is more influenced by the electrode material and the type of shielding, whereas current, interaction between current × voltage and current × flow rate significantly influence microhardness. Welding voltage influences both tensile strength and microhardness. Double layer shielding with CO₂ as an outer shielding layer helps in controlling the cooling rate which improves the tensile strength and microhardness. Microstructural observations by scanning electron microscopy reveal that moderate to low heat input with a single layer of shielding results in poor joint strength and severe damage or lack of fusion, and the duplex 2205 filler gives the maximum joint strength due to the presence of a ferrite structure.     

SUS304不锈钢三通裂纹产生原因分析

某电厂氨气输送管道上的SUS304不锈钢三通多次出现裂纹,通过宏观观察、渗透检测、化学成分分析、硬度测试、力学性能测试、金相检验等方法,分析了该三通裂纹产生的原因。结果表明:由于三通成型后没有进行规范的固溶热处理,导致显微组织中存在较多的形变马氏体和弥散分布的碳化物,增加了材料的硬度和脆性,加之三通成型内应力没有充分释放,三通在应力最大的肩部产生了裂纹。     

Dissolution-facilitating Dislocation Emission, Motion andInitiation of SCC in 310 Stainless Steel

Using a special constant deflection device, the in situ TEM observations of dislocation emission,motion and the initiation of nanocrack in 310 stainless steel in water were carried out. The results show that SCC in thin foil specimen of 310 stainless steel can occur in water. A nanocrack initiated in the DFZ or at the blunt crack tip in corrosion solution after dislocation emission,multiplication and motion, which were induced by the localized anodic dissolution, reached a critical condition. The nanocrack propagated by a cleavage mode because of the influence of the corrosion solution.     

Use of a Fracture Surface Cleaning Method to Evaluate Elevated Temperature Cracking in Steel

Journal of Failure Analysis and Prevention - The nature of cracking during continuous casting of steel strip was investigated. Samples removed from steel strip for fractographic analysis were...     

粉末冶金多孔高氮奥氏体不锈钢的制备及性能

采用粉末冶金方法制备了多孔高氮奥氏体不锈钢并研究其力学性能和耐腐蚀性能。结果表明,高温气固渗氮能促进双相不锈钢向奥氏体不锈钢的转变,在其显微组织中出现了细条状和颗粒状CrN相析出物。随着造孔剂含量的提高孔隙率随之提高,而力学性能和耐腐蚀性能降低。与普通的多孔不锈钢相比,这种多孔高氮奥氏体不锈钢的力学性能更加优越,源于N的固溶强化和CrN等析出物的强化机制。随着孔隙率的提高多孔高氮奥氏体不锈钢的腐蚀倾向和腐蚀速率逐渐增大,造孔剂含量(质量分数)为10%的试样具有最佳的耐腐蚀性能。提高烧结温度有利于烧结块体的致密化,使腐蚀速率明显下降。     

超级13Cr马氏体不锈钢油管表面缺陷原因分析

通过宏观检验、化学成分分析、金相检验和力学性能测试等方法,对超级13Cr马氏体不锈钢油管表面缺陷的形成原因进行了分析。结果表明:油管表面缺陷为折叠裂纹和轧制沟槽,其产生原因主要是工厂轧制工艺不当所致。针对该表面缺陷对油管使用寿命的影响、油管表面缺陷的修磨和检验标准等进行了探讨,建议严格油管表面质量验收标准。     

无镍不锈钢冠脉支架力学行为的有限元模拟

以无镍不锈钢为支架材料,以冠脉支架结构为研究对象,对其压缩和扩张过程中的力学行为和柔顺性能进行了模拟计算,研究了支架压握并扩张后的轴向回弹率、径向回弹率以及不同端部网丝宽度支架的变形行为,计算出支架的弯矩-挠度曲线及支架的柔软度。结果表明,所研究的无镍不锈钢支架具有较小的轴向与径向回弹率,在变形过程中表现出良好的弹性弯曲变形性能。     

304不锈钢白色短擦缺陷成因及控制

针对304不锈钢冷轧2B板表面出现的白色短擦缺陷,对该缺陷进行电镜分析,明确其微观形貌和主要成分,并提出改进措施。通过中间坯厚度优化、精轧轧制速度优化、精轧各机架负荷优化调整和轧辊辊面温度优化调整的有效实施,冷轧2B板白色短擦缺陷得到有效控制,缺陷发生率由原来的2.58%降低至0.13%。     

Root Cause Analysis of Low Impact Toughness of Cast Steel Yokes Used in Railway Freight Cars

Journal of Failure Analysis and Prevention - The yoke is a safety-critical component of the coupler assembly of railway freight cars and is responsible for absorption of impact loads during...     

Q460C钢板力学性能不合格原因分析

利用光学显微镜和扫描电子显微镜分析了某厂生产的多个批次Q460C钢板力学性能低于GB/T 1591-2008技术要求的原因.结果表明:钢板中心偏析造成的贝氏体组织、微裂纹、MnS以及铌和钛复合夹杂物的存在是导致该Q460C钢板力学性能不合格的主要原因;另轧制工艺控制不当造成的魏氏体组织也会降低钢板的力学性能.     

抗高温碱腐蚀的新型高铬铸造不锈钢的研制

设计了用于含有固相颗粒的高温碱介质中的新型高铬铸造不锈钢的组织及化学成分。用金相显微镜和Ｘ射线衍射仪分析了此新型钢的组织,通过多种腐蚀试验研究了该钢的腐蚀与腐蚀行为。试验结果表明,新型高铬铸造不锈钢在含有固相颗粒的高温碱苛刻介质中,具有较好的抗磨蚀、点蚀与晶间腐蚀的性能,此外,该钢还具有良好的综合力学性能与铸造性能。     

316L不锈钢薄板焊缝成形及力学性能研究

目的 减少1 mm厚度316L不锈钢薄板在焊接生产过程中出现的缺陷等问题,并提高不锈钢薄板焊缝成形质量和焊接接头力学性能。方法 采用脉冲激光焊接技术实现对厚度1 mm的316L不锈钢薄板的精确焊接,并利用金相显微镜、维氏硬度计、万能拉伸试验机和扫描电镜对焊缝的表面形貌、微观结构、力学性能、断口形貌进行表征分析。结果 当激光功率为403 W、输出电流为150 A、焊接速度为150 mm/min、离焦量为−5.525 mm时,焊缝正反面的形貌规则无缺陷。焊缝区内的微观结构主要由δ-铁素体和奥氏体2种晶粒构成,相较于母材及热影响区,焊缝区晶粒尺寸更细小均匀,平均硬度为156HV,表现出更高的硬度特性。焊接接头的抗拉强度和屈服强度均值分别达到643.28 MPa和305.95 MPa,相对于母材的强度分别提高了7%和49%;平均断后伸长率为37.2%,达到原始母材伸长率的55%;断裂呈现韧性断裂的塑性变形和延展性特征。结论 优化调整焊接工艺参数后,1 mm厚度316L不锈钢薄板的焊缝成形质量提高,无缺陷且微观组织分布均匀,焊接接头强度显著提高。     

Microstructure and Mechanical Properties of a Dissimilar Friction Stir Weld between Austenitic Stainless Steel and Low Carbon Steel

Dissimilar fusion welding of austenitic stainless steels to carbon steels has some metallurgical and technical problems.It was suggested that the solid-state nature of friction stir welding(FSW) can overcome these problems and produce a sound weld with reliable mechanical properties.In this study,plates of 304 stainless steel and st37 steel were welded together by FSW at tool rotational speed of 600 r/min and welding speed of 50 mm/min.In the stir zone(SZ) of 304 stainless steel,the results showed a refined grain structure with some features of metadynamic recrystallization.In the SZ of st37 steel,the hot deformation of material in the austenite region produced small austenite grains.These grains transformed to fine ferrite and pearlite by cooling the material after FSW.The production of fine grains increased the hardness and tensile strength in the SZ of both sides with respect to their base metals(BMs).     

Structural and Mechanical Characteristics of AISI 420 Stainless Steel After Annealing

Strength of Materials - The temperature influence on the structural and mechanical properties of AISI 420 stainless steel is studied. The iron-based alloy underwent normalizing at three...     

Knowledge and Use of Heat-Treating Procedures Employed to Analyze the Cause of a Pair of Aluminum Piston Fractures

Aluminum alloy pistons, one each from two of the same model internal combustion engines, experienced fracture. The alloy would have been heat treated—solution treated and aged—to obtain an intended as-manufactured hardness. Hardness tests suggested that both pistons had been subjected to elevated temperature and, hence, were overaged. To prove the point, material from an undamaged piston was purposely overaged. The overaged hardness was consistent with the hardness of the materials from the fractured pistons. Fragments from a damaged piston were then solution treated and optimum aged, the result being restoration of material hardness. The heat-treatment experiments determined that the reduced hardness of the fractured pistons was incident related and not manufacturing related. Physical evidence also indicated that the pistons had seized in the engines. The result was fracture of the pistons because of overaging by heating when the pistons seized. The result of the heating was to reduce the hardness and strength of the piston material.     

钛和18/8不锈钢冶金结合层的研究

用金相、显微硬度,扫描电镜、X 射线能谱及 X 射线衍射等方法研究了钛和18/8不锈钢之间的扩散结合层和爆炸结合层。确定了结合层中各相的成份和晶体结构。扩散结合层中分为六层,它们是靠近不锈钢侧的α—Fe、Fe_(35)、Cr_(13)、Ni_3、Ti_7和 Ti(Fe_(0.75)Cr_(0.15)Ni_(0.1))_2三层和靠近Ti 侧的β一Ti 和含有 Fe、Cr、Ni 的α—Ti 两层,在这之间是一层液相凝固层,其中又有 Ti(Fe_(0.81)Cr_(0.13)Ni_(0.06))和β一Ti 两相。爆炸焊熔区的成份大约相当于钛与不锈钢以1∶1混合而成,其中主要的相是 Ti(Fe_(0.75)Cr_(0.15)Ni_(0.1))_2。本文并讨论了各相层的形成规律。