304不锈钢法兰失效分析

通过宏观检查,化学成分分析,金相和扫描电镜分析,断口能谱分析以及晶间腐蚀试验分析,对某甲烷出口管线的法兰产生的裂纹进行了分析.结果表明:不锈钢晶间有碳化物析出,晶粒粗大,发生沿晶开裂,晶间腐蚀比较敏感,在沿海大气中Cl-的作用下产生了应力腐蚀开裂.     

TP304不锈钢三通失效分析

电厂脱硝设施中所使用的TP304不锈钢三通出现裂纹缺陷,通过成分分析、断口宏观和微观分析、微观组织观察、硬度检测,并结合生产工艺对三通裂纹的产生原因进行分析。研究结果表明：材料中Ni含量偏低使材料的奥氏体稳定化程度降低;基体内含有的2.5~3.0级球状非金属夹杂物对基体造成撕裂作用,促进疲劳裂纹的萌生;同时,三通在加工完成后也缺少固溶处理步骤,使得材料内应力过大。这些原因综合导致材料奥氏体含量降低,硬度过高,同时造成材料塑性变形部位内应力过高,在支管颈部产生较大的应力集中现象。三通内表面同时存在大量加工损伤,强化了应力集中现象,在疲劳载荷的作用下,促进了三通裂纹的萌生。     

The Study of Plasma Nitriding of AISI304 Stainless Steel

This paper presents results on the plasma nitriding of AISI 304 stainless steel at different temperatures in NH3gas. The working pressure was 100～200 Pa and the discharge voltage was 700～800V. The phase of nltrided layer formed on the surface was confirmed by X-ray diffraction. The hardness of the samples was measured by using a Vickers microhardness tester with the load of 50g. After nitriding at about 400℃ for two hours a nitrided layer consisting of single γN phase with thickness of 51.tm was obtained. Microhardness measurements showed significant increase in the hardness from 240 HV (for untreated samples) up to 950 HV (for nltrided samples at temperature of 420℃). The phase composition, the thickness, the microstructure and the surface topography of the nltrided layer as well as its properties depend essentially on the process parameters.     

火焰加热炉炉管泄漏原因分析

通过对泄漏的火焰加热炉开裂炉管裂纹及断口形貌观察、断口表面产物的EDX能谱分析,结果表明该加热管为304奥氏体不锈钢无缝管。管子泄漏是发生连多硫酸应力腐蚀开裂所致。对发生连多硫应力腐蚀开裂的原因进行了分析与讨论。     

Corrosion Resistance of Friction Surfaced AISI 304 Stainless Steel Coatings

Corrosion resistance of friction surfaced AISI 304 coating in boiling nitric acid and chloride containing environments was found to be similar to that of its consumable rod counterpart. This was in contrast to the autogenous fusion zone of GTAW weld which showed inferior corrosion resistance with respect to the consumable rod. The superior corrosion resistance of friction surfaced coatings was attributed to the absence of δ-ferrite in it.     

Microstructure and Mechanical Properties of Plasma Arc Brazed AISI 304L Stainless Steel and Galvanized Steel Plates

Plasma arc brazing is used to join the AISI 304L stainless steel and galvanized steel plate butt joints with the CuSi3Mn1 filler wire. The effect of parameters on weld surface appearance, interfacial microstructure, and composition distribution in the joint was studied. The microhardness and mechanical tests were conducted to determine the mechanical properties of the welded specimens. The results indicated that good appearance, bead shape, and sufficient metallurgical bonding could be obtained when the brazing process was performed with a wire feeding speed of 0.8 m/min, plasma gas flow rate of 3.0 l/min, welding current of 100 A, and welding speed of 27 cm/min. During plasma arc brazing process, the top corner of the stainless steel and galvanized steel plate were heated and melted, and the melted quantity of stainless steel was much more than that of the galvanized steel due to the thermal conductivity coefficient difference between the dissimilar materials. The microhardness test results shows that the microhardness value gradually increased from the side of the galvanized steel to the stainless steel in the joint, and it is good for improving the mechanical properties of joint. The tensile strength was a little higher than that of the brazing filler, and the fracture position of weld joint was at the base metal of galvanized steel plate.     

某304不锈钢管道泄漏的失效分析

某氟化工企业304不锈钢管道在运行三年半后发生泄漏失效。通过直读光谱仪、光学显微镜、扫描电镜和X射线衍射仪等对失效部位材料的化学成分、显微组织、腐蚀形貌及腐蚀产物进行了分析。结果表明:该304不锈钢管道的失效主要为Cl-浓缩造成的点蚀穿孔,H_2S的存在则对点蚀起到了促进作用。     

304不锈钢封头应力腐蚀开裂失效分析

通过化学成分、金相组织、马氏体含量、扫描电镜观察和能谱分析等手段,对某304奥氏体不锈铜容器封头开裂原因进行了分析.结果表明:封头开裂属于形变马氏休和氯离子共同作用引起的应力腐蚀开裂.提出了相应的改进措施.     

Corrosion Resistance of PAPVD TiN Coating on AISI 304 Stainless Steel

In this work the corrosion resistance of PAPVD TiN hard coatings on AISI 304 stainless steel with a titanium interlayer has been addressed. Cyclic voltammetry corrosion tests in NaCl 3.5% solutions were performed for samples prepared by depositing TiN/Ti onto steel using different deposition parameters. The surface morphology of the samples was examined by using a scanning electron microscope (SEM) and phase analysis was performed by X-ray diffraction (XRD). The cyclic voltammetry curves showed two distinct behaviours. Firstly, a reduction in corrosion resistance was observed when current density was increased for the whole potential range studied. The second observation, no less important, was the increase in corrosion resistance compared to the uncoated steel. The TiN films deposited showing (III) preferred orientation showed better corrosion resistance than films presenting other orientations.     

TP304H不锈钢再热器管泄漏原因失效分析

对某电厂锅炉后屏再热器最外圈TP304H管泄漏进行了失效原因分析,主要工作内容包括宏观观察、几何尺寸测量、金相分析、硬度测试、扫描电镜分析和能谱分析。结果表明,后屏再热器最外圈TP304H管的失效类型是热疲劳,烟气温度过高且燃烧不稳定是造成其失效的主要原因。     

Inverse Thermal Analysis of 304L Stainless Steel Laser Welds

An inverse thermal analysis of 304L stainless steel laser welds is presented. This analysis employs a methodology that is in terms of analytical basis functions. The results of this analysis provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations. In addition, these temperature histories can be used to construct parametric-function representations for inverse thermal analysis of welds corresponding to other process parameters or welding processes whose process conditions are within similar regimes. Specific aspects of the inverse-analysis methodology employed that relevant to its understanding and further development are examined.     

SUS304不锈钢膨胀节腐蚀失效分析

分析了杭州市热力管道膨胀节腐蚀失效的原因。SUS304不锈钢波纹管在制作过程中的塑性变形造成的残余应力使得表面出现滑移台阶，导致钝化膜破裂。CEBF耐腐蚀涂层在高温下起泡破损失去保护作用，该不锈钢膨胀节在电化学腐蚀和残余应力双重作用下腐蚀泄漏。为解决SUS304不锈钢波纹管应力腐蚀开裂问题提出了一些可行建议。     

Pack Cementation Coatings for High-Temperature Oxidation Resistance of AISI 304 Stainless Steel

Aluminum and titanium are deposited on the surface of steel by the pack cementation method to improve its hot-corrosion and high-temperature oxidation resistance. In this research, coatings of aluminum and titanium and a two-step coating of aluminum and titanium were applied on an AISI 304 stainless steel substrate. The coating layers were examined by carrying out scanning electron microscopy (SEM) and x-ray diffraction (XRD). The SEM results showed that the aluminized coating consisted of two layers with a thickness of 450???m each, the titanized coating consisted of two layers with a thickness of 100???m each, and the two-step coatings of Al and Ti consisted of three layers with a thickness of 200???m each. The XRD investigation of the coatings showed that the aluminized coating consisted of Al₂O₃, AlCr₂, FeAl, and Fe₃Al phases; the titanized layers contained TiO₂, Ni₃Ti, FeNi, and Fe₂TiO₅ phases; and the two-step coating contained AlNi, Ti₃Al, and FeAl phases. The uncoated and coated specimens were subjected to isothermal oxidation at 1050?°C for 100?h. The oxidation results revealed that the application of a coating layer increased the oxidation resistance of the coated AISI 304 samples as opposed to the uncoated ones.     

Assessment of Sensitization in AISI 304 Stainless Steel by Nonlinear Ultrasonic Method

A nonlinear ultrasonic technique has been developed to evaluate sensitization in Type 304 stainless steel.In order to achieve diferent degree of sensitization(DOS),specimens have been subjected to heat treatment at 675℃ at varying soaking time(0.5,1.0,2.0,3.0 and 4.0 h).Heat treated specimens were subjected to intergranular corrosion tests as per ASTM standards A262 and G108.Sensitization in longer soaked material has been confirmed through ditch microstructures,cracks on the bend tested specimens and higher degree of sensitization.Nonlinear ultrasonic studies showed variation in the nonlinearity parameter with soaking time which also confirms sensitization.A good correlation was observed between the degree of sensitization measured by the electrochemical potentiokinetic reactivation test and the ultrasonic nonlinearity parameter.This study clearly demonstrated that nonlinear ultrasonic technique can be used as a potential technique for non-destructive characterization of sensitization in austenitic stainless steel.     

Optimizing HVOF Spray Parameters to Maximize Bonding Strength of WC-CrC-Ni Coatings on AISI 304L Stainless Steel

High velocity oxygen fuel (HVOF)-sprayed cermet coatings are extensively used to combat erosion-corrosion in naval applications and in slurry environments. HVOF spray parameters such as oxygen flow rate, fuel flow rate, powder feed rate, carrier gas flow rate, and spray distance have significant influence on coating characteristics like adhesion bond strength and shear strength. This paper presents the use of statistical techniques in particular response surface methodology (RSM), analysis of variance, and regression analysis to develop empirical relationships to predict adhesion bond strength and lap shear bond strength of HVOF-sprayed WC-CrC-Ni coatings. The developed empirical relationships can be effectively used to predict adhesion bond strength and lap shear bond strength of HVOF-sprayed WC-CrC-Ni coatings at 95% confidence level. Response graphs and contour plots were constructed to identify the optimum HVOF spray parameters to attain maximum bond strength in WC-CrC-Ni coatings.     

304不锈钢晶间腐蚀裂纹失效分析

304不锈钢是一种应用范围最为广泛的不锈钢,具有优良的使用性能,但在某工厂使用中的一次检测中,发现在腐蚀后的工艺性能中出现了弯曲开裂现象。为确定该材料是否存在晶间腐蚀现象,本文采用GB/T4334-E《不锈钢硫酸-硫酸铜腐蚀试验方法》和GB/T232《金属材料弯曲试验方法》进行腐蚀试验和弯曲试验、然后通过微观检查和宏观检查等方法,对304不锈钢腐蚀裂纹进行了分析,结果表明,304不锈钢所产生的裂纹为晶间腐蚀所造成,造成原因是应力和腐蚀介质所为,而腐蚀程度的不同也造成了裂纹深浅程度的不同。     

304不锈钢在硝酸环境中的腐蚀电化学行为

采用极化曲线和电化学阻抗谱研究了硝酸温度和含量对304不锈钢耐蚀性能的影响。结果表明,在钝化电位下,304不锈钢在硝酸溶液中的阻抗呈现容抗特征,阻抗值达到104Ω·cm2,形成的钝化膜致密完整,随着温度的升高,阻抗值和相位角都减小,局部腐蚀加剧。高温和高含量均会促进钝化膜的溶解,进而加速304不锈钢在硝酸中的腐蚀。     

Corrosion Performance of AISI 304 Stainless Steel in CO2-Saturated Brine Solution

Protection of Metals and Physical Chemistry of Surfaces - Corrosion behavior of 304 stainless steel exposed to a NaCl (3.5 wt %) solution saturated with CO2 has been analyzed using electrochemical...     

AISI304不锈钢渗铜后的微观组织及抗菌性能

以CuO＋NH4Cl为渗剂对AISI 304不锈钢表面进行化学渗铜处理,获得了具有优良抗菌性能的渗铜层。用扫描电镜及小掠射X射线衍射仪分析了渗层深度、微观组织及相组成。试验结果表明,当渗铜处理温度大于900℃后,渗铜层深度及渗层中富铜相Cu9.9Fe0.1及Cu3.8Ni的生成量快速增加。渗层中富铜相生成量越多,不锈钢的抗菌效果越佳,尤其是金黄色葡萄球菌。AISI304不锈钢经950℃保温4h渗铜处理后得到了较深的渗铜层,铜以富铜相形式均匀分布于渗层,具有优良的抗大肠杆菌和金黄色葡萄球菌的效果。     

AISI304奥氏体不锈钢低温离子渗碳工艺优化研究

用正交实验法研究了AISI304奥氏体不锈钢低温离子渗碳工艺。结果表明,优化后的奥氏体不锈钢低温离子渗碳工艺参数为渗碳温度500℃、C3H8：H2=1：30、氩气流量20ml／min、渗碳时间6h。用优化工艺参数处理的奥氏体不锈钢表面可获得单一的Sc相组织,硬度高达780HV0．05。