Electrochemical release testing of a stainless steel in a glucose solution using thin layer activation

The contamination of consumer products, e.g. food, during production, storage and/or transport, due to release of chemicals caused by contact with technical components is of some concern. Various methods can be used to study the release of these chemicals. These include those using radiotracers, such as thin layer activation (TLA). A dedicated facility combining TLA with electrochemical tests is presented. Its use is illustrated with Ni and Cr release during electrochemical testing of 316L stainless steel in a glucose solution. TLA offers various advantages, which include area selectivity, high sensitivity, and the possibility for in situ and on-line monitoring of elements. Due to the complementarity of TLA with the conventional electrochemical methods it contributes to a better understanding of the underlying release processes. Additionally, the usefulness of TLA to develop more reliable test methodology is indicated.     

New methods of predicting dissimilar steel weld metal microstructures by Schaeffler Diagram

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Feasibility study of the minimum quantity lubrication in high-speed end milling of NAK80 hardened steel by coated carbide tool

High-speed milling of hardened steels generates high cutting temperature and leads to detrimental effects on tool life and workpiece surface finish. In this paper, feasibility study of the minimum quantity lubrication (MQL) in high-speed end milling of NAK80 hardened steel by coated carbide tool was undertaken. Flood cooling and dry cutting experiments were conducted also for comparison. It is found that cutting under flood cooling condition results in the shortest tool life due to severe thermal cracks while the use of MQL leads to the best performance. MQL is beneficial to tool life both in the lower speed cutting and the higher speed cutting conditions. A less viscous oil of MQL is essential in high cutting speed so that cooling effect can be effective. SEM micrograph of the insert shows that the use of MQL in high-speed cutting can delay welding of chips on the tool and hence prolongs tool life as compared with dry cutting condition. The application of MQL also improves machined surface finish in high-speed milling of die steels.     

Effect of nitrogen on corrosion behavior of 28Cr-7Ni duplex and microduplex stainless steels in air-saturated 3.5 wt% NaCl solution

The corrosion behavior of 28Cr-7Ni-O-0.34N duplex stainless steels in air-saturated 3.5-wt% NaCl solution at pH 2, 7, 10 and 27 °C was studied by the potentiodynamic method. Two types of microstructures were investigated: the as-forged duplex and microduplex (average austenite grain size 5-16 μm) structures. The austenite volume fractions of the tested steels were between 0.35 and 0.64. The nitrogen effect on corrosion behaviors of both duplex and microduplex stainless steels were the same. At pH 2, the corrosion potential increased when the nitrogen content increased, however, corrosion current density as well as corrosion rate decreased. At pH 7 and 10, the effect of nitrogen on corrosion potential and corrosion rate could not be observed. Corrosion potential at pH 10 was lower than at pH 7. Pitting potential increased when the nitrogen content in the tested steels increased at all tested pH. For the nitrogen effect on the passive current density, it seemed that only at pH 2, the average passive current densities reduced when the nitrogen content increased. Nitrogen may have participated in the passive film or has been involved in the reaction to build up passive film. The ammonium formation and nitrogen enrichment at the interface metal/passive film with adsorption mechanism were discussed. The dissolute nitrogen might have combined with the hydrogen ions in solution to form ammonium ions, resulting in increasing solution pH. The steel could then easily repassivate, hence the corrosion potential and pitting potential would increase. However, the ammonium formation mechanism could not explain the decrease of corrosion potential in basic solution. Nitrogen enrichment at the metal/passive film interface with adsorption mechanism seemed to be an applicable consideration in increasing pitting potential. However, this mechanism did not involve the ammonium ion formation. In general, for the duplex and microduplex stainless steels tested, nitrogen increased the general corrosion resistances in acid solution and pitting corrosion resistance at all solution pH. Metallographic observation in both tested duplex and microduplex steels after pitting corrosion at all tested pH revealed that, the corroded structure in the tested steels without nitrogen alloying was austenite, but those with nitrogen alloying was ferrite. Even though ferrite had a higher chromium content than austenite but higher dissolved nitrogen in austenite than in ferrite may have increased the pitting resistance equivalent number (PRE) of austenite to be higher than that of ferrite.     

Friction welding of TiAI intermetallics and structural steel by applying Inconel 718 as interlayer

Inconel 718 with thickness ranged from 0. 1 - 1.7 mm was chosen as interlayer to promote weldability in friction welding of TiAl intermetallics and structural steel such as AIS14140, in which the welded joint presents single fin showing less welding deformation on TiAl side. The correlations between tensile strength and the interlayer thickness were analyzed and fitted to a model. It indicates an optimum interlayer thickness ranged from 0.9 - 1.1 mm where the tensile strength reaches as high as 360 MPa. Otherwise, while the interlayer thickness decreases to 0. 1 mm, brittle compounds of TiC, Al2Ti4C2 and MTC3 are formed in the welded zone so that the tensile strength decays. Thicker interlayer should be also avoided as double joints may occur at TiAl -lnconel 718 and lnconel 718 -AISI 4140, respectively, which lowers the tensile strength to some extent.     

用微型杯突试验法评价和估算钢的强度和塑性

采用一种新型在线无损检测的试验方法--微型杯突试验法研究电站锅炉管道用9Cr-1Mo-V-Nb-N钢的强度和塑性.结果表明:该试验方法与常规的单轴拉伸试验之间有很好的可比性,并且通过微型杯突试验的结果估算9Cr-1Mo-V-Nb-N钢的屈服强度与抗拉强度及伸长率,给出相应的经验公式.同时在采用微型杯突试验法估算9Cr-1Mo-V-Nb-N钢的塑性时,首次提出断裂挠度率的概念.     

回火过程对40Cr钢淬火残余应力的影响

使用40Cr钢偏心圆环试样,淬火后经不同温度和时间回火,用X-射线应力仪测定其不同部位的残余应力。对测定结果处理分析后认为,X-射线应力仪测出的残余应力值,其中有一部分是和该材料强度相对应的;回火过程中残余应力的变化,不仅与回火温度和时间有关,而且与组织转变中各相比容变化有着密切关系;同时发现,回火时也可能使残余应力增加。     

Optimisation of specimen temperature and pulse fraction in atom probe microscopy experiments on a microalloyed steel

This paper details the effects of systematic changes to the experimental parameters for atom probe microscopy of microalloyed steels. We have used assessments of the signal-to-noise ratio (SNR), compositional measurements and field desorption images to establish the optimal instrumental parameters. These corresponded to probing at the lowest possible temperature (down to 20 K) with the highest possible pulse fraction (up to 30%). A steel containing a fine dispersion of solute atom clusters was used as an archetype to demonstrate the importance of running the atom probe at optimum conditions.     

Crack propagation of pipeline steel exposed to a near-neutral pH environment under variable pressure fluctuations

This investigation attempts to understand the corrosion fatigue crack propagation behavior of pipeline steels exposed to near-neutral pH environments. The fatigue loading was designed to simulate the underload-type variable amplitude pressure fluctuations found during pipeline operation. The effects of amplitudes (R ratios) of underload and minor cycles were investigated. It has been found from this investigation that the crack growth rate is enhanced significantly through load interaction of the variable amplitude fatigue. The acceleration factor is found to be up to 2.7 and 5.3 for tests in air and in the near-neutral pH solution, respectively. The crack growth rate decreases with R ratios of underload and minor cycles for tests both in air and in near-neutral pH environments. The latter could enhance crack propagation by a factor of up to 11, as compared with the crack growth rate in air. The critical R ratio of minor cycles at which the minor cycles do not contribute to crack propagation through load interaction was determined to be as high as 0.982, which is much lower than the threshold determined by constant amplitude fatigue. This critical R ratio could be utilized to demarcate stress corrosion cracking and corrosion fatigue, and should be incorporated as one of the design principles for components/structures subjected to variable amplitude cyclic loading.     

深冷处理对AISI 310S不锈钢耐腐蚀磨损性能的影响

研究了深冷处理对AISI 310S不锈钢在3.5%(质量分数)Na Cl溶液中耐腐蚀磨损性能的影响,将310S不锈钢在-196℃进行保温深冷处理,结果表明:相对未深冷处理,深冷处理之后,材料的晶粒得到细化,更多碳化物弥散析出基体;深冷处理之后材料的耐腐蚀性能得到提高,在深冷处理4 h时达到最佳值,相比未深冷处理,自腐蚀电位从-0.525 V提高到-0.423 V,提升了19.4%;且深冷处理之后,材料的耐腐蚀磨损性能得到提升,经过深冷处理4 h,材料的磨损率从120×10-6mm3/Nm降低到63×10-6mm3/Nm,降低90%。