Accelerated fretting wear testing using ultrasonics

The room temperature fretting wear characteristics of a stainless steel (AISI 304) have been studied using an ultrasonic frequency of vibration. In the work the influence of number of cycles, normal load and displacement amplitude on wear rate and wear mechanisms has been explored. It is found that ultraosnic fretting displays many of the characteristics of low frequency fretting described in literature, especially once steady state conditions have developed. The results are promising with respect to the application of ultrasonic fretting as a new technique for accelerated fretting wear testing.     

Guided ultrasonic waves for non-destructive monitoring of the stress levels in prestressed steel strands

The safety of prestressed civil structures such as bridges, dams, nuclear power plants, etc. directly involves the security of both environment and users. Health monitoring of the tensioning components, such as strands, tendons, bars, anchorage bolts, etc. is an important research topic and a challenging task bringing together the non-destructive evaluation (NDE) and civil engineering communities. This paper deals with a guided ultrasonic wave procedure for monitoring the stress levels in seven-wire steel strands (15.7 mm in diameter). The mechanical and geometrical characteristics of the prestressed strands were taken into account for optimizing the measurement configuration and then the choice of the guided ultrasonic mode at a suitable frequency. Simplified acoustoelastic formulations were derived from the acoustoelasticity theory according to either calibration test or in situ measurement. The results from acoustoelastic measurements on the seven-wire steel strands are presented and discussed in the case of calibration tests and industrially prestressed strands. They show the potential and the suitability of the proposed guided wave method for evaluating the stress levels in the tested seven-wire steel strands.     

Kinetic approach to mild steel corrosion

Summary The rate of steel corrosion in hydrochloric acid solutions in the absence and in the presence of inhibitors is studied. It is found that the process dynamics is described by an exponential kinetic equation of self-accelerating reactions in the absence of inhibitor and by an equation of a zero order in its presence.     

Investigation of the Thermal Stability of Laser Nitrided Iron and Stainless Steel by Annealing Treatments

Laser nitriding has revealed to be a very promising and effective treatment to improve the technical properties, like surface hardness and corrosion-wear resistance, of iron and steels. The high nitrogen concentration, the fastness and precision of the treatment and the easy experimental setup make this technique very suitable for applications on industrial scale. Samples of pure iron and austenitic stainless steel have been irradiated with ns laser pulses in the UV radiation range and analyzed by means of Conversion Electron Mössbauer Spectroscopy (CEMS), Resonant Nuclear Reaction Analysis (RNRA), Grazing Incidence X-Ray Diffraction (GXRD) and Microhardness. Mössbauer Spectroscopy, in particular, is capable of detecting the phase composition of the nitrided layer and therefore represents an essential tool for these kind of analysis. The thermal stability of the treated samples have been investigated by subsequent annealings at increasing temperatures in vacuum and in air. For iron samples the annealing treatment at 250°C shows a rather drastic phase transformation from phase (fcc) into (Fe₄N) while a strong depletion of N has been observed for 400°C or higher, regardless of the ambient pressure (atmospheric or vacuum). On the other hand, the stainless steel shows a very good thermal stability up to 500°C, but higher temperatures induce a gradual decrease in the nitrogen concentration which seems to be a common feature for both pure iron and stainless steel. Furthermore, annealing in air leads to the formation of a thin oxide layer on the surface of the iron sample which is easily characterized by Mössbauer spectroscopy.     

Morphology and composition of nanoscale surface oxides on Fe–20Cr–18Ni{1 1 1} austenitic stainless steel

Surface oxidation ranging from initial stages to the onset of passive oxide layer formation have been investigated on Fe–20Cr–18Ni{1 1 1} single crystal surface by X-ray photoelectron spectroscopy (XPS). Surface segregation of the alloying elements and the morphology of the surface oxide nanostructure were characterized quantitatively by inelastic electron background analysis. Our results demonstrate that by increasing the oxidation temperature the relative concentrations of Fe²⁺ and Fe³⁺ cations increase due to their enhanced mobility. Higher temperature also improves the mobility of chromium, thus enhancing its segregation to the oxygen-rich surface and thereby reinforcing the passive layer on the alloy. This is in agreement with the results showing the sudden decrease in oxide film thickness at the oxidation temperatures exceeding 600 K. Additionally, a pronounced segregation of metallic nickel is found in the interface between the surface oxide layer and the bulk alloy.     

Corrosion behaviour of AISI 304 stainless steel with Cu coatings in H2SO4

The work addresses the influence of cementation and electrodeposition of copper coatings on the corrosion resistance of AISI 304 stainless steel immersed in 30 wt.% H₂SO₄ at temperatures of 25 and 50 °C. Corrosion process was evaluated by gravimetric tests, DC measurements and electrochemical impedance spectroscopy (EIS). The specimen surfaces were analysed by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. The corrosion performance of AISI 304 stainless steel in sulphuric acid solution was greatly improved by copper coatings. The amount of copper deposited by the cementation process was sufficient to protect the stainless steel of corrosion. A greater amount of copper obtained by electrodeposition treatments does not supply further improvement in the corrosion behaviour. The improved corrosion resistance is related to copper dissolution at the initial stages of immersion tests and the presence of Cu²⁺ in the solution, which makes the medium more oxidizing, increasing the stability of the passive layer. In addition, the presence of copper at the surface reduces the overpotential of cathodic reaction, enabling the transition from an active region to the passive one.     

Electrochemical, theoretical and XPS studies of 2-mercapto-1-methylimidazole adsorption on carbon steel in 1 M HClO4

The inhibition of the corrosion of carbon steel in 1 M HClO₄ by 2-mercapto-1-methylimidazole (MMI) has been investigated in relation to the concentration of the inhibitor as well as the temperature using weight loss and electrochemical measurements. The effect of the temperature on the corrosion behaviour with addition of different concentrations of MMI was studied in the temperature range 30-60 °C. Polarization curves reveal that MMI is a mixed type inhibitor. The inhibition efficiency of MMI is temperature independent but increases with the inhibitor concentration. Changes in impedance parameters (charge transfer resistance, R_t, and double-layer capacitance, C_dl) were indicative of adsorption of MMI on the metal surface, leading to the formation of a protective film. Adsorption of MMI on the carbon steel surface is found to obey the Langmuir adsorption isotherm. Some thermodynamic functions of dissolution and adsorption processes were also determined. The X-ray photoelectron spectroscopy (XPS) of the carbon steel indicated that MMI is chemically adsorbed on the steel surface. Moreover, the electronic properties such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels and molecular orbital densities were calculated.     

Application of LIBS to the in-line process control of liquid high-alloy steel under pressure

A process optimization and control system called VAI-CON Chem has been developed that uses laser-induced breakdown spectroscopy (LIBS) to quasi-continuously chemically analyze liquid high-alloy steel under pressure. The beam from a Nd:YAG laser, located on safe ground and operating at its fundamental wavelength, is guided by a mirror system to a process tuyere below bath level. Passing through the ∼1.5 m long tuyere, the beam is then focused onto the steel bath. Light emitted from the induced plasma passes back through the tuyere, which is coupled to a fiber optic cable that carries the information over a distance of approximately 10 m back to an Echelle spectrometer located beside the laser. Calibrations were performed using the complete system, located in a laboratory, during system testing. An induction furnace was used to simulate the AOD converter, wherein the samples were molten and superheated to a temperature of ∼1600 °C and kept at a pressure of ∼1.7 bar under an argon atmosphere. Twelve different high alloyed reference samples taken from normal AOD production with Fe concentrations of >48 wt.% and non-Fe element concentrations of up to 25 wt.% were available for calibration. The mean residual deviations (defined as the square root of the variance of the concentration ratios determined by LIBS and the reference element concentration ratios) obtained were close to those reported for other comparable high-alloy samples that were investigated at room temperature under normal atmospheric pressure.     

分光光度法快速测定低合金钢中的铌

用盐酸—过氧化氢溶解试样，在2．9mol／L盐酸溶液介质中，铌与氯磺酚—S形成稳定的蓝紫色络合物，其最大吸收波长约为650nm，用分光光度法可以测定低合金钢中的铌。用该法对含铌标准样品进行测定，测得值与标准值基本一致，测定结果的相对标准偏差为2．1％～6．7％。     

光电直读光谱法测定重轨钢中碳偏析的方法研究

采用类型校正法消除了光谱法与红外吸收法在测定重轨钢中碳含量时的系统误差。结合金相低倍组织检验，分析了光谱法在重轨腰部碳分析结果异常偏高的原因，并建立了相应的分析方法。该方法已用于重轨钢样的均匀性检验中，取得了良好的效果。