Electrochemical methods for studying hydrogen diffusivity,permeability, and solubility in AISI 420 and AISI 430 stainless steels

Abstract

Hydrogen permeation and diffusivity were studied electrochemically at temperatures between 283 and 343 K at constant current for annealed and hardened AISI 420 and annealed AISI 430 stainless steel. Permeation rate, effective diffusivity, and solubility were calculated from these data. Annealed AISI 420 shows higher permeation rate and lower diffusivity than annealed AISI 430 stainless steel. Hardened AISI 420 has the highest permeation rate and lowest effective diffusivity. The calculation of solubility values from permeation data is in good agreement with the values obtained using a newly developed electrochemical hydrogen solubility measurement technique.

MST/1026     

Thermal Diffusivity Measurement for Titanium Thin Films on Copper Substrate by Laser Produced Plasmas

The transport properties of condensed phase materials are, in principle, dependent on the local structure and composition of the specimen. This is particularly evident near the free surface of a solid alloy specimen where the morphology, composition, and thermal diffusivity exhibit significant depth dependence, as demonstrated in an earlier study of the depth-resolved thermal diffusivity of a galvanized steel specimen. A new non-contact method was used, based on time-resolved, spectroscopic measurement of the total mass removed from the specimen surface representatively in elemental composition by a high-power laser pulse. A new study of a titanium thin film of varying thickness deposited on a copper substrate is presented. The titanium thin film is first fabricated in a vacuum and then immediately analyzed for composition and thermophysical properties in situ, both by the method of representative laser-produced plasmas (LPP). Successive ablation layers of the thin film, as exposed by LPP ablation, have revealed the dependence of the thermophysical properties on film thickness as well as on depth. The existence of a characteristic length over which the substrate influences the dynamics of thermal transport in the titanium thin film has also been observed.     

基于脉冲涡流热成像的面内方向性热扩散率测量

针对导电材料面内方向性热扩散率的测量,提出脉冲涡流热成像法这一新方法。该方法采用感应式脉冲线激励源,在导电试件表面形成沿一定方向的感应涡流,实现局部热激励,在非稳态条件下实现了材料面内方向热扩散率的测量;简单调节试件与线感应激励线圈的角度,就可以快速无损非接触地测量试件在垂直线圈方向上的热扩散率值。对感应线激励下面内热传导及高斯温度分布进行了分析,分别对AISI304不锈钢、纯铁、纯镍3种材料的热扩散率进行了测量,测量结果与手册值相符,偏差小于9.0%,相对扩展不确定度分别为3.18%,3.72%,3.70%。     

The influence of complexing agent and proteins on the corrosion of stainless steels and their metal components

The present work is devoted to the problem of biodegradation of orthopaedic implants manufactured from stainless steel. In vitro simulations of the biocompatibility of two types of stainless steel, AISI 304 and AISI 316L, and their individual metal components, i.e. iron, chromium, nickel and molybdenum, were carried out in simulated physiological solution (Hank's) containing complexing agents. Knowledge of the effects of the chemical and biological complexing agents, EDTA and proteins, respectively, on the corrosion resistance of a metal should provide a better understanding of the processes occurring in vivo on its surface. The behavior of stainless steels and metal components was studied under open circuit and under potentiostatic conditions. The concentration of dissolved corrosion products in the form of released ions was determined by differential pulse polarography (DPP) and atomic emission spectrometry using inductively coupled plasma (ICP-AES). The composition of solid corrosion products formed on the surface was analyzed by energy dispersive X-ray spectroscopy (EDS) and their morphology was viewed by scanning electron microscopy (SEM). The addition of EDTA and proteins to physiological solution increased the dissolution of pure metals and stainless steels. The effect of particular protein differs on different metals and alloys.     

Numerical and experimental analysis of microstructure formation during stainless steels solidification

The aim of this work is to examine microstructure formation during the solidification of unidirectional solidified AISI 304 stainless steel. Numerical and experimental results indicate that this numerical model allows a precise analysis of the AISI 304 stainless steel microstructure formation. This model determines temperature profiles, position of liquid and solid isotherms, thermal parameters (thermal gradients, tip rate movement, rate cooling), and finally, the secondary inter dendritic spacing. This model was tested by comparing the experimental values results, and thus a reasonable correlation was found.     

Hard TiC Coating on AISI304 Steel by Laser Surface Engineering Using Pulsed Nd:YAG Laser

The surface mechanical property of AISI304 stainless steel was improved by TiC coating deposited through laser surface engineering process using a pulsed Nd:YAG laser. The produced coating exhibited significantly higher hardness (650–1900 HV_0.1) compared to the steel substrate (190 HV_0.1). Coating thickness, dilution of TiC on substrate surface, and hardness of the coating were determined using various pulse laser processing parameters, i.e., peak power and pulse frequency. At low pulse frequency and peak power condition, relatively thick and uniform coating of TiC was deposited over the substrate. However, at higher pulse frequency and peak power condition, TiC-dispersed steel composite coating was produced.     

Thermal wave interferometry for measuring the thermal diffusivity of thin slabs

Thermal wave interferometry applied to the evaluation of thermal diffusivity of freestanding coatings and single layers is herewith presented. Measurements on a set of eight different materials (oxides free copper, an aluminium alloy, Armco iron, AISI 316 stainless steel, Nimonic90 and IN738 nickel based alloys and Yttria partially stabilised Zirconia coatings) have been carried out. The corresponding thermal diffusivity values cover a very large range (about three order of magnitude). A comparison of 1D and 3D models has been done in order to optimise the main measurement parameters. Sample thickness, heating beam size and modulation frequency range have been selected in order to maximise the photothermal signal and its phase variation as a function of the frequency. Experimental results give evidence of a very good agreement between literature and experimental values for all samples confirming the capability of this technique for measuring the thermal diffusivity of thin slabs.     

Evolution of the metal–oxide interface during the initial stage of the high temperature oxidation of ferritic stainless steels

Abstract

Two grades of ferritic stainless steel, a bi-stabilised Ti, Nb (AISI 441) and a stabilised Ti (AISI 439), were oxidised at 1060°C under the simulated process atmosphere for durations between 45 and 1800 s. Focused ion beam coupled with field emission gun and scanning electron microscopy was carried out to investigate the cross-section morphology of the oxide growing on ferritic stainless steels. Matrix protrusions localised at the metal – chromia interface through the silica layer are observed and the following mechanism for their formation is proposed. During the first step of oxidation, interface undulation, induced by growth stresses, in combination with silica precipitation at the metal – oxide interface lead to the formation of matrix protrusions in the chromia layer. For an increased oxidation time, due to the laterally silica growth matrix protrusions are trapped into the Cr₂O₃ layer as matrix inclusions.     

Metallurgical investigation on stainless steel bellows used in satellite launch vehicle

Bellows made of austenitic stainless steel AISI 304 grade are being used as conduit for liquid fuel and oxidizer in propellant tank of satellite launch vehicle. These bellows encountered frequent leakage problems. Leakage locations were found to be along the fusion line of ring to ply weld. In many of such failures, synergistic effect of chloride ions and thermal stresses from welding was the cause identified. Detailed metallurgical characterization of bellows with different weld parameters have been carried out, which served as an efficient tool for qualification of the processing of bellows. This paper highlights various metallurgical features observed in stainless steel bellows during process qualification programme and their impact on the performance.     

Laser ablation threshold dependence on pulse duration for fused silica and corneal tissues: experiments and modeling

The surface ablation threshold fluence of fused silica and two porcine cornea layers, the epithelium and the stroma, is characterized as a function of the laser pulse duration in the range of 100 fs-5 ps for a wavelength of 800 nm (Ti:sapphire laser system). The plateaulike region observed between 100 fs and 1 ps for the corneal layers indicates that for use in laser surgery, laser pulse durations chosen within this range should be practically equivalent. Our model predicts that the ablation threshold will decrease rapidly for pulse durations in the low end of the femtosecond regime.     

Tensile and Impact Properties of Shielded Metal Arc Welded AISI 409M Ferritic Stainless Steel Joints

The present study is concerned with the effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the joints fabricated by austenitic stainless steel, ferritic stainless steel and duplex stainless steel filler metals were evaluated and the results were reported. From this investigation, it is found that the joints fabricated by duplex stainless steel filler metal showed higher tensile strength and hardness compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Joints fabricated by austenitic stainless steel filler metal exhibited higher ductility and impact toughness compared with the joints fabricated by ferritic stainless steel and duplex stainless steel filler metals.     

Laser surface hardening of AISI 420 stainless steel treated by pulsed Nd:YAG laser

The AISI 420 martensitic stainless steel was surface-hardened by a pulsed Nd:YAG laser. The influences of process parameters (laser pulse energy, duration time and travel speed) on the depth and hardness of laser treated area and its corrosion behavior were Investigated. In the optimum process parameters, maximum hardness (490 VHN) in the laser surface treated area was achieved. The pitting corrosion behavior was studied by potentiodynamic polarization technique in 3.5% NaCl solution at 25 °C. Metallographical and electrochemical corrosion studies illustrated beneficial effects of laser surface hardening by refining the microstructure and enhancing the pitting corrosion resistance of the martensitic stainless steel. The pitting corrosion resistance of laser surface treated samples in 3.5% NaCl solution depends on the overlap ratio clearly. The pitting potential (E_pp) decreased significantly by increasing the ratio of pulse overlapping.     

Microstructural,Structural, and Thermal Characterization of Annealed Carbon Steels

As is well known, the metallurgical microstructure of carbon steel is formed by ferrite and pearlite after the annealing heat treatment. When the cooling rate increases, the diffusive process is interrupted causing a change in the metallurgical microstructure which will affect steel properties. The aim of this work was to study thermal, structural, and microstructural properties of annealed carbon steel samples with four different carbon contents. Crystalline structure and crystalline quality were studied by the X-ray diffraction technique, where the full width at half maximum analysis showed that as the carbon content increased, the crystalline quality decreased. The metallurgical microstructure morphology was studied by scanning electron microscopy. The thermal diffusivity and the heat capacity were determined by the photoacoustic technique and by the thermal relaxation method, respectively. The thermal diffusivity and the thermal conductivity decreased as the carbon content increased. The amplitude signal of photothermal radiometry increased as the carbon content increased, while the phase signal of photothermal radiometry did not show significant differences among studied carbon steel types. The photoacoustic technique represents an important alternative in the steel characterization field.     

Effects of Surface Morphology and Composition Modification on Spectral Emissivity and Thermal Diffusivity Profile at High Temperatures

A new all-spectroscopic method for depth-resolved thermal diffusivity measurement of metallic specimens has been demonstrated. The method entails measurement of the mass entrained into a laser-produced plasma (LPP) plume in such a manner that the plume is representative of the specimen in elemental composition. Both the abundance of matter and its elemental composition are measured by time-resolved spectroscopy for each LPP plume. In order to delineate the morphology versus composition basis of the depth dependence, a new study on a Nichrome ribbon specimen heated by ohmic heating in a vacuum is presented. A set of depth-resolved thermal diffusivity measurements is carried out, while noting the attendant changes in the spectral emissivity and elemental composition at succeeding ablation layers. Additional measurements are carried out after the specimen has been treated under varying heating conditions. Preferential diffusion of chromium at high temperatures has been found to contribute to the dynamics of surface thermophysical properties at high temperatures. Representative LPP ablation is well suited for removal of surface impurities prior to thermophysical property measurements by the pulse heating technique.     

Corrosion of a stainless steel handrail

AISI 304 and 304L stainless steels are “workhores” grades of austenitic stainless steel frequently used in architectural applications, as well as in cookware, appliances, and numerous other applications where resistance to corrosion is required. This paper examines a corrosion failure (the appearance of rustlike stains on the surface) of a 304 stainless steel handrail that appears to have occurred as a result of contamination during the fabrication process.     

Stress relaxation in bending of type AISI304 stainless steel at 773 and 823 K

Stress relaxation measurements at 773 and 823 K in bending and for different initial stresses in type AISI 304 stainless steel are reported. Several thermal treatments were given to the specimens prior to the relaxation testing. The data are fitted to a general equation that describes thermally activated dislocation motion and it is shown that, in some cases, the internal stress changes with the applied stress. No substantial differences were found in the stress relaxation behaviour on changing the thermal treatment. This is attributed to the influence of dynamic strain ageing; an equation which can be used to describe experimental log stress against log strain rate curves is presented.     

Sensitization evaluation of the austenitic stainless steel AISI 304L, 316L, 321 and 347

This work presents a systematic investigation of the influence of time and temperature in the sensitization of stainless steel AISI 304L, AISI 316L, AISI 321 and AISI 347 pipes used in petroleum refining plants. The sensitization was assessed by Scanning Electron Microscopy (SEM) according to ASTM A-262 and by the Double Loop Electrochemical Potentiokinetic Reactivation test (DLEPR). The results showed that all steels did not present sensitization at operating temperature (380°C) in the desulfurizers process, but the temperature of 500°C was critical to the appearing of sensitization for the both low carbon stainless steels and AISI 321 SS, while for the AISI 347 the critical temperature was 550°C. The stabilized steels confirmed to be more resistant to sensitization than the low carbon stainless steels, and niobium showed to be more efficient stabilizing agent than titanium.     

热轧304不锈钢表面氧化皮特性的探讨

304不锈钢冷轧钢卷应用广泛,其表面质量的好坏与后续的酸洗密切相关,而冷轧前其热轧表面氧化皮的结构及与基材的结合力是影响酸洗效果的重要因素.分析了热轧304不锈钢在空冷、水冷和空冷干轧后表面氧化皮的形貌,测试了其与基体的结合力.结果表明:空冷后的氧化皮厚而疏松,上下表面的差别较大,其结合力分别为3.71,5.98 MP...     

Stellite 21 coatings on AISI 410 martensitic stainless steel by gas tungsten arc welding

Abstract

Degradation of AISI 410 martensitic stainless steel, a typical alloy for many applications such as steam turbine blade, could impair its efficiency and lifetime. To overcome this problem, critical surfaces could be modified by weld cladding via gas tungsten arc welding technique. In the present research, a comparative study of Stellite 21 weld overlays deposited in three different thicknesses, i.e. dilutions, at various preheat and post-weld heat treatment temperatures on the surface of AISI 410 martensitic stainless steel, has been made. The surface of coatings has been examined to reveal their microstructures, phase characterisation and mechanical properties using XRD, microhardness tester and metallographic techniques. The results showed that the deposition of Stellite 21 coating on AISI 410 martensitic stainless steel improved its corrosion resistance. Moreover, the volumetric dilution had a considerable effect on the hardness, microstructure and electrochemical corrosion behaviour of Stellite 21 weld overlays.