Investigation of high cycle and Very-High-Cycle Fatigue behaviors for a structural steel with smooth and notched specimens

The high cycle and Very-High-Cycle Fatigue (VHCF) properties of a structural steel with smooth and notched specimens were studied by employing a rotary bending machine with frequency of 52.5 Hz. For smooth specimens, VHCF failure did occur at fatigue cycles of 7.1 x 10(8) with the related S-N curve of stepwise tendency. Scanning Electron Microscopy (SEM) was used for the observations of the fracture surfaces It shows that for smooth specimens the crack origination is surface mode in the failure regime of less than 10(7) cycles While at VHCF regime, the material failed from the nonmetallic inclusion lies in the interior of material, leading to the formation of fisheye pattern. The dimensions of crack initiation region were measured and discussed with respect to the number of cycles to failure. The mechanism analysis by means of low temperature fracture technique shows that the nonmetallic inclusion in the interior of specimen tends to debond from surrounding matrix and form a crack. The crack propagates and results to the final failure. The stress intensity factor and fatigue strength were calculated to investigate the crack initiation properties. VHCF study on the notched specimens shows that the obtained S-N curve decreases continuously. SEM analysis reveals that multiple crack origins are dominant on specimen surface and that fatigue crack tends to initiate from the surface of the specimen. Based on the fatigue tests and observations, a model of crack initiation was used to describe the transition of fatigue initiation site from subsurface to surface for smooth and notched specimens. The model reveals the influences of load, grain size, inclusion size and surface notch on the crack initiation transition. (C) 2010 Elsevier Ltd. All rights reserved

The thermal fatigue resistance of vermicular cast iron coupling with H13 steel units by cast-in process

This paper focuses on improving the thermal fatigue resistance on the surface of vermicular cast iron coupling with inserted H13 steel blocks that had different cross sections, by cast-in processing. The microstructure of bionic units was examined by scanning electron microscope. Micro-hardness and thermal fatigue resistance of bionic samples with varied cross sections and spacings were investigated, respectively. Results show that a marked metallurgical bonding zone was produced at interface between the inserted H13 steel block and the parent material - a unique feature of the bionic structure in the vermicular cast iron samples. The micro-hardness of the bionic samples has been significantly improved. Thermal resistance of the samples with the circular cross section was the highest and the bionics sample with spacing of 2 mm spacing had a much longer thermal fatigue life, thus resulting in the improvement for the thermal fatigue life of the bionic samples, due to the efficient preclusion for the generation and propagation of crack at the interface of H13 block and the matrix. Crown Copyright (c) 2010 Published by Elsevier Ltd. All rights reserved.

Void swelling in MA956 ODS steel irradiated with 122 MeV Ne-ions at elevated temperatures

An investigation of a commercial oxide dispersion-strengthened steel (MA9561) irradiated with high energy Ne-ions to high doses at elevated temperatures is presented. Specimens of MA956 oxide dispersion strengthened steel together with a 9% Cr ferritic/martensitic steel, e.g., Grade 92 steel were irradiated simultaneously with 20Ne-ions (with 122 MeV) to successively increasing damage levels of 1, 5 and 10 dpa at the damage peak at 440 C and 570 C, respectively. Cross-sectional microstructures of the specimens were investigated with transmission electron microscopy. MA956 oxide dispersion strengthened steel showed a higher resistance to void swelling especially to void growth at the grain boundaries than the ferritic/martensitic steel, e.g., Grade 92 steel did, and thus exhibited a prominence for an application in the situation of a high He production at high temperatures. The suppression of the growth of voids especially at the grain boundaries in MA956 is ascribed to an enhanced recombination of the point defects and a trapping of Ne atoms at the interfaces of the yttrium–aluminum oxide particles and the matrix.

Void swelling in a 9Cr ferritic/martensitic steel irradiated with energetic Ne-ions at elevated temperatures

In this work the void swelling behavior of a 9Cr ferritic/martensitic steel irradiated with energetic Ne-ions is studied. Specimens of Grade 92 steel (a 9%Cr ferritic/martensitic steel) were subjected to an irradiation of Ne-20-ions (with 122 MeV) to successively increasing damage levels of 1, 5 and 10 dpa at a damage peak at 440 and 570 degrees C, respectively. And another specimen was irradiated at a temperature ramp condition (high flux condition) with the temperature increasing from 440 up to 630 degrees C during the irradiation. Cross-sectional microstructures were investigated with a transmission electron microscopy (TEM). A high concentration of cavities was observed in the peak damage region in the Grade 92 steel irradiated to 5 dpa, and higher doses. The concentration and mean size of the cavities showed a strong dependence on the dose and irradiation temperature. Enhanced growth of the cavities at the grain boundaries, especially at the grain boundary junctions, was observed. The void swelling behavior in similar 9Cr steels irradiated at different conditions are discussed by using a classic void formation theory. (c) 2008 Elsevier B.V. All rights reserved.

Preparation of palladium membrane over porous stainless steel tube modified with zirconium oxide

A palladium membrane has been prepared by electroless plating on the surface of a porous stainless steel tube. Since the large surface pores of the tube are obstacle for preparation of a defect-free palladium film on the surface, zirconium oxide particles were deposited inside the pores. The mean thickness of the resulting Pd membrane on the modified tube was ca. 10 mum. It is suggested that the permeability of hydrogen is partly governed by gas diffusion in the pores. (C) 2004 Elsevier B.V. All rights reserved.

Study of sintered stainless steel fiber felt as gas diffusion backing in air-breathing DMFC

Adoption of a sintered stainless steel fiber felt was evaluated as gas diffusion backing in air-breathing direct methanol fuel cell (DMFC). By using a sintered stainless steel fiber felt as an anodic gas diffusion backing, the peak power density of an air-breathing DMFC is 24 mW cm(-2), which is better than that of common carbon paper. A 30-h-life test indicates that the degraded performance of the air-breathing DMFC is primarily due to the water flooding of the cathode. Twelve unit cells with each has 6 cm(2) of active area are connected in series to supply the power to a mobile phone assisted by a constant voltage diode. The maximum power density of 26 mW cm(-2) was achieved in the stack, which is higher than that in single cell. The results show that the sintered stainless steel felt is a promising solution to gas diffusion backing in the air-breathing DMFC, especially in the anodic side because of its high electronical conductivity and hydrophilicity. (C) 2004 Elsevier B.V. All rights reserved.

Oxidation of cyclohexane - A significant impact of stainless steel reactor wall

The selective oxidation of cyclohexane to cyclohexanol and cyclohexanone is an important chemical process and it has been paid more attentions recently. In the present work, the stainless steel reactor wall was found to influence the selective oxidation of cyclohexane very significantly, and a quasi-crystalline Ti45Zr35Ni17Cu3 alloy with the similar compositions as the reactor wall was used as a catalyst for the cyclohexane oxidation, as expected, a higher activity was obtained with it. The present results open up a new avenue for developing new catalyst for alkane oxidation.

Long-term anticorrosion behaviour of polyaniline on mild steel

Anticorrosion performances of polyaniline emeraldine base/epoxy resin (EB/ER) coating on mild steel in 3.5% NaCl solutions of various pH values were investigated by electrochemical impedance spectroscopy (EIS) for 150 days. In neutral solution (pH 6.1), EB/ER coating offered very efficient corrosion protection with respect to pure ER coating, especially when EB content was 5-10%. The impedance at 0.1 Hz of the coating increased in the first 1-40 immersion days and then remained constant above 10(9) Omega cm(2) until 150 days, which in combination with the observation of a Fe2O3/Fe3O4 passive film formed on steel confirmed that the protection of EB was mainly anodic. In acidic or basic solution (pH 1 or 13), EB/ER coating also performed much better than pure ER coating. However, these media weakened the corrosion resistance due to breakdown of the passive film or deterioration of the ER binder.

Polyaniline for corrosion prevention of mild steel coupled with copper

Polyaniline emeraldine base/epoxy resin (EB/ER) coating was investigated for corrosion protection of mild steel coupled with copper in 3.5% NaCl solution. EB/ER coating with 5-10 wt% EB had long-term corrosion resistance on both uncoupled steel and copper due to the passivation effect of EB on the metal surfaces. During the 150 immersion days, the impedance at 0.1 Hz for the coating increased in the first 1-40 days and subsequently remained constant above 10(9) Omega cm(2), whereas that for pure ER coating fell below 10(6) Omega cm(2) after only 30 or 40 days. Immersion tests on coated steel-copper galvanic couple showed that EB/ER coating offered 100 times more protection than ER coating against steel dissolution and coating delamination on copper, which was mainly attributed to the passive metal oxide films formed by EB blocking both the anodic and cathodic reactions. Salt spray tests showed that 100 mu m EB/ER coating protected steel-copper couple for at least 2000 h.

INHIBITION OF CORROSION BY HEXADECYL TRIMETHYL AMMONIUM BROMIDE LANGMUIR-BLODGETT MONOLAYERS ON CARBON-STEEL

Langmuir-Blodgett (LB) monolayers of hexadecyl trimethyl ammonium bromide (HTAB) were deposited onto a carbon steel surface to investigate the inhibition of corrosion by measurement of the polarization resistance and cyclic voltammetry. The corrosion proc

Adsorption and Corrosion Inhibition Behavior of Mild Steel by One Derivative of Benzoic-Triazole in Acidic Solution

A newly synthesized benzoic-triazole derivative 3,5-dimethylbenzoic acid [1,2,4]triazol-l-ylmethyl ester (DBT) was investigated as a corrosion inhibitor of mild steel in 1 M HCl solution using weight loss measurements, potentiodynamic polarization, SEM, and EIS methods. The results revealed that DBT was an excellent inhibitor, and the inhibition efficiencies obtained from weight loss and electrochemical experiments were in good agreement. Using the potentiodynamic polarization technique, the inhibitor was proved to have a mixed-type character for mild steel by suppressing both anodic and cathodic reactions on the metal surface. The number of water molecules (X) replaced by a molecule of organic adsorbate was determined from the Flory-Huggins, Dhar-Flory-Huggins, and Bockris-Swinkels substitutional adsorption isotherms applied to the data obtained from the gravimetric experiments performed on a mild steel specimen in 1 M HCl solution at 298 K.

Corrosion behaviour of steel in beach soil along Bohai Bay

Research on corrosion of steel structures in various marine environments is essential to assure the safety of structures and can effectively prolong their service life. In order to provide data for anticorrosion design of oil exploitation structures in the Bohai Bay, the corrosion behaviour and properties of steel in beach soil, using typical steel samples (Q235A carbon steel and API 5Lx52 pipeline steel) buried 0.5, 1.0 and 1.5 m deep under typical beach soils in Tanggu, Yangjiaogou, Xingcheng, Yingkou and Chengdao for 1-2 years were studied. The carbon steel and pipeline steel were both corroded severely in the beach soil, with the form of corrosion being mainly uniform with some localised attack (pitting corrosion). The corrosion rate of the carbon steel was up to 0.16 mm/year with a maximum penetration depth of 0.76 mm and that of the pipeline steel was up to 0.14 mm/year, with a maximum penetration depth of 0.53 mm. Compared with carbon steel, the pipeline steel generally had better corrosion resistance in most test beach soils. The corrosion rates and the maximum corrosion depths of carbon steel and pipeline steel were in the order: Tanggu>Xingcheng>Chengdao>Yingkou>Yangjiaogou with corrosion altering with depth of burial. The corrosion of steel in the beach soil involves a mixed mechanism with different degrees of soil aeration and microbial activity present. It is concluded that long term in situ plate laying experiments must be carried out to obtain data on steel corrosion in this beach soil environment so that the effective protection measures can be implemented.