Experimental Study of crack propagation in carbon steel using acoustic emission

Acoustic emission technique has become a significant and powerful structural health monitoring tool for structures. Researches to date have been done on crack location, fatigue crack propagation in materials and severity assessment of failure using acoustic emission technique. Determining severity of failure in steel structures using acoustic emission technique is still a challenge to accurately determine the relationship between the severity of crack propagation and acoustic emission activities. In this study three point bending test on low carbon steel samples along with acoustic emission technique have been used to determine crack propagation and severity. A notch is introduced at the tension face of the loading point to the samples to initiate the crack. The results show that the percentage of load drop of the steel specimen has a reciprocal relationship with the crack opening i.e. crack opening zones are influenced by the loading rate. In post yielding region, common acoustic emission signal parameters such as, signal strength, energy and amplitudes are found to be higher than those at pre-yielding and at yielding.

Criteria for prediction of flow instabilities and microstructural manifestations during warm working of AISI 304L stainless steel

The deformation characteristics of 304L stainless steel in compression in the temperature range 20–700°C and strain rate range 0·001–100 s−1 have been studied with the aim of characterising the .flow instabilities occurring in the microstructure. At higher temperatures and strain rates the stainless steel exhibits flow localisation, whereas at temperatures below 500°C and strain rates lower than 0·1 s−1 the flow instabilities are due to dynamic strain aging. Strain induced martensite formation is responsible for the flow instabilities at room temperature and low strain rates (0·01 s−1). In view of the occurrence of these instabilities, cold working is preferable to warm working to achieve dimensional tolerance and reproducible properties in the product. Among the different criteria tested to explain the occurrence of instabilities, the continuum criterion, developed on the basis of the principles of maximum rate of entropy production and separability of the dissipation function, predicts accurately all the above instability features.

Electron Beam Surface Treatment. Part I: Surface Hardening of AISI D3 Tool Steel

The effects of electron beam surface hardening treatment on the microstructure and hardness of AISI D3 tool steel have been investigated in this paper. The results showed that the microstructure of the hardened layer consisted of martensite, a dispersion

Effect of Cold Rolling Ratio and Heating Rate of Batch Annealing on Textures of Micro-Carbon Steel Sheet

在四辊冷轧试验机和Gleeble-1500试验机上进行了热轧微碳钢板的冷轧和退火试验。用D/max-RC衍射仪测量了试样的,/”层织构,并用Roe软件进行了ODF分析。研究表明,所研究的热轧微碳深冲板压下率约为75%,退火升温速度为20-40℃/h时,试样为{111}织构特征；压下率较大(80%)时,退火织构为较弱的{111}组分。无论{111}织构还是非{111}织构都是在形核阶段开始形成,在晶粒长大优先长大,受到定向形核和选择生长双重机制的作用。

Mixed-mode fracture mechanisms near the fatigue threshold of aisi-316 stainless-steel

Near threshold, mixed mode (I and II), fatigue crack growth occurs mainly by two mechanisms, coplanar (or shear) mode and branch (or tensile) mode. For a constant ratio of ΔK_I/ΔK_II the shear mode growth shows a self-arrest character and it would only start again when ΔK_I and ΔK_II are increased. Both shear crack growth and the early stages of tensile crack growth, are of a crystallographic nature; the fatigue crack proceeds along slip planes or grain boundaries. The appearance of the fracture surfaces suggest that the mechanism of crack extension is by developing slip band microcracks which join up to form a macrocrack. This process is thought to be assisted by the nature of the plastic deformation within the reversed plastic zone where high back stresses are set up by dislocation pile-ups against grain boundaries. The interaction of the crack tip stress field with that of the dislocation pile-ups leads to the formation of slip band microcracks and subsequent crack extension. The change from shear mode to tensile mode growth probably occurs when the maximum tensile stress and the microcrack density in the maximum tensile plane direction attain critical values.

Boundary Element Method (BEM) Analysis for Galvanic Corrosion of Hot Dip Galvanized Steel Immersed in Seawater

A numerical analysis of galvanic corrosion of hot-dip galvanized steel immersed in seawater was presented. The analysis was based on the boundary element methods (BEMs) coupled with Newton-Raphson iterative technique to treat the nonlinear boundary conditions, which were determined by the experimental polarization curves. Results showed that galvanic current density concentrates on the boundary of steel substrate and zinc coating, and the sacrificial protection of zinc coating to steel substrate results in overprotection of steel cathode. Not only oxygen reduction but also hydrogen reduction could occur as cathode reactions, which probably led up to the adsorption and absorption of hydrogen atoms. Flat galvanized steel tensile sample shows a brittle behavior similar to hydrogen embrittlement according to the SSRT (show strain rate test) in seawater.

Effect of Cl- on the corrosive wear of AISI 321 stainless steel in H2SO4 solution

The effect of Cl- on the corrosive wear behaviour of AISI 321 stainless steel in H2SO4 solution was studied via the corrosive wear rate, the load bearing capacity of passive film and the relationship between pitting and corrosive wear. There is a critical load at natural potential, below which the corrosive wear rate is slightly lowered by Cl-, while above which is increased. At natural potential there are more pits at low load than that at a higher one in the wear tracks and the pits are also deeper. The load bearing capacity is lowered by Cl- at passive region and then the corrosive wear rate increased.

Effect of alloy elements on the anti-corrosion properties of low alloy steel

Effect of alloy elements on corrosion of low alloy steel was studied under simulated offshore conditions. The results showed that the elements Cu, P, Mo, W, V had evident effect on corrosion resistance in the atmosphere zone; Cu, P, V, Mo in the splash zone and Cr, Al, Mo in the submerged zone.

Hydrogen permeation and corrosion behaviour of high strength steel 35CrMo under cyclic wet-dry conditions

Hydrogen permeation behaviours of high strength steel 35CrMo under different cyclic wet-dry conditions have been investigated by using Devanathan-Stachurski's technique. Four electrolytes were used: distilled water, seawater, seawater containing 1500 ppm H2S and seawater containing 0.03 mol L-1 SO2. The corrosion weight loss of 35CrMo in the wet-dry cycles was measured simultaneously. The experimental results show that hydrogen can be detected at the surface opposite to the corroding side of the specimen during wet-dry cycles and the permeation current density during a wet-dry cycle showed a maximum during the drying process. The hydrogen permeation was obviously promoted by Cl- ions, H2S and SO2. The hydrogen permeation in the real marine atmosphere has also been investigated. There is a clear correlation between the amount of hydrogen permeated and the corrosion weight losses. Results show the importance of hydrogen permeation that merits further investigation.

Aminic nitrogen-bearing polydentate Schiff base compounds as corrosion inhibitors for iron in acidic media: A quantum chemical calculation

Quantum chemical calculations based on DFT method were performed on three polydentate Schiff base compounds (PSCs) used as corrosion inhibitors for iron in acid media to determine the relationship between the molecular structure of PSC and inhibition efficiency. The structural parameters, such as the frontier molecular orbital energy HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), the charge distribution of the studied inhibitors, the absolute electronegativity (chi) values, and the fraction of electrons (Delta N) transfer from inhibitors to iron, were also calculated and correlated with inhibition efficiencies. The results showed that the inhibition efficiency of PSCs increased with the increase in E-HOMO and decrease in E-LUMO-E-HOMO; and the areas containing N atoms are most possible sites for bonding the metal iron surface by donating electrons to the metal. (C) 2007 Elsevier Ltd. All rights reserved.

Electrochemical and thermodynamic investigation of diniconazole and triadimefon as corrosion inhibitors for copper in synthetic seawater

This paper presents the investigation of diniconzole and triadimefon as chemical corrosion inhibitors for freshly polished copper in synthetic seawater (3.5% NaCl solution). Determination of weight loss, polarization curves, electrochemical impedance spectroscopy (EIS), and SEM, were performed to analyze the inhibiting performance of these compounds. Polarization curves show that they act as mixed-type inhibitors. EIS indicates that an adsorption film of the inhibitors is formed on copper surface. The highest values of inhibition efficiency are respectively, 99.2% and 97.3% at 100 mg/L concentration. Thermodynamic calculation suggests that chemisorptions between the compounds and copper are accordance with Langmuir adsorption isotherm. (C) 2010 Elsevier Ltd. All rights reserved.

The electrochemical reduction reaction of dissolved oxygen on Q235 carbon steel in alkaline solution containing chloride ions

Cyclic voltammetry, electrochemical impedance spectroscopy, and rotating disk electrode voltammetry have been used to study the effect of chloride ions on the dissolved oxygen reduction reaction (ORR) on Q235 carbon steel electrode in a 0.02 M calcium hydroxide (Ca(OH)(2)) solutions imitating the liquid phase in concrete pores. The results indicate that the cathodic process on Q235 carbon steel electrode in oxygen-saturated 0.02 M Ca(OH)(2) with different concentrations of chloride ions contain three reactions except hydrogen evolution: dissolved oxygen reduction, the reduction of Fe(III) to Fe(II), and then the reduction of Fe(II) to Fe. The peak potential of ORR shifts to the positive direction as the chloride ion concentration increases. The oxygen molecule adsorption can be inhibited by the chloride ion adsorption, and the rate of ORR decreases as the concentration of chloride ions increases. The mechanism of ORR is changed from 2e(-) and 4e(-) reactions, occurring simultaneously, to quietly 4e(-) reaction with the increasing chloride ion concentration.

Characteristics of sulfide corrosion products on 316L stainless steel surfaces in the presence of sulfate-reducing bacteria

It has been found that microbial communities play a significant role in the corrosion process of steels exposed in aquatic and soil environments. Biomineralization influenced by microorganisms is believed to be responsible for the formation of corrosion products via complicated pathways of electron transfer between microbial cells and the metal. In this study, sulfide corrosion products were investigated for 316L stainless steel exposed to media with sulfate-reducing bacteria media for 7 weeks. The species of inorganic and organic sulfides in the passive film on the stainless steel were observed by epifluorescence microscope, environmental scanning electron microscope combined with energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The transformation from metal oxides to metal sulfides influenced by sulfate-reducing bacteria is emphasized in this paper. (c) 2005 Elsevier B.V. All rights reserved.