Stress Corrosion Cracking of Novel Steel for Automotive Applications

AbstractIn the present study, susceptibility of a high manganese TWIP steel to stress corrosion cracking (SCC) in a 3.5% NaCl solution was investigated using slow strain rate tests (SSRT), constant load (CL) tests and fractography. Strain rates employed for SSRT were in the range of 10-06 - 10-08 s-1. The specimens tested in air revealed a ductile type of failure, whereas those tested in the corrosive solution exhibited a brittle feature that is attributed to stress corrosion cracking. SCC was observed at a relatively low strain rate of 10-07s-1

The steel–concrete interface

Although the steel–concrete interface (SCI) is widely recognized to influence the durability of reinforced concrete, a systematic overview and detailed documentation of the various aspects of the SCI are lacking. In this paper, we compiled a comprehensive list of possible local characteristics at the SCI and reviewed available information regarding their properties as well as their occurrence in engineering structures and in the laboratory. Given the complexity of the SCI, we suggested a systematic approach to describe it in terms of local characteristics and their physical and chemical properties. It was found that the SCI exhibits significant spatial inhomogeneity along and around as well as perpendicular to the reinforcing steel. The SCI can differ strongly between different engineering structures and also between different members within a structure; particular differences are expected between structures built before and after the 1970/1980s. A single SCI representing all on-site conditions does not exist. Additionally, SCIs in common laboratory-made specimens exhibit significant differences compared to engineering structures. Thus, results from laboratory studies and from practical experience should be applied to engineering structures with caution. Finally, recommendations for further research are made

Stress corrosion cracking of a wrought Mg-Mn alloy under plane strain and plane stress conditions

Stress corrosion crack growth of a rare earth containing Mg-Mn hot rolled alloy was studied using compact tension and circumferential notch tensile specimens employing constant load in 0.1 N NaCl solution saturated with Mg(OH)(2). Circumferential notch tensile specimens satisfied plane strain conditions; Log crack velocity versus stress intensity plots yielded slope of 0.5 and 1 for stage I region and threshold stress intensity of 10 and 13 MPa m(1/2) for circumferential notch tensile and compact tension specimens respectively. Fractography showed transgranular features involving hydrogen in stress corrosion cracking. (C) 2013 Elsevier Ltd. All rights reserved

Theoretical model for concrete-filled stainless steel circular stub columns under axial compression

Experimental studies on concrete-filled stainless steel (SS) circular stub columns (in the form of fully filled and double-skin) have been reported in the last 10 years, but there is still a lack of theoretical model to predict the complete load-axial strain curve of such stub columns under axial compression. This study presents a load-axial strain model for concrete-filled SS tubes, which takes account of the interaction between the encasing tube and concrete core. A dilation model is first proposed in which the dilation rate is expressed as a function of axial strain and outer tube diameter-to-thickness ratio. The theory of metal plasticity in the form of deformation type is adopted to calculate the bi-axial stresses in the SS outer tube. The SS inner tube is assumed to be under uni-axial compression and continuous strength method (CSM), which is suitable for strain hardening material such as SS, is adopted. The effect of SS tube buckling on reducing the axial stress and confining stress is considered in the model. Numerical procedures are proposed to generate the complete load-axial strain curve which involve an incremental process. Finally, the predicted load-axial strain curves are compared with the experimental results obtained by the authors and other researchers, and a good agreement is achieved

Development of Self-Healing Coatings Based on Linseed Oil as Autonomous Repairing Agent for Corrosion Resistance

In recent years corrosion-resistant self-healing coatings have witnessed strong growth and their successful laboratory design and synthesis categorises them in the family of smart/multi-functional materials. Among various approaches for achieving self-healing, microcapsule embedment through the material matrix is the main one for self-healing ability in coatings. The present work focuses on optimizing the process parameters for developing microcapsules by in-situ polymerization of linseed oil as core and urea-formaldehyde as shell material. Characteristics of these microcapsules with respect to change in processing parameters such as stirring rate and reaction time were studied by using optical microscopy (OM), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The effectiveness of these microcapsules in coatings was characterized by studying their adhesion, performance, and mechanical properties

Stress corrosion cracking of a recent rare-earth containing magnesium alloy, EV31A, and a common Al-containing alloy, AZ91E

Stress corrosion cracking of the magnesium alloy Elektron 21 (ASTM-EV31A) and AZ91E was studied using constant load test in 0.1 M NaCl solution (saturated with Mg(OH)(2), and slow strain rate test using glycerol, distilled water and Mg(OH)(2) saturated, 0.01 M and 0.1 M NaCl solutions. Slow strain rate test indicated that EV31A was less susceptible to stress corrosion cracking than AZ91E. Under less intense loading of constant load, EV31A was found to be resistant to stress corrosion cracking. Fractography of EV31A specimens showed little evidence of hydrogen embrittlement. The superior resistance of EV31A is attributed to a more robust oxide/hydroxide layer. (C) 2013 Elsevier Ltd. All rights reserved

Stress corrosion cracking behavior of magnesium alloys EV31A and AZ91E

The stress corrosion cracking of the sand cast magnesium alloys, Elektron 21 (ASTM-EV31A) and AZ91E, was studied using compact tension specimens in distilled water and in Mg(OH)(2) saturated 0.1 M NaCl solution under constant load. EV31A showed a higher K-ISCC than AZ91E, but exhibited a higher stage II crack growth rate than the latter. Fractography showed transgranular cracking for AZ91E and EV31A in distilled water, whereas mixed intergranular and transgranular cracking was observed for EV31A in the chloride environment. The crack propagation involved hydrogen embrittlement. (c) 2013 Elsevier B.V. All rights reserved

Investigation of hydrogen assisted cracking of a high strength steel using circumferentially notched tensile test

The novel circumferentially notched tensile (CNT) test technique is used for the first time for an investigation of hydrogen assisted stress corrosion cracking. Effect of hydrogen on the fracture strength of high strength steel AS-4340 is examined in neutral 3.5% NaCl solution at room temperature and under hydrogen supply from within the material and/or external environment. A progressive drop in the stress intensity factor at the fracture was observed as a result of: (a) increasing span of hydrogen pre-charging (hence increasing internal hydrogen) and (b) decreasing rate of loading (hence increasing external supply of hydrogen). The measured critical stress intensity factors corresponding to varying degrees of supply of internal hydrogen are consistent with the computed hydrogen concentrations ahead of the crack tip. The experimentally determined threshold for hydrogen embrittlement in the regime of slower loading rates are consistent with the published data. The results presented here establish the usefulness of the CNT test technique for the investigation of HASCC in high strength steel over a wider range of loading rate. (C) 2012 Elsevier B.V. All rights reserved

Effect of chromium and aluminum addition on anisotropic and microstructural characteristics of ball milled nanocrystalline iron

Prior studies on synthesis of nanocrystalline elements have discussed the effect of ball milling on lattice parameter, crystallite size, and micro-strain. For elemental milled powders, the anisotropic peak broadening does not change with increasing milling time. However, the effect of alloying addition on the anisotropic behavior of ball milled nanocrystalline powders remains an unexplored area. Here we report the effect of chromium and aluminum addition on the anisotropic behavior of iron in nanocrystalline Fe-20Cr-5Al (wt%) alloy powders synthesized by ball milling. The experimental results show that the anisotropic behavior of iron changes towards isotropic with milling. This change was also correlated to the theoretically calculated anisotropic factor from the change in elastic constant of iron due to milling. Addition of alloying elements exhibited a monotonic rise in the lattice parameter with crystallite size, which was attributed to the excess grain boundary interfacial energy and excess free volume at grain boundaries. Transmission electron microscopy image confirmed the crystallite size and nature of dislocation obtained using modified Williamson-Hall method. (C) 2016 Elsevier B.V. All rights reserved