Stress Corrosion Cracking Mode Research Articles

A Review of the Governing Factors in Pit-to-Crack Transitions of Metallic Structures

Through a combination of mechanical stresses and corrosive environments, a material’s performance may be hindered by the complex evolution of damage due to stress corrosion cracking (SCC) or corrosion fatigue (CF). Understanding the contribution of the localized corrosion features, loading state, crack-formation features, local microstructure, and environment remains a critical issue when predicting crack initiation and propagation leading to potential metal failure. As such, the lifetimes of many exposed alloys are greatly reduced by the presence of corrosion damage and the prediction of this deleterious influence via standard fracture mechanics methods is nontrivial. Current knowledge is insufficient to fully address governing features and mechanism of the pit-to-crack transition, a common initiation mode of SCC and CF. This review examines current research of pit-to-crack transitions for various alloys and loading conditions and highlights critical areas of research necessary for informing the mechanism related to a material’s lifetime in a stressed corrosive environment.

ChemInform Abstract: Dissolution Condensation Mechanism of Stress Corrosion Cracking in Liquid Metals: Driving Force and Crack Kinetics

AbstractReview: 64 refs.

Dissolution Condensation Mechanism of Stress Corrosion Cracking in Liquid Metals: Driving Force and Crack Kinetics

Stress corrosion cracking (SCC) in aqueous solution is driven by exothermic reactions of metal oxidation. This stimulus, as well as classical mechanisms of SCC, does not apply to SCC in liquid metals (LMs). In the framework of the dissolution-condensation mechanism (DCM), we analyzed the driving force and crack kinetics for this nonelectrochemical mode of SCC that is loosely called “liquid metal embrittlement” (LME). According to DCM, a stress-induced increase in chemical potential at the crack tip acts as the driving force for out-of-the-tip diffusion mass transfer that is fast because diffusion in LMs is very fast and surface energy at the solid-liquid interface is small. In this article, we review two versions of DCM mechanism, discuss the major physics behind them, and develop DCM further. The refined mechanism is applied then to the experimental data on crack velocity Vvs stress intensity factor, the activation energy of LME, and alloying effects. It is concluded that DCM provides a good conceptual framework for analysis of a unified kinetic mechanism of LME and may also contribute to SCC in aqueous solutions.

Film Breakdown and Anodic Dissolution during Stress Corrosion Cracking of Carbon Steel in Bioethanol

The stress corrosion cracking (SCC) behavior of X-65 carbon steel was investigated in simulated fuel-grade ethanol (SFGE) using the slow strain rate test method, potentiodynamic polarization, electrochemical impedance spectroscopy, open-circuit potential, and potentiostatic current monitoring. Results indicate that crack initiation on carbon steel in the SFGE environment is associated with plastic deformation in the material, which leads to a surface film breakdown. The competition between active anodic dissolution and repassivation ahead of the crack tip controlled the propagation of these cracks in SFGE. Within the anodic dissolution range, both crack density and crack growth rate in the through-thickness direction increased as the potential increased. The applied cathodic potential eliminated the SCC in this system. The mode of SCC for the carbon steel in aerated SFGE was predominately transgranular.

The mode of stress corrosion cracking in Ni-base alloys in high temperature water containing lead

The mode of stress corrosion cracking (SCC) in Ni-base alloys in high temperature aqueous solutions containing lead was studied using C-rings and slow strain rate testing (SSRT). The lead concentration, pH and the heat treatment condition of the materials were varied. TEM work was carried out to observe the dislocation behavior in thermally treated (TT) and mill annealed (MA) materials. As a result of the C-ring test in 1M NaOH + 5000 ppm lead solution, intergranular stress corrosion cracking (IGSCC) was found in Alloy 600MA, whereas transgranular stress corrosion cracking (TGSCC) was found in Alloy 600TT and Alloy 690TT. In most solutions used, the SCC resistance increased in the sequence Alloy 600MA, Alloy 600TT and Alloy 690TT. The number of cracks that was observed in Alloy 690TT was less than in Alloy 600TT. However, the maximum crack length in Alloy 690TT was much longer than in Alloy 600TT. As a result of the SSRT, at a nominal strain rate of 1 × 10 −7/s, it was found that 100 ppm lead accelerated the SCC in Alloy 600MA (0.01% C) in pH 10 at 340°C. IGSCC was found in a 100 ppm lead condition, and some TGSCC was detected on the fracture surface of Alloy 600MA cracked in the 10 000 ppm lead solution. The mode of cracking for Alloy 600 and Alloy 690 changed from IGSCC to TGSCC with increasing grain boundary carbide content in the material and lead concentration in the solution. IGSCC seemed to be retarded by stress relaxation around the grain boundaries, and TGSCC in the TT materials seemed to be a result of the crack blunting at grain boundary carbides and the enhanced Ni dissolution with an increase of the lead concentration.

The effect of ageing at 973 K on stress corrosion cracking of type 304 stainless steel

Stress corrosion cracking (SCC) behaviour of a Type 304 stainless steel aged at 973 K for various times was studied in boiling MgCl 2 solution at free corrosion potential using constant load and slow strain rate methods. The SCC resistance of the steel was found to improve on ageing. Scanning electron microscopic observation of the fracture surfaces revealed transgranular to intergranular transition in cracking mode in the solution annealed steel. Ageing of the steel was found to inhibit the above transition, when the SCC test was conducted in MgCl 2 solution boiling at 428 K. The absence of intergranular mode of SCC in aged steel is attributed to the sequestering of grain boundary phosphorus by the carbides precipitated at the boundaries and also to the homogenisation of slip by the carbides precipitated in the matrix.

ジルカロイ‐２のＣＨ３ＯＨ／ＨＣｌ溶液中における応力腐食割れとその電位依存性

The susceptibility to stress corrosion cracking (SCC) and its potential dependence of Zircaloy-2 were investigated. The SCC tests were conducted with CH3OH solutions containing HCl under given potentials at room temperature. The critical potential for SCC in 0.4% HCl solution moved to the negative direction, and the susceptibility to SCC increased. The potential range for SCC corresponded with the active region in the potentiostatic anodic polarization diagram, and the test specimen was attacked by uneven general corrosion when the potential was moved to the positive direction. The fracture mode of SCC differed from that of general corrosion, i.e., the transition of intergranular fracture to cleavage-like fracture was observed in the SCC potential region, whereas only intergranular corrosion was found in the active region. It is, therefore, considered that cleavage-like fracture is caused by mechanical stresses associated with the absorption of hydrogen generated by an intergranular corrosion reaction. A model for cracking was proposed based on these experimental results.

Stress Corrosion Cracking Susceptibility of Various AISI Austenitic Stainless Steels in Polythionic Acids

Abstract Studies on the stress corrosion cracking (SCC) of austenitic stainless steels (SSs) in polythionic acids were conducted using U-bend specimens. The effect of stress and sensitization on the electrochemical behavior of these steels was studied by anodic polarization. Open circuit potential (OCP) vs time studies were conducted that gave an indication of the time for the crack initiation for each grade of SS investigated. X-ray photoelectron spectroscopy (XPS) studies of the surface film formed on the SSs by interaction of polythionic acids were also made. They revealed the presence of oxides and sulfides of Fe and Mn in the surface film. Fractographic studies revealed the intergranular mode of SCC.

Effect of cold work on stress corrosion cracking behavior of types 304 and 316 stainless steels

The influence of cold work (prestraining) in the range 2.3 to 56 pct on stress corrosion cracking (SCC) properties of types 304 and 316 stainless steels in boiling MgCl2 solution at 154 °C was investigated using a constant load method. In both materials, SCC initiation was in transgranular mode. Transition in stress corrosion cracking mode from transgranular to intergranular, as the crack proceeds, was observed at all cold work levels in 316 stainless steel and at cold work levels of 26 pct and 56 pct in 304 stainless steel. Both prestraining and increase in the initial applied stress facilitated the transition in crack morphology to intergranular mode. Increased tendency to intergranular SCC at high applied stresses and in cold worked specimens appears to be mechanistically analogous.

18Cr-10Niステンレス鋼のMgCl<SUB>2</SUB>溶液中における応力腐食割れ形態の電位依存性

18Cr-10Niステンレス鋼のMgCl<SUB>2</SUB>溶液中における応力腐食割れ形態の電位依存性