Stress-corrosion cracking mechanisms alloys

E.N. Pugh, The Mechanisms of Stress Corrosion Cracking of Alpha-Brass in Aqueous Ammonia, The Theory of Stress Corrosion Cracking in Alloys, J.C. Scully, Ed., NATO, Brussels, 1971, p 418-441... 

G.S. Duffo, J.R. Galvele, Surface-mobdity stress corrosion cracking mechanism in silver alloys, in R.P. Gangloff, M.B. Ives (Eds.), Environment-induced Cracking of Metals, NACE, Houston, TX, 1990, pp. 261—264. 

R.B. Rebak, Z. Szklarska-Smialowska, The mechanism of stress corrosion cracking of Alloy 600 in high temperature water, Corros. Sci. 38 (1996) 971—988. 

Duffo, G. S. and Galvele, J. R., Experimental Confirmation of the Surface Mobility-Stress Corrosion Cracking Mechanism Ag-15Pd, Ag-15Au, and Ag-30Cd Alloys in Hallide and Sulphate Containing Solutions, Corrosion Science, Vol. 30, No. 2/3, 1990, pp. 249-265. 

Mechanism of Stress Corrosion Cracking of Alloy X-750 in High-Piuity Water Conference Corrosion of Nickel-Base Alloys Cincinnati, Ohio, USA, 23-25 Oct. 1984... 

P. M. Scott and M. Le Calvar, Some possible mechanisms of intergranular stress corrosion cracking of alloy 600 in PWR primaiy water. Proceedings of 6th... 

Corrosion control requires a change in either the metal or the environment. The first approach, changing the metal, is expensive. Also, highly alloyed materials, which are resistant to general corrosion, are more prone to failure by localized corrosion mechanisms such as stress corrosion cracking. 

Fracture Mechanics Methods These have proved very usebd for defining the minimum stress intensity K[scc. t which stress corrosion cracking of high-strength, low-ductihty alloys occurs. They have so far been less successful when apphed to high-ductility alloys, which are extensively used in the chemicm-process industries. 

Alloy 400 has good mechanical properties and is easy to fabricate in all wrought forms and castings. K-500 is a modified version of this alloy and can be thermally treated and is suitable for items requiring strength, as well as corrosion resistance. Alloy 400 has immunity to stress corrosion cracking and pitting in chlorides and caustic alkali solutions. 

Heterogeneities associated with a metal have been classified in Table 1.1 as atomic see Fig. 1.1), microscopic (visible under an optical microscope), and macroscopic, and their effects are considered in various sections of the present work. It is relevant to observe, however, that the detailed mechanism of all aspects of corrosion, e.g. the passage of a metallic cation from the lattice to the solution, specific effects of ions and species in solution in accelerating or inhibiting corrosion or causing stress-corrosion cracking, etc. must involve a consideration of the detailed atomic structure of the metal or alloy. 

Wilde, B. E. and Kim, C. D., The R61e of Hydrogen in the Mechanism of Stress-corrosion Cracking of Austenitic Stainless Steel in Hot Chloride Media , Corrosion, 28, 350 (1972) Lin, F. and Hochman, R. F., Electrochemical Study of Stress-corrosion Cracking of Ti 8-1-1 Alloy and NaCl Solutions , Corrosion, 28, 182 (1972)... 

Any test (several such tests are used) in which time to failure of smooth specimens is determined is an overall measure of the incubation period to initiate a crack, the ability to resist the propagation of a stress corrosion crack and the ability to resist final mechanical fracture. Since this test does not indicate the relative merits of an alloy in each individual aspect of the... 

Only certain specific environments appear to produce stress corrosion of copper alloys, notably ammonia or ammonium compounds or related compounds such as amines. Mercury or solutions of mercury salts (which cause deposition of mercury) or other molten metals will also cause cracking, but the mechanism is undoubtedly differentCracks produced by mercury are always intercrystalline, but ammonia may produce cracks that are transcrystalline or intercrystalline, or a mixture of both, according to circumstances. As an illustration of this, Edmundsfound that mercury would not produce cracking in a stressed single crystal of brass, but ammonia did. 

It is not surprising that hardness is important because the mechanical toughness can be expected to decrease with increasing hardness, and the level of residual stress present will also depend on the hardness of the steel, especially for welded components. Thus, the important role of the microstructure in influencing susceptibility to stress-corrosion cracking is consistent with the observation that hardness levels are a good guide to stress-corrosion resistance, but they should not be used universally without due consideration of the specific alloy and the environment in which it is to be used. 

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