Improvement of the resistance to stress corrosion cracking in austenitic stainless steels by cyclic prestraining
- PDF / 1,939,917 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 101 Downloads / 222 Views
NTRODUCTION
THE deleterious effect of an aqueous corrosive environment on the fracture processes in ductile fcc metals and alloys is experimentally well established.[1–4] Many models have been proposed in the last 15 years to describe the damage mechanisms that govern stress corrosion cracking (SCC). Recent models are based on corrosion-deformation interactions (CDI),which can play a central role in SCC mechanisms[5,6] through dissolution and hydrogen-plasticity interactions. Among theses models (for a review, refer to Reference 5), one can find the corrosion-enhanced plasticity model (CEPM) proposed by one of the present authors.[5,6] A recent study has actually shown a good agreement between the CEPM and experimental results obtained on austenitic stainless steels in MgCl2 and on pure copper in nitrites.[7] This work, essentially based on single crystals, outlines the importance of slip conditions on the overall SCC process. In most cases, cracking occurs by an alternative process on {111} slip planes at a microscopic scale, as predicted by the CEPM. One of the objectives of the models is to describe the role of the key factors influencing the SCC processes. This is of interest in the research of improvements to SCC damage. The purpose of this article is to test the main hypotheses of the CEPM in this way. In particular, from the key role of local CDI, it would be of interest to modify the deformation conditions through different prestraining processes and to analyse the consequences of these modifications on the SCC resistance. Thus, in the first part of this article, the different hypotheses of the CEPM will be recalled. Then, research on the improvement of SCC resistance will be conducted through the analysis of the influence of prestraining processes on SCC of austenitic stainless steels in MgCl2. Two points will be emphasized. (1) The deleterious effect of a monotonic pre-straining (which is often used in order to increase the mechanical A. CHAMBREUIL-PARET, Ph.D., and T. MAGNIN, Professor, are with the Ecole Nationale Supe´rieure des Mines de St-Etienne, Centre SMS, 58, Cours Fauriel, 42023 Saint-Etienne, Cedex 02, France. Manuscript submitted May 19, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
properties of austenitic stainless steels) will be confirmed. This deleterious effect has already been pointed out by Madgowski and Speidel,[8] who showed that a 5 pct tensile elongation prior to the stress corrosion test strongly increases the crack growth rate during SCC in austenitic stainless steels. In fact, both crack initiation and crack propagation are enhanced in this case, which will be explained through the CEPM and the dislocation structure related to monotonic prestraining (Lomer locks configuration[5]). (2) Thanks to the main ideas of the CEPM, the beneficial effect of cyclic prestraining process on both crack initiation and crack propagation will be shown, using slow-strain-rate tests. Such an improvement can be understood in terms of the delayed effects of CDI related to the low-energy dislocatio
Data Loading...
