A Consideration Of Possible Mechanisms Of Stress Corrosion Cracking In Single Crystals Of Three Austenitic Stainless Steels

The problem of stress corrosion cracking (SCC), which causes sudden failure of metals and other materials subjected to stress in corrosive environment(s), has a significant impact on a number of sectors including the oil and gas industries and nuclear power production. Stress corrosion cracking reviews the fundamentals of the phenomenon as well as examining stress corrosion behaviour in specific materials and particular industries. The book is divided into four parts. Part one covers the mechanisms of SCC and hydrogen embrittlement, while the focus of part two is on methods of testing for SCC in metals. Chapters in part three each review the phenomenon with reference to a specific material, with a variety of metals, alloys and composites discussed, including steels, titanium alloys and polymer composites. In part four, the effect of SCC in various industries is examined, with chapters covering subjects such as aerospace engineering, nuclear reactors, utilities and pipelines. With its distinguished editors and international team of contributors, Stress corrosion cracking is an essential reference for engineers and designers working with metals, alloys and polymers, and will be an invaluable tool for any industries in which metallic components are exposed to tension, corrosive environments at ambient and high temperatures. Examines the mechanisms of stress corrosion cracking (SCC) presenting recognising testing methods and materials resistant to SCC Assesses the effect of SCC on particular metals featuring steel, stainless steel, nickel-based alloys, magnesium alloys, copper-based alloys and welds in steels Reviews the monitoring and management of SCC and the affect of SCC in different industries such as petrochemical and aerospace

Fe-20Cr-20Ni, Fe-20Cr-12Ni, and commercial type 304 stainless steel single crystals were loaded in tension in boiling 42% MgCl2 solution. The commercial type 304 stainless steel cracked or fractured in 4 to 17 hours, the Fe-20Cr-12Ni in 16-62 hours, and the Fe-20Cr-20Ni in 70-170 hours. The crack in all three alloys nucleated (over) from elongated pits formed when portions of slip lines were attacked by the solution. The crack plane of the Fe-20Cr-20Ni specimens followed the (100) plane with the highest normal stress upon it. This is believed to be the first time that brittle cracks have been noted to follow a particular crystallographic plane in fcc material. Electron diffraction patterns made of the corrosion product from a Fe-20Cr-20Ni crack face showed that it may be a chromium-iron oxide. Colorimetric analysis of the corrosion solution showed an increase in nickel during the test. The general crack plane in type 304 and Fe-20Cr12Ni specimens was approximately normal to the tensile axis. Electron micrographs of the fracture surface on a type 304 specimen revealed possible crystallographic steps on a small scale. It is proposed that the mechanism for this process probably consists of two stages: (1) a slow electrochemical crack initiation and re-initiation step and (2) a rapid mechanical fracture step.

High-strength steels are susceptible to delayed cracking under suitable conditions. Frequently such a brittle failure occurs at a stress that is only a fraction of the nominal yield strength. Considerable controversy exists over whether such failures result from two separate and distinct phenomena or whether there is but one mechanism called by two different names. Stress-corrosion cracking is the process in which a crack propagates, at least partially, by the stress induced corrosion of a susceptible metal at the advancing tip of the stress-corrosion crack. There is considerable evidence that this cracking results from the electrtrochemical corrosion of a metal subjected to tensile stresses, either residual or externally applied. Hydrogen-stress cracking is cracking which occurs as the result of hydrogen in the metal lattice in combination with tensile stresses. Hydrogen-stress cracking cannot occur if hydrogen is prevented from entering the steel, or if hydrogen that has entered during processing or service is removed before permanent damage has occurred. It is generally agreed that corrosion plays no part in the actual fracture mechanism. This report was prepared to point out wherein the two fracture mechanisms under consideration are similar and wherein they differ. From the evidence available today, the present authors have concluded that there are two distinct mechansims of delayed failure. (Author).