This article presents an overview of the developments in stainless steels made since the 1990s. Some of the new applications that involve the use of stainless steel are also introduced. A brief introduction to the various classes of stainless steels, their precipitate phases and the status quo of their production around the globe is given first. The advances in a variety of subject areas that have been made recently will then be presented. These recent advances include (1) new findings on the various precipitate phases (the new J phase, new orientation relationships, new phase diagram for the Fe–Cr system, etc.); (2) new suggestions for the prevention/mitigation of the different problems and new methods for their detection/measurement and (3) new techniques for surface/bulk property enhancement (such as laser shot peening, grain boundary engineering and grain refinement). Recent developments in topics like phase prediction, stacking fault energy, superplasticity, metadynamic recrystallisation and the calculation of mechanical properties are introduced, too. In the end of this article, several new applications that involve the use of stainless steels are presented. Some of these are the use of austenitic stainless steels for signature authentication (magnetic recording), the utilisation of the cryogenic magnetic transition of the sigma phase for hot spot detection (the Sigmaplugs), the new Pt-enhanced radiopaque stainless steel (PERSS) coronary stents and stainless steel stents that may be used for magnetic drug targeting. Besides recent developments in conventional stainless steels, those in the high-nitrogen, low-Ni (or Ni-free) varieties are also introduced. These recent developments include new methods for attaining very high nitrogen contents, new guidelines for alloy design, the merits/demerits associated with high nitrogen contents, etc.

Recent developments in stainless steels

A pulsed eddy current (PEC) system has been used to characterize atmospheric corrosion on steel samples. International Paint has supplied coated and uncoated mild steel (S275) samples with marine atmospheric corrosion (exposure time between 1 and 10 months). The PEC response due to corrosion is a complex mix of many factors, including conductivity, permeability and material thickness variation, which are all taken into account through experimental studies and the extraction of signal features. Considering the conductivity and permeability variation in the corrosion layer or the actual rust region, two time-domain features, each representing the conductivity and permeability, are extracted and used to characterize corrosion. The relationship between PEC features and exposure time has been derived, which can be useful for corrosion rate measurement and early-stage corrosion evaluation and prediction. In conclusion, PEC testing has the potential for corrosion characterization and monitoring in areas such as the marine industry.

Steel Corrosion Characterization Using Pulsed Eddy Current Systems

Pitting and uniform corrosion source recognition using acoustic emission parameters

Influence of temper and surface condition on the exfoliation behaviour of high strength Al-Zn-Mg-Cu alloys

Detection of stress corrosion cracking of high-strength steel used in prestressed concrete structures by acoustic emission technique

Initiation and propagation steps in pitting corrosion of austenitic stainless steels: monitoring by acoustic emission

This experimental work was aimed at investigating the ability of acoustic emission (AE) technique for detection and monitoring of crevice corrosion on 304L austenitic stainless steel. Crevice initiation, propagation and repassivation was controlled by additions of hydrogen peroxide and hydrochloric acid and by the extent of the applied torque of crevice assembly, in the presence of chloride ions. The simultaneous measurements of corrosion potential of the specimen and AE global activity during the test, as well as the characterization of acoustic parameters of AE signals, evidences a good correlation between potential and AE activity fluctuations, AE rate and amplitude of crevice damage in terms of weight loss and metallic surface affected, in each tested experimental condition. Moreover, the evolution of cumulative% of AE signals number versus selected acoustic parameters shows that rise time, counts number, duration and cumulative energy of AE signals are affected by crevice development. Finally, visualization of crevice initiation and propagation during the test allows to propose that bubbles formation from cathodic reactions within the crevice is the emissive mechanism.

Ability of acoustic emission technique for detection and monitoring of crevice corrosion on 304L austenitic stainless steel

Exfoliation corrosion of aluminum alloys is a form of localized corrosion which affects many industries, specially aeronautics. The study of this corrosion mode using only electrochemical techniques is not fully efficient for the detection and control on line of this phenomenon. Therefore, we developed a non-destructive testing technique based on the acoustic emission recordings in order to follow-up this form of corrosion on aluminum alloys. Indeed, recent works have shown the interest of the acoustic emission for the detection, the monitoring and the localization of pitting corrosion on aluminum alloys. This pitting corrosion phenomenon is currently well understood and the experimental methodology acquired during that study is transposed to the study of exfoliation corrosion of aluminum alloys. The present study is conducted on two aluminum alloys: (Al 2024 T3, and Al 7449 T6 and T7). Samples are immersed 4 days in the modified ASTM STP 1134 saline solution. Observations of the structures after tests show that the exfoliation corrosion sensitivity of alloy 7449 T6 is more important than for alloy 7449 T7 which exhibits only the presence of small and non-occluded pits. Very severe exfoliation corrosion was also observed on Al 2024 T3, but after a longer immersion time or in a more acid solution. The recording of the acoustic emission activity shows evident links between this activity and the exfoliation corrosion rate. The analysis of the signal's characteristics reveals a population corresponding to the release of hydrogen bubbles. A few more energetic signals have also been observed. Their source can be either, the cracking resulting from the separation of sheets of metal, or the development and evolution of hydrogen bubbles formed inside blisters during exfoliation corrosion.

Use of acoustic emission technique for the early detection of aluminum alloys exfoliation corrosion

In industrial environment, many materials are subjected to the abrasion–corrosion phenomenon. In such cases, stainless steels are often used for their good corrosion resistance. However, the synergistic effect between abrasion and corrosion may be a serious contributor to the total wear even when pure corrosion rates do not appear to be significant. In order to select the more resistant alloy for each particular application, it is important to understand this phenomenon. This paper presents a study on the characterization by acoustic emission and electrochemical techniques of AISI 304L stainless steel abrasion–corrosion, in saline environment. The abrasion mechanism is first examined for three angles of impingement in non-corrosive conditions. Then, the synergistic effect between mechanical damage and corrosion is investigated. The results indicate that the lower the impingement angle, the lower is the mechanical contribution. In corrosive conditions, it is shown that, at low abrasion rate, the synergistic effect depends on the impingement angle. Some hypothesis are proposed in order to separate, in the overall synergistic damage, the effect of abrasion on corrosion and the effect of corrosion on abrasion.

H Mazille

Papers

Initiation and propagation steps in pitting corrosion of austenitic stainless steels: monitoring by acoustic emission

Ability of acoustic emission technique for detection and monitoring of crevice corrosion on 304L austenitic stainless steel

Use of acoustic emission technique for the early detection of aluminum alloys exfoliation corrosion

A study of abrasion–corrosion of AISI 304L austenitic stainless steel in saline solution using acoustic emission technique

Laser Surface Alloying on a Mild Steel