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

Enhancement of corrosion protection of AISI 304 stainless steel by nanostructured sol–gel TiO2 films

The onset of pitting corrosion at MnS inclusions on 304 stainless steel in 1 M NaCl was studied with and without applied mechanical stress with use of microelectrochemical cells. Polarization curves of areas (100 μm diam) without inclusion showed no pitting at potentials below that of oxidation evolution; stress had no effect on the corrosion behavior. Areas containing five round inclusions of about 4 μm in size showed stable pitting at about 400 mV; the effect of stress shifted the pitting potential to values that were 150 mV more negative. Polarization curves measured on large deep MnS inclusions showed active pitting. Curves of areas with single large, shallow MnS inclusions showed multiple current transients during dissolution of the inclusion without stress, but the metastable events did not initiate stable pitting. The dissolution of shallow MnS inclusion did not form a deep microcrevice between the MnS and stainless steel matrix. However, under applied stress, cracks were formed within the shallow MnS inclusion and active pitting occurred. To explore whether such cracks might serve to generate locally high concentrations of aggressive species, the pH and chloride concentration inside a crack were simulated using a finite difference model. For experimental conditions where stable pitting was observed, the simulations predicted that the solution composition at the base of a typical 13 μm deep crack correspond to a pH of around 2, and a chloride concentration of about 6 M led to stable pitting.

Pit Initiation on Stainless Steels in 1 M NaCl With and Without Mechanical Stress

Correlations of electrochemical noise, acoustic emission and complementary monitoring techniques during intergranular stress-corrosion cracking of austenitic stainless steel

Detection and characterization of stress-corrosion cracking on 304 stainless steel by electrochemical noise and acoustic emission techniques

Development of a hydrothermal deposition process for applying zirconia coatings on BWR materials for IGSCC mitigation

Acoustic emission response has been used to detect the development of short intergranular stress corrosion cracks in laboratory samples of sensitized type 304 (UNS S30400) stainless steel (SS). Tests were conducted at 25°C in water containing either 15 ppm of Na2S2O3 or 100 ppm of NaCl. Cylindrical samples with piezoelectric detectors mounted on both ends and the corrosion cell confined to the gauge section were used. The dual detectors allowed discrimination between signals generated within the sample from those generated from the surroundings. It was found that intergranular stress corrosion cracks of 200 to 300 µm length by 100 to 200 µm depth could be reliably detected with this technique. Shallow 10-µm-deep longitudinal flaws were also detected in tests conducted in the 100 ppm NaCl environment.

Evaluation of stress corrosion crack initiation using acoustic emission

Mechanical and metallurgical considerations on the effects of ppb-level chloride on stress corrosion cracking of low alloy steels in high-temperature water

Overview of Environmentally Assisted Cracking in LWR Components

Low alloy steels (LAS) used in the fabrication of reactor pressure vessel (RPV) and nozzles have been resistant to stress corrosion cracking (SCC) in the Boiling Water Reactor (BWR) environment. The plate material is SA533 Grade B and the nozzle material is SA508 Class 2 for most operating BWRs. While BWR service field experience with the LAS materials has been very good for there have been a limited number of SCC incidents where cracking has been reported especially in Alloy 182 RPV attachment (dissimilar metal) welds. This paper describes the methodology for the assessment of SCC crack growth rate (CGR) of LAS RPV components in the BWR environment. Specifically, it describes the development of CGR disposition lines (also called reference crack growth rate curves) for normal water chemistry (NWC) and hydrogen water chemistry (HWC) in BWR environments. In addition, based on more recent data from tests on the effect of chloride transients in NWC environments are also proposed.

R. Pathania

Papers

Development of a hydrothermal deposition process for applying zirconia coatings on BWR materials for IGSCC mitigation

Evaluation of stress corrosion crack initiation using acoustic emission

Mechanical and metallurgical considerations on the effects of ppb-level chloride on stress corrosion cracking of low alloy steels in high-temperature water

Overview of Environmentally Assisted Cracking in LWR Components

Evaluation of Stress Corrosion Crack Growth in Low Alloy Steel Vessel Materials in the BWR Environment