There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

Processing parameters in laser powder bed fusion metal additive manufacturing

Metallographic Methods for Revealing the Multiphase Microstructure of TRIP-Assisted Steels - some applications for steels

Phase transformation and mechanical behavior in annealed 2205 duplex stainless steel welds

In the present work, the creep behavior and microstructure before and after creep test of the dissimilar modified 9Cr–1Mo steels welded joint were investigated in detail. Firstly, creep tests were carried out at different stress values/levels under the temperature of 538 °C and 500 °C, and then the power law equation of steady-state stage were achieved based on the results. The microstructure of welded joint were characterized in detail, the tempered martensite structure is the typical microstructure of whole welded joint, and the δ-ferrite phase is observed in heated affect zone (HAZ) and the base metal without Co and B elements (BM1). A soft zone called over-tempering zone (OTZ) occurred in both HAZs, which was determined by micro-hardness measurement, due to the lower dislocation density and coarsened M 23 C 6 carbides of this zone. The fracture location is in OTZ adjacent to BM1 side determined by microstructure, micro-hardness and geometric calculation. Lots of voids are observed along the triple grain boundaries associated with large second phase particles after creep rupture. The stress concentration caused by the coarsened carbides at the triple boundaries and softening matrix are considered as the main factor of creep voids occurring in the OTZ of welded joint.

Creep behavior and microstructure evaluation of welded joint in dissimilar modified 9Cr–1Mo steels

A comparative study on fiber laser and CO2 laser welding of Inconel 617

Study on fatigue property and microstructure characteristics of welded nuclear power rotor with heavy section

A technology employing σ transformation (α→γ+σ) and its reverse transformation (γ+σ→α) to refine grain of duplex stainless steels has been devised. The experimental results indicated that the σ phases nucleate and grow both at the α/γ phase interfaces and in the interior of the α phases when the temperature was higher, whereas the σ phases nucleate at the α/γ phase interfaces primarily when a lower temperature was used. The coarse α grain decomposed into fine γ and σ grains at 750 °C for 38 h (the σ treated), and fine α grains were obtained after a revise transformation (γ+σ→α) being performed, leading to an significant improved toughness. The highest impact toughness value was achieved by the process that σ transformation was carried out at 750 °C for 38 h followed by a reverse transformation, heated at 1200 °C for 1.5 min, at a heating rate of 13 °C/s.

Xia Liu

Papers

Creep behavior and microstructure evaluation of welded joint in dissimilar modified 9Cr–1Mo steels

A comparative study on fiber laser and CO2 laser welding of Inconel 617

Study on fatigue property and microstructure characteristics of welded nuclear power rotor with heavy section

Grain refinement of Cr25Ni5Mo1.5 duplex stainless steel by heat treatment

Liquation cracking in fiber laser welded joints of inconel 617