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

Tensile specimens of type 316L stainless steel with a grain size of 5.0 μm have been deformed at a constant strain rate of 10−3 s−1 over the temperature range 21–900°C and by differential strain-rate test technique over strain rates from about 10−5 to 10−3 s−1 at temperatures in the range 750–900°C. The normalized yield and flow stresses against temperature plots exhibit three regions. While in regions I and III the stresses decrease with increasing temperature, they increase with increasing temperature in region II. Transmission electron microscopy studies on deformed specimens show that at small strains the dislocations generated at grain boundaries have characteristic distributions: in region I the dislocations are confined to the vicinity of the grain boundary, in region II the dislocations are spread into the grain interior, and in region III the dislocations rearrange to form walls. The evolution of substructure and the work-hardening behaviour are explained by considering both intragranula...

Study on the substructure evolution and flow behaviour in type 316L stainless steel over the temperature range 21-900°C

Effect of boundary structure on slip-induced cavitation in polycrystalline nickel

The role of matrix dislocations in the superplastic deformation of a copper alloy

The threshold stress and departure side pinning of dislocations by dispersoids

Interfacial microstructure and low stress, high temperature creep of an austenitic stainless steel

The stability of intergranular TiC in a 20% Cr-30% Ni, Ti stabilized stainless steel and the transformation of TiC to M23C6, has been investigated as a function of creep deformation over a wide range of stresses at 800° C. It was found that diffusion creep does not make a significant contribution to the general ageing process or to the transformation of TiC to M23C6. However, dislocation creep strongly accelerates this transformation and increases the general rate of coarsening of intergranular carbides. It is concluded that this acceleration occurs through the combined action of an increase in the number of available nucleation sites (extrinsic grain boundary dislocations) and dislocation enhanced diffusion.

The effect of creep deformation on the stability of intergranular carbide dispersions in an austenitic stainless steel

Grain boundary migration during high temperature creep of an austenitic steel

SUMMARY

The interactions between grain boundary dislocations (GBDs) and intergranular TiC precipitates in an austenitic stainless steel (Alloy 800) have been investigated after creep at very low stresses at 800°C. The absence of Orowan looping suggests that the GBDs by-pass the precipitates by glide/climb in the particle/matrix interfaces. An approximate calculation shows that the stress for bowing of GBDs between TiC precipitates is consistent with a measured value of the threshold stress for diffusion creep. However, it is suggested that an additional factor may be present in the threshold stress due to attractive forces between the precipitates and the GBDs.

J.-O. Nilsson

Papers

Interfacial microstructure and low stress, high temperature creep of an austenitic stainless steel

The effect of creep deformation on the stability of intergranular carbide dispersions in an austenitic stainless steel

Grain boundary migration during high temperature creep of an austenitic steel

Interaction Of Grain Boundary Dislocations With Precipitates During High Temperature Creep