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

The effect of heat treatment on mechanical properties and corrosion behavior of AISI420 martensitic stainless steel

Serration and noise behaviors in materials

Mechanism of dynamic strain aging and characterization of its effect on the low-cycle fatigue behavior in type 316L stainless steel

In order to identify the microstructural mechanisms leading to the softening effect usually presented by martensitic steels under cyclic loadings (with or without hold times), a study of the cyclic stress partition is presented. As the usual stress partitioning methods were found to be inadequate in the present case, a new method based both on Cottrell's method and on the Statistical Process Control principles, is proposed. This new method is used to distinguish between the kinematic, the isotropic and the viscous parts of the cyclic stress. The evolutions of these different stresses are evaluated for several strain amplitudes and temperatures under pure fatigue loading in this first part. It is shown that the softening effect is mainly due to a decrease of the backstress: the higher the strain amplitude, the stronger and the faster the softening effect. The isotropic stress is found to be independent of the strain amplitude, but increases when the temperature decreases. Whereas the viscous stress represents a large part of the total stress at 823 K, it becomes almost negligible below 673 K. These results are finally linked to the microstructural coarsening previously observed and modelled. Therefore, the decrease of the kinematic stress can be related to grain size effect.

Analysis of the hysteresis loops of a martensitic steel: Part I: Study of the influence of strain amplitude and temperature under pure fatigue loadings using an enhanced stress partitioning method

AISI 403, a martensitic stainless steel in the quenched and tempered condition has been subjected to uni-axial tension test at a range of strain rates (2×10−5–10−2 s−1) and a range of temperatures (25–500°C) to investigate the effect of temperature and strain rate on its mechanical properties. Serrated flow behaviour, predominately of type A and B, has been observed in the temperature range of 250–375°C and at strain rates lower than 10−3 s−1, which suggests the presence of dynamic strain aging (DSA) in this parametric domain. In this domain, while an increase in ultimate tensile strength and work hardening have been observed, the yield strength has been found to be nearly independent of temperature. A loss in ductility, due to the presence of DSA has also been seen in this material. The solute responsible for serrated flow has been identified to be chromium, which is the major alloying addition in this material. McCormick’s method has been employed to determine the activation energy from the knowledge of critical strain for the appearance of serrations as a function of strain rate and temperature. The magnitude of activation energy is approximately 50% of that for bulk diffusion of chromium in body centered cubic iron suggesting that a mechanism other than volume diffusion is involved.

Effect of serrated flow on deformation behaviour of AISI 403 stainless steel

Power plant components from modern 9–12% CrMoV-steels having fine precipitate stabilized subgrain structure undergo cyclic deformation as well as creep during service. The present work studies changes in subgrain structure due to cyclic straining and their effects on the creep behaviour in 12CrMoWVNbN10-1-1 steel. It was found that the cyclic plastic straining causes significant coarsening of the subgrain structure. Presence of hold periods during deformation significantly increases the extent of coarsening. Evolution of subgrain structure during cyclic deformation has been treated by extending the phenomenological law known from creep. Subgrain coarsening induced by cyclic deformation leads to significant increase in the resistance against creep.

Effects of cyclic deformation on subgrain evolution and creep in 9–12% Cr-steels

Assessment of hydrogen embrittlement of Zircaloy-2 pressure tubes using unloading compliance and load normalization techniques for determining J–R curves

In contrast to the general work-hardening (WH) behavior of a polycrystalline fcc material, increase in the work-hardening rate is observed in Alloy 625 following precipitation of Ni2(Cr,Mo) and γ″ phases. A typical stage II WH behavior of an fcc single crystal is seen in this alloy, before and after the precipitation. Appearance of such WH behavior is attributed to the domination of planar slip during deformation. TEM results from samples, before and after deformation, indicate that the precipitates are coherent or semi-coherent in nature and hence, partially or fully dissolved due to repeated shearing by dislocations. A gradual increase in WH rate of the alloy due to aging appears to justify the role of various types of geometrically necessary dislocations, which are formed as a result of precipitation.

J.S. Dubey

Papers

Effect of serrated flow on deformation behaviour of AISI 403 stainless steel

Effects of cyclic deformation on subgrain evolution and creep in 9–12% Cr-steels

Assessment of hydrogen embrittlement of Zircaloy-2 pressure tubes using unloading compliance and load normalization techniques for determining J–R curves

Role of dislocation density in raising the stage II work-hardening rate of Alloy 625

Elevated temperature fracture toughness of AISI 403 martensitic stainless steel