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 critical review of experimental results and constitutive descriptions for metals and alloys in hot working

Failure of metals I : brittle and ductile fracture

http://doras.dcu.ie/17607/1/Review_of_residual_stresses-Final.pdf

Methods of measuring residual stresses in components

A new material constitutive law is implemented in a 2D finite element model to analyse the chip formation and shear localisation when machining titanium alloys. The numerical simulations use a commercial finite element software (FORGE 2005®) able to solve complex thermo-mechanical problems. One of the main machining characteristics of titanium alloys is to produce segmented chips for a wide range of cutting speeds and feeds. The present study assumes that the chip segmentation is only induced by adiabatic shear banding, without material failure in the primary shear zone. The new developed model takes into account the influence of strain, strain rate and temperature on the flow stress and also introduces a strain softening effect. The tool chip friction is managed by a combined Coulomb–Tresca friction law. The influence of two different strain softening levels and machining parameters on the cutting forces and chip morphology has been studied. Chip morphology, cutting and feed forces predicted by numerical simulations are compared with experimental results.

/pdf/a-new-material-model-for-2d-numerical-simulation-of-serrated-2dy2n4o4ge.pdf

A new material model for 2D numerical simulation of serrated chip formation when machining titanium alloy Ti–6Al–4V

This study investigates the plastic deformation and fracture behaviour of titanium alloy (Ti–6Al–4V) under high strain rates and various temperature conditions. Mechanical tests are performed at constant strain rates ranging from 5×102 to 3×103 s−1 at temperatures ranging from room temperature to 1100°C by means of the compressive split-Hopkinson bar technique. The material's dynamic stress–strain response, strain rate, temperature effects and possible deformation mechanisms are discussed. Furthermore, the plastic flow response of this material is described by a deformation constitutive equation incorporating the effects of temperature, strain rate, strain and work hardening rate. The simulated results based on this constitutive equation are verified. The fracture behaviour and variations of adiabatic shear band produced by deformation at each test condition are investigated with optical microscopy and scanning electron microscopy. The results show that the flow stress of Ti–6Al–4V alloy is sensitive to both temperature and strain rate. Nevertheless, the effect on flow stress of temperature is greater than that of strain rate. Fracture observations reveal that adiabatic shear banding turns out to be the major fracture mode when the material is deformed to large plastic strain at high temperature and high strain rate.

Plastic deformation and fracture behaviour of Ti–6Al–4V alloy loaded with high strain rate under various temperatures

High-temperature deformation behaviour of Ti6Al4V alloy evaluated by high strain-rate compression tests

Mechanical properties and microstructural features of AISI 4340 high-strength alloy steel under quenched and tempered conditions

The strain rate and temperature dependence of the dynamic impact properties of 7075 aluminum alloy

The impact properties and microstructure evolution of 304L stainless steel have been studied systematically by means of a split Hopkinson bar and TEM metallographic techniques. Cylindrical specimens were deformed at room temperature under strain rates ranging from 102 to 5×103 s−1, with the true strains varying from 0.05 to 0.3. Results indicate that the mechanical properties and the microstructure largely depend on impact loading. Increasing the strain rate of impact loading increases both flow stress and strain rate sensitivity. However, the inverse tendency is observed for the activation volume. The effect of loading rate on mechanical response and impacted substructure of 304L stainless steel is found to be directly related to the amount of dislocation and the amount of transformed α′ martensite. By using the proposed constitutive equation with the experimentally determined specific material parameters, the flow behaviour of tested material can be described successfully for the range of test conditions. Microstructural observations reveal that the morphologies and characteristics of both dislocation and α′ martensite are sensitive to changes of loading conditions. At high strain rates and large deformation, greater dislocation density, more shear bands and more α′ martensite transformation are observed. Significant strengthening was found to result from dislocation multiplication and α′ martensite transformation, but the latter's effect is more evident as high rate loading is imposed. Correlation between dislocation density, fraction of α′ martensite, flow stress and strain rate is confirmed and is discussed in terms of the observed microstructure.

Woei-Shyan Lee

Papers

Plastic deformation and fracture behaviour of Ti–6Al–4V alloy loaded with high strain rate under various temperatures

High-temperature deformation behaviour of Ti6Al4V alloy evaluated by high strain-rate compression tests

Mechanical properties and microstructural features of AISI 4340 high-strength alloy steel under quenched and tempered conditions

The strain rate and temperature dependence of the dynamic impact properties of 7075 aluminum alloy

Impact properties and microstructure evolution of 304L stainless steel