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

In the area of materials science, corrosion of biomaterials is of paramount importance as biomaterials are required for the survival of the human beings suffering from acute heart diseases, arthritis, osteoporosis and other joint complications. The present article discusses various issues associated with biological corrosion of different kinds of implants used as cardio stents, orthopedic and dental implants. As the materials used for these implants are manifold starting from metallic materials such as stainless steel (SS), cobalt chromium, titanium and its alloys, bioceramics, composites and polymers are in constant contact with the aggressive body fluid, they often fail and finally fracture due to corrosion. The corrosion behavior of various implants and the role of the surface oxide film and the corrosion products on the failure of implants are discussed. Surface modification of implants, which is considered to be the best solution to combat corrosion and to enhance the life span of the implants and longevity of the human beings is dealt in detail and the recent advances in the coating techniques which make use of the superior properties of nanomaterials that lead to better mechanical properties and improved biocompatibility are also presented.

Biomedical Implants: Corrosion and its Prevention - A Review~!2009-12-22~!2010-01-20~!2010-05-25~!

Metallic biomaterials are used in medical devices in humans more than any other family of materials. The corrosion resistance of an implant material affects its functionality and durability and is a prime factor governing biocompatibility. The fundamental paradigm of metallic biomaterials, except biodegradable metals, has been “the more corrosion resistant, the more biocompatible.” The body environment is harsh and raises several challenges with respect to corrosion control. In this invited review paper, the body environment is analysed in detail and the possible effects of the corrosion of different biomaterials on biocompatibility are discussed. Then, the kinetics of corrosion, passivity, its breakdown and regeneration in vivo are conferred. Next, the mostly used metallic biomaterials and their corrosion performance are reviewed. These biomaterials include stainless steels, cobalt-chromium alloys, titanium and its alloys, Nitinol shape memory alloy, dental amalgams, gold, metallic glasses and biodegradable metals. Then, the principles of implant failure, retrieval and failure analysis are highlighted, followed by description of the most common corrosion processes in vivo. Finally, approaches to control the corrosion of metallic biomaterials are highlighted.

Corrosion of Metallic Biomaterials: A Review

Stainless steel, Co-Cr and Ni-Cr alloys have played an important role in many industrial sectors to combat environmental degradation. However, low hardness and poor wear properties have impeded their tribological and tribochemical applications. Conventional thermochemical treatments can be used to significantly harden these passive alloys but at the expense of their corrosion resistance due to precipitation induced depletion of Cr in the matrix. Research in 1980s led to the discovery of a new expanded austenite phase, i.e. so called S-phase with combined improvement in wear and corrosion resistance. Recent research has revealed that S-phase can be formed not only in stainless steels but also in Co-Cr alloys and Ni-Cr alloys. It is the purpose of this paper to critically review the S-phase surface engineering of stainless steels, Co-Cr alloys and Ni-Cr alloys. Particular attention will be paid to the structure, formation conditions, supersaturation, hardening mechanisms and metastability of...

S-phase surface engineering of Fe-Cr, Co-Cr and Ni-Cr alloys

Effect of initial pH and temperature of iron salt solutions on formation of magnetite nanoparticles

On the pitting corrosion resistance of nitrogen alloyed cold worked austenitic stainless steels

Effect of thermal aging on the room temperature tensile properties of AISI type 316LN stainless steel

The excellent characteristics of diamond such as its high wear resistance and chemical inertness raise the possibility to improve the performance and life time of industrial steel components by the deposition of a protective diamond coating. Therefore, we have investigated the direct deposition of diamond onto tool and stainless steel substrates by means of hot-filament-assisted chemical vapor deposition. Our growth studies show that, without any pretreatment procedure, the formation of interlayers consisting of a mixture of graphite, amorphous carbon and iron carbides prior to diamond film growth is unavoidable. For the tool steel substrates, ballas type diamond with large quantities of graphite is formed. For the stainless steel, the carbon in-diffusion leads to lesser amounts of graphite. However, as a result of the competitive growth of non-diamond phases, the obtained diamond films are still not continuous. The differences in graphitization effects of iron between both types of steel are explained by the differences in generation and decomposition of the metastable cementite (Fe 3 C) phase. Our results are discussed with the outcomes of recent works on multiple-stage diamond deposition processes and the application of diffusion barrier layers to overcome the above-mentioned problems.

Direct deposition of polycrystalline diamond onto steel substrates

A gas-phase nitridation procedure has been investigated using a home-assembled TGA-MS system to enhance the high-temperature hardness and wear resistance of electroplated chromium on AISI 316 LN austenitic stainless steel. The sluggish diffusion kinetics of nitrogen in chromium and the presence of a thin oxide layer at the surface are the major constraints encountered during low-temperature gas nitridation process. This paper attempts to bring out a detailed correlation of the effect of nitridation environment, ammonia dissociation rate, substrate temperature and catalytic role of a thin nickel layer, on the nitriding characteristics towards addressing the above-mentioned limitations. XRD and SEM investigations on the nitrided specimens unambiguously reveal the morphology and the distribution of CrN and Cr 2 N phases formed during nitridation.

P. Shankar

Papers

On the pitting corrosion resistance of nitrogen alloyed cold worked austenitic stainless steels

Effect of thermal aging on the room temperature tensile properties of AISI type 316LN stainless steel

Direct deposition of polycrystalline diamond onto steel substrates

Morphology and growth aspects of Cr(N) phases on gas nitridation of electroplated chromium on AISI 316 LN stainless steel

Clustering and ordering of nitrogen in nuclear grade 316LN austenitic stainless steel