Stainless steels are primarily alloys of iron and chromium. They are grouped into five families, primarily based on their microstructure: ferritic, austenitic, martensitic, duplex, and precipitation hardening. Three out of the five families of stainless steels, namely, austenitic, ferritic, and martensitic, are well suited for manufacture via conventional powder metallurgy (PM) processes. This article presents the iron-chromium partial phase diagram to illustrate the changes in the temperature range when pure iron is alloyed with chromium. It describes AISI and UNS numbering systems, which are used as an identification system for stainless steels. The article tabulates the material designations of stainless steels in accordance with the Metal Powder Industries Federation. It also details the characteristics and chemical composition of wrought and PM stainless steels.

This article describes the physical properties of powder metallurgy (PM) stainless steels. These include thermal diffusivity, conductivity, thermal expansion coefficient, Poisson's ratio, and elastic modulus. The article contains a table that lists the characteristics of various grades of PM stainless steels. It discusses the applications of various PM stainless steels such as rearview mirror brackets, anti-lock brake system sensor rings, and automotive exhaust flanges and sensor bosses.

This article describes the factors influencing the room-temperature and elevated-temperature mechanical properties of powder metallurgy (PM) stainless steels. It contains tables that list the mechanical property specifications of the Metal Powder Industries Federation (MPIF) Standard 35.

Powder metallurgy (PM) stainless steels, as with conventional PM steels, are often used in the as-sintered condition. In addition to cost considerations, minimization of postsinter handling and secondary operations is also preferred because it reduces the potential for contamination of the parts with particulates and residues, which can result in the appearance of surface rust. This article provides information on various secondary operations, including tumbling, re-pressing, resin impregnation, annealing or heat treating, brazing, machining, and welding. It describes those aspects relating to welding of PM stainless steels, specifically, the effects of density, residual porosity, and sintered chemistry on weldability. Further, the article investigates the influence the sintering atmosphere has on machinability, as well as differences created by the presence of residual porosity.

This article provides a detailed discussion on the most commonly employed tests and specific examples of the use of these tests in evaluating the corrosion resistance of powder metallurgy (P/M) stainless steels. It describes the influence of various processing parameters on the corrosion resistance of P/M stainless steels. The approaches used to improve the corrosion resistance of sintered stainless steels are discussed briefly. The article also presents a discussion on the manufacturing and corrosion characteristics of P/M superalloys.

Nitric acid is a strongly oxidizing acid that is aggressively corrosive to many metals. Its oxidizing nature is affected by acid temperature and concentration, and composition of the alloy exposed to it. This article focuses on the corrosion behavior of various ferrous and nonferrous metals and alloys when exposed to a nitric acid environment. The ferrous and nonferrous metals and alloys discussed are carbon and alloy steels, stainless steels, aluminum alloys, titanium, zirconium alloys, niobium and tantalum, and nonmetallic materials.

Metallic alloys that are typically used for medical purposes include stainless steels, Ti-6Al-4V, and Co-Cr-Mo. This article discusses the relative merits of each of these alloys. The utilization of stainless steels in the biomedical industry, especially in relation to the additive manufacturing (AM) process, is the main focus of this article. The characteristics of various stainless steels are described subsequently, and the categories that are of relevance to the biomedical industry are identified. The types of stainless steels covered are austenitic, ferritic, martensitic, duplex, and precipitation-hardened stainless steels. The article discusses the potential benefits of AM for biomedical devices. It describes the types of AM processes for stainless steels, namely binder jet, directed-energy deposition, and laser powder-bed fusion. The article reviews the AM of austenitic, martensitic, and PH stainless steels for biomedical applications. In addition, the challenges and obstacles to the clinical use of AM parts are covered.

This article describes the sintering behavior of austenitic, ferritic, and martensitic stainless steels. It presents different sintering schedules that are selected by Metal Powder Industries Federation (MPIF). The article provides information on the equipment and atmospheres used for sintering and the steps involved in the process. It discusses the factors that influence the dimensional changes in sintering, namely, powder-related, compaction-related, and sintering-related factors.

Metallurgical variables, mainly carbon distribution and the presence of nitrogen and metallic phases, can influence the corrosion behavior of austenitic, ferritic, duplex, and martensitic stainless steels. This article describes the effects of these metallurgical and processing variables on the susceptibility of the stainless steels to intergranular corrosion and intergranular stress-corrosion cracking and their testing methods. It explains the effect of sigma and related phases on the corrosion behavior of stainless steels.

This article briefly describes the welding of various stainless steels to dissimilar steels. The stainless steels include austenitic stainless steels, ferritic stainless steels, and martensitic stainless steels. The dissimilar steels include carbon and low-alloy steels. In addition, the article provides information on the cladding of austenitic stainless steel to carbon or low-alloy steels.

This article reviews various test methods used for evaluating the corrosion resistance of powder metallurgy stainless steels. These include immersion testing, salt spray testing, and electrochemical testing. The article discusses the factors that affect corrosion resistance of sintered stainless steels: compaction-related factors, sintering-related factors, and effects of alloy composition. Corrosion resistance data for sintered stainless steels is provided.

This article provides information on the process details that differ from general water atomization of metals as they relate to basic and engineering properties that are specific to stainless steel powders. The discussion focuses on the compacting-grade stainless steel powders. The process details include raw materials, melting method, and control of physical and chemical powder characteristics. The article describes the gas atomization of stainless steel powders and processes that are done after water atomization: drying, screening, annealing, and lubricating. It also discusses the two types of quality assurance testing measures for powder metallurgy stainless steels: tests for powder contamination and tests of chemical and physical properties.

This article provides information on the metallurgy of austenitic stainless steels, and the formation of their intermediate phases (Sigma, Chi, and Laves). It discusses sensitization, a major problem associated with the austenitics, and solutions to avoid the problem. The article describes heat treatments applied to austenitic stainless steels, namely, soaking for homogenization and preparation for hot working; annealing to remove the effects of cold work and to put alloying elements into solid solution; and stress relieving. It provides information on the stabilizing anneal process, which is conducted on stabilized alloys, and discusses the metallurgical characteristics of austenitic stainless steels that may affect the selection of a stress-relieving treatment and prevention of stress corrosion by stress relieving. The article also discusses the heat treatments applied to duplex stainless steels, which involve soaking and annealing, achieving the austenite-ferrite balance, precipitation of intermetallics, and alpha prime precipitation.

Fabrication of wrought stainless steels requires use of greater power, more frequent repair or replacement of processing equipment, and application of procedures to minimize or correct surface contamination because of its greater strength, hardness, ductility, work hardenability and corrosion resistance. This article provides a detailed account of such difficulties encountered in the fabrication of wrought stainless steel by forming, forging, cold working, machining, heat treating, and joining processes. Stainless steels are subjected to various heat treatments such as annealing, hardening, and stress relieving. Stainless steels are commonly joined by welding, brazing, and soldering. The article lists the procedures and precautions that should be instituted during welding to ensure optimum corrosion resistance and mechanical properties in the completed assembly.

This article discusses the corrosion characteristics of superaustenitic stainless and duplex stainless steels, which are used in pharmaceutical industry. It describes passivation treatments and the electropolishing of stainless steels. The article informs that electropolishing is not a passivation treatment, although the proper execution of the process will result in a passive surface. The article concludes with a discussion on roughing, which is a phenomenon of particular interest to the pharmaceutical industry.

Stainless steel powder metallurgy (P/M) parts represent an important and growing segment of the P/M industry. This article describes the processing, properties, and composition of medium-density and high-density P/M stainless steels. Medium-density materials are processed by pressing and sintering prealloyed stainless powders. High-density materials are produced by hot isostatic pressing, cold isostatic pressing followed by extrusion, or metal injection molding. The comparison of mechanical properties of these P/M stainless steels is represented graphically. The article contains a table that lists the effect of iron, carbon, nitrogen, oxygen, and density on the corrosion resistance of the sintered austenitic stainless steels.

Most alloys are susceptible to intergranular corrosion, also known as intergranular attack (IGA), when exposed to specific environments. This article reviews the theory and application of acceptance tests for detecting the susceptibility of stainless steels and nickel-base alloys to IGA. It describes the most serious forms of structure-dependent corrosion, such as stress-corrosion cracking and exfoliation, in aluminum alloys including strain-Hardened 5xxx (Al-Mg) alloys and heat treated high-strength alloys. The article concludes with information on the evaluation tests for other alloys such as magnesium alloys and zinc die casting alloys.

This article discusses two categories of stainless steel casting alloys and their nomenclature. It provides information on two situations in which welding of stainless steel castings is required. These situations are based on casting defects and selection of welding processes. The article presents compositions and typical microstructures of corrosion-resistant stainless steel casting alloys in tabular form. It presents special considerations for the welding of martensitic stainless steel castings. The article reviews the two most serious problems encountered in the welding of stainless steel castings, namely, solidification hot cracking and heat-affected zone hot cracking. It concludes with a discussion on the some useful considerations for welding corrosion-resistant alloys to avoid defects.

Stainless steels are widely used at elevated temperatures when carbon and low-alloy steels do not provide adequate corrosion resistance and/or sufficient strength at these temperatures. This article deals with the wrought stainless steels used for high temperature applications. It gives some typical compositions of wrought heat-resistant stainless steels, which are grouped into ferritic, martensitic, austenitic, and precipitation-hardening (PH) grades. Quenched and tempered martensitic stainless steels are essentially martensitic and harden when air cooled from the austenitizing temperature. These alloys offer good combinations of mechanical properties. The article focuses on mechanical property considerations and corrosion resistance considerations of stainless steels. The corrosion and oxidation resistance of wrought stainless steels is similar to that of cast stainless steels with comparable compositions.

This article provides a general overview of additively manufactured steels and focuses on specific challenges and opportunities associated with additive manufacturing (AM) stainless steels. It briefly reviews the classification of the different types of steels, the most common AM processes used for steel, and available powder feedstock characteristics. The article emphasizes the characteristics of the as-built microstructure, including porosity, inclusions, and residual stresses. It also reviews the material properties of AM steel parts, including hardness, tensile strength, and fatigue strength, as well as environmental properties with respect to corrosion resistance, highlighting the importance of postbuild thermal processing.