This chapter provides information on the properties and behaviors of stainless steels and stainless steel powders. It begins with a review of alloy designation systems and grades by which stainless steels are defined. It then describes the composition, metallurgy, and engineering characteristics of austenitic, ferritic, martensitic, duplex, and precipitation hardening stainless steel powders and metal injection molding grades.

This chapter discusses the mechanical properties of powder metal stainless steels and the extent to which they can be controlled through appropriate alloying and processing steps. It describes how process-related factors, such as porosity, interstitial content, sintering atmosphere, and heating and cooling profiles, affect strength, ductility, and corrosion resistance. It also provides an extensive amount of property data – including tensile and yield strength, elongation, hardness, and creep and stress rupture measurements as well as fatigue curves – for various grades of powder metal stainless steel.

This chapter discusses the sintering process for stainless steel powders and its influence on corrosion resistance. It begins with a review of sintering furnaces and atmospheres and the effect of temperature and density on compact properties such as conductivity, ductility, and strength. It then describes the relationship between sintered density and corrosion resistance and how it varies for different types of powders and operating environments. The chapter also explains how stainless steel powders respond to different sintering atmospheres, including hydrogen, hydrogen-nitrogen, and vacuum, and liquid-phase sintering processes.

This chapter describes the most effective ways to improve the corrosion resistance of sintered stainless steels, including increasing alloy content, optimizing the sintering process, and the use of surface treatments and modifications.

This chapter discusses the growing use of sintered stainless steels in automotive applications and various types of filters and filtering media. It also describes how these materials are produced in the form of metal foams and cellular structures and how they serve as flake pigments in corrosion-resistant coatings.

This chapter describes a number of corrosion testing methods for sintered stainless steels, including immersion, salt spray, and electrochemical tests, ferric chloride and ferroxyl tests, and elevated-temperature oxidation resistance tests. It also provides corrosion resistance and performance data from various sources.

This chapter describes secondary processes employed in the production of powder-metal stainless steel parts, including various machining operations, welding, brazing, sinter bonding, resin impregnation, re-pressing and sizing, and surface finishing. It also discusses the factors that affect the machinability and weldability of sintered stainless steels.

Stainless steel powders are usually made by water or gas atomization. This chapter describes both processes and the properties and characteristics of the powders they produce. It also discusses secondary processes, including drying, screening, annealing, and lubricating, and the effects of iron contamination on corrosion resistance.

This atlas contains images showing how sintering conditions (time, temperature, and atmosphere) and compaction pressure affect the microstructure of different types of stainless steel. It also includes images of stainless steel powders, fracture surfaces, and test specimens characterized by the presence of compounds, such as oxides, carbides, and nitrides, and various forms of corrosion.

This chapter recounts some of the early efforts and milestones in the development of stainless steel powders and their use in powder metallurgy applications.

Steels that resist corrosive attack from normal atmospheric exposure and contain a minimum of 10.5% Cr and 50% Fe are generally classified as stainless steels. Their special qualities lie in a chromium-rich oxide surface film that quickly regrows when damaged. This chapter discusses the classification, composition, properties, treatments, and applications of austenitic, ferritic, martensitic, duplex, precipitation-hardening, powder metallurgy, and cast stainless steels. It also reviews the history of stainless steels and provides information on alloy designation systems.

Stainless steels derive their name from their exceptional corrosion resistance, which is attributed to their finely tuned compositions. This chapter discusses the alloying elements used in stainless steels and the some of the processing challenges they present. One of the biggest challenges is that stainless steels cannot be hardened by heat treatment. As a result, they are highly sensitive to processing-induced defects and the formation of detrimental phases. The chapter explains how alloy design, phase equilibria, microstructure, and thermomechanical processing can be concurrently optimized to produce high-quality austenitic, ferritic, and duplex stainless steels.

This chapter reviews the major marine applications of stainless steels, including the desalination equipment, shipping containers, and heat exchangers that handle seawater.

With typical alloy systems, casting is often the most convenient method by which to produce components. This is true for stainless steels, both for corrosion-resisting and for heat-resisting applications. This chapter discusses stainless steel casting alloys and their metallurgy. Foundry methods are discussed to the degree they are specific to the stainless alloys.

This chapter is dedicated mostly to the metallurgical effects on the corrosion behavior of corrosion-resistant alloys. It begins with a section describing the importance of alloying elements on the corrosion behavior of nickel alloys. The chapter considers the metallurgical effects of alloy composition for heat-resistant alloys, nickel corrosion-resistant alloys, and nickel-base alloys. This chapter also discusses the corrosion implications of changing the alloy microstructure via solid-state transformation, second-phase precipitation, or cold work. It concludes with a comparison of corrosion behavior between cast and wrought product forms.

This chapter discusses the composition and classification of stainless steels and focuses on the processes involved in heat treatment and applications of these steels. The wrought and the cast stainless steels covered are ferritic, austenitic, duplex (ferritic-austenitic), martensitic, and precipitation-hardening. In addition, information on special considerations for stainless steel castings is also provided. The heat treatment processes explained in the chapter are preheating, annealing, stress relieving, hardening, tempering, austenite conditioning, heat aging, and nitride surface hardening. Finally, some special considerations for stainless steel castings are discussed.

This chapter discusses the processes involved in heat treating of stainless steels, providing information on the classification, chemical compositions, and corrosion resistance of stainless steels and the effect of specific elements on the characteristics of iron-base alloys. Five groups of stainless steels are discussed: austenitic, ferritic, martensitic, precipitation-hardening, and duplex grades. The chapter also describes the heat treatment conditions that should be maintained for processing of stainless steels.

This chapter discusses the methods by which stainless steel powders are shaped and compacted prior to sintering, including rigid die compaction, metal injection molding, extrusion, and hot isostatic pressing. It explains where each process is used and how processing parameters, such as temperature and pressure, and powder characteristics, such as particle size and shape, influence the quality of manufactured parts. It describes the various stages of metal powder compaction, the role of lubricants, and how to account for dimensional changes in the design of tooling and process sequences.

This chapter discusses the advantages of using powder metallurgy to produce magnetic materials, particularly its ability to control chemistry and near-net shape. It also explains how process parameters and powder characteristics influence the physical and magnetic properties of common stainless steels.