Fundamentals of Engineering Steels

**3**

**Chapter 1**

**Abstract**

**1. Introduction**

Integrated Manufacturing of

Industries and Medicals

Fine-Grained Stainless Steels for

*Tatsuhiko Aizawa, Tomomi Shiratori and Takafumi Komatsu*

Austenitic stainless steels have been widely utilized in industries, infrastructures, housing structures, kitchen components, and medical tools. Higher hardness and strength as well as more improvement of wear and corrosion toughness are often required in the industrial and medical applications. Fine-grained stainless steel (FGSS) provides a solution to increase the strength without loss of ductility and toughness. Deeper research and development in manufacturing of FGSS is required to make full use of its properties toward its applications in industries and medicals. First, its mechanical properties and microstructure is introduced as a basic knowledge of FGSS with comparison to the normal stainless steels. Mechanical and laser machinability of FGSS is stated and discussed to finish the products in seconds. Its performance in metal forming and diffusion bonding is explained to explore its applications in third. Its surface treatment and tooling is discussed to describe the grain-size effect on the low temperature plasma nitriding and to demonstrate its effectiveness in die-making in forth. Finally, every aspect in

manufacturing of FGSS sheets and solids is summarized as a conclusion.

diffusion bonding, surface treatment, tooling, medical applications

**Keywords:** stainless steels, fine grain, milling, laser machining, metal forming,

Hall-Petch relationship was found in 1951 [1] and 1953 [2]. Since this finding, the grain-size refinement has become one of the key development topics to improve properties of metals and alloys. High-pressure torsion (HPT) is one of the early technologies to refine microstructure for aluminum or copper [3]. A disk of these material is confined in a cylinder and subjected to torsion by rotating punch under high vertical pressure. As the strains increased during torsions in a disk, the grain size of these materials becomes smaller; then rounding by four times increases its hardness together with homogeneity of grain size [4]. However, the method is only applicable for relatively soft metallic alloys. It is difficult to apply to hard metals such as carbon steels or stainless steels. In addition, since the strains during a torsion is different in the radial direction of disk, the grain size remains larger than that in outer diameter; the rotation is not enough. Hence, this method might be suitable to create hard surface around the edge of products like a miller disk in the office copy machine; its application to bulk work materials is limited by cost
