Development of Ultra High Strength Steels for Engineering Applications

Abstract

The present work is focused on studies undertaken to improve the mechanical properties of different ultra-high strength steels (UHSS). The subject matter resulting out of the present study has been arranged in nine chapters in this Ph.D. thesis. The outline of the chapters is as follows: Ø Chapter 1: The chapter introduces the basic terms involved in the present research viz. steels, the classifications of steels, etc. This chapter discusses the need and benefit of UHSS steels and also presents the origin of the present research work. The outline of the complete thesis is also covered in this chapter. Ø Chapter 2: This chapter presents a detailed review of literature on the processing and mechanical properties of UHSS. This includes (i) AMS-4340 steels, (ii) 10.7CrMoVNbN steels, (iii) AISI321 steels, (iv) C250 steels, and (v) 300M steels on which the present work has been done. The chapter also brings forth the summary of the existing literature and also the main gaps in the existing literature in their field of work. Ø Chapter 3: The chapter presents a brief description of equipment used for testing and characterization of UHSS. This include X-ray diffraction (XRD), Optical microscopy, Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS), and different Mechanical tests done for the processed UHSS to fulfill the basic objectives mentioned in this chapter. Ø Chapter 4: This chapter presents the processing methodology of AMS-4340 steels developed for defense applications viz. gun barrel and ballistic applications. Four different ESR heats E1, E2, E3 and E4 were prepared under different processing conditions. The microstructural investigations revealed that the hydrogen flaking was dominant factor in E1 heat. Because of this the ESR heat E1 was rejected as it could not achieve the desired yield strength. Although, ESR heats E2 and E3 have shown the desired mechanical properties but got rejected during the ultrasonic testing.