Development of fracture toughness of ultrahigh strength, medium carbon, low alloy steels for aerospace applications

Abstract

Ultrahigh strength, low alloy, steels with a medium carbon (0·25–0·50 wt-%) content and various amounts of chromium, molybdenum, nickel, silicon, and vanadium have been needed for high performance aerospace parts. The steels can be successfully employed at yield strengths of ≥1400 MPa, but their commercial use is often limited in practice by their poor fracture toughness. The present review surveys studies carried out over about the past 10 years to improve the fracture toughness of ultrahigh strength, medium carbon, low alloy steels, and the present understanding of this property is outlined. Particular emphasis is placed on improving the fracture toughness by microstructural control via thermal and thermomechanical treatments, modification of sulphide inclusions, and new alloying design. The major metallurgical factors controlling the fracture toughness are discussed for each of these techniques.