Detecting second-layer fatigue cracks under installed skins and fasteners with low-frequency eddy current array: Hill, B. and Sheppard, W. Mater. Eval. (Dec. 1992) 50 (12), 1398, 1400–1402, 1404–1405

Abstract

In recent years, there has been significant interest in the development of high silicon bainitic steels. This has been due to their excellent mechanical properties, including very high strength, good ductility, high fracture toughness, and high wear resistance. Recently, a high-strength, high-toughness bainitic steel with a high silicon content has been developed by two of the authors. In this paper, the mechanical properties as a function of austempering are presented. A low-carbon, low-alloy (LCLA) bainitic steel with a high (2%) silicon content was quenched and isothermally austempered at temperatures from 260 °C to 343 °C for 2 h. The heat treatment produced a microstructure consisting of tempered martensite with austenite located between the martensite laths. The mechanical properties of these austempered samples, including plane-strain fracture toughness, were characterized and compared with as-cast samples. All of the austempering treatments produced high strength (>1500 MPa UTS) and high fracture toughness (>105 MPa) with reasonable ductility (>4%).A promising potential application of this steel is a military vehicle armor plate; therefore, a small number of impact tests were performed to qualitatively assess the improvement in resistance. Impact testing was performed using projectiles propelled by a light gas gun; targets of mild steel and LCLA austempered at 316 °C were evaluated. Qualitative results reveal that, in comparison to the mild steel sample, the austempered LCLA samples suffered reduced damage and no penetration.