Effect of Microstructure on Ballistic Performance of ESR (Electroslag Remelted) 4340 Steel.

摘要

The objective of this investigation was to develop heat treating procedures which will consistently produce microstructures essentially free from large spheroidal carbides and, thus, provide reproducible and predictable ballistic behavior. Increasing normalizing temperature of ESR 4340 from 1600F to 2000F has little effect in reducing the size or number of carbide spheroids which are 1 micrometer in diameter or larger. In the range of 1500f to 2000F, increasing austenitizing temperature drastically reduces spheroid size and population. Grain coarsening produced by high austenitizing temperatures is reduced by a second austenitizing treatment at 1600 F. As spheroid population decreases, hardness, ultimate strength, and fracture toughness increase slightly while elongation, reduction of area, and Charpy impact values decrease. Ballistic test plates which were heat treated to produce microstructures with very few carbide spheroids has V(50) values which were more than 50 percent higher than those of plates which were normalized at 1600F and austenitized at 1500F. None of the standard static mechanical test can be used to predict the ballistic performance of ESR 4340. Keywords: Heat treatment; Mechanical properties; Ballistic testing; Fracture toughness; Electroslag welding. (SDW)