Although a great deal of mechanical properties data on titanium alloys have appeared in the literature, no attempt has been made to relate the fine structures in beta titanium alloys to strength and fracture toughness. Therefore, strength and fracture toughness properties of B-120VCA—obtained through a variety of thermal and thermomechanical treatments—were related to fine structures by transmission electron microscopy, electron fractography, etc. Effects of (1) prior solution-treating temperatures, (2) cold working after solution treating, and (3) cold working both before and after solution treating were evaluated in terms of strength and fracture toughness, and parallel fine structure studies. The double cold-work treatment, without aging, produced σt with a fracture toughness of 115 ksi√in. and may be promising for certain high-strength applications. Also short aging times produce unique combinations of strength and fracture toughness (σt ≈ 190 ksi, Kc ≈ 70 ksi√in. The kinetics of β→ α transformation were characterized and related to fracture toughness and strength properties. Precipitation of omega was suggested in the solution-annealed material during cooling to room temperature; further growth of this phase upon prolonged aging at 600 F was established. At 900 F, omega growth was limited, being replaced by alpha precipitation first in a discontinuous and later in a general dispersion.

The relation of fine structure of an 18Ni 300 maraging steel to mechanical properties and fracture toughness was investigated. Sheet specimens were annealed by 1500 F austenizing for 1 hr followed by air cooling to room temperature. Some specimens were aged at 900 F for various times, while other specimens were aged for 1 hr at temperatures from 300 to 1300 F. Microstructure was studied by replication and by transmission electron microscopy. Aging kinetics at 900 F were very rapid; nearly 90 per cent of maximum strength was attained after 1 hr exposure. Between room temperature and 900 F, microstructure changed from a precipitate free blocky martensite to one that had a finely dispersed precipitate throughout the martensite structure. At higher temperatures than 900 F overaging caused a decrease in toughness. Strength and hardness increased rapidly from 400 to 1000 F. The precipitate was identified as Ni3Mo with possibly some Ni3Ti also present. The effect of test temperature on fracture toughness was evaluated at temperatures from +100 to −320 F. A distinct ductile-brittle transition occurred between −100 and −320 F. Fracture toughness decreased from a room-temperature value of 212 ksi √in. to 50 ksi √in at −320 F.

A comprehensive characterizing of fine structures in Type 422 stainless steel has effectively related structural parameters to smooth- and notch-tensile properties and to corrosion and stress-corrosion resistance. By a departure from conventional heat treatment for this steel, fracture toughness can be increased nearly fourfold at the same yield strength, and corrosion properties can be substantially improved. These marked improvements in properties are explained in terms of dislocation rearrangements and precipitation strengthening effects.