## 4 Results and Discussion
### Attenuation Behavior of Ferrous Alloys
This behavior was also observed in copper, nickel, and a beta-Ti alloy (Beta-III), which will be shown in the next section. The case of 304 stainless steel (UNS S30400) is the most dramatic. Test F85 showed the lowest \(\alpha\) value measured in all of the ferrous alloys tested, and this sample had a Vickers hardness of 321, corresponding to 20% to 25% plastic deformation [75]. In practical terms, this steel was in the quarter-hard condition. Softer 304 stainless steel samples (tests F86-F88) gave more than ten-times higher attenuation. These had Vickers hardness values of 193 to 199, corresponding to the no deformation case in [75], but this was higher than the Vickers hardness of 129 listed for soft 304 stainless steel [76]. In 302 stainless steel (UNS S30200), the same trend was evident as with tests F82 and F83 (low hardness and high \(\alpha\)), compared to test F84 (high hardness and low \(\alpha\)). Such attenuation behavior may possibly be rationalized if residual dislocations in annealed states are highly mobile, while this dislocation damping is suppressed in work-hardened states from interlocking conditions. Inboth stainless steels, interstitial segregation to dislocations is unlikely and no carbide precipitation occurs, offering no possible mechanism for dislocation locking. This differs from a low-C steel that has interstitial C atoms forming the Cottrell atmospheres [77]. The resultant dislocation locking reduces \(\alpha\). The cold-worked 304 sample was weakly magnetic due to strain-induced martensitic transformation. The pre-martensitic state may possibly contribute to attenuation, but this effect is absent in 302 steel samples, as all the 302 steel samples are faintly magnetic. In any event, copper and Beta-III Ti alloy have no magnetism and only dislocations can explain observed changes in damping behavior with or without prior deformation. This dislocation-related attenuation has received scant attention in recent decades and more work is certainly needed to elucidate its base cause. The concept of two different attenuation levels for high or low dislocation density makes no sense if all dislocations behave equally. Thus, some currently unknown dislocation interactions are needed to vary the damping contributions, and no rational account for the contradictory observations can be offered at present. Anisotropic directional effects on attenuation were found in eight more cases, in addition to the cold-worked steel plate. These occurred in two 4340 plates (tests F38-F40 and F41-F43; UNS G43400), 4142 (tests F44 and F45; UNS G41420), a high-strength, low-alloy (HSLA) steel (tests F58-F60), two A533B pressure vessel steel plates (tests F62-F64, F66, and F67), a 1 Cr-Mo-V turbine rotor steel (tests F68 and F69), and 304 stainless steel (tests F86-F88). Their \(\alpha\) values at 1 MHz in the through-thickness (S) direction were 1.7 to 10.7 times higher than the longitudinal (L) or transverse (T) direction of the same sample, except for one case of 4340 steel. The S direction in rolled steel plates often has reduced ductility from non-metallic inclusions (mainly MnS) that are flattened by hot rolling, which contribute to lamellar tearing and heightened acoustic emission activities [78; 79]. The acoustic emission is a manifestation of the decohesion of MnS inclusion during loading. On the other hand, one heat-treated 4340 (tests F38-F40) did not show this anisotropy. This difference is expected from better impurity control for high-strength steels, with dispersed spherical oxide inclusions being more common [78]. Further tests on the electro-slag remelted (ESR) 4340 plate (tests F36 and F37) may offer additional clues, as it showed medium \(\alpha\) values. In addition to the CW and directional effects on attenuation discussed in the previous paragraphs, the presence of some phase transformation products increased attenuation in low- to medium-carbon steels. The effects of heat treatment were examined using three grades of steels (1020, F30, and F50).