Continuous Cooling Transformation Behavior of High Carbon Pearlitic Steel

The continuous cooling transformation behavior of high-carbon pearlitic steel was studied by employing optical microscopy, scanning electron microscopy, and the Vickers hardness test. The results show that the microstructure of the test steel is composed of proeutectoid cementite and lamellar pearlite in the cooling rate range of 0.05–2 °C/s and lamellar pearlite in the range of 2–5 °C/s. Further, martensite appears at 10 °C/s. With the increase in the cooling rate, the Vickers hardness of the test steel first decreases and then increases. In the industrial production of high-carbon pearlite steel, the formation of proeutectoid cementite at a low cooling rate needs to be avoided, and at the same time, the formation of martensite and other brittle-phase at a high cooling rate needs to be avoided.

Phase Transformation Kinetics of High Nb-TiAl Alloy during Continuous Heating

In this work, the phase transformation behavior of Ti-45Al-8.5Nb-(W, B, Y) alloy during continuous heating was investigated using dilatometer and optical microscopy. Results indicated that the phase transformation process of high Nb-TiAl alloy during continuous heating included two stages: ordered α2 → disorder α and tetragonal γ → hexagonal α. According to the microstructure analysis, the initial α2/γ lamellar structure transformed into the massive γ phase and α phase (retained as α2) during the heating process. The activation energy of α2 → α and γ → α was 989.65 kJ/mol and 995.30 kJ/mol, respectively. Moreover, the lower the heating rate was, the faster the phase transformation reached the equilibrium state.

Effect of Concave Stave on Class I Barrel-Stave Flextensional Transducer

To meet the requirements of low frequency, high power, small size and light weight, a type of Class I barrel-stave flextensional transducer employing improved concave stave is presented. As the key component of flextensional transducer, concave stave plays an important role in vibrating efficiently to radiate acoustic energy. The structure of concave stave has a great effect on its behavior. In this paper, the main parameters of concave stave are discussed, especially the effect of radius on flextensional transducer. Both concave stave and transducer are analyzed through finite element method, including mechanical transformation behavior of concave stave and performances of flextensional transducer. On the basis of finite element design, five prototypes employing concave staves with different radii are manufactured and measured. The simulations and tests reveal that concave stave can affect performances of flextensional transducer. A larger radius of concave stave will result in a greater amplification of vibration and a lower resonance frequency of transducer. This can be a feasible way to optimize the resonance frequency or source level of flextensional transducer through adjusting the radius of concave stave in a small range. According to the electrical and acoustical tests, our Class I barrel-stave flextensional transducer is capable of being used as underwater low-frequency small-size projector.