Sound comes from the propagation of a wave from an oscillating body. Solid objects, in particular metals and their alloys, air, water - all this medium. Sound may occur in them.
Many are surprised by the situation when the train is still out of sight and is not audible, and if you put your ear to steel rails, the clatter of the wheels will be distinct. Obviously, the reason is the different speed of sound in steel and air. This issue will be discussed in more detail in the article.
How a sound wave propagates in solids
Consider the physics of the process. The sound in steel, as well as in solids in general, does not propagate at all, as in gases and liquids. This is explained by differences in the structure of substances. Atoms of a solid are interconnected by invisible electric forces. Together, they form a crystal lattice. Connections act like springs. If some atom is shifted, then others are shifted with it.
Sound in a solid is created by vibrations of particles and their propagation through the crystal lattice. Moreover, the movements of the atoms are ordered, have the same frequency and direction. The process becomes possible due to elasticity, i.e., the body's ability to resist pressure. This property and density determine how fast the sound wave propagates. In metals, this happens ten times faster than in air.
What determines the speed of sound propagation in steel
To answer this question, you need to know what else plays a role in this process. In addition to elasticity, the direction of the sound wave also affects the speed of sound. It is longitudinal and transverse. The first diverges in the direction of the oscillatory motion, and the second - against it. In solids, unlike air, sound can spread in both directions. It is interesting that the longitudinal wave velocity at the same oscillation frequency is always higher than the transverse one. The difference is a few seconds.
Steel grades differ in carbon content (it determines hardness), in the number of non-metallic inclusions, etc. Let us give one more interesting fact. It seems that if we take one type of this alloy, then the speed of sound in steel will be constant, since it depends on elasticity. However, it is not. This property characterizes the resistance to deformation, which is different: torsion, compression, bending. The type of exposure also determines the speed of sound. So, the longitudinal wave diverges in stainless steel at a speed of 5,800 m / s, the compression wave is 5,000 m / s, the shear and torsion wave is 3,100 m / s.