This is a muffler like part that converts harmful carbon monoxide and hydrocarbons to water vapor and carbon dioxide. Some converters often reduce harmful nitrogen oxides. The converter is positioned between the exhaust manifold and the muffler.
The muffler works to quiet the exhaust down to required levels. Bear in mind that the combustion process is a series of explosions that create allot of noise. Most mufflers use baffles to bounce the exhaust around dissipating the energy thus quieting the noise. Some mufflers also use fiberglass packing that absorbs the sound energy as the gases flow through.
Among all of the above mentioned parts is the exhaust pipe which transfers the gas through it’s journey out your tail pipe. Exhaust tubes are usually made of steel but can be stainless steel (which lasts longer because of it’s corrosion resistance) or aluminized steel tubing. Aluminized steel has better corrosion resistance abilities than plain steel but not better than stainless steel. It is however cheaper than stainless steel