Complex sentence: After 20 foldings, (2 20, or about a million individual layers), there is too much diffusion in the carbon content, the steel becomes almost homogeneous in this respect, and the act of folding no longer gives any benefit to the steel.
Split into simpler sentences: After 20 foldings, (2 20, or about a million individual layers), there is too much diffusion in the carbon content. The steel becomes almost homogeneous in this respect, and the act of folding no longer gives any benefit to the steel.