I believe that "steps" and "stages" are equally correct. They have very slightly different shades of meaning.
"Stages" emphasizes the idea of each process taking a while. Crush, crush, crush, crush, crush, it is in the crushing stage. Now it is in the mixing stage: mix, mix, mix, mix, mix.
"Steps" emphasizes order, sequence, and transition. You might use the word if you were describing a block diagram.
One can imagine a tour guide taking someone through a cement factor. "The first step is crushing. Here we are at the crusher. In this stage of production, the rock is reduced to a fine powder. The next step is mixing, and if you walk with me down this ramp we can view the cement in the next stage of production..."