@Larrin, I don't quite understand the explanation. There's not much width growth while rolling. The strain seems to be because the center stays hotter longer and grows faster than the edges causing it to split like it did. In diagram (a) it shows the strain opposite from my experience.
Most of my rolling is with non ferrous metals, butt I see quite a bit of width growth when rolling.
"The Buddha resides as comfortably in the circuits of a digital computer or the gears of a cycle transmission as he does at the top of a mountain."
Typically there is little increase in the width in rolling. Oftentimes it is zero. With thick pieces you can have spreading, however.