Q.Casehardening occurs when the outside tries to shrink, but can't because of the wet core.

A: What you are seeing is called casehardening or drying stress. It occurs because at the beginning of drying, the outside tried to shrink, but could not because of the wet core. So, the outside dried to a larger shape than if it had been free to shrink. This creates a stress condition that, when the pieces are ripped, will cause the pieces to bow; the left piece will be a mirror image of the warp in the right piece. (Sometimes there is stress in the tree and this stress will cause immediate warp but it will not be balanced, left to right.) It is not uncommon that construction lumber will have casehardening; it does not hurt anyone and would cost money to remove during drying. Casehardening does not affect nailing as it is a stress condition so nothing is harder.

So, how do you remove casehardening? Existing casehardening is removed by steaming the material for a few hours. (Water misting might work too.) As you only need a few pieces to be stress free, I wonder if you can find someone with a steamer for cleaning car engines, etc. or a rental place where you can borrow a steamer when needed?