Steel impregnated plywood

[eLuSiVeMiTe]

I'd expect pices of metal in chipboard but not in plywood.

If it was just one bit I wouldn't be worried. If it was occurring every cut I'd be having words

 

[eLuSiVeMiTe]

Try cutting a sheet of ply or even better chipboard, in the dark. The amount of sparks that come off is crazy

Kitchen worktops are the worst.
Kill tracksaw blades in no time.