I know this is using two different materials but for a good and easy to understand example lets think about lead and S90V stainless.
Lead is tough - you can pound it and bend it and beat it and it still won't break. (it'll just give) But, lead isn't strong - it doesn't take much force to deform or bend it.
S90V is strong - it takes a lot of force to bend or deform it and it is hard and holds a great edge that doesn't break down easily. However, If you start to pounding on it it will crack, break or shatter - hence, not tough.
I hope this helps. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />
