sentences:  The compound armor was constructed by welding hardened steel together with more flexible wrought iron plates to take advantage of the hardness of steel and the greater flexibility of wrought iron to break up and then contain incoming shells.Krupp's nickel steel armor was based on the Harvey process, which enriched the upper layers of the steel with carbon.The process hardened the outer layer while retaining greater flexibility at the back of the plate; the fact that the new armor plate consisted of a single forging instead of multiple plates welded together gave it greater strength.