Steel is used, for example, in structures where its high strength and resistance to impact loads may be of importance, and for tools for machining purposes. The so-called ‘high-speed’ steels retain their hardness to a marked degree even at higher temperatures, so that cutting tools of this steel will retain a sharp cutting edge under conditions of high-speed machining and at high temperature. ‘High-tensile’ steels have a high value of ultimate tensile stress and are used to make springs or to sustain high-tensile loads.