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The Steel Story

The Steel Story. Learning Objectives Relate properties of metals to their structures HSW: Explain how properties of alloys are related to models of their structures Explain how we can change its properties. Properties of metals. Metallic structure.

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The Steel Story

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  1. The Steel Story Learning Objectives Relate properties of metals to their structures HSW: Explain how properties of alloys are related to models of their structures Explain how we can change its properties

  2. Properties of metals

  3. Metallic structure • Atoms of pure metals are arranged in a regular structure:

  4. Metallic structure • When they are hammered, atoms can slide over each other, the metal dents (malleable) Force

  5. Metallic structure • Because the atoms can slide over each other they can also be stretched (ductile):

  6. Cast Iron • Carbon impurities from the blast furnace mix into the iron lattice: Iron atoms cannot roll over each other they are blocked by the carbon atoms and the metal smashes (it is brittle) Force

  7. Steelmaking (BOS) • Iron straight from the blast furnace is too brittle to be useful, it is used in Steelmaking. • Impurities such as carbon silicon, phosphorous and sulfur are removed by blowing oxygen gas into the molten iron. • This turns them into oxides, that are acidic. • Limestone is basic. It reacts with the acidic waste products and makes slag. Slag does not mix with the metal, but floats on top of it. It can be decanted.

  8. Steel • Steel has had most of the carbon impurities removed, but a little bit left over (approx 1%) gives it extra strength. Force

  9. Iron and Steel • Pure iron is fairly soft and has limited uses. It is easily worked and moulded, used for fences gates, garden furniture etc. • Pig Iron (or cast iron)from the blast furnace is not pure it contains around 4% carbon and some other elements (S, Si, P) it is very brittle. It also has limited uses, e.g. drain covers, engine blocks. • Steel usually contains around 1% carbon. It can be tailor made for certain jobs by varying the carbon content, and adding small amounts of other elements.

  10. Carbon Steel • Low carbon steel (0.4% C) • Soft, easy to bend & shape, e.g. car bodies • Medium carbon steel (0.8% C) • Harder and stronger, but more difficult to bend and shape, e.g tools (hammer) • High carbon steel (up to 1.5% C) • Very hard, e.g. knives and razors (but can be brittle, may snap if bent or misused)

  11. Designer Steel Alloys Small amounts of other metals are added to the steel to ‘tweak’ its properties (expensive!!) • Nickel- resistant to acids (chemical industry) • Chromium- resists corrosion (oxidation) ‘stainless’ • Molybdenum- stronger and tougher (weaponary) • Tungsten- strong at high temps (tools) • Cobalt-highly magnetic • Vanadium-adds springiness (tools e.g. spanners)

  12. Steel alloys Larger metal atoms disrupt the structure and add strength: Dislocation

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