6.1.1 Aircraft Materials and Corrision

这是一篇关于6.1.1 Aircraft Materials and 的思维导图，主要内容包括：Metal Properties，Ferrous Metals，Identification of Steels，Alloying Agents in Steel，Heat Treatment of Steel。

6.1.1 Aircraft Materials and Corrosion

• Metal Properties
  • Strength
  • Metal Loading Forces
    • Tensile strength
    • Compressive strength
    • Shear strength
    • Torsional strength
    • Bending strength
    • fundamental loading forces
    • Others
      • Fatigue strength, or endurance strength
      • Impact strength (toughness)
  • Hardness
  • Malleability
  • Ductility
  • Brittleness
  • Elasticity
  • Toughness
  • Conductivity
  • Thermal Expansion
  • Fusibility
• Ferrous Metals
  • Iron (Ferrite)
  • Steel Composition
• Identification of Steels
  • Society of Automotive Engineers Steel Numbering
  • SAE Steel Numbering System
• Alloying Agents in Steel
  • Purpose of Ferrous Metal Alloys
  • Carbon
  • Other Alloying Agents
    • Silicon
    • Manganese
    • Sulphur
    • Phosphorous
    • Nickel
      • Nickel adds strength and hardness to steel and increases its yield strength. It also slows the rate of hardening when steel is heat-treated, which increases the depth of hardening and produces a finer grain structure. The finer grain structure reduces steel’s tendency to warp and scale when heat-treated.
    • Chromium
      • Chromium is alloyed with steel to increase strength and hardness as well as improve its wear andcorrosion resistance. Because of its characteristics, chromium steel is used in balls and rollers of antifriction bearings. In addition to its use as an alloying element in steel, chromium is electrolytically deposited on cylinder walls and bearing journals to provide a hard, wear-resistant surface.
    • Nickel-Chromium Steel
      • Nickel toughens steel, and chromium hardens it. Therefore, when both elements are alloyed, they give steel desirable characteristics for use in high-strength structural applications.
    • Molybdenum
      • One of the most widely used alloying elements for aircraft structural steel is molybdenum. It reduces the grain size of steel and increases both its impact strength and elastic limit. Molybdenum steels are extremely wear resistant and possess a great deal of fatigue strength. Chrome-molybdenum (chrome-moly) steel machines readily, is easily welded by either gas or electricarc, and responds well to heat treatment. Chrome-moly steel is an ideal choice for landing gear structures and engine mounts. Furthermore, chrome-moly’s toughness and wear resistance make it a good material for engine cylinders and other highly stressed engine parts.
    • Vanadium
      • When combined with chromium, vanadium produces a strong, tough, ductile steel alloy. Ball bearingsare made of chrome-vanadium steel.
    • Tungsten
      • Tungsten has an extremely high melting point and adds this characteristic to steel it is alloyed with. Because tungsten steels have high density (high mass) and retain their hardness at elevated operating temperatures, they are typically used for control surface balance weights and breaker contacts in magnetos.
    • Titanium
      • Titanium steel alloys have very high tensile strength and toughness (and at higher temperatures). Titanium steel is also lightweight and has high corrosion resistance whilst the ability to withstand extreme temperatures.
  • Stainless Steel
    • Stainless steel is a classification of corrosion-resistant steels that contain large amounts of chromiumand nickel. Their strength and resistance to corrosion make them well suited for high-temperature applications such as firewalls and exhaust system components.
• Heat Treatment of Steel
  • Purpose of Steel Heat Treatment
  • Annealing
    • Annealing softens steel and relieves internal stress. Annealing steel involves heating it, soaking it for a specified time and then cooling it. The steel can be cooled by leaving it in the furnace and allowing both the furnace and steel to cool together or by packing the steel in hot sand or ash so the heat is conducted away slowly.
  • Normalising
    • The processes of forging, welding and machining usually leave stresses within steel that could lead to failure. These stresses are relieved in ferrous metals by a process known as normalising. This process involves heating the steel and maintaining the temperature until the metal is uniformly heat-soaked. The steel is then removed from the oven and allowed to cool in still air. Although this process does allow particles of carbon to precipitate out, the particles are not as large as those formed when steel is annealed. One of the most important uses of normalising in aircraft work is on welded parts. When a part is welded, internal stresses and strains set up in the adjacent material.
  • Hardening
    • Carbon steel can be hardened readily. The maximum hardness attained by carbon steel depends almost entirely on its carbon content. Hardening steel involves heating it so carbon can disperse uniformly. Once this occurs, the alloy is cooled rapidly by quenching it in water, oil or brine (water with a high salt content). The speed of the quench is determined by the quenching medium. Oil provides the slowest quench, and brine 浓盐水 is the most rapid.
  • Tempering
    • Tempering reduces the undesirable qualities of the steel's brittleness. Tempering an alloy is done by heating it to a certain temperature and holding it there until it becomes heat-soaked. It is then allowed to cool to room temperature in still air. Tempering not only reduces hardness and brittleness,but also relieves stress and improves steel’s ductility and toughness.
  • Case Hardening
    • Aircraft components like bearings and gears that require metal with hard, durable surfaces and core material that remains tough. This is accomplished through a process called case-hardening. Low-carbon and low-alloy steels are best suited for case-hardening. If high-carbon steel is case-hardened,the hardness penetrates the core and causes brittleness.