Normalizing正火 formalizing is achieved by heating the metal to a specified temperature(which is higher than either the hardening or annealing temperatures), soaking the metal until it is uniformly heated, and cooling it in still air Ferrous metals are normalized to relieve the internal stresses produced by machining, forging, or welding Steel is much tougher in the normalized condition than in any other condition Parts that will be subjected to impact and parts that require maximum toughness and resistance to external stresses are usually normalized Case Hardening表面强化 During the case-hardening process, a low-carbon steel is heated to a specific temperature in the presence of a material which decomposesand deposits more carbon into the surface of a steel. Then, when the part is cooled rapidly, the outer surface or case becomes hard, leaving the inside of the piece soft but very tough. Case hardening is an ideal heat treatment for parts which require a wear-resistant surface and a tough core, such as gears, cams, cylinder sleeves, and so forth. The most common case-hardening processes are carburizing and nitriding Carburizing is a process of diffusing Carbon into the surface of steel. (W) Nitriding is a process of diffusing Nitrogen into the surface of steel. ( Ba0) 7. Energy and Environment Pollutants emitted during the combustion of fossil fuels are responsible for smog, acid rain, and global warming and climate hange( the greenhouse effects) The environmental pollution has reached such high levels that it became a serious threat to vegetation, wild life, and human health. Air pollution has been the cause of numerous health problems including asthma and cancer Acid rain The sulfur oxides and nitric oxides react with water vapor and other chemicals high in the atmosphere in the pres of sunlight to form sulfuric and nitric acids The acids formed usually dissolve in the suspended water droplets in clouds or fog These acid-laden droplets, are washed from the air on to the soil by rain 8. Summary Mechanical engineers involved in the design and analysis of machinery must be aware of the change in the thermodynamic state during the cycle of the machinery The total energy must be conserved, as stated by the first law of thermodynamics. Real processes al ways obey the first law of thermodynamic As the second law of thermodynamics states, not all the available heat can be converted to work, since some heat is always lost to the surroundings naturally from high to low temperatures can be utilized to produce work through a heat engme 3 Natural heat transfer is from a body at a high temperature to a body at a low temperature. The potential of heat to goNormalizing 正火 Normalizing is achieved by heating the metal to a specified temperature (which is higher than either the hardening or annealing temperatures), soaking the metal until it is uniformly heated, and cooling it in still air. Ferrous metals are normalized to relieve the internal stresses produced by machining, forging, or welding. . Steel is much tougher in the normalized condition than in any other condition. Parts that will be subjected to impact and parts that require maximum toughness and resistance to external stresses are usually normalized. Case Hardening 表面强化 During the case-hardening process, a low-carbon steel is heated to a specific temperature in the presence of a material which decomposesand deposits more carbon into the surface of a steel. Then, when the part is cooled rapidly, the outer surface or case becomes hard, leaving the inside of the piece soft but very tough. Case hardening is an ideal heat treatment for parts which require a wear-resistant surface and a tough core, such as gears, cams, cylinder sleeves, and so forth. The most common case-hardening processes are carburizing and nitriding. Carburizing is a process of diffusing Carbon into the surface of steel. (渗碳) . Nitriding is a process of diffusing Nitrogen into the surface of steel. (渗氮) 7. Energy and Environment Pollutants emitted during the combustion of fossil fuels are responsible for smog, acid rain, and global warming and climate change (the greenhouse effects). . The environmental pollution has reached such high levels that it became a serious threat to vegetation, wild life, and human health. Air pollution has been the cause of numerous health problems including asthma and cancer. Acid Rain The sulfur oxides and nitric oxides react with water vapor and other chemicals high in the atmosphere in the presence of sunlight to form sulfuric and nitric acids. . The acids formed usually dissolve in the suspended water droplets in clouds or fog. These acid-laden droplets, are washed from the air on to the soil by rain. 8. Summary Mechanical engineers involved in the design and analysis of machinery must be aware of the change in the thermodynamic state during the cycle of the machinery. . The total energy must be conserved, as stated by the first law of thermodynamics. Real processes always obey the first law of thermodynamics. As the second law of thermodynamics states, not all the available heat can be converted to work, since some heat is always lost to the surroundings. . Natural heat transfer is from a body at a high temperature to a body at a low temperature. The potential of heat to go naturally from high to low temperatures can be utilized to produce work through a heat engine.