Unit 4 Heat Treatment& Hot Working of MetalsⅠ. Lead-inSteel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten. Carbon and other elements act as a hardening agent, preventing dislocations in the iron atom crystal lattice from sliding past one another. Varying the amount of alloying elements and the form of their presence in the steel (solute elements, precipitated phase) controls qualities such as the hardness, ductility, and tensile strength of the resulting steel. Steel with increased carbon content can be made harder and stronger than iron, but such steel is also less ductile than iron.Though steel had been produced by various inefficient methods long before the Renaissance, its use became more common after more-efficient production methods were devised in the 17th century. With the invention of the Bessemer process in the mid-19th century, steel became an inexpensive mass-produced material. Further refinements in the process, such as basic oxygen steelmaking (BOS), lowered the cost of production while increasing the quality of the metal. Today, steel is one of the most common materials in the world, with more than 1.3 billion tons produced annually. It is a major component in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons. Modern steel is generally identified by various grades defined by assorted standards organizations.II. Word Stud y1. molecular[mə'lekjələ] a. 由分子组成的, 分子的1)molecular structure 分子结构2) We think of magnetism as a molecular phenomenon.我们认为电磁是一种分子现象。
3) The investigations were performed at molecular level.研究是在分子的层次上进行的。
2. liable ['laiəbl] a. 有责任的，有义务的，应受罚的，有…倾向的1) be liable to seasickness容易晕船2) One who works under the hot sun is liable to sunstroke.在炎热的阳光底下工作很容易引起中暑。
3) People are liable to judge others from their own first impressions.人们容易用他们自己的最初印象来评价别人。
3. squeeze [skwi:z] v. 挤(压，干)，压榨，勒索，紧握1) squeeze out tears挤出眼泪2) squeeze through the crowd挤入人群3) I tried to squeeze the water out of my soaking skirt.我用力拧掉我那件湿透了的裙子上的水。
4. prior ['praiə] a. 在先的，在前的，优先的1) agree without prior consultation不谋而合2) She has a prior engagement.她已另有约会。
3) This work is prior to all others.这是一项压倒一切的工作。
5. crack [kræk] v. &n．破裂，裂纹，打开1) a crack 一道缝儿2) crack a book 打开书本阅读3) crack a person over the head在某人头上重重一击4) There's a sinister-looking crack in the roof.屋顶上有一条危险的裂缝。
6. influence ['influəns] n. 影响，作用1) negative influence 消极影响2) My influence over her is small. 我对她的影响不大。
3) His influence reaches the next village. 他的势力扩展到邻村。
III．Language Points1. These stresses are liable to occur through hammering or working the metal, or through rapid cooling.金属在锻打加工或快速冷却时外层收缩比内层收缩速度快，极易导致内应力。
be liable to: 易于…的；有…倾向的；应付有责任，应遵守…(1) A third party, whose fault causes the fuel gas accident, shall be liable topay damages according to law.因第三人的过错造成燃气事故的，第三人应当依法承担损害赔偿责任。
(2) Non-complying trusts are also deemed to be liable to taxation on thetrust's worldwide income.“非照办信托”同时也被推定为按其信托之全球收入征税。
2. We heat it up beyond the critical temperature, and then quench it in water or some other liquid.我们将金属加热到超过极限温度，然后在水或其他液体中淬火。
heat up：加热（1）The electronic heater can heat up fast and safely. It also functions as a steamer.以电热为燃料能源，既方便，而且加热速度快，有蒸气锅炉之同功效。
（2）Material spiraling into a black hole can heat up to millions of degrees and glow brightly .捲入黑洞中的物质，将会被加热至数百万度并放出耀眼的光芒。
3. The properties of tempered steel enable US to use it in the manufacture of tools, which need a fairly hard steel.当制造的工具需要高硬度的钢铁时，我们可以用回火钢。
enable …to…: 使… ; 使…能够; 能够(1) Using ICON controlling circuit, enable to detect the status of themechanism operation.本机采用ICON控制回路，可侦测机械操作状况。
(2) The space between the inner and outer plate is full of heat insulationmaterials which enable to provide the nice performance of heatinsulation.内外板之间形成的空间可以填充保温材料，能够提供良好的保温功能。
4. Other shaping operations include drawing into wire, casting in moulds,and forging.其他的塑性加工有拉丝、模铸和锻造。
drawing into: 使卷入(1) SMS Draw integrates into the target application and appears as a newservice in the toolbar. 短信抽奖集成到目标应用，似乎作为一种新的服务工具栏。
(2) Now the pattern repeat with manual twist, will itself draw into theactive level of the Photoshop data file and the original is maintained again ona separate level.现在的模式重复与手工捻，本身将提请进入活跃水平的Photoshop的数据文件和原再次是保持在一个单独的水平。