机电专业英语第2版电子教案unit 4

Unit 4 Heat Treatment& Hot Working of Metals

Ⅰ. Lead-in

Steel 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 y

1. 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 Points

1. 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 to

pay 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 the

trust'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.