《机械专业英语》课件第4章.ppt

1、Unit 4TEXTLEARN TO SPEAK NEW WORDS AND PHRASESNOTES EXERCISES READING MATERIAL PROFESSIONAL WORDS AND PHRASESTEXTKinds of SteelThere are two general kinds of steels:carbon steel and alloy steel.Carbon steel contains only iron and carbon,while alloy steel contains some other“alloying elements”such as

2、 nickel,chromium,manganese,molybdenum,tungsten,vanadium,etc.1Carbon steels(1)Low carbon steel containing from 0.05 to 0.15 percent carbon;this steel is also known as machine steel.(2)Medium carbon steel containing from 0.15 to 0.60 percent carbon.(3)High carbon steel containing from 0.6 to 1.50 perc

3、ent carbon;this steel is sometimes called“tool steel”.2Alloy steels(1)Special alloy steel,such as nickel,chromium steel;(2)High-speed steel also known as self-hardening steel.Carbon steels are the most common steels used in industry.The properties of these steels depend only on the percentage of car

4、bon they contain.Low carbon steels are very soft and can be used for bolts and for machine parts that do not need strength.Medium carbon steels are a better grade and stronger than low carbon steels.It is also more difficult to cut than low carbon steels.High carbon steels may be hardened by heating

5、 it to a certain temperature and then quickly cooling in water.The more carbon the steels contains and the quicker the cooling is,the harder it becomes.Because of its high strength and hardness this grade of steel may be used for tools and working parts of machines.But for some special uses,for exam

6、ple,for gears,bearings,springs,shafts and wire,carbon steels cannot be always used because they have no properties needed for these parts.Some special alloy steels should be used for such parts because the alloying elements make them tougher,stronger,or harder than carbon steels.Some alloying elemen

7、ts cause steel to resist corrosion,and such steels are called stainless steels.Stainless steels contain a high percentage of chromium.Chromium also makes steel harder.Nickel is used in steel to increase strength and toughness.Some alloying elements(such as chromium and tungsten)make the grain of ste

8、el finer,thus increasing the hardness and strength of steel,because the finer the grain is,the stronger the steel becomes.Heat-resistant steel is made by adding some tungsten and molybdenum,while manganese increases the wear resistance of steel.Vanadium steels resist corrosion and can stand shocks a

9、nd vibration.Tools made of high-speed steel containing tungsten,chromium,vanadium,and carbon,may do the work at much higher speeds than carbon tool steels.LEARN TO SPEAKMr.Yang:Morning!Mr.Smith:Morning!Mr.Yang:Do you know about the kinds of steels?Mr.Smith:Yes,there are two general kinds of steels:c

10、arbon steel and alloy steel.Mr.Yang:Could you describe it in detail?Mr.Smith:OK.Carbon steel contains only iron and carbon,while alloy steel contains some other“alloying elements”such as nickel,chromium,etc.Mr.Yang:What can the carbon steel be used for?Mr.Smith:The carbon steel contains low,medium a

11、nd high carbon steel,and can be used for bolts,tools and working parts of machines.Mr.Yang:Then,what can the alloy steel be used for?Mr.Smith:Alloy steel can be used for gears,bearings,springs and wires,etc.Because the alloying elements make them tougher,stronger,or harder than carbon steel.Mr.Yang:

12、How about the tools which made of high speed steel?Mr.Smith:The tools made of high-speed steel of alloy steel containing tungsten,chromium,vanadium and carbon,may do the work at much higher speeds than carbon tool steels.NEW WORDS AND PHRASESnickel 5nIk(E)l n.镍镍chromium 5krEJmIEm n.铬铬manganese mANE5

13、ni:z n.锰锰molybdenum mE5lIbdInEm n.钼钼tungsten 5tQNst(E)n n.钨钨vanadium vE5neIdIEm n.钒钒medium 5mi:dIEm n.介质介质adj.中间的中间的harden 5hB:d(E)n v.淬火淬火NEW WORDS AND EXPRESSIONSnickel n.镍 chromium n.铬 manganese n.锰 molybdenum n.钼 tungsten n.钨 vanadium n.钒 medium n.介质 adj.中间的 harden v.淬火 bolt n.螺栓，螺钉 v.用螺栓固定 gear

14、 n.齿轮 bearing n.轴承 shaft n.轴 corrosion n.腐蚀 stainless n.不锈钢 grain n.晶粒 tool steel 工具钢 self-hardening steel 自硬钢 heat-resistant 耐热的 heat-resistant steel 耐热钢 high-speed 高速的 NOTES1High-speed steel also known as self-hardening steel.高速钢，也称为自硬钢。“also known as self-hardening steel”为分词短语作定语，修饰“high-speed st

15、eel”。高速钢是一种含有钨、铬、钒等合金元素的高合金工具钢，它可以在空气中自行淬硬，因而又称“self-hardening steel”，即风钢。2The more carbon the steel contains and the quicker the cooling is,the harder it becomes.钢的含碳量越高，冷却速度越快，钢就变得越硬。“the+比较级(从句)+the+比较级(主句)”结构表示“越越”之意。本句中的比较状语从句为“The more carbon the steel contain and the quicker the cooling is”，主

16、句为“the harder it becomes”。句中第一个“the”和第二个“the”均为副词，分别引出两个并列的比较状语从句。在这种情况下，第一个“the”相当于“by so much”，第二个“the”相当于“by that much”。3because the alloying elements make them tougher,stronger or harder than carbon steels.Some alloying elements cause steel to resist corrosion,and such steel are called stainless

17、 steels.因为合金元素能提高钢的韧性、强度和硬度(在碳钢的基础上)。有些合金元素能提高钢的耐蚀性，这种钢称做不锈钢。句中的“make”和“cause”均为及物动词，它们的宾语分别为“them”和“steel”。宾语“them”的补足语是形容词比较级“tougher,stronger,harder”等，而宾语“steel”的补足语是不定式短语“to resist corrosion”。“stainless steels”是主语“such steel”的补足语。4Tools made of high-speed steel containing tungsten,chromium,vanad

18、ium and carbon,may do the work at much higher speeds than carbon tool steels.用含有钨、铬、钒、碳的高速钢制成的刀具能以比碳素工具钢(制成的刀具)高得多的速度进行切削加工。“made of high-speed steel”作为分词短语，修饰“Tools”，而“containing tungsten,chromium,chromium,vanadium and carbon”是另一分词短语作后置短语，修饰“high-speed steel”。EXERCISES1Discuss the following questio

19、ns in English:(1)What methods are available for improving the hardness of high carbon steel?(2)What are the machine parts made of,that do not need strength?(3)How do the alloying elements such as chromium and tungsten increase the hardness and strength of steel?2Use English for replacing Chinese or

20、use Chinese for replacing English.(1)碳钢和合金钢(2)材料的性能(3)高速钢(4)heat-resistant steel(5)self-hardening steel(6)nickel steel 3Place a“T”after sentences that are true and an“F”after those that are false.(1)Alloys having more than 0.6%carbon are called high carbon steels.()(2)Alloys containing 0.15%(or less

21、)carbon are called low carbon steels.()(3)High speed steel is sometimes called self-hardening steel.()(4)The properties of carbon steels depend not only on the percentage of carbon they contain,but also on the alloying elements.()(5)Steels contain more carbon than cast irons.()(6)Low carbon steel is

22、 harder than high carbon steel.()(7)Tools made of high-speed steel do the work at much lower speeds than carbon steels.()(8)Stainless steels contain some alloying elements which cause steels to resist corrosion.()READING MATERIALMechanical Properties of MetalsMechanical properties are the characteri

23、stic responses of a material to applied forces.The knowledge of mechanical properties of materials is very essential in order to construct a mechanically sound structure such as a bridge on the river.Mechanical properties can be determined by conducting experimental tests on the material specimen.So

24、me important mechanical properties of materials are strength,stiffness,ductility,impact strength,hardness,toughness.Strength.Strength or Mechanical Strength of a material may be defined as the ability of the material to sustain loads without undue distortion or failure.Material should have adequate

25、strength when subjected to tension,compression,shear,bending or torsion as per the intended use.Stiffness.Stiffness is the ability of a material or shape to resist elastic deflection.For identical shapes,the stiffness is proportional to the modulus of elasticity.Ductility.Ductility refers to the cap

26、acity of a material to undergo deformation under tension without rupture as in a wire drawing operation.Impact strength.It is the strength of a material when subjected to high rates of loading,usually in bending,tension or torsion.The amount of energy required to fracture the material by a single bl

27、ow is measured by means of a Charpy test.Hardness.Hardness is the resistance of a material to plastic deformation usually by indentation.However,the term may refer to stiffness or refer to resistance to scratching,abrasion or cutting.Tests such as Vickers,Brinell and Rockwell are generally employed

28、to measure hardness.Toughness.Toughness refers to the ability of a material to withstand bending or the application of shear stresses without fracture.Fig.4 Tensile test specimen(a)Specimen before pulling；(b)Specimen after pulling PROFESSIONAL WORDS AND PHRASESessential I5senF(E)l adj.主要的，根本的n.本质，基础

29、sound saJnd adj.健全的，坚固的conduct kEn5dQkt vt.实施，进行experimental Ik5sperIment(E)l adj.试验(用)的specimen 5spesImEn n.样品，试样strength streNW n.强度tension 5tenF(E)n n.张(拉)力，拉伸compression kEm5preF(E)n n.压力，压缩shear FIE(r)n.剪(切)stiff adj.刚(性)的 stiffness n.刚度，强度 impact n.冲击 ductility n.延(展)性，韧性 hardness n.硬度 toughne

30、ss n.韧性，韧度 load n.负载，载荷 sustain vt.支持，维持 undue adj.过度的 distortion n.变形，歪曲 failure n.故障，断裂 subject vt.使受到 per prep.按照，根据 elastic adj.弹性的 elasticity n.弹性 modulus n.模数 deflection n.偏转，挠曲 identical adj.同一的，相同的 proportional adj.比例的，相称的 capacity n.容量，能力 deformation n.变形，挠曲 drawing n.绘图，拉长 blow n.打击，冲击 pla

31、stic adj.塑料的，可塑的 indentation n.压痕，压坑 scratch v.划痕 abrasion n.擦伤，磨损 employ vt.使用，采用 withstand vt.抵抗，经得起 fracture v.&n.断裂，破裂 bending strength 抗弯强度be subjected to 易受到elastic deflection 弹性(挠曲)变形modulus of elasticity 弹性模量wire drawing 拉丝plastic deformation 塑性变形single blow 一击，一下子Charpy impact test (摆锤式)冲击试验Vickers test 维氏硬度试验Brinell test 布氏硬度试验Rockwell test 洛氏硬度试验