机电专业英语Part1-Material-and课件

Part 1 Material and Heat TreatmentPart 1 Unit 1 Metals Unit 2Heat Treatment Unit 3Iron-Carbon Equilibrium Diagram Reading Target Unit 1 Metals Unit 2Heat Trea Unit 1 MetalsReading Target1Introduce the categories of metals and how to distinguish them.2Make you know what mechanical properties metals have and the definition about each property.Unit 1 MetalsReading TargetTextAs we have seen,ferrous metals are alloys of iron with carbon,these alloys may contain also some other elements such as silicon(Si),phosphorus(P),etc.,but carbon is the most important of all elements present in ferrous alloys 1.TextAs we have seen,ferrous Ferrous metals are used in industry in two general forms:cast iron and steel.These two ferrous alloys are usually produced from pig iron,and they have different carbon content.Steel is iron containing from 0.0218 to 2.11 percent carbon,while cast iron is an alloy of iron and carbon with the carbon content more than 2.11 percent 2.Ferrous metals are used in indPure iron is not used in industry because it is too soft.Steel is an alloy of iron and carbon with other elements added to produce specific properties 3.Pure iron is not used in indusThe various types of steel can be grouped under two major headings:（1）Carbon steel.Steel in which the main alloying element is carbon.Carbon steels are further divided into three groups.The various types of steel cana Low carbon steel.This steel has a carbon content of less than 0.30 percent.It is the most common type and is often called mild steel.It is relatively inexpensive,ductile,soft,and is easily machined and forged.Mild steel cannot be heattreated(hardened).Low carbon steel is a general purpose steel.aLow carbon steel.This steelbMedium carbon steel.This steel has a carbon content between 0.30 percent and 0.80 percent.Harder and stronger than mild steel,it can be hardened by heat treating.Medium carbon steel is most commonly used for forgings,castings,and machined parts for automobiles,agricultural equipment,machines,and aircraft.bMedium carbon steel.This stcHigh carbon steel.This type of steel is easily heattreated to produce a strong,tough part.The material has a carbon content above 0.80 percent.It finds wide use in hand tools,cutting tools,springs,and piano wire.cHigh carbon steel.This type（2）High alloy steel.These steels contain significant amounts of other elements in addition to carbon.The common high alloy steels are:aStainless steel which is produced by using chromium as a significant alloying element along with nickel and other metals.The result is a tough,hard,corrosionresistant metal.（2）High alloy steel.These stebTool steel which is a special group of high carbon steels produced in small quantities to high quality specifications.Tool steels are used for a wide range of cutting tools and forming dies.bTool steel which is a speciacManganese steel which is an alloy containing 12 percent manganese and one percent carbon.This metal is used in mining,railroad,and construction equipment because of its high tensile strength.cManganese steel which is an Mechanical properties are the characteristic responses of a material to applied forces.These properties fall into five broad categories:strength,hardness,elasticity,ductility,and toughness.Mechanical properties are the（1）Strength is the ability of a material to resist applied forces.Bridge girders,elevator cables,and building beams all must have this property.（1）Strength is the ability of A material can be subjected to a number of different types of forces.They may be tension,shear,torsion,compression,or a combination of these forces.Each possible force causes a material to respond in a different way.A material has several different mechanical strengths.The strength depends on the force applied.A material can be subjected toThe most common mechanical strengths are:aTensile strength:the maximum tension loads a material can withstand before fracturing.Tensile strength is the easiest strength to measure and,therefore,is widely used.The most common mechanical strbCompression strength:the ability to resist forces which tend to squeeze the material into a new shape.It is basically the opposite of tensile strength.Excessive compression force will cause the material to rupture(buckling and splitting).bCompression strength:the abc Shear strength:the ability to resist fracture under shear forces.The shear force is caused by offset forces applied in opposite directions.These forces cause the grains or molecules of the material to slide by one another and eventually fracture.cShear strength:the ability dTorsion strength:the ability to resist twisting forces.Forces which exceed the torsion strength(modulus of rupture)will cause the material to rupture.dTorsion strength:the abilit（2）Hardness is the resistance of a material to penetration or scratching,it accounts for abrasion resistance as well as resistance to denting.Hardness is also directly related to strength.The harder a material the stronger it is.（2）Hardness is the resistance Metallic materials are almost always harder and stronger than polymeric materials.A number of different testers have been designed to test the hardness of a variety of materials.Cutting tools,files,and drills must resist abrasion,or wear.Armor plate,crushing machinery,and metal rolls for steel mills all must resist penetration.Metallic materials are almost（3）Elasticity is the ability to spring back to original shape.Auto bumpers and all springs should have this quality.As stress is applied,the material first resists permanent deforming.This area is in the materials elastic range.This is a range in which the material will return to its original length when the force is released.（3）Elasticity is the ability tApplying additional stress(force)will bring the material to its yield point.At this point,additional strain(elongation)occurs without additional force(stress)being applied.Strain above this point is produced with smaller amounts of force 4.Applying additional stress(foThe force also produces permanent changes in the length of the material.This elongation which is above the materials elastic limit(point at which the material will not return to its original length)is called plastic deformation.The force also produces perman（4）Ductility is the plastic flow characteristic of a material under normal temperature.The higher the ductility of a material the greater is its ability to be formed without fracturing.Highly ductile materials can be easily bent,drawn into wire,or extruded.Modern,deepformed auto bodies and fenders,and other stamped and formed products must have this property.（4）Ductility is the plastic fl（5）Toughness is the ability to absorb mechanically applied energy.Strength and ductility determine a materials toughness.Toughness is needed in railroad cars,automobile axles,hammers,rails,and similar products.（5）Toughness is the ability toNotes1but carbon is the most important of all elements present in ferrous alloys.但黑色金属里存在的各种元素中，要但黑色金属里存在的各种元素中，要数碳最为重要。数碳最为重要。“present”是形容词作后置定语，修饰是形容词作后置定语，修饰“all elements”，宜译作，宜译作“在黑色金属所在黑色金属所存在的各种元素中存在的各种元素中”。Notes1but carbon is the most2Steel is iron containing from 0.0218 to 2.11 percent carbon,while cast iron is an alloy of iron and carbon with the carbon content more than 2.11 percent.钢是含碳量为钢是含碳量为0.0218%到到2.11%的铁；的铁；而铸铁是含碳量超过而铸铁是含碳量超过2.11%的铁碳合金。的铁碳合金。2Steel is iron containing fr “containing from 0.0218 to 2.11 percent carbon”为分词短语作定语，修饰为分词短语作定语，修饰“iron”。“while”此处表示同时存在的两种事物此处表示同时存在的两种事物的对比，引出并列的分句，译成的对比，引出并列的分句，译成“而而”。“containing from 0.02183Steel is an alloy of iron and carbon with other elements added to produce specific properties.钢是一种包含铁碳以及其他元素的铁碳钢是一种包含铁碳以及其他元素的铁碳合金，加入其他元素可产生某种特殊性能。合金，加入其他元素可产生某种特殊性能。3Steel is an alloy of iron a “added to produce specific properties”作作定语，修饰定语，修饰“other elements”。而而“with”同样又是定语，修饰同样又是定语，修饰“an alloy”。“added to produce speci 4 At this point,additional strain(elongation)occurs without additional force(stress)being applied.Strain above this point is produced with smaller amounts of force.4At this point,additional s 在屈服点上，即使没有施加附加的应在屈服点上，即使没有施加附加的应力，附加应变还是会出现。力，附加应变还是会出现。在这一点上存在很小的应力这种应变在这一点上存在很小的应力这种应变都会发生。都会发生。“without”、“with”此处的此处的用法一致，均是作状语，分别修饰用法一致，均是作状语，分别修饰“occurs”、“is produced”。在屈服点上，即使没有施加附加的应力，附加应变Unit 2Heat TreatmentReading Target1 Illustrate the function of the heat treatment and what will happen after the heat treatment.2Make you know common forms of the heat treatment and the different roles of them.Unit 2Heat TreatmentReading TaTextHeat treatment is thermal cycling involving one or more reheating and cooling operations after forging for the purpose of obtaining desired microstructures and mechanical properties in a forging 1.TextHeat treatment is thermal Few forgings of the types are produced without some form of heal treatment.Untreated forgings are usually relatively lowcarbon steel parts for noncritical applications or are parts intended for further hot mechanical work and subsequent heat treatment.Few forgings of the types are The chemical compositions of the steel,the size and shape of the product,and the properties desired are important factors in determining which of the following production cycles to use.The chemical compositions of tThe object of heat treating metals is to impart certain desired physical properties to the metal or to eliminate undesirable structural conditions which may occur in the processing or fabrication of the material 2.The object of heat treating meIn the application of any heat treatment it is desirable that the previous history or structural condition of the material be known so that a method of treatment can be prescribed to produce the desired result.In the absence of information as to the previous processing,a microscopic study of the structure is desirable to determine the correct procedure to be followed.In the application of any heatThe commercial heat treatments in common use are annealing,normalizing,hardening and tempering.They involve the heating of the material to certain predetermined temperatures,soaking or holding at the temperature,and cooling at a prescribed rate in air,liquids,or retarding media 3.The above treatments may be briefly defined as follows:The commercial heat treatmentsAnnealing:Annealing consists of heating steel slightly above its critical range and cooling very slowly.Annealing relieves internal stresses and strain caused by previous heat treatment,machining,or other coldworking processes.Annealing:Annealing consists The type of steel governs the temperature to which the steel is heated for the annealing process.The purpose for which annealing is being done also governs the annealing temperature.The type of steel governs the There are three different types of annealing processes used in industry:(1)full annealing,(2)process annealing,(3)spheroidizing.There are three different typeFull annealing is used to produce maximum softness in steel.Machinability is improved.Internal stresses are relieved.Process annealing is also called stress relieving.It is used for relieving internal stresses that have occurred during coldworking or machining processes.Full annealing is used to prodSpheroidizing is used to produce a special kind of grain structure that is relatively soft and machinable.This processes generally used to improve the machinability in highcarbon steels and in wiredrawing processes.Spheroidizing is used to produNormalizing:Normalizing is a process used to relieve the internal stresses due to hotworking,coldworking,and machining.The process consists of heating steel slightly above the upper critical range 30 to 50 and cooling to room temperature after holding for a while.Normalizing:Normalizing is a This process is usually used with low and mediumcarbon as well as alloy steels.Normalizing removes all previous effects due to heat treatment.This process is usually used wThe more rapid cooling in air，used in normalizing,causes the austenite to decompose at lower temperatures.This increases the dispersity of the ferritecementite structure and the amount of pearlite or,more exactly,the quasieutectoid(of the sorbite or troostite type).The more rapid cooling in air，This raises the strength and hardness of normalized mediumand highcarbon steels by 10 percent to 15 percent as compared to annealed steel.This raises the strength and hThe normalizing of hotrolled steel increases its resistance to brittle failure by lowering the coldshortness threshold and increasing the work required for crack propagation.The normalizing of hot-rolled The purpose of normalizing may differ in accordance with the composition of the steel.Normalizing is applied for lowcarbon steels in place of annealing.By slightly increasing the hardness,normalizing enables a better surface finish to be obtained in machining and raises the production capacity.The purpose of normalizing mayNormalizing alone or normalizing with hightemperature tempering is used for castings of mediumcarbon steel instead of hardening and hightemperature tempering.The resulting mechanical properties are lower,but the work is warped less than in hardening and the possibility of crack formation is practically excluded.Normalizing alone or normaliziNormalizing followed by hightemperature tempering(at 600 to 650)is often applied instead of full annealing to correct the structure of alloy steel because the productivity of the two operations is greater than that of a single annealing operation.Normalizing followed by high-tHardening:In any heattreating operation the rate of heating is important.Heat flows from the exterior to the interior of steel at a definite maximum rate.If steel is heated too fast,the outside of the part becomes hotter than the interior.A uniform structure is hard to obtain.Hardening:In any heat-treatinThe hardness that can be obtained from a given treatment depends upon the following three factors:1Quenching rate.2Carbon content.3Workpiece sue.The hardness that can be obtaiRapid quenching is needed to harden low carbon and medium plain carbon steels.Water is generally used as a quench for these steels.For highcarbon or alloy steel,oil is used.Its action is not as severe as that of water.Where extreme cooling is desired,brine is used.Rapid quenching is needed to hThe maximum degree of hardness obtainable in steel by direct hardening is determined largely by the carbon content 4.Steel with a low carbon content will not respond greatly to the hardening process.Carbon steels are generally considered as shallow hardening steels.The hardening temperature varies for different steels.The temperature depends upon the carbon content.The maximum degree of hardnessThe temperature at which steel is usually quenched for hardening is known as the hardening temperature.It is usually 10 to 38 above the upper critical temperature at which structural change takes place.The temperature at which steelTempering:Hardening makes highcarbon steels and tool steels extremely hard and brittle and not suitable for most uses.By tempering or drawing internal stresses developed by the hardening process are relieved.Tempering increased the toughness of the hardened piece.It also seems to make them more plastic,or ductile.Tempering:Hardening makes higThe tempering temperature has the principal effect on the properties of the steel.Distinction is made between three tempering procedures.The tempering temperature has Lowtemperature tempering is performed by heating to 250.This reduces the internal stresses,the martensite produced by quenching is transformed into tempered martensite,the strength is increased and the toughness is improved slightly without any appreciable loss in hardness.Low-temperature tempering is pHardened steel(containing from 0.6%C to 1.3%C)retains a hardness of 58 to 63 RC following such tempering and,consequently,high wear resistance.The tempered components,however,can not withstand considerable impact loads(unless they have a tough core).Hardened steel(containing froFor these reasons,lowtemperature tempering is applied in the manufacture of cutting and measuring tools of carbon and lowalloy steels,as well as components that undergo surface hardening,carburizing,cyaniding or carbonitriding.The holding time usually ranges from 1 to 2.5 hours,but a longer time is specified for work of large cross section or measuring tools.For these reasons,low-temperaMediumtemperature tempering at 350 to 500 is employed chiefly for coil and laminated springs,as well as for dies.This operation provides a high elastic limit,endurance limit and resistance to relaxation.Medium-temperature tempering aThe tempered steel has a structure consisting of temper troostite and troostomartensite,and a hardness of 40 to 50 RC.The tempering temperature should be selected so as to avoid irreversible temper brittleness.The tempered steel has a strucAfter tempering at 400 to 450,the work should be cooled in water.This promotes the development of compressive residual stresses at the surface,which raise the endurance limit of springs.After tempering at 400 to 450Hightemperature tempering is performed in the range from 500 to 680.The tempered steel has a structure consisting of temper sorbite.This operation provides for the best combination of strength and toughness of the steel.High-temperature tempering is In comparison to the normalized or asannealed condition,hardening followed by hightemperature tempering simultaneously raises the tensile strength and yield point,reduction in area and,especially,the impact strength.For this reason,a heattreatment consisting of hardening followed by hightemperature tempering is called structural improvement.In comparison to the normalizeStructural improvement is applied to mediumcarbon structural steels(0.3%C to 0.5%C)which must meet high requirements with respect to their yield point,endurance limit and impact strength.Owing to the reduced hardness,however,the wear resistance of structurally improved steel is not high.Structural improvement is applThis operation substantially raises the structural strength of steel by reducing its sensitivity to stress raisers,by increasing the work of plastic deformation in,crack propagation(work requited in crack development),and by reducing the temperatures of the upper and lower coldshortness thresholds.This operation substantially rTempering in the range from 550 to 600 for 1 to 2 hours almost completely relieves residual stresses developed in hardening.The holding time for a hightemperature tempering operation more often ranges from 1 to 6 hours,depending upon the overall size of the work.Sometimes the holding time is increased to several dozen hours to reduce the danger of flakes being formed in the steel.Tempering in the range from 55Notes1Heat treatment is thermal cycling involving one or more reheating and cooling operations after forging for the purpose of obtaining desired microstructures and mechanical properties in a forging.Notes1Heat treatment is the 热处理是锻后进行一次或多次重新加热处理是锻后进行一次或多次重新加热和冷却操作的热循环过程，以便使锻件热和冷却操作的热循环过程，以便使锻件获得所需的显微组织和机械性能。获得所需的显微组织和机械性能。句中句中involving one or more是分词短是分词短语，作语，作thermal cycling的后置定语，的后置定语，in a forging是动名词是动名词obtaining的状语。的状语。热处理是锻后进行一次或多次重新加热和冷却操作2The object of heat treating metals is to impart certain desired physical properties to the metal or to eliminate undesirable structural conditions which may occur in the processing or fabrication of the material.2The object of heat treating 金属热处理的目的是使金属获得所需的金属热处理的目的是使金属获得所需的物理性能，或者消除那些在材料生产和加工物理性能，或者消除那些在材料生产和加工中可能出现的不好的组织状态。中可能出现的不好的组织状态。句中不定式句中不定式to impartor to eliminate为并列结构，作为并列结构，作is的表语，的表语，which引导定语从引导定语从句修饰句修饰conditions。金属热处理的目的是使金属获得所需的物理性能，3 They involve the heating of the material to certain predetermined temperatures,soaking or holding at the temperature,and cooling at a prescribed rate in air,liquids,or retarding media.3They involve the heating of 热处理包括把材料加热到预定的温度，热处理包括把材料加热到预定的温度，在此温度下，在此温度下，“均热均热”即保温，然后在空气、即保温，然后在空气、液体或保温介质中按规定的速率冷却。液体或保温介质中按规定的速率冷却。句中的句中的the heating