机械全APS.docx

1、机械全APS一、Engineering Materials and Heat TreatmentThis lesson, i study engineering materials and heat treatment. Engineering materials , i study steel and cast iron, include iron-carbon phase diagram.Heat treatment, i study normalizing quenching tempering and annealing.Iron-carbon phase diagram, showi

2、ng the temperature and carbon ranges for certain types of heat treatments. With the carbon rise/increase, materials become more and more brittle, strength increase, hardness increase, but plasticity decrease.ABCD-liquid line ,up is liquid zoneAHJECF-solid line, down is solid zoneHJB-peritectic line,

3、 when the carbon range from 0.09 percent to 0.53 percent, materials cool down this line, it will peritectic transformation ECF-eutectic line, when the carbon range from 2.11 percent to 6.69 percent, materials cool down this line, it will eutectic transformationproduce ledeburite.PSK-eutectoid line,

4、when the carbon range from 0.0218 percent to 2.11 percent, materials cool down this line, it will eutectoid transformation produce pearlite.Ferrite: an interstitial solid solution of carbon in Fe, at room temperature ferrite is ductile but not very strong.Austenite: an interstitial solid solution of

5、 carbon in FeCementite: a compound of carbon and FeSteel is an alloy of carbon and iron and other alloying elements(e.g. Mn, Si) with content up to 2.11% intended for wrought products or semi-products.Cast iron is an alloy of carbon and iron and other alloying elements(e.g. Mn, Si) with carbon conte

6、nt over 2.11% intended for casting.Perlite is a structure (i.e. Consists of two phases) consists of alternate layers of ferrite and cementite in the proportion 87:13 by weightPerlite is formed from austenite at eutectoid temperature (A1) 727 upon slow cooling.There are three groups of steels accordi

7、ng to carbon content:Hypoeutectoid steels containing less than 0.77% CEutectoid steels with carbon content about 0.77%Hypereutectoid steels contain more than 0.77% C (up to 2.11% C)Ledeburite is a structure (i.e. Consists of two phase) consists of alternate layers of austenite and cementite.Ledeburi

8、te is formed from liquid at eutectic temperature 1148 upon slow cooling.From eutectic temperature 1148 to eutectoid temperature 727, ledeburite is called by high temperature ledeburite.Below eutectoid temperature 727，ledeburite is called by low temperature ledeburite.There are three groups of cast i

9、ron according to caarbon content:Hypoeutectic cast iron containing less than 4.3% C(up to 2.11% C )Eutectic cast iron with carbon content about 4.3%Hypereutectic cast iron contain more than 4.3% C (up yo 6.69% C)Normalizing Heat the steel to a certain temperature , keep the temperature for a period

10、of time, then put it in the air, slowly cool it to the room temperature.Certain temperature is above AC3 or ACm, from 30 to 50。Carbon steel heated to approximately 55 above AC3 or ACm for 1 hour ,this assures the steel completely transforms to austenite. The steel is then air-cooled, which is a cool

11、ing rate of approximately 38 per minute. This results in a fine pearlitic structure , and a more-uniform structure.Normalizing steel has a higher strength than annealed steel, it has a relatively high strength and ductility.Quenching Heat the steel to a certain temperature, keep the temperature for

12、a period of time,then put it into water or oil, make it to be cooled quickly to the room temperature.Certain temperature is above AC3 or AC1,from 30 to 50。Carbon steel with at least 0.4%C is heated to normalizing temperature and then rapidly cooled (quenched) in water, brine or oil to the critical t

13、emperature.Quenched steel is extremely hard but brittle, usually too brittle for practical purposes. These internal stresses cause stress cranks on the surface. Quenched steel is approximately three to four fold harder than normalized steel.Tempering Heat the quenched to be martensite steel to a cer

14、tain temperature, keep the temperature for a period of time, then cool it to the room temperature in the air.Certain temperature is below AC1 150260 370650Tempering involves reheating quenched steel to a temperature below the eutectoid temperature then cooling.Function :1. Improves ductility and tou

15、ghness2. Reduce cranking 3. Improves machinability4. Increase impact resistance5. Improves malleabilityTempering in the range of 260370 is sometimes avoided to reduce tempering brittling.Low tempering 150260 1 moldAverage tempering 370500 5 springHigh tempering 500650 3 gearAnnealing Heat the steel

16、to a certain temperature , keep the temperature for a period of time, put it in the furnace slowly cool it to room temperature.Annealing is used to induce ductility , soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.Proces

17、s annealing 500650 restores some of the ductility to a workpiece allowing it be worked further without breaking.Full annealing . Carbon steel is heated to approximately 40 above Ac3 or Ac1 for 1 hour, this assures all the ferrite transforms into austenite. The steel must then be cooled slowly in the

18、 realm of 38 per hour. Usually it is just furnace cooled, where the furnace is turned off with the steel still inside. This results in a coarse pearlitic structure, which means the bands of pearlite are thick. Fully-annealed steel is soft and ductile, with no internal stresses, which is often necess

19、ary for cost-effective forming. Only spheroidized steel is sofer and more ductile.Spheroidizing . Spheroidize forms when carbon steel is heated to approximately 700 for over 30 hours. The results is a structure of rods or spheres of cementite within ferrite or pearlite. The purpose is to soften high

20、er carbon steels and allow more formability.2、Mechanics of materials(问过此课程)In materials science, the strength of a material refers to materials ability to resist an applied force.Compress stress:(or compression) is the stress state when the material (compression member) tends to compact.Tensile stre

21、ss: is a loading that tends to produce stretching of a material by the application of axially directed pulling force.Shear stress: is caused when a force is applied to produce a sliding failure of a material along a plane that is parallel to the direction of the applied force.Yield strength: is the

22、lowest stress that gives permanent deformation in a material. In some materials, like aluminum alloys, the point of yielding is hard to define, thus it is usually given as the stress required to cause 0.2% plastic strain.Compressive strength: is a limit state of compressive stress that leads to comp

23、ressive failure in the manner of ductile failure or in the manner of brittle failure.Tensile strength: or ultimate tensile failure is a limit state of tensile stress that leads to tensile failure in the manner of ductile failure or in the manner of brittle failure.Fatigue strength: is a measure of t

24、he strength of a material or a component under cyclic loading, and is usually more difficult to assess than the static strength measures.Impact strength: it is the capability of the material in withstanding by the suddenly applied loads in terms of energy.Deformation of the material is the change in

25、 geometry when stress is applied.Strain or reduced deformation is a mathematical term to express the trend of the deformation change among the material field.Deflection is a term to describe the magnitude t which a structural element bends under a load.Elasticity is the ability of a material to retu

26、rn to its previous shape after stress is released. In many materials, the relation between applied stress and the resulting strain is directly proportional(up to a certain limit), and a graph representing those two quantities is a straight line.The slope of this line known as Youngs Modulus, or the

27、Modulus of Elasticity. The modulus of elasticity can be used to determine stress-strain relationships in the linear-elastic portion of the stress-strain curve. The linear-elastic region is taken to be between 0 and 0.2% strain, and is defined as the region of strain in which no yielding (permanent d

28、eformation) occurs.Plasticity or plastic deformation is the opposite of elastic deformation and is accepted as unrecoverable strain. Plastic deformation is retained even after the relaxation of the applied stress. Most materials in the linear-elastic category are usually capable of plastic deformati

29、on. Brittle materials, like ceramics, do not experience any plastic deformation and will fracture under relatively low stress. Materials such as metals usually experience a small amount of plastic deformation before failure while soft of ductile polymers will plasticity deform much more.Plastic mate

30、rial:tensile strength is well, compressive strength is bad.ab: elastic phase: give a force/tensile for workpiece, this part have not the obvious deformation, when we cancel the force, the stress and strain will disappear, the steel will return to the original shape.bc: yield phase: give a force for

31、workpiece, the strain will increase, the stress has a little changing, if we cancel the force, the workpiece has plastic deformation.cd: strength phase: give a force for workpiece, the strain and stress will increase, workpiece has a obvious deformation, the inner structure has be destroy, it will b

32、ecome slender, point d means the material can bear the biggest stress.de: local deformation phase: give a force for workpiece, the stress will reduce, the stain will increase, the plastic deformation will go on increasing, at this time, the material will have a phenomenon, we called necking deformation focus on necking, at last, the material will break out.Brittle material: tensile strength is bad, compressive is well.3、Fundamentals of mechanic