机械工程材料双语课件第一章

1、Chapter 1 Alloying of Steels 钢的合金化钢的合金化 Chapter 1 Alloying of Steels 1 Structures and Properties of Metals 2 Iron-carbon phase diagram 3 Effect of alloying elements on iron- carbon phase diagram 4 Phase composition of alloy steels 5 Heat treatment of steels- Phase transformation in alloy steels 金属的结

2、构与性能金属的结构与性能 铁碳合金相图铁碳合金相图 合金元素对铁碳合金相合金元素对铁碳合金相 图的影响图的影响 合金钢的相组成合金钢的相组成 钢的热处理钢的热处理钢中的相转变钢中的相转变 机械工程材料双语课件第一章 6 Strengthening and toughening of steels 7 Effect of alloying elements on steels processing property 8 Types and grade of alloy steels 钢的强韧化钢的强韧化 合金元素对钢工艺性的影响合金元素对钢工艺性的影响 合金钢的分类与编号合金钢的分类与编号 1

3、Structures and Properties of Metals（金属结构与性能）（金属结构与性能） Crystal and Amorphous Structure in Materials (晶态与非晶态结构晶态与非晶态结构) crystalline and amorphous solids （晶体与非晶体）（晶体与非晶体） The physical structure of solid materials depends mainly on the arrangements of the atoms, ions or molecules that make up the solid

4、and the bonding forces between them. 机械工程材料双语课件第一章 crystalline materials lDefinition: if the atoms or ions are arranged in order-long-range order (LRO)-the solid of material is called a crystalline material. lExamples: metals, alloys and some ceramic materials. lCrystalline solids have fixed melting

5、 points. 长程长程 有序有序 机械工程材料双语课件第一章 noncrystalline/amorphous materials（非晶体）（非晶体） Definition: materials whose atoms and ions are not arranged in a long-range manner and possess only short-range order (SRO). Examples: most polymers, glasses and some metals. They dont have fixed melting point. 短程有序：只在很小的范

6、围内原子呈规则排短程有序：只在很小的范围内原子呈规则排 列，而在大范围内无规则可循。列，而在大范围内无规则可循。 the space lattice and unit cells (空间晶格与晶胞空间晶格与晶胞) 将原子抽象为空间点，用假想的空间直将原子抽象为空间点，用假想的空间直 线按一定规律将这些点连起来形成三维线按一定规律将这些点连起来形成三维 空间构架，称为晶格（空间构架，称为晶格（a space lattice， Fig.1.1）。 这些线的交点即原子的中心这些线的交点即原子的中心 位置。位置。 机械工程材料双语课件第一章 晶晶 格格 In a space lattice, ther

7、e are repeating units which can describe the characteristic of the whole lattice, we call the units-unit cells. 晶胞晶胞 The space lattice can describe the atomic arrangements in crystalline solids. the lattice constants （晶格常数）（晶格常数） Three lattice vectors： a, b, c; They are the axial lengths. The intera

8、xial angles: 、 and ; a, b, c, 、are called the lattice constants of the unit cell. 机械工程材料双语课件第一章 Most metals (about 90%) crystallize into three crystal structures: body-centered cubic (bcc), 体心立方；体心立方； face-centered cubic (fcc) , 面心立方；面心立方； hexagonal close-packed cubic (hcp）, 密排六方。密排六方。 Principal Met

9、allic Crystal Structures（典型晶体结构）（典型晶体结构） Principal Metallic Crystal Structures Fig.1.2 Three metallic crystal structures 机械工程材料双语课件第一章 BCC: In this unit cell, there is one lattice point (atom) at each corner of the cube and one at the center of the cube. Each atom at the corner is shared by eight ne

10、ighbor unit cells. 机械工程材料双语课件第一章 体心立方（体心立方（BCC） BCC: 晶胞的晶胞的8个顶角各有个顶角各有1个原子，在晶胞个原子，在晶胞 体心有体心有1个原子。每个角上的原子被相邻的个原子。每个角上的原子被相邻的 8个晶胞所共有。个晶胞所共有。 机械工程材料双语课件第一章 FCC: one atom at each corner and one at the center of each cube face. The atom at each corner is also shared by eight neighbor unit cells and the

11、atom at the center of each cube face is shared by two neighbor unit cells. 机械工程材料双语课件第一章 面心立方（面心立方（FCC） FCC: 晶胞晶胞8个顶角各有个顶角各有1个原子，每个侧面个原子，每个侧面 的中心各有的中心各有1个原子。顶角上的每个原子为个原子。顶角上的每个原子为 相邻的相邻的8个晶胞所共有，每个侧面上的原子个晶胞所共有，每个侧面上的原子 为相邻的两个晶胞所共有。为相邻的两个晶胞所共有。 HCP: In bcc and fcc, a=b=c and =90; while in hcp, the bot

12、tom and top face are both hexagon (六边形) and the constant “a” is the basal side length. The height of the hexagon prism is c. The ratio of c to a is called the axial ratio. For an ideal hcp crystal structure, the ratio is 1.633. 机械工程材料双语课件第一章 密排六方晶格（密排六方晶格（HCP）: 体心和面心立方中体心和面心立方中, a=b=c,=90 0; 而在而在HCP

13、中中,晶胞的上下晶胞的上下 底面均为边长为底面均为边长为a的正的正六边形。正六棱柱的高六边形。正六棱柱的高 为为c。c/a 称为轴比，对于理想的正六棱柱，称为轴比，对于理想的正六棱柱， c/a =1.633。 机械工程材料双语课件第一章 密排六方晶格（密排六方晶格（HCP） 晶胞晶胞1212个顶角各有个顶角各有1 1个原子，每个原子被相个原子，每个原子被相 邻的邻的6 6个晶胞所共有；上下底面中心各有个晶胞所共有；上下底面中心各有1 1个个 原子，每个原子被相邻的原子，每个原子被相邻的2 2个晶胞所共有；在个晶胞所共有；在 晶胞内部还有晶胞内部还有3 3个原子，完全属于该晶胞。个原子，完全属于

14、该晶胞。 机械工程材料双语课件第一章 2. Properties of Metal Materials 金属材料的性能金属材料的性能 Behavior in service of metal materials includes mechanical properties, physical and chemical performance etc. 力学性能力学性能: 材料在外加载荷或载荷与环境材料在外加载荷或载荷与环境 因素（温度、介质和加载速率）的共同作因素（温度、介质和加载速率）的共同作 用下所表现出来的力学行为。用下所表现出来的力学行为。 机械工程材料双语课件第一章 To obtai

15、n the mechanical properties of metals, the engineering stress- strain diagram should be firstly discussed. 应力应变曲应力应变曲 线线 Tensile test and the stress- strain(/) diagram 静拉伸试验与应力应变（静拉伸试验与应力应变（/）曲）曲 线线 Elastic and plastic behavior（弹性与塑性（弹性与塑性 变形）变形） - Elastic deformation: the material deforms under ext

16、ernal load, when the load (or stress) is moved, the material returns to the dimension it had before the load was applied. 弹性变形：材料在外加载荷作用下产生变弹性变形：材料在外加载荷作用下产生变 形，当载荷去除后仍能恢复原状的变形。形，当载荷去除后仍能恢复原状的变形。 机械工程材料双语课件第一章 塑性变形塑性变形 -Plastic deformation: when the stress is removed, the material doesnt return to i

17、ts previous dimension but there is a permanent, irreversible deformation, which is called plastic deformation. 撤掉外力后不能恢复原状而形成撤掉外力后不能恢复原状而形成 不可逆的永久的变形称为塑性变不可逆的永久的变形称为塑性变 形。形。 机械工程材料双语课件第一章 Tensile test and stress-strain diagram(拉伸试验与应力应变曲线拉伸试验与应力应变曲线) The tensile test is used to evaluate the strength

18、 of metals and alloys. A metal sample is pulled axially to fracture in a short time at a constant rate. The force and the length of the specimen can be measured by instruments. 机械工程材料双语课件第一章 From the tensile test, we get the stress-strain diagram. Stress is defined as force per unit area（单（单 位面积上的力）

19、位面积上的力）. The companion term strain is defined as the change in length per unit length（每单位长（每单位长 度上长度的变化量）度上长度的变化量）. Fig.1.3 is the stress-strain curve of low carbon steel. 机械工程材料双语课件第一章 Analysis on stress-strain curve 机械工程材料双语课件第一章 From the stress-strain curve, we can obtain the mechanical propertie

20、s as follows: a. Modulus of elasticity (弹性模量弹性模量) b. Yield strength (屈服强度屈服强度) c. Ultimate tensile strength (抗拉强度极限抗拉强度极限) d. Ductility (塑性塑性) 机械工程材料双语课件第一章 a. Modulus of elasticity (or Youngs modulus) 弹性模量（杨氏模量）弹性模量（杨氏模量） In the first part of the tensile test, the metal is deformed elastically. In

21、general, metals and alloys show a linear relationship between stress and strain in the elastic region of the curve. The slope of the line is called modulus of elasticity, represented by the letter E: E=/（Mpa） Metals with high elastic modulus are relatively stiff and don not deflect (偏转，挠曲偏转，挠曲) easi

22、ly. 机械工程材料双语课件第一章 a.弹性模量（杨氏模量）弹性模量（杨氏模量） 拉伸变形第一阶段，材料在载荷作用下拉伸变形第一阶段，材料在载荷作用下 产生弹性变形。应力与应变在此阶段呈产生弹性变形。应力与应变在此阶段呈 线性关系。则该直线的斜率称为弹性模线性关系。则该直线的斜率称为弹性模 量量: E=/（Mpa） 弹性模量弹性模量E越大，表示材料越不易发生越大，表示材料越不易发生 挠曲或变形挠曲或变形. 机械工程材料双语课件第一章 b. Yield strength（屈服强度） Yield strength is the strength at which metals and alloys

23、 show significant plastic deformation. Because there is no definite point on the stress-strain curve where elastic strain ends and plastic strain begins, the yield strength is chosen to be that strength when a definite amount of plastic deformation/strain has occurred. 机械工程材料双语课件第一章 b. Yield strengt

24、h（屈服强度s ） 屈服强度表征金属或合金抵抗明显塑性 变形的能力。 由于应力应变曲线上没有弹性变形结 束和塑性变形开始的明确的界限，因此 就用屈服强度作为明显的塑性变形开始 时的强度。 机械工程材料双语课件第一章 Yield strength is usually less than the maximum attainable stress, at which an increase in strain occurs without an increase in stress. 屈服强度通常小于材料能够承受的最大强屈服强度通常小于材料能够承受的最大强 度。试验中应力达到屈服强度时力不增加但

25、度。试验中应力达到屈服强度时力不增加但 试样却继续伸长，这种现象称为屈服。试样却继续伸长，这种现象称为屈服。 机械工程材料双语课件第一章 Only certain materials have a yield point， and not all materials have apparent yield points. For American engineering structural design, the yield strength is chosen when 0.2 percent plastic strain has taken place, as indicated on

26、the stress-strain curve of the following picture（Fig.1.4）. 机械工程材料双语课件第一章 Fig.1.4 The 0.2percent yield strength for a aluminum alloy 机械工程材料双语课件第一章 First, a line is drawn parallel to the elastic linear part of the curve at 0.002 on the strain axis. Then at the point where this line intersects the uppe

27、r part of the curve, a horizontal line is drawn to the stress axis. The cross point value of the horizontal line and the stress axis is the 0.2% yield strength. 机械工程材料双语课件第一章 c. Ultimate tensile strength 抗拉强度抗拉强度b 应力应变曲线上的最高值即抗拉强度值。在应力应变曲线上的最高值即抗拉强度值。在 达到最高点之前，金属或合金属于均匀变形。达到最高点之前，金属或合金属于均匀变形。 在此之后，试

28、样变形集中在在此之后，试样变形集中在局部薄弱之处，局部薄弱之处， 此处截面积急剧减小，产生缩颈（此处截面积急剧减小，产生缩颈（necking）. 缩颈之后试样能够承受的应力减小，直至断缩颈之后试样能够承受的应力减小，直至断 裂。裂。b是材料在断裂前能够承受的最大应力。是材料在断裂前能够承受的最大应力。 机械工程材料双语课件第一章 The ultimate tensile strengthb of a metal is determined by drawing a horizontal line from the peak on the curve to the stress axis. Th

29、e stress value where this line intersects the stress a x i s i s c a l l e d t h e ultimate tensile strength. /curvecurve for a aluminum alloy 机械工程材料双语课件第一章 d. Ductility （塑性）（塑性） 塑性表征材料断裂前具有塑性变形的塑性表征材料断裂前具有塑性变形的 能力，常用的塑性指标：能力，常用的塑性指标： -Percent Elongation (伸长率) -Percent Reduction in Area (断面收缩率断面收缩率)

30、 机械工程材料双语课件第一章 Percent Elongation (伸长率) = (final length l1 1 initial length l0 0) / initial length l0 0 100% = initial length l0 0 : the length between the gage marks on the specimen, usually 2 inches. final length l1 1: the length between these same gage marks after testing when the fractured surfa

31、ce of the specimen is fitted together. 最终长度l1 1 ：试验后将试 样断裂处接在一起后测出的 原始测量记号之间的长度 。 机械工程材料双语课件第一章 The amount of elongation that a tensile specimen undergoes during testing expresses the ductility of a metal. In general, the higher the ductility (the more deformable the metal is), the higher the percen

32、t elongation is. 试验中被拉伸试样的伸长率表示金属的塑性。试验中被拉伸试样的伸长率表示金属的塑性。 塑性越好，伸长率塑性越好，伸长率的值约大。的值约大。 机械工程材料双语课件第一章 Percent Reduction in Area (断面收缩率) = (initial area A0final area Af) / initial areaA0100%= (A0-Af)/A0 100% is also a measure of the ductility of the metal. ， the ductility 。 机械工程材料双语课件第一章 Hardness and ha

33、rdness testing 硬度与硬度测试硬度与硬度测试 Hardness is a measure of the resistance of a metal to plastic deformation. Hardness test is used extensively in industry. The most common hardness tests are Brinell and Rockwell hardness test（布氏硬度和洛氏硬度）. 硬度表征材料表面抵抗塑性变形的能力硬度表征材料表面抵抗塑性变形的能力。 机械工程材料双语课件第一章 It is measured b

34、y forcing an indenter (压头) slowly into its surface at 90. The force P is usually known. The indenter is usually a ball, pyramid（棱锥） or cone（圆锥） made of hardened steel, tungsten carbide（硬质合金） or diamond（金刚石）,which is much harder than the material being tested. 机械工程材料双语课件第一章 After the indenter is with

35、drawn（撤除，撤掉） from the surface, the indentation(压痕) has been made. Measure the cross-sectional area(截面积) or the depth(深度) of the impression(压痕) ，an hardness number can be calculated or read off the dial（表盘）. 机械工程材料双语课件第一章 Toughness and impact test 韧性与冲击试验韧性与冲击试验 Toughness is a measure of the amount o

36、f energy a material can absorb before fracturing（断裂）（断裂）. It is an important ability for a material to withstand(承受承受) an impact load（冲击载荷）（冲击载荷） without fracturing. 韧度是衡量材料断裂前所吸收的能量。表示韧度是衡量材料断裂前所吸收的能量。表示 材料抵抗冲击载荷而不断裂的能力。材料抵抗冲击载荷而不断裂的能力。 机械工程材料双语课件第一章 One of the simplest methods of measuring toughness is the impact-testing. A schematic diagram of a simple impact-testing machine is shown in fig.1.5. Place a Charpy V-notch(却贝槽口，切口) specimen across parallel jaws in the machine. A heavy pendulum released from a known height strikes the sample on its downward swing, fracturing i