MetalMaterials-1

1、Metal MaterialsWANG, YongYongwangcquextbook左汝林等编，金属材料学，重庆大学出版社，2008.2Do you know what the following things are made of, and what processes they were experienced?（用途和性能要求？） 厨房餐刀和手术刀 混凝土中的钢筋 石门大桥的钢缆 汽车车身外壳、滚动轴承 Why do we learn this course? Understand the basic theories of alloying. Unders

2、tand the roles of different alloying elements in an alloy. Chose the correct materials for a certain usage. (Properties, price, availability) Apply the correct working, forming and/or heat-treating to the material for a special purpose.Engineering Materials and Materials Engineering Engineering Mate

3、rials deals with the structures, properties of materials in different applications, including metals, polymers, ceramics, composites and combinations of them. Materials Engineering deals with the design, manufacture, working, forming, treating, etc. of materials for different purposes. Structural Ma

4、terials & Functional Materials Structural Materials（结构材料）: Mechanical properties are the most important for these materials. Functional Materials（功能材料）: Physical and chemical properties are the most important for these materials.这种区分不是绝对的！这种区分不是绝对的！Chapter 1. Induction to alloying theories of st

5、eelsSteels are the alloys composed of irons, carbons, and other elements, in which the content of carbon is less than 2.11%. They can be formed under cold and/or hot condition.Carbon & Alloy SteelsProperties are the basis of material selection.Mechanical Properties: Hardness（硬度）, Strength（强度）, D

6、uctility（塑性）, Toughness（韧性）Physical Properties: Gravimetric（重力）, Electrical（电）, Magnetic（磁）, Optical（光）, Thermal（热）, Acoustic（声） Chemical Properties: Composition（化学成分）, Microstructure（微观组织）, Phases（相）, Grain Size（晶粒尺寸）, Corrosion Resistance（耐蚀性）, Inclusion（夹杂物）The above three are service properties.

7、 注意使用性能和本征性能的区别。注意使用性能和本征性能的区别。Manufacturing Properties（工艺性能或加工性能）: Weldability（焊接性）, Castability（铸造性能）, formability （成型性能）, Machinability （切削性能） 1.1 Alloying elements in steelsAlloy elements 特意添加到钢中以保证获得所要求的组织结构和性能的化学元素。（C、Mn、Si、Ni、Cr、Mo、V、Nb、Cu、Al、Ti、W、Co、RE等）Impurity elements 由冶炼时所用原材料以及冶炼方法和工艺操作

8、等所带入钢中的化学元素。（P、S、O、N、H等） 两者的区分不是绝对的！两者的区分不是绝对的！ 如：易切削钢中的S、焊接用钢中过量的Cr。 （常存元素常存元素）Carbon is the most important alloying element in steels. No carbon, no steel.Strength,MPaElongation, %C, (wt%)ductilitys (quenched)b (quenched)b (normalized)s (normalized)Effects of alloyingMechanical properties （高温）强度、硬

9、度、塑性、韧性Corrosion resistance 针对不同介质及温度Processing performance 淬透性、回火稳定性、切削、铸、锻、焊等性能Microstructure 晶粒、析出相Purity 脱氧、除杂Classifications of SteelsComposition: Carbon steel: low-carbon steel: less than 0.25wt%C medium-carbon steel: 0.25-0.55%C high-carbon steel: more than 0.55% Alloy steel: With alloying el

10、ements (AE) other than carbon, such as manganese, silicon, chromium, nickel, titanium, vanadium, tungsten, molybdenum. low-alloy steel: less than 5wt% AE medium-alloy steel: 5-10% AE high-alloy steel: more than 10% AEApplication: Structural steels Tool steels Special steels: heat-resistant steels, w

11、ear-resistant steels, stainless steelsMicrostructure: (as-normalized （正火态） or as-cast （退火态）, small-sized samples（横断面上组织一致）) ferrite, austenite, martensite, pearlite, bainite钢中碳钢(0.25%0.55%C)低碳钢(0.55%C)铁素体(F)铁素体-珠光体(F-P)奥氏体(A)马氏体(M)珠光体(P)贝氏体(B)沉淀硬化奥氏体-铁素体 (A-F)按组织分类 (碳含量小于2.11%)按化学成分或用途分类碳钢合金钢中合金钢(总量

12、5%10%)低合金钢(总量10%)耐蚀钢耐热钢耐磨钢1.2 Interactions of alloying elements with iron and carbon1.2.1 Interaction with iron 1. Primary phase transformations in steels 三种相的结构和性质？三种相的结构和性质？ 349121394CCAAFeFeFe 2. Iron-based solid solutions 1) Austenite-forming elements: Mn、Ni、Co, C, N, Cu, A. Open the fieldWith t

13、he addition of Mn, Ni, Co, etc, phase can persist to room temperature. B. Extend the field With the increase of C, N, Cu, Zn, etc, field is enlarged, but not persists to room temperature. 2) Ferrite-forming elements: V, Ti, W, Mo, Al, P, Cr, Si, B, Zr, Nb, Ta, S A. Close the field With the increase

14、of V, Ti, W, Mo, Al, P, Cr, Si, etc., the field tends to be completely surrounded by the + field. B. Reduce the field With the increase of B, Zr, Nb, Ta, S, etc., the field is reduced but not completely surrounded by the + field.3 Solubility of alloying elements in iron 1) Substitutional solution (m

15、aybe unlimited) A. Lattice pattern 点阵相同时，溶解度大。 B. Atomic radius difference 原子半径差不大于15%时，可形成有限固溶体；原子半径差不大于8%时，可形成无限固溶体。 C. Electron structure 原子价相差越大，固溶度越小。 多元系中，由于合金元素之间存在交互影响，固溶体的形成规律要复杂得多。（一般可采用一些软件计算，然后试验验证。） 3 Solubility of alloying elements in iron 2) Interstitial solution (always limited) A. L

16、attice pattern of the solvent 决定着间隙数量和尺寸。 B. Atomic radius of the solute 决定着进入间隙的能力，溶质与溶剂的原子半径之比小于0.59时，易于形成间隙固溶体。 C. Location of the interstice 不同间隙的尺寸不同。 -Fe和和-Fe中的四面体间隙和八面体间隙尺寸？中的四面体间隙和八面体间隙尺寸？ 1.2.2 Interaction with carbon Carbide-forming elements: Ti, Zr, Nb, V, W, Mo, Cr, Mn, Fe Non-carbide-fo

17、rming elements: Ni, Co, Cu, Si, Al, N, P, S 1 Stability of carbidesStrong bonding: Carbides of Ti, Zr, Nb, V Medium bonding: Carbides of W, Mo, Cr Weak bonding: Carbides of Mn, FeThe less is the electron in d shell of the element, the more stable is its carbide. 2 Classification of carbides1) Simple

18、 lattice interstitial carbide rC/rMe0.592) Complex lattice carbide rC/rMe0.59Carbides in steels3) Solubility of carbides with each otherSome metallic atoms can be substituted by other metals.渗碳体Fe3C是钢中最重要的强化相；溶入其它元素时，如形成（FeMn）3C、（FeCr）3C等，称为合金渗碳体。4) Nitride and Nitrogen Carbide Almost all nitride ar

19、e interstitial phases with simple lattice.C and N can be placed by each other to form nitrogen carbide, such as Ti(C,N).1.2.3 Intermetallic compound phase (avoid) 通常是Fe-Cr金属间化合物，容易出现在含铬较高的钢中。相硬脆，使钢的塑性和韧性显著下降，脆性增加。 Laves phase (expect) AB2相。在含钨、钼、铌、钛的耐热钢中容易出现，具有较高的热稳定性，是耐热钢中的重要强化相。 Ordered phase (exp

20、ect) B3A相。介于无序固溶体和化合物之间的过渡状态，是耐热钢和耐热合金中重要的强化相。 碳化物形成元素在钢中先形成碳化物，超过生成碳化物碳化物形成元素在钢中先形成碳化物，超过生成碳化物所需的量后，才能生成金属间化合物。所需的量后，才能生成金属间化合物。1.2.4 Effects of alloying elements on Fe-C phase diagram1. & fields：与前述作用基本相同。2. Critical points (E and S)Eutectoid point ()Content of element (%)Carbon of pearlite (%

21、)Content of element (%)几乎所有合金元素都使S点和E点左移。S点左移意味着共析体含碳量减少；E点左移意味着出现莱氏体的含碳量降低。1.3 Effect of alloying element on heat treatment1.3.1 Heating process1. Forming rate of austenite The forming rate depends on the diffusion rate of carbon in iron.The higher is the affinity of the alloying element with carbo

22、n, the lower is the forming rate of austenite. It takes more time to get a homogeneous composition in alloying steel.2. Austenite grain sizeMost alloying elements restrain the growth of grains, thus reduce the danger of hot shortness（过热）.Some exception: Mn, P, C, N, O, B . Generally, the said effect

23、 increases with the infinity of the element with carbon. 1.3.2 Transformation of undercooling austeniteNon-carbide-forming elements Carbide-forming elements Effect of alloying elements on the TTT curve of steels Improve the hardenability （淬硬性） of steels (easier to obtain martensite upon cooling).It

24、is essential for the alloying elements to completely dissolve in austenite to improve the quenchability（淬透性）, otherwise the opposite results occurs（Why？）.多个合金元素同时作用，对淬透性的提高比单个元素的作用更大，因此，通常采用“少量多元”的合金化手段。淬透性提高后，可采用较低的淬火冷速，减小变形和开裂倾向。 1. Effect on pearlite and bainite transformations Alloying elements

25、other than Co increase the induction time of the transformation of undercooling austenite. Those elements that extend the field decrease the A1 temperature. Those elements that reduce the field increase the A1 temperature. Alloying elements change the driving force（驱动力） of bainite transformation and

26、 the diffusivity of carbon.Alloying elements other than Al and Co inhibit the formation of bainite.2. Effect on martensite transformationMost elements decrease the Ms and Mf temperatures.Relation of composition and Ms temperature:Ms()=539-423C-30.4Mn-12.1Cr-17.7Ni-7.5MoEffect of C content on the mor

27、phology of martensitelathmixturelamellarC (%)Temperature1.3.3 Effect on tempering transformation Increase the tempering stability 合金元素在回火过程中推迟马氏体的分解和残余奥氏体的转变(即在较高温度才开始分解和转变)，提高铁素体的再结晶温度，使碳化物难以聚集长大，因此提高了钢对回火软化的抗力（有什么好处？），即提高了钢的回火稳定性，也称为抗回火性。 作用较强的合金元素有：V、Si、Mo、W、Ni、Co等。2. Secondary hardening and Seco

28、ndary quenching 在含强碳化物形成元素（W、Mo、V等）的淬火钢中，较低温度回火时，由于马氏体的分解，会使钢的硬度和强度降低；而在较高温度（约450以上）回火时，钢中开始析出弥散稳定的难熔碳化物Mo2C、W2C、VC等，这些难熔碳化物与相保持共格关系，产生强烈的弥散强化，钢的硬度和强度升高，这种现象称为二次硬化二次硬化。 若继续升高温度，由于碳化物的长大，弥散度减小，共格性被破坏，共格畸变消失，从而使硬度迅速下降。 2. Secondary hardening and Secondary quenching 在某些高合金钢淬火组织中，残余奥氏体量较多，且十分稳定，当加热到5006

29、00时仍不分解，仅是析出一些特殊碳化物，但由于特殊碳化物的析出，使奥氏体中碳及合金元素含量下降，提高了Ms点温度，故在随后回火冷却过程中残余奥氏体会转变为马氏体，这就是二次淬火二次淬火现象。 Tempering temperature ()Rockwell C HardnessEffect of Mo on the hardness of as-tempered steels.二次硬化和二次淬火在机理和性能表现上有何区别？二次硬化和二次淬火在机理和性能表现上有何区别？3. Temper embrittlementThe impact toughness decreases after temp

30、ering. First type (low temperature or irreversible) temper embrittlement. 250-400特点： 第一类回火脆性是不可逆的，断口沿原奥氏体晶界的晶粒间破坏。 不仅发生在普通碳素钢中，也发生在合金钢中。 这一脆化现象与沿晶界析出的碳化物和杂质的再分布有关。含硅的合金钢，由于硅延缓碳化物的析出，发生脆化的温度移至较高的范围； 含磷等杂质的钢对这类脆性敏感。 3. Temper embrittlementSecond type (high temperature or reversible) temper embrittleme

31、nt. 450-600特点： 第二类回火脆性是可逆的，将钢加热到450以上快冷就可消除或预防回火脆性。破断常常发生在原奥氏体晶界。 含磷、锑、砷和锡等杂质的钢，对这类脆性非常敏感。这些杂质的偏析使晶界的结合力减弱。 添加硅、锰、铬和镍等元素会使脆化加速。 加入适当Mo或W(0.5%Mo，1%W)可基本上消除这类脆性。1.4 Strengthening and toughening resulting from alloying1.4.1 Strengthening Solid-Solution strengthening 对同一合金系，固溶体浓度越大，强化效果越好。 强度随浓度增加呈曲线关系升

32、高。在浓度较低时，强度升高较快，以后渐趋平缓，大约在原子分数为50 %时达到极大值。 固溶强化降低合金的塑性。 采用多元少量的合金化原则，其强化效果更好，并且能保持到较高温度。固溶原子阻碍位错运动。1.4 Strengthening and toughening resulting from alloying1.4.1 Strengthening2. Boundary strengthening (Fine-grained) s =o + k d-1/2 细晶强化在提高强度的同时, 也提高塑性和韧性。这是因为细晶材料在发生塑性变形时各个晶粒变形比较均匀, 可以承受较大变形量。 细晶强化对高温合

33、金并不适用。 细化组织，如减小珠光体片层间距，也提高强韧性。位错塞积1.4 Strengthening and toughening resulting from alloying1.4.1 Strengthening3. Work hardening (Strain) 金属材料在冷变形（再结晶温度以下进行的塑性变形）过程中强度逐渐升高的现象称为形变强化，也叫加工硬化。 随着变形量增加，强度提高而塑性和韧性降低。 形变强化的效果十分明显，强度增值较大；但形变强化受塑性限制，变形量过大时，材料将发生断裂。 形变强化可以通过再结晶退火消除，使材料的组织和性能基本上恢复到冷变形之前的状态。因此受到使

34、用温度的限制。1.4 Strengthening and toughening resulting from alloying1.4.1 Strengthening4. Dispersive strengthening (precipitation, particle, second-phase) 沉淀相的体积比越大，强化效果越显著。 第二相颗粒越细小、弥散度越大，强化效果越好。 对位错运动阻力越大的硬质点，其强化效果也越大。 熔点越高、在基体中的溶解度越小，产生强化作用的温度范围越大。1.4.2 Toughening1. Reducing grain size2. Adjusting com

35、position 随碳、氮、磷含量增加，钢的冲击韧性下降冷脆转折温度升高且范围变宽。 加入镍和少量锰可提高韧性并降低冷脆转折温度。3. Ausforming 形变热处理是将形变(锻、轧等)与热处理相结合，使金属材料同时经历形变和相变从而使晶粒细化、位错密度升高、晶界发生畸变，以达到提高综合力学性能的目的。4. Obtaining low carbon martensite (lath martensite)1.5 Effect on Manufacturing Properties1.5.1 Heat treatabilityHardenability, Sensitivity to hot

36、shortness, Tendency of temper embrittlement, oxidation and decarbonization1.5.2 WeldabilityWeldability is against to heat-treatability to some extent. CE= C+( Mn+Si)/6+(Ni+Cu)/15+(Cr+Mo+V)/5 CE is the effective carbon content.碳当量越低，焊接性越好。1.5.3 MachinabilityParameters: Life of cutting tools, cutting

37、rate, surface roughness of products, cutting resistance, shape of chipsEffective factors: hardness (170 HB 230 HB for steels), inclusions, composition (S)1.5.4 CastabilityFlowability, shrinkage, segregation固、液相线的温度愈低和结晶温度区间愈窄，铸造性能愈好。1.5.5 Formability Hot-work and cold-work 提高塑性、改善析出相形态（接近球状），有利于提高塑性

38、加工性能。1.6 Common defects of metal materials 两大类缺陷：一类来自制造过程： 熔炼、浇铸、锻、轧、热处理等 一类产生于服役过程 腐蚀、磨损、疲劳等1.6.1 铸造缺陷1 缩孔和疏松 铸件或铸锭中，集中的空隙称为缩孔，分散的空隙称为疏松。产生的原因都是补缩不足。 危害：降低力学性能（对铸件影响更大） 增加机加工后的粗糙度 壳状凝固，流动性好，缩孔集中在冒口部位c）糊状凝固，流动性最差，大量分散缩孔（疏松）b）混合凝固，介于a、c之间缩缩 孔孔疏疏 松松铸锭组织示意图例：中心缩孔导致锻件四角裂2 偏析 凝固过程中，由于某种原因造成的化学成分不均匀现象。 1）晶内偏析和枝晶偏析2）区域偏析 凝固不是在整个截面上同时进行，而是在同铸锭接触的外层先开始，于是高熔点组元富集于外层，而心部富集低熔点组元。心部同时也富集气泡和夹杂（因此夹杂物分析应在心部取样）。3）比重偏析 析出的晶体与余下的液体金属比重不同，而造成的成分不均匀现象称为比重偏析。 结晶温度范围增大、比重差增大，偏析加剧。区域偏析区域偏析与方形钢锭模对与方形钢锭模对应的方框偏析应的方框偏析3 气泡和白点 1）气泡： 液态金属溶解的气体在凝固时