MetalMaterials-1

1、Metal MaterialsWANG, YongYongwangcquextbook左汝林等編，金屬材料學(xué)，重慶大學(xué)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？） 廚房餐刀和手術(shù)刀 混凝土中的鋼筋 石門(mén)大橋的鋼纜 汽車(chē)車(chē)身外殼、滾動(dòng)軸承 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（結(jié)構(gòu)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.這種區(qū)分不是絕對(duì)的！這種區(qū)分不是絕對(duì)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（強(qiáng)度）, D

6、uctility（塑性）, Toughness（韌性）Physical Properties: Gravimetric（重力）, Electrical（電）, Magnetic（磁）, Optical（光）, Thermal（熱）, Acoustic（聲） Chemical Properties: Composition（化學(xué)成分）, Microstructure（微觀組織）, Phases（相）, Grain Size（晶粒尺寸）, Corrosion Resistance（耐蝕性）, Inclusion（夾雜物）The above three are service properties.

7、 注意使用性能和本征性能的區(qū)別。注意使用性能和本征性能的區(qū)別。Manufacturing Properties（工藝性能或加工性能）: Weldability（焊接性）, Castability（鑄造性能）, formability （成型性能）, Machinability （切削性能） 1.1 Alloying elements in steelsAlloy elements 特意添加到鋼中以保證獲得所要求的組織結(jié)構(gòu)和性能的化學(xué)元素。（C、Mn、Si、Ni、Cr、Mo、V、Nb、Cu、Al、Ti、W、Co、RE等）Impurity elements 由冶煉時(shí)所用原材料以及冶煉方法和工藝操作

8、等所帶入鋼中的化學(xué)元素。（P、S、O、N、H等） 兩者的區(qū)分不是絕對(duì)的！兩者的區(qū)分不是絕對(duì)的！ 如：易切削鋼中的S、焊接用鋼中過(guò)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 （高溫）強(qiáng)度、硬

9、度、塑性、韌性Corrosion resistance 針對(duì)不同介質(zhì)及溫度Processing performance 淬透性、回火穩(wěn)定性、切削、鑄、鍛、焊等性能Microstructure 晶粒、析出相Purity 脫氧、除雜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 （正火態(tài)） or as-cast （退火態(tài)）, small-sized samples（橫斷面上組織一致）) ferrite, austenite, martensite, pearlite, bainite鋼中碳鋼(0.25%0.55%C)低碳鋼(0.55%C)鐵素體(F)鐵素體-珠光體(F-P)奧氏體(A)馬氏體(M)珠光體(P)貝氏體(B)沉淀硬化奧氏體-鐵素體 (A-F)按組織分類(lèi) (碳含量小于2.11%)按化學(xué)成分或用途分類(lèi)碳鋼合金鋼中合金鋼(總量

12、5%10%)低合金鋼(總量10%)耐蝕鋼耐熱鋼耐磨鋼1.2 Interactions of alloying elements with iron and carbon1.2.1 Interaction with iron 1. Primary phase transformations in steels 三種相的結(jié)構(gòu)和性質(zhì)？三種相的結(jié)構(gòu)和性質(zhì)？ 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 點(diǎn)陣相同時(shí)，溶解度大。 B. Atomic radius difference 原子半徑差不大于15%時(shí)，可形成有限固溶體；原子半徑差不大于8%時(shí)，可形成無(wú)限固溶體。 C. Electron structure 原子價(jià)相差越大，固溶度越小。 多元系中，由于合金元素之間存在交互影響，固溶體的形成規(guī)律要復(fù)雜得多。（一般可采用一些軟件計(jì)算，然后試驗(yàn)驗(yàn)證。） 3 Solubility of alloying elements in iron 2) Interstitial solution (always limited) A. L

16、attice pattern of the solvent 決定著間隙數(shù)量和尺寸。 B. Atomic radius of the solute 決定著進(jìn)入間隙的能力，溶質(zhì)與溶劑的原子半徑之比小于0.59時(shí)，易于形成間隙固溶體。 C. Location of the interstice 不同間隙的尺寸不同。 -Fe和和-Fe中的四面體間隙和八面體間隙尺寸？中的四面體間隙和八面體間隙尺寸？ 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.滲碳體Fe3C是鋼中最重要的強(qiáng)化相；溶入其它元素時(shí)，如形成（FeMn）3C、（FeCr）3C等，稱(chēng)為合金滲碳體。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金屬間化合物，容易出現(xiàn)在含鉻較高的鋼中。相硬脆，使鋼的塑性和韌性顯著下降，脆性增加。 Laves phase (expect) AB2相。在含鎢、鉬、鈮、鈦的耐熱鋼中容易出現(xiàn)，具有較高的熱穩(wěn)定性，是耐熱鋼中的重要強(qiáng)化相。 Ordered phase (exp

20、ect) B3A相。介于無(wú)序固溶體和化合物之間的過(guò)渡狀態(tài)，是耐熱鋼和耐熱合金中重要的強(qiáng)化相。 碳化物形成元素在鋼中先形成碳化物，超過(guò)生成碳化物碳化物形成元素在鋼中先形成碳化物，超過(guò)生成碳化物所需的量后，才能生成金屬間化合物。所需的量后，才能生成金屬間化合物。1.2.4 Effects of alloying elements on Fe-C phase diagram1. & fields：與前述作用基本相同。2. Critical points (E and S)Eutectoid point ()Content of element (%)Carbon of pearlite (%

21、)Content of element (%)幾乎所有合金元素都使S點(diǎn)和E點(diǎn)左移。S點(diǎn)左移意味著共析體含碳量減少；E點(diǎn)左移意味著出現(xiàn)萊氏體的含碳量降低。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（過(guò)熱）.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？）.多個(gè)合金元素同時(shí)作用，對(duì)淬透性的提高比單個(gè)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，可采用較低的淬火冷速，減小變形和開(kāi)裂傾向。 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（驅(qū)動(dòng)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 合金元素在回火過(guò)程中推遲馬氏體的分解和殘余奧氏體的轉(zhuǎn)變(即在較高溫度才開(kāi)始分解和轉(zhuǎn)變)，提高鐵素體的再結(jié)晶溫度，使碳化物難以聚集長(zhǎng)大，因此提高了鋼對(duì)回火軟化的抗力（有什么好處？），即提高了鋼的回火穩(wěn)定性，也稱(chēng)為抗回火性。 作用較強(qiáng)的合金元素有：V、Si、Mo、W、Ni、Co等。2. Secondary hardening and Seco

28、ndary quenching 在含強(qiáng)碳化物形成元素（W、Mo、V等）的淬火鋼中，較低溫度回火時(shí)，由于馬氏體的分解，會(huì)使鋼的硬度和強(qiáng)度降低；而在較高溫度（約450以上）回火時(shí)，鋼中開(kāi)始析出彌散穩(wěn)定的難熔碳化物Mo2C、W2C、VC等，這些難熔碳化物與相保持共格關(guān)系，產(chǎn)生強(qiáng)烈的彌散強(qiáng)化，鋼的硬度和強(qiáng)度升高，這種現(xiàn)象稱(chēng)為二次硬化二次硬化。 若繼續(xù)升高溫度，由于碳化物的長(zhǎng)大，彌散度減小，共格性被破壞，共格畸變消失，從而使硬度迅速下降。 2. Secondary hardening and Secondary quenching 在某些高合金鋼淬火組織中，殘余奧氏體量較多，且十分穩(wěn)定，當(dāng)加熱到5006

29、00時(shí)仍不分解，僅是析出一些特殊碳化物，但由于特殊碳化物的析出，使奧氏體中碳及合金元素含量下降，提高了Ms點(diǎn)溫度，故在隨后回火冷卻過(guò)程中殘余奧氏體會(huì)轉(zhuǎn)變?yōu)轳R氏體，這就是二次淬火二次淬火現(xiàn)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機(jī)理和性能表現(xiàn)上有何區(qū)別？二次硬化和二次淬火在機(jī)理和性能表現(xiàn)上有何區(qū)別？3. Temper embrittlementThe impact toughness decreases after temp

30、ering. First type (low temperature or irreversible) temper embrittlement. 250-400特點(diǎn)： 第一類(lèi)回火脆性是不可逆的，斷口沿原奧氏體晶界的晶粒間破壞。 不僅發(fā)生在普通碳素鋼中，也發(fā)生在合金鋼中。 這一脆化現(xiàn)象與沿晶界析出的碳化物和雜質(zhì)的再分布有關(guān)。含硅的合金鋼，由于硅延緩碳化物的析出，發(fā)生脆化的溫度移至較高的范圍； 含磷等雜質(zhì)的鋼對(duì)這類(lèi)脆性敏感。 3. Temper embrittlementSecond type (high temperature or reversible) temper embrittleme

31、nt. 450-600特點(diǎn)： 第二類(lèi)回火脆性是可逆的，將鋼加熱到450以上快冷就可消除或預(yù)防回火脆性。破斷常常發(fā)生在原奧氏體晶界。 含磷、銻、砷和錫等雜質(zhì)的鋼，對(duì)這類(lèi)脆性非常敏感。這些雜質(zhì)的偏析使晶界的結(jié)合力減弱。 添加硅、錳、鉻和鎳等元素會(huì)使脆化加速。 加入適當(dāng)Mo或W(0.5%Mo，1%W)可基本上消除這類(lèi)脆性。1.4 Strengthening and toughening resulting from alloying1.4.1 Strengthening Solid-Solution strengthening 對(duì)同一合金系，固溶體濃度越大，強(qiáng)化效果越好。 強(qiáng)度隨濃度增加呈曲線關(guān)系升

32、高。在濃度較低時(shí)，強(qiáng)度升高較快，以后漸趨平緩，大約在原子分?jǐn)?shù)為50 %時(shí)達(dá)到極大值。 固溶強(qiáng)化降低合金的塑性。 采用多元少量的合金化原則，其強(qiáng)化效果更好，并且能保持到較高溫度。固溶原子阻礙位錯(cuò)運(yùn)動(dòng)。1.4 Strengthening and toughening resulting from alloying1.4.1 Strengthening2. Boundary strengthening (Fine-grained) s =o + k d-1/2 細(xì)晶強(qiáng)化在提高強(qiáng)度的同時(shí), 也提高塑性和韌性。這是因?yàn)榧?xì)晶材料在發(fā)生塑性變形時(shí)各個(gè)晶粒變形比較均勻, 可以承受較大變形量。 細(xì)晶強(qiáng)化對(duì)高溫合

33、金并不適用。 細(xì)化組織，如減小珠光體片層間距，也提高強(qiáng)韌性。位錯(cuò)塞積1.4 Strengthening and toughening resulting from alloying1.4.1 Strengthening3. Work hardening (Strain) 金屬材料在冷變形（再結(jié)晶溫度以下進(jìn)行的塑性變形）過(guò)程中強(qiáng)度逐漸升高的現(xiàn)象稱(chēng)為形變強(qiáng)化，也叫加工硬化。 隨著變形量增加，強(qiáng)度提高而塑性和韌性降低。 形變強(qiáng)化的效果十分明顯，強(qiáng)度增值較大；但形變強(qiáng)化受塑性限制，變形量過(guò)大時(shí)，材料將發(fā)生斷裂。 形變強(qiáng)化可以通過(guò)再結(jié)晶退火消除，使材料的組織和性能基本上恢復(fù)到冷變形之前的狀態(tài)。因此受到使

34、用溫度的限制。1.4 Strengthening and toughening resulting from alloying1.4.1 Strengthening4. Dispersive strengthening (precipitation, particle, second-phase) 沉淀相的體積比越大，強(qiáng)化效果越顯著。 第二相顆粒越細(xì)小、彌散度越大，強(qiáng)化效果越好。 對(duì)位錯(cuò)運(yùn)動(dòng)阻力越大的硬質(zhì)點(diǎn)，其強(qiáng)化效果也越大。 熔點(diǎn)越高、在基體中的溶解度越小，產(chǎn)生強(qiáng)化作用的溫度范圍越大。1.4.2 Toughening1. Reducing grain size2. Adjusting com

35、position 隨碳、氮、磷含量增加，鋼的沖擊韌性下降冷脆轉(zhuǎn)折溫度升高且范圍變寬。 加入鎳和少量錳可提高韌性并降低冷脆轉(zhuǎn)折溫度。3. Ausforming 形變熱處理是將形變(鍛、軋等)與熱處理相結(jié)合，使金屬材料同時(shí)經(jīng)歷形變和相變從而使晶粒細(xì)化、位錯(cuò)密度升高、晶界發(fā)生畸變，以達(dá)到提高綜合力學(xué)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.碳當(dāng)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、液相線的溫度愈低和結(jié)晶溫度區(qū)間愈窄，鑄造性能愈好。1.5.5 Formability Hot-work and cold-work 提高塑性、改善析出相形態(tài)（接近球狀），有利于提高塑性

38、加工性能。1.6 Common defects of metal materials 兩大類(lèi)缺陷：一類(lèi)來(lái)自制造過(guò)程： 熔煉、澆鑄、鍛、軋、熱處理等 一類(lèi)產(chǎn)生于服役過(guò)程 腐蝕、磨損、疲勞等1.6.1 鑄造缺陷1 縮孔和疏松 鑄件或鑄錠中，集中的空隙稱(chēng)為縮孔，分散的空隙稱(chēng)為疏松。產(chǎn)生的原因都是補(bǔ)縮不足。 危害：降低力學(xué)性能（對(duì)鑄件影響更大） 增加機(jī)加工后的粗糙度 殼狀凝固，流動(dòng)性好，縮孔集中在冒口部位c）糊狀凝固，流動(dòng)性最差，大量分散縮孔（疏松）b）混合凝固，介于a、c之間縮縮 孔孔疏疏 松松鑄錠組織示意圖例：中心縮孔導(dǎo)致鍛件四角裂2 偏析 凝固過(guò)程中，由于某種原因造成的化學(xué)成分不均勻現(xiàn)象。 1）晶內(nèi)偏析和枝晶偏析2）區(qū)域偏析 凝固不是在整個(gè)截面上同時(shí)進(jìn)行，而是在同鑄錠接觸的外層先開(kāi)始，于是高熔點(diǎn)組元富集于外層，而心部富集低熔點(diǎn)組元。心部同時(shí)也富集氣泡和夾雜（因此夾雜物分析應(yīng)在心部取樣）。3）比重偏析 析出的晶體與余下的液體金屬比重不同，而造成的成分不均勻現(xiàn)象稱(chēng)為比重偏析。 結(jié)晶溫度范圍增大、比重差增大，偏析加劇。區(qū)域偏析區(qū)域偏析與方形鋼錠模對(duì)與方形鋼錠模對(duì)應(yīng)的方框偏析應(yīng)的方框偏析3 氣泡和白點(diǎn) 1）氣泡： 液態(tài)金屬溶解的氣體在凝固時(shí)