1、Heat treatment: A process that achieves the desired properties by changing the structure of the interior of the steel by heating, holding and cooling in a solid state. 熱處理：通過在固態(tài)下加熱、保溫和冷卻， 使鋼材內部的組織結構發(fā)生變化， 獲得所需性能的一種工藝方法。,Heat treatment process curve,A,B, + ,L,Can all metal materials be heat treated? 是

2、不是所有的金屬材料都可以進行熱處理呢？,Only the alloys in which the solid phase transformation occur can be heat treatment. 只有固態(tài)相變發(fā)生的合金才能進行熱處理。,E,F,G 912 ,S,P,Q,1148,727,A,F,A+F,A+ Fe3C,F + Fe3C,K,Fe3C,Fe,A1,Acm,A3,T , C%,Transformation Temperature 轉變溫 度,Ac1,Ac3,Accm,A3,Acm,Arcm,Ar3,Ar1,A1,A,G,S,E,P,Q,F,727,1148,P+Cm,

3、F+P,2.11,0.77,0.0218,Fe,C%,Austenitizing of hypoeutectoid steel亞共析鋼的奧氏體化, 室溫下組織為F+P。 A1以上，F(xiàn)+A A3以上，A,A,F,A1,A3,Acm,Austenitizing of hypereutectoid steel 過共析鋼的奧氏體化, 室溫下組織為 P+Fe3C A1以上，F(xiàn)e3C+A Acm以上，A 在A1Acm之間的奧氏體化， 稱為不完全奧氏體化，熱處理工藝中常用。,1,2,VI-1 Formation of Austenite in Steels,The growth of A is carrie

4、d out by the dissolution of cementite, the diffusion of C atoms in A, and the transition between F and Fe on both sides. A的長大是通過滲碳體的溶解，C原子在A中的擴散以及A兩側界面向F和Fe3C推移來進行的。,2. Proccess of Austenite Formationin,F,Homogenization,Nucleation,Dissolution of Fe3C,Growth,Fe3C,The austenite formation process,VI-1

5、Formation of Austenite in Steels,(1)Kinetics of austenite isothermal formation 奧氏體等溫形成動力學,1) Isothermal transformation map等溫轉變圖(TTA) Time Temperature Austenitization,t/s,Austenite transformation start line,Austenite transformation completion line,P,P+A,A,3.Austenite transformation kinetics,TTA Illus

6、tration of the diagram,不均勻A,均勻A,P+ A,A+ Fe3C,P,T(s),T/,It can be seen that the time required for the dissolution of residual Fe3C, especially the homogenization of the composition is the longest. 可見：殘余Fe3C的溶解，特別是成分均勻化所需時間最長。,Ac1,1,2,3,4,1A transformation start line A轉變開始線 2A transformation completio

7、n line A轉變終止線 3Residual Fe3C dissolved termination line 殘余Fe3C溶解終止線 4A homogenization termination line A均勻化終止線,0,101,102,103,104,(1)Kinetics of austenite isothermal formation 奧氏體等溫形成動力學,3.Austenite transformation kinetics,1) Nucleation rate 形核率,Nucleation rate :The number of nuclei that reach the cr

8、itical nucleus size is formed per unit volume per unit time 單位時間單位體積內形成達到臨界晶核尺寸的晶核個數(shù),I=Nexp-(Q+G*)/kT,N: 單位體積舊相中的原子數(shù)目；: 原子中振動頻率；Q: 原子擴散激活能。,=Nexp(-Q/kT)exp(-G*/kT),溫度的影響,(2)Austenite isothermal kinetics analysis,3.Austenite transformation kinetics,The temperature increases, the nucleation rate I inc

9、reases exponentially. 1) the temperature increases, GV increases, the G * decreases, I further increases; 2) the temperature increases, the atomic diffusion rate is accelerated, is conducive to the ferrite to the austenite lattice restructuring, but also to promote the dissolution of cementite to ac

10、celerate the nucleation of austenite; 3) the temperature increases, the ferrite C% increase, on the other hand austenite in the ferrite nucleation in the required concentration of carbon along the SG and reduce the austenite nucleation required carbon concentration Undulating to promote the nucleati

11、on of austenite. 溫度升高, 形核率I以指數(shù)關系增加； 1）溫度升高, GV增大, 使G*減小, I進一步增大； 2）溫度升高, 原子擴散速度加快,有利于鐵素體向奧氏體點陣改組,也促進滲碳體溶解, 加速奧氏體的形核； 3）溫度升高,鐵素體的C%增加,另一方面奧氏體在鐵素體中形核時所需的碳濃度沿SG而降低,減小奧氏體形核所需要的碳濃度起伏,促進奧氏體的形核。,The effect of temperature on nucleation rate,1) Nucleation rate 形核率,(2)Austenite isothermal kinetics analysis,Li

12、near growth rate: 線性長大速率,Assume: ignore the concentration gradient in F and Fe3C the interface to maintain local balance the diffusion of C in A reaches the quasi-steady state 假設：忽略F和Fe3C中的濃度梯度 相界面處維持局部平衡 C在A中擴散達準穩(wěn)態(tài),D the diffusion coefficient of carbon in A(C在A中擴散系數(shù))， dC/dxcarbon concentration grad

13、ient in A (A中濃度梯度) CBconcentration difference between the two phases at the interface 兩相在界面上的濃度差,2) Growth rate長大速率,The expanding speed of the interface: 相界面推移速度為：,1)T，G ,討論：,2) GAF G A Fe3C,A3,Acm,A1,A,G,S,E,P,Q,F,727,1148,P+Cm,F+P,2.11,0.77,0.0218,Fe,C%,0.23,0.93,0.41,0.68,0.89,0.79,1) Temperature

14、,(3) Factors Affecting A Transformation 奧氏體轉變影響因素,4) Alloy elements,3.Kinetics of austenite formation,(4) The formation kinetics of continuous heating連續(xù)加熱時A形成動力學,連續(xù)轉變圖,V1 V2V3,不均勻A,均勻A,P+ A,A+ Fe3C,P,t/s,T/,Ac1,3.Kinetics of austenite formation,特點： (1)加熱速度,轉變溫度 ; (2)轉變在一個溫度范圍內完成; (3)形成速度隨加熱速度而， (4)A

15、起始晶粒度隨加熱速度速度 而細化， (5)A成分不均勻性隨加熱速度而。,V1,Continuous heating transformation kinetics 連續(xù)加熱轉變動力學示意圖,3.Austenite transformation kinetics,(4) The formation kinetics of continuous heating連續(xù)加熱時A形成動力學,Austenite grain size - the scale of the grain size, of evaluation indicators of steel heating quality. 奧氏體晶粒度

16、-表示晶粒大小的尺度,評定鋼加熱質量重要指標。 1) The initial grain size: the formation of austenite above the critical temperature has just been completed, grain boundaries just touch each other when the grain size. 2) The actual grain size: in a heat treatment conditions, the resulting grain size. 3)The inherent grain s

17、ize: steel under certain conditions, austenite grain growth tendency. 1)起始晶粒度：臨界溫度以上奧氏體形成剛剛完成，晶粒邊界剛互相接觸時晶粒大小。 2)實際晶粒度：在某一熱處理加熱條件下，所得到的晶粒尺寸。 3)本質晶粒度：鋼在一定條件下奧氏體晶粒長大的傾向性。,4. Austenite grain growth and its control 奧氏體晶粒長大及控制,(1) Austenite grain size A grain characterization奧氏體晶粒表征,n=2N-1或n=2N+3 N：晶粒度級別;

18、 n：金相觀察放大100倍進行時每平方英寸(6.45cm2)視野中所含平均晶粒數(shù)目; n: 實際上每1mm2試樣面積中的平均晶粒數(shù)目。,Austenite grain evaluation criteria奧氏體晶粒評定標準,Standard experimental conditions（標準實驗條件）: 93010/38h,Coarse grain size steel粗晶粒度鋼,Fine grain size steel細晶粒度鋼,本質升高迅速長大的鋼。如經(jīng)錳硅脫氧的鋼、沸騰鋼等,本質細晶粒度：奧氏體晶粒長大傾向小，加熱到較高溫度時才顯著長大的鋼。如經(jīng)鋁脫氧的鋼、鎮(zhèn)靜鋼等,1) heat

19、ing temperature and holding time T , t , A grain size 2) heating rate Rapid heating and short-term insulation can get fine A grain. 3) Carbon content 4) alloying elements 5) Original structure,（2） Austenite grain growth factors 奧氏體晶粒長大影響因素,4. Austenite grain growth and its control 奧氏體晶粒長大及控制,Increas

20、e the dispersion of the second phase particles: 增加第二相顆粒起彌散分布: steel by adding Al, Forming AlN particles to refine the structure. Carbides (TiC, NbC, etc.) to refine the structure. Increase the heating rate提高加熱速度: The use of temperature and time on the austenite grain growth to refine the grain. Such

21、 as high-frequency induction heating, laser heating, electron beam heating. 利用溫度和時間對奧氏體晶粒長大影響來細化晶粒。 如高頻感應加熱、激光加熱、電子束加熱等。,(3) Austenite size control and its application奧氏體大小控制,4. Austenite grain growth and its control 奧氏體晶粒長大及控制,思考題： 1、以共析鋼為例，簡述奧氏體轉變過程，為什么奧氏體全部形成后還會有部分滲碳體未溶解？ 2、奧氏體晶核優(yōu)先在什么地方形成？為什么？ 3、

22、奧氏體在珠光體中分別沿什么方向長大？哪個方向長大速度高？為什么？ 4、說明奧氏體長大過程中擴散的作用。 5、什么是奧氏體的本質晶粒度、起始晶粒度和實際晶粒度，鋼中彌散析出的第二相對奧氏體晶粒的長大有何影響？,VI-2 Pearlite 珠光體,（1）Tissue morphology: lamellar, granular,When the austenite of the eutectoid composition is cooled below A1, it is decomposed into a mixture of ferrite and cementite, called pear

23、lite.,1.Morphology and properties,共析成分的奧氏體冷卻到A1以下時，將分解為鐵素體與滲碳體的混合物，稱為珠光體。,珠光體領域/團：片狀珠光體的片層位向大致相同的區(qū)域稱為珠光體團， 在一個奧氏體晶粒內，可有幾個珠光體團。,lamellar pearlite Pearlite colony/group: The regions where the lamellar orientation are substantially the same is called pearlite group, within an austenite grains, there ma

24、y be several pearlite group.,（2）pearlite layer spacing 珠光體的層間距,The factors affecting the spacing of layers 層間距的影響因素： T、 S 。,C-Constant常數(shù)（8.02103nmK） TThe degree of subcooling過冷度,Pearlite珠光體,Sorbite索氏體,Troostite 屈氏體,The presence of pearlite: the annealing or normalizing of steel,珠光體的存在：鋼的退火或正火組織中,1)l

25、amellar pearlite eutectic steel s =139+46.4S-1 b =436.5+98.1S-1,(3) The mechanical properties of pearlite,layer spacing , strength and hardness , while the plastic and toughness has improved,片間距，強度和硬度，同時塑性和韌性有所改善,Mechanical properties of the hypo-(hyper-)eutectic steel 亞（過）共析鋼的珠光體力學性能,2)Granular Pea

26、rlite 球狀珠光體,Performance depends on: (1) F grain size (substrate) (2) Fe3C size, quantity, distribution. Fe3C small, uniform distribution, the strength, hardness, toughness is also . Compared with the same component flake P: the hardness is slightly lower, higher toughness 性能取決于： （1）F晶粒大?。ɑw） （2）Fe3C

27、大小、數(shù)量，分布。 Fe3C 細小，分布均勻， 則強度、硬度較高，韌性也。 與同成分片狀P相比：強度硬度稍低，塑韌性較高,Nucleation + Growth Because it is a two-phase mixture, so there is a problem about leading phase. 因為是兩相混合物，因此有一個領先相的問題。,1) leading phase Related to chemical composition Hypoeutectoid steel: F Hypereutectoid steel: Fe3C Eutectic steel: both

28、 can be, is generally considered to be Fe3C,In the presence of insoluble cementite in austenite, the transition of P is promoted.,2.Pearlite transformation,(1)lamellar pearlite,2) Formation mechanism 形成機理（以共析鋼為例）,A F + Fe3C 0.77% 0.0218% 6.69% fcc bcc 復雜正交,形核：,在A晶界和缺陷密集區(qū)，形成薄片狀Fe3C晶核。,長大：擴散進行 長大方式：縱向

29、長大，沿著珠光體片長軸方向長大； 橫向長大，沿著珠光體片垂直方向長大,依靠C的擴散,界面過程， 依靠Fe的自擴散,Carbon diffusion mechanism of the slice pearlite growth 片狀珠光體長大碳的擴散機制,CA/F：A/F界面上A一側的碳濃度 CA/ Fe3c ：A/Fe3C界面上A一側的碳濃度 CA：原A中的碳濃度 CF/A： F/A界面上F一側的碳濃度 CF/ Fe3c ：F/Fe3C界面上F一側的碳濃度 C Fe3c ：Fe3C的碳濃度為6.69%,Fe3C,F,A,CA/Fe3C，造成碳從A/F界面擴散到A/Fe3C界面，這便破壞了界面平

30、衡，使CA/F,CA/Fe3C，進而導致F長大(使CA/F )，F(xiàn)e3C長大(使CA/Fe3C )。 （b）Away from the P zone 由遠離P區(qū)擴散 因為CA/FCACA/Fe3C，F(xiàn)前沿的碳將向遠處擴散，而遠處的碳(濃度為CA)將擴散至Fe3C前，使F、Fe3C長大。 （c）Diffusion of C in ferrite 鐵素體中C的擴散 如圖，因為CF/ACF/Fe3C ，這就造成F內部的碳的擴散，使F前沿碳濃度下降，有利于F長大，F(xiàn)e3C長大。,The self-diffusion of iron atoms 鐵原子的自擴散 Pearlite transformati

31、on, the crystal lattice reorganization is completed by the diffusion of iron atoms. 綜上所述，珠光體轉變時珠光體團的形成是鐵素體與滲碳體橫向沿奧氏體晶界或沿已形成的珠光體團界交替形核、縱向長大的結果。,Pearlite transformation process,(2) The formation mechanism of granular pearlite 粒狀珠光體的形成機制,Is obtained by spheroidizing the cementite in the lamellar pearli

32、te,lamellar P to granular P process: The Fe3C in the pearlite is likely to spontaneously break and spheroidize during heating. Lamellar pearlite (lamellar P + network Fe3C) Fe3C fracture the role of interfacial tension, Fe3C spherulite granular pearlite 片狀珠光體（片狀P 網(wǎng)狀Fe3C） Fe3C斷裂 界面張力的作用， Fe3C球化 粒狀珠光體

33、,片狀P,粒狀P,Spheroidizing annealing球化退火,片狀P,A未溶Fe3C,A粒狀Fe3C,粒狀P,Spheroidizing conditions: heating: A low temperature, short holding time When cooling: P high temperature, long holding time 球化條件： 加熱時：A化溫度低，保溫時間短 冷卻時：P化溫度高，保溫時間長,(2) The formation mechanism of granular pearlite 粒狀珠光體的形成機制,Pearlite spheroi

34、dization process珠光體球化過程,A1,C,T,T1,Pseudo eutopic transformation: 偽共析轉變： In the case of rapid cooling, the A of the non-eutectoid composition is supercooled into the SEG zone and can be decomposed directly into the mixture of F+Cm without precipitating the first eutectoid phase. The decomposition mec

35、hanism and the decomposition product are exactly the same as the eutectoid transformation. Called pseudo eutectoid transformation, the transformation of products as pseudo eutectomics.,(3) The pearlite transformation of the hypo-(hyper-)eutectic steel 亞（過）共析鋼的珠光體轉變,G,S,E,E,G,快速冷卻時，非共析成分的A被過冷到SEG區(qū)后，可

36、以不析出先共析相而直接分解為FCm的混合物，分解機制和分解產物與共析轉變完全相同，這一轉變稱為偽共析轉變，轉變產物為“偽共析組織”。,Proeutectoid ferrite 先共析F析出：,A precipitates the proeutectoid F in the area enclosed by SE and GS.,A1,C%,T,G,S,E,E,G,偽共析,先析F,Proeutectoid cementite先共析滲碳體析出：,After the proeutectoid transformation is completed, the remaining A in SE - S

37、G undergoes pseudo eutectoid transformation 先共析轉變完成后，在SE SG內剩余A發(fā)生偽共析轉變,A precipitates the proeutectoid Fe3C in the area enclosed by SE and GS.,P,P,P,Fe3C+P,P,F+P,(3) The pearlite transformation of the hypo-(hyper-)eutectic steel 亞（過）共析鋼的珠光體轉變,Pseudo-eutectoid transformation application: 1) to speed

38、up the cold speed, improve the pseudo-P content, will help improve the strength of low-carbon steel. 2) Inhibition of the network cementite in hypereutectoid steel by rapid cooling.,The faster the cooling rate, the lower the transition temperature, The proeutectoid phase less, P pseudo more.,冷速越快，轉變

39、溫度越低， 先析相越少，P偽越多。,The morphology of proeutectoid F of hypoeutectoid steel 亞共析鋼先共析F的形態(tài),The morphology of proeutectoid Fe3C of hypereutectoid steel 過共析鋼先共析Fe3C的形態(tài),網(wǎng)狀 片狀,等軸狀（塊狀）,網(wǎng)狀,片狀,A晶粒細小，轉變溫度較高（或慢冷）,A晶粒粗大，轉變溫度較低（或快冷）,A晶粒粗大，冷速適中,Widmanstatten structure 魏氏組織 片（針）狀F（或Fe3C）P Significantly reduce the mec

40、hanical properties of steel, especially plasticity and toughness. Must be eliminated. 顯著降低鋼的力學性能，特別是塑韌性， 必須消除 Normalizing, annealing or forging with fine grain 采用細化晶粒的正火，退火或鍛造,必須消除,網(wǎng) 狀 鐵 素 體,網(wǎng) 狀 滲 碳 體,片 狀 鐵 素 體,片 狀 滲 碳 體,A large needle - like Widmanstatten ferrite structure in the heat - affected zo

41、ne of a low carbon steel gas welding某低碳鋼氣焊熱影響區(qū)過熱段出現(xiàn)的粗大針狀魏氏鐵素體組織,Widmanstatten cementite structure 魏氏滲碳體組織,6.2.3.Pearlite transformation kinetics (isothermal) 珠光體轉變動力學（等溫） 1.The effect of transition temperature on pearlite nucleation and growth 轉變溫度對珠光體形核與長大影響,Nucleation rate and growth rate with T ,

42、 the first after . 形核率和長大速度隨T ，先后。 the reason: (1) T , T , driving force(驅動力) Gv , favorable P - nucleation and growth; (2) T , T , A concentration gradient (濃度梯度), P -layer spacing , Favorable P - nucleation and growth; (3) T , T , atomic activity(原子活動能力), unfavorable nucleation. The above three to

43、gether, the curve appears extreme value. 以上三者共同作用，曲線出現(xiàn)極值。,2.The transformation time on the pearlite nucleation and growth 轉變時間對珠光體形核與長大影響,t 時間(S),0,當溫度T一定，形核率隨t ，先后。 長大速度基本為定值，轉變時間沒有明顯影響,The amount P transformation P轉變量,100,6.2.3.Pearlite transformation kinetics (isothermal) 珠光體轉變動力學（等溫）,At a certai

44、n temperature, the nucleation rate with t , the first after .,the growth rate is basically fixed, t has no obvious effect,3. Pearlite transformation kinetics map珠光體轉變動力學圖,550 ,T1T2T3T4,6.2.3.Pearlite transformation kinetics (isothermal)珠光體轉變動力學,550,650,Compared with eutectoid steel, the C curve of t

45、he eutectoid steel has increased one precipitate of the first eutectoid phase. The stability of the supercooled A is reduced by the precipitation of the first phase, and the C curve is shifted to the left. 與共析鋼相比，亞（過）共析鋼的C曲線上都多出一條先共析相的析出線，由于先析相的析出，降低了過冷A的穩(wěn)定性，C曲線左移。,TTT of Hypo(hyper)-eutectoid Steel 亞（過）共析鋼的TTT圖,亞共析鋼,過共析鋼,3. Pearlite transformation kinetics map珠光體轉變動力學圖,6.2.3.Pearlite transformation kinetics (isothermal)珠光體轉變動力學,（1）Carbon content Eutectoid composition of the C curve of the most right (eutectoid A most stable), 共析成分的C曲線最靠右（共