本文選題：臨界區(qū)淬火 + 馬氏體演化��； 參考：《安徽工業(yè)大學》2017年碩士論文

【摘要】：本文以低碳、微合金鋼為基礎,結合組織調控思路利用熱處理工藝匹配材料固態(tài)相變組織,充分發(fā)揮雙相物理冶金結合組織組成(F及回火M)的各自力學性能優(yōu)勢,期冀獲得具有高強塑積為特征的重載汽車大梁鋼。針對設計低碳、微合金成分材料,本文研究內容如下。(1)利用Gleeble3500研究了試驗鋼過冷奧氏體連續(xù)相變轉變。試樣鋼加熱過程靜態(tài)轉變相變點分別為AC1=731.84℃、AC3=873.85℃。過冷奧氏體連續(xù)轉變大致分為:F+P轉變、B轉變、M轉變,其中B轉變有著寬泛的冷速區(qū)間(3-20℃/s)。冷速為0.05-1℃/s時,試驗鋼相轉變組織為F+P;冷速在3-10℃/s范圍時,過冷奧氏體主要發(fā)生B轉變,在5℃/s的冷速下得到典型的粒狀貝氏體(GB),并于此冷速范圍內,B形貌依據冷速的提高,逐漸由單一GB過渡到GB與LB(板條貝氏體)共存;冷速處于10℃/s~20℃/s范圍時,相變組織構成為少量GB、LB和LM(板條馬氏體);冷速≥30℃/s試驗鋼過冷奧氏體得到全部的LM組織。(2)IQ(Inter-critical Quenching,直接臨界兩相區(qū)淬火)及IQ'(固溶處理后迅速冷卻至不同臨界區(qū)溫度保溫一定時間后淬火)工藝條件下,不同臨界兩相區(qū)溫度對試驗鋼馬氏體及鐵素體兩相形貌演化的影響:a)IQ工藝臨界兩相區(qū)溫度不僅與試驗鋼M相含量有關并且影響此溫度下形成的馬氏體的C、Mn等元素合金含量進而影響M的形態(tài)。M體積分數隨著IQ溫度升高而升高,800℃以下時M大體呈島狀分布于F基體,800℃及以上淬火時M開始成為基體相并且部分開始具有明顯板條狀形貌。b)IQ'工藝下,試驗鋼在較低的臨界區(qū)溫度(≤780℃)馬氏體及鐵素體交替分布并且呈現出明顯帶狀組織特征(F晶粒呈多邊形特征),在較高的臨界區(qū)溫度下馬氏體與鐵素體呈彌散分布組織特征(鐵素體晶粒由多邊形部分轉變?yōu)槠瑺钚蚊?。(3)經受IQ(760、780、800、810、820℃,1 h)+T(Temper:520℃,1 h)工藝試樣的拉伸試驗表明:Ys及Ts隨著IQ溫度增加而升高,硬質相M成為基體相時,強化作用明顯;比例延伸隨著IQ溫度的升高而降低,軟質相F成為次組成相時,比例延伸A5下降明顯;屈強比與IQ溫度的關系比較復雜出現“谷底”,在IQ溫度為800℃時獲得最低的屈強比(0.835)及符合指標強度(YS-568 MPa,TS-680 MPa)。目前,IQ+T組織調控工藝已成功應用于南鋼工業(yè)化大生產。(4)對基于IQ+T工藝工業(yè)化大生產的20 mm成品板材的不同焊接熱輸入的CGHAZ(TH=1320℃,t8/5=10、20、30、60、120 s)沖擊及硬度試驗表明:a)CGHAZ不存在軟化現象;b)撇除晶粒尺寸對沖擊韌性的影響外,較短t8/5時間(≤20s)形成的位向不同的板條馬氏體束(或貝氏體束)或島狀相呈彌散分布的粒狀貝氏體,在裂紋擴展過程中板條束與原奧晶界可使裂紋在擴展過程中產生偏移(或偏向),損耗部分沖擊勢能,并且島狀相彌散分布對材料的沖擊韌性影響較小;c)t8/5≥30 s時,沖擊韌性劇烈下降,主要原因為島狀相(為可能的馬氏體、貝氏體或M/A組元)粗化將減少與B鐵素體基體界面的接觸,導致塑性α相變形時滑移自由程減少,裂紋擴展容易,沖擊韌性降低。
[Abstract]:In this paper, on the basis of low carbon and microalloy steel, combined with the idea of microstructure regulation, the solid phase transformation of materials is matched by heat treatment technology, and the mechanical properties of the biphasic physical metallurgical structure (F and tempering M) are fully played. The heavy load car beam steel with high strength plasticity is expected to be obtained. The contents of this paper are as follows. (1) the continuous transformation of the supercooled austenite in test steel is studied by Gleeble3500. The static transition phase transition point of the sample steel is AC1=731.84 C and AC3=873.85 C respectively. The continuous transformation of the supercooled austenite is roughly divided into F+P transformation, B transformation, and M transformation, in which the B transformation has a wide cold speed range (3-20). When the cooling rate is 0.05-1 C /s, the transformation structure of the steel phase is F+P, and the supercooled austenite is mainly B transition at 3-10 centigrade /s, and the typical granular bainite (GB) is obtained at the cold speed of 5 C /s, and in this cold speed range, the B morphology is gradually changed from single GB to GB and LB (lath bainite). At the range of 10 C /s~20 C /s, the phase transformation structure consists of a small amount of GB, LB and LM (lath martensite), and the supercooled austenite of the test steel at 30 degrees centigrade at cold speed is all LM tissue. (2) IQ (Inter-critical Quenching, direct critical two-phase quenching) and IQ'(quenching to a certain time after solid solution treatment to a certain time after a certain temperature for a certain time). The influence of different critical two phase region temperature on the evolution of martensite and ferrite morphology in test steel: a) the critical two phase temperature of IQ process is not only related to the M phase content of the test steel, but also affects the C of the martensite formed at this temperature, and the content of Mn and other elements, and then the form.M volume fraction of M increases with the increase of IQ temperature. At the height of 800, M is mostly island shaped in F matrix, and at 800 and above, M begins to become matrix phase and part of which begins to have clear strip shape.B) IQ'process. The test steel is distributed alternately at lower critical zone temperature (less than 780 degrees) and ferrite (F grain is polygonal). Characteristics) the dispersion distribution of martensite and ferrite at high critical temperature (the ferrite grain from polygon to sheet shape). (3) the tensile test of IQ (760780800810820 C, 1 h) +T (Temper:520, 1 h) shows that Ys and Ts increase with the increase of IQ temperature, and the hard phase M becomes the matrix phase When the IQ temperature increases, the proportion extension decreases with the increase of the IQ temperature. When the soft phase F becomes the sub component phase, the proportional extension A5 decreases obviously; the relationship between the ratio of the flexion ratio and the IQ temperature is more complex, and the lowest yield strength ratio (0.835) and the index strength (YS-568 MPa, TS-680 MPa) are obtained at the IQ temperature of 800 and IQ+T MPa, TS-680 MPa. Currently, IQ+T The tissue regulation technology has been successfully applied to the industrial production of Nansteel. (4) the impact and hardness test of different welding heat input of 20 mm finished sheet based on IQ+T process industrial production (TH=1320, t8/5=10,20,30,60120 s) shows that a) CGHAZ does not exist softening appearance; b) is shorter than the effect of grain size on impact toughness. The t8/5 time (less than 20s) forms a granular bainite with diffused distribution of the lath martensitic bundle (or bainite bundle) or the island phase. In the process of crack propagation, the crackle and the original crystal boundary can cause the crack to be offset (or biased) in the process of expansion, loss of partial impact potential energy, and the impact toughness of the island phase dispersion distribution to the material. The impact toughness of C) is less than that of t8/5. The impact toughness decreases sharply when t8/5 > 30 s. The main reason is that the coarsening of the island phase (for possible martensite, bainite or M/A) will reduce the contact with the interface of the B ferrite matrix, which leads to the reduction of the slip free range in the plastic alpha phase deformation, the easy crack propagation and the decrease of the impact toughness.

【學位授予單位】：安徽工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG142.1

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