中碳合金鋼高溫相變的晶體學(xué)分析
發(fā)布時(shí)間：2018-09-12 18:01
【摘要】：本文主要研究50Si2Mn3鋼在不同強(qiáng)度磁場(chǎng)的作用下于高溫等溫相變過程中的晶體學(xué)特征及擴(kuò)散型相變的磁誘發(fā)作用機(jī)制。從形核長(zhǎng)大和晶體學(xué)等角度分析了中碳硅錳鑄鋼在不同強(qiáng)度磁場(chǎng)作用下的晶體取向特征,并研究了不同磁場(chǎng)強(qiáng)度對(duì)磁誘發(fā)珠光體(MIP)相變開始點(diǎn)及可誘發(fā)出珠光體組織的最高溫度,建立了相變起始點(diǎn)與磁場(chǎng)場(chǎng)強(qiáng)-相變溫度-相變時(shí)間的關(guān)系曲線。具體研究?jī)?nèi)容與結(jié)果如下：12 T,973 K不同磁處理時(shí)間作用下MIP的形核與生長(zhǎng)研究表明：低轉(zhuǎn)變量的相變初期,組成相之一的珠光體鐵素體相(PF)主要沿著110//ND方向生長(zhǎng),111//ND和100//ND等其他位向所占比例相對(duì)較低,表現(xiàn)出一定的擇優(yōu)形核與生長(zhǎng)；隨著轉(zhuǎn)變量的增加,初期成核的PF維持其擇優(yōu)晶向長(zhǎng)大,新生相的晶體學(xué)位向除受到界面能、體積自由能以及磁自由能等的綜合影響外,還將受到母相中逐漸累積的彈性應(yīng)變能的限制,空間取向趨于多向化,表現(xiàn)為中后期形成的MIP的擇優(yōu)生長(zhǎng)趨勢(shì)變?nèi)?其他取向的MIP相對(duì)比例也有所降低,失去了110//ND的擇優(yōu)性；將100%轉(zhuǎn)變量的試樣繼續(xù)延長(zhǎng)磁處理時(shí)間,表現(xiàn)為無(wú)微織構(gòu)特征。更高磁場(chǎng)下的研究重點(diǎn)考察：鐵磁性PF在晶體生長(zhǎng)中是否可能呈現(xiàn)體心立方結(jié)構(gòu)(BCC)鐵001易磁化方向的擇優(yōu)性或仍延續(xù)12T的生長(zhǎng)規(guī)律。20 T場(chǎng)強(qiáng)是綜合樣品大小、等溫爐爐膛尺寸、磁體有效內(nèi)腔及實(shí)驗(yàn)操控等各因素所能采用的最高磁場(chǎng)強(qiáng)度,實(shí)際所用場(chǎng)強(qiáng)為19.8 T。19.8 T磁場(chǎng)作用下的MIP在組織演變過程中的晶體取向變化研究表明：MIP在形成過程中存在著與等溫溫度、受磁時(shí)間密切相關(guān)的晶體取向變化。在臨界點(diǎn)(963 K)以上相對(duì)較低的等溫溫度(983 K)下,MIP晶體的某一特定晶向(100)在轉(zhuǎn)變量范圍內(nèi)呈現(xiàn)出隨受磁時(shí)間延長(zhǎng)而增強(qiáng)的趨勢(shì);而在相對(duì)較高的等溫溫度(995 K)下,隨受磁時(shí)間的延長(zhǎng)100晶向所占的份額則表現(xiàn)為逐漸減弱；相同的受磁時(shí)間下,相變溫度越高,初期生長(zhǎng)的MIP晶體中的100取向的相對(duì)份額越高；因此,MIP的擇優(yōu)取向100與PF的生長(zhǎng)速度相關(guān),且主要于MIP的形成初期較強(qiáng),當(dāng)MIP達(dá)到一定轉(zhuǎn)變量后晶體中的其他晶向(如110)轉(zhuǎn)而呈現(xiàn)生長(zhǎng)優(yōu)勢(shì),甚至在難磁化方向也出現(xiàn)生長(zhǎng)速度相對(duì)增快的趨勢(shì)。根據(jù)不同磁處理?xiàng)l件下MIP的轉(zhuǎn)變量,研究了其相變開始點(diǎn)(產(chǎn)生1%MIP)及可誘發(fā)出珠光體組織的最高溫度(在所采用的等溫時(shí)間范圍內(nèi),意味著此溫度以上將觀察不到珠光體組織),建立了相變起始點(diǎn)與磁場(chǎng)場(chǎng)強(qiáng)-相變溫度-相變時(shí)間的關(guān)系曲線。表明磁場(chǎng)對(duì)誘發(fā)珠光體相變最高溫度的影響并不呈線性變化；此外,MIP增量變化及電子背散射衍射技術(shù)(EBSD)取向分析結(jié)果均表明磁場(chǎng)促進(jìn)了易磁化100方向的晶粒于珠光體相變初期的形核與長(zhǎng)大,存在著滲碳體以顆粒狀或短桿狀形態(tài)在塊狀鐵素體內(nèi)部的不連續(xù)析出方式,且后期珠光體轉(zhuǎn)變量的增加主要是來(lái)自于原優(yōu)先形成珠光體的長(zhǎng)大,而非形核量的增加。
[Abstract]:In this paper, the crystallographic characteristics of 50Si2Mn3 steel during high temperature isothermal transformation and the mechanism of magnetic induction of diffusion-type transformation under the action of different magnetic fields are studied.The crystal orientation characteristics of medium carbon silicon manganese cast steel under different magnetic fields are analyzed from the viewpoints of nucleation, growth and crystallography. For the starting point of magnetic induced pearlite (MIP) phase transition and the highest temperature at which pearlite can be induced, the relationship between the starting point of phase transition and magnetic field intensity, phase transition temperature and phase transition time is established. At the beginning of transformation, the pearlite ferrite phase (PF), one of the constituent phases, grows mainly along the direction of 110 / / ND, the proportion of 111 / / ND and 100 / / / ND is relatively low, showing a certain preferred nucleation and growth; with the increase of the amount of transformation, PF maintains its preferred crystal growth at the beginning of nucleation, and the crystallographic degree of the new phase is subjected to the interface energy. Besides the influence of volume free energy and magnetic free energy, the spatial orientation tends to be multi-directional due to the gradually accumulated elastic strain energy in the parent phase. The preferential growth trend of MIP formed in the middle and late stages is weakened, and the relative proportion of MIP with other orientations is also reduced, thus losing the preference of 110//ND. The magnetic treatment time of the samples was prolonged and the samples were characterized by non-microtexture. The research focus of higher magnetic field was to investigate whether the ferromagnetic PF could show the preferred magnetization direction of BCC Fe 001 or continue the growth rule of 12T. The field strength of 20T was the comprehensive sample size, the size of the furnace, and the magnet had the same magnetism. The crystal orientation of MIP under the magnetic field of 19.8 T.19.8 T shows that there are crystal orientation changes closely related to the isothermal temperature and magnetic time during the formation of MIP. At a relatively low isothermal temperature (983 K), a specific orientation (100) of MIP crystals tends to increase with the extension of the magnetization time in the range of transformation, while at a relatively high isothermal temperature (995 K), the fraction of 100 orientations decreases with the extension of the magnetization time. Therefore, the preferred orientation 100 of MIP is related to the growth rate of PF, and is mainly stronger in the early stage of MIP formation. When the MIP reaches a certain amount of transformation, other crystal orientations (such as 110) turn to show growth advantage, even in the direction of difficult magnetization, the growth rate of MIP also appears. The starting point of phase transition (producing 1% MIP) and the highest temperature of induced pearlite structure (in the range of isothermal time, which means that no pearlite structure can be observed above this temperature) are studied according to the transformation amount of MIP under different magnetic treatment conditions. The starting point of phase transition and the magnetic field intensity-phase transition temperature are established. The results show that the effect of magnetic field on the maximum temperature of pearlite transformation is not linear. In addition, the results of MIP incremental change and electron backscatter diffraction (EBSD) orientation analysis show that magnetic field promotes the nucleation and growth of easily magnetized 100-direction grains at the initial stage of pearlite transformation, and cementite exists. In the latter stage, the increase of pearlite transformation is mainly due to the growth of the primary pearlite rather than the increase of nucleation.
【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG142.1
本文編號(hào)：2239813
[Abstract]:In this paper, the crystallographic characteristics of 50Si2Mn3 steel during high temperature isothermal transformation and the mechanism of magnetic induction of diffusion-type transformation under the action of different magnetic fields are studied.The crystal orientation characteristics of medium carbon silicon manganese cast steel under different magnetic fields are analyzed from the viewpoints of nucleation, growth and crystallography. For the starting point of magnetic induced pearlite (MIP) phase transition and the highest temperature at which pearlite can be induced, the relationship between the starting point of phase transition and magnetic field intensity, phase transition temperature and phase transition time is established. At the beginning of transformation, the pearlite ferrite phase (PF), one of the constituent phases, grows mainly along the direction of 110 / / ND, the proportion of 111 / / ND and 100 / / / ND is relatively low, showing a certain preferred nucleation and growth; with the increase of the amount of transformation, PF maintains its preferred crystal growth at the beginning of nucleation, and the crystallographic degree of the new phase is subjected to the interface energy. Besides the influence of volume free energy and magnetic free energy, the spatial orientation tends to be multi-directional due to the gradually accumulated elastic strain energy in the parent phase. The preferential growth trend of MIP formed in the middle and late stages is weakened, and the relative proportion of MIP with other orientations is also reduced, thus losing the preference of 110//ND. The magnetic treatment time of the samples was prolonged and the samples were characterized by non-microtexture. The research focus of higher magnetic field was to investigate whether the ferromagnetic PF could show the preferred magnetization direction of BCC Fe 001 or continue the growth rule of 12T. The field strength of 20T was the comprehensive sample size, the size of the furnace, and the magnet had the same magnetism. The crystal orientation of MIP under the magnetic field of 19.8 T.19.8 T shows that there are crystal orientation changes closely related to the isothermal temperature and magnetic time during the formation of MIP. At a relatively low isothermal temperature (983 K), a specific orientation (100) of MIP crystals tends to increase with the extension of the magnetization time in the range of transformation, while at a relatively high isothermal temperature (995 K), the fraction of 100 orientations decreases with the extension of the magnetization time. Therefore, the preferred orientation 100 of MIP is related to the growth rate of PF, and is mainly stronger in the early stage of MIP formation. When the MIP reaches a certain amount of transformation, other crystal orientations (such as 110) turn to show growth advantage, even in the direction of difficult magnetization, the growth rate of MIP also appears. The starting point of phase transition (producing 1% MIP) and the highest temperature of induced pearlite structure (in the range of isothermal time, which means that no pearlite structure can be observed above this temperature) are studied according to the transformation amount of MIP under different magnetic treatment conditions. The starting point of phase transition and the magnetic field intensity-phase transition temperature are established. The results show that the effect of magnetic field on the maximum temperature of pearlite transformation is not linear. In addition, the results of MIP incremental change and electron backscatter diffraction (EBSD) orientation analysis show that magnetic field promotes the nucleation and growth of easily magnetized 100-direction grains at the initial stage of pearlite transformation, and cementite exists. In the latter stage, the increase of pearlite transformation is mainly due to the growth of the primary pearlite rather than the increase of nucleation.
【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG142.1
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