本文選題：過(guò)共晶高鉻鑄鐵 + 脈沖電流��； 參考：《昆明理工大學(xué)》2017年碩士論文

【摘要】：因?yàn)檫^(guò)共晶高鉻鑄鐵中有大量的M7C3型初生碳化物和共晶碳化物存在,材料具有很高的硬度,在耐磨領(lǐng)悟具有很好的應(yīng)用潛質(zhì)。但由于常規(guī)鑄態(tài)下M7C3型初生碳化物尺寸粗大,對(duì)基體的割裂作用明顯,增加了材料的脆性,造成過(guò)共晶高鉻鑄鐵的實(shí)際應(yīng)用受到了極大的限制。因此,為了提高過(guò)共晶高鉻鑄鐵的實(shí)際應(yīng)用價(jià)值,只有控制初生碳化物尺寸及形態(tài),降低其對(duì)基體的割裂作用,才能提高材料的韌性并保證其耐磨性。本文將在凝固過(guò)程及凝固后的熱處理過(guò)程中過(guò)共晶高鉻鑄鐵施加脈沖電流,然后通過(guò)LOM、SEM、EDS、TEM、XRD等手段研究其組織,分析脈沖電流的作用機(jī)理,并對(duì)比常規(guī)鑄態(tài)和脈沖處理后過(guò)共晶高鉻鑄鐵的性能。研究發(fā)現(xiàn),在凝固過(guò)程中施加脈沖電流(Electric Current Pulse,ECP),可以顯著細(xì)化初生碳化物尺寸,減少初生碳化物裂紋、孔洞等缺陷,提高初生碳化物致密度。初生碳化物等效直徑從約150μm減小到約65μm,顯微硬度由HV1398～1420提高到HV 1485～1501。脈沖電流處理后的凝固組織中初生碳化物依舊保持六棱柱形態(tài),但對(duì)基體組織的割裂效果明顯減弱減少,有利于提高其使用性能。脈沖電流細(xì)化初生碳化物的機(jī)理是:在凝固過(guò)程中,脈沖電流對(duì)熔體起到了磁致收縮效應(yīng),提高熔體壓力,進(jìn)而實(shí)現(xiàn)了“電致過(guò)冷”作用,能夠顯著提高熔體中初生碳化物的形核率,細(xì)化初生碳化物;同時(shí),脈沖電流還會(huì)對(duì)熔體產(chǎn)生電遷移作用,使C原子的擴(kuò)散能力得到明顯的提高,增強(qiáng)了C原子向初生碳化物內(nèi)部穿透擴(kuò)散,增加了初生碳化物的含碳量,并使碳C原子固溶到了碳化物密排六方晶格中的四面體間隙中,增加了晶格畸變,提高了固溶強(qiáng)度和致密性,改善初生碳化物性能。但脈沖電流沒(méi)有改變出生碳化物的整體生長(zhǎng)過(guò)程,只是通過(guò)提高C原子的擴(kuò)散能力,維持了碳化物生長(zhǎng)后期的持續(xù)生長(zhǎng)能力,從而減少了內(nèi)部孔洞缺陷。另外,在700℃到1000℃奧氏體化過(guò)程中,在進(jìn)行常規(guī)工藝及脈沖電流處理時(shí),雖然過(guò)共晶高鉻鑄鐵中初生碳化物及共晶碳化物尺寸及形態(tài)均不會(huì)發(fā)生變化,依然維持處理前的狀態(tài),但是脈沖電流能夠降低過(guò)共晶高鉻鑄鐵發(fā)生固態(tài)相變的溫度,并提高相變發(fā)生的程度。在1100℃奧氏體化時(shí),在常規(guī)工藝脈沖處理工藝下,過(guò)共晶高鉻鑄鐵基體組織均轉(zhuǎn)變?yōu)閵W氏體,共晶碳化物大量溶解并粗化;脈沖處理處理工藝下,初生碳化物溶解程度很大,但常規(guī)工藝下,初生碳化物較好保持了處理前的形態(tài)。在700℃時(shí)脈沖電流熱處理時(shí),試樣基體硬度和宏觀硬度最高,分別為HV 958和HRC 82;隨著脈沖電流熱處理溫度從700℃升高到800℃,基體組織顯微硬度和試樣宏觀硬度均降低,在800℃到1000℃范圍內(nèi)出現(xiàn)一個(gè)平臺(tái);在1100℃時(shí)再次下降,分別為HV 390和HRC71。
[Abstract]:Because there are a large number of M7C3 primary carbides and eutectic carbides in hypereutectic high chromium cast iron, the materials have high hardness and have good application potential in wear-resisting comprehension. However, due to the coarse size of M7C3 primary carbides in the conventional cast state, the cleavage effect on the matrix is obvious, and the brittleness of the material is increased, which results in a great limitation on the practical application of hypereutectic high chromium cast iron. Therefore, in order to improve the practical application value of hypereutectic high chromium cast iron, only by controlling the size and morphology of primary carbides and reducing its splitting effect on matrix can the toughness and wear resistance of the materials be improved. In this paper, the hypereutectic high chromium cast iron is applied pulse current during solidification and heat treatment after solidification. Then the structure of hypereutectic high chromium cast iron is studied by means of LOMSEMSEM EDS Tem XRD and the mechanism of pulse current is analyzed. The properties of hypereutectic high chromium cast iron after conventional and pulse treatment were compared. It is found that the application of pulse current in the solidification process can significantly refine the size of primary carbides, reduce the defects of primary carbides, such as cracks and voids, and increase the density of primary carbides. The equivalent diameter of primary carbides decreased from about 150 渭 m to about 65 渭 m, and the microhardness increased from HV1398~1420 to HV 1485 / 1501. The primary carbides in the solidified microstructure after pulse current treatment remain in hexagonal shape, but the cleavage effect of the matrix structure is obviously weakened and reduced, which is beneficial to improve the performance of the solidified structure. The mechanism of refining primary carbides by pulse current is as follows: during solidification, pulse current plays a magnetically induced shrinkage effect on the melt, increases the melt pressure, and realizes the effect of "electrically induced undercooling". The nucleation rate of the primary carbides in the melt can be increased significantly and the primary carbides can be refined. At the same time, the pulse current will also produce the electromigration effect on the melt, and the diffusion ability of the C atoms will be improved obviously. The diffusion of C atoms into the primary carbides is enhanced, the carbon content of the primary carbides is increased, and the carbon C atoms are dissolved into the tetrahedron gaps in the dense hexagonal lattice of the carbides, thus increasing the lattice distortion. The solution strength and densification were improved, and the properties of primary carbides were improved. But the pulse current does not change the whole growth process of the born carbides, only by improving the diffusion ability of the C atoms, it can maintain the growth ability of the carbides in the later stage of growth, thus reducing the defects of the internal pores. In addition, during austenitization from 700 鈩，

本文編號(hào)：1925915