【摘要】：摻雜鎢具有熔點(diǎn)高、膨脹系數(shù)低和良好的高溫抗下垂性能等優(yōu)點(diǎn),被廣泛用作于照明、氣體放電光源以及電子管的陰極材料。通過熱變形方法,獲得組織與性能優(yōu)異的細(xì)晶摻雜鎢棒是制備摻雜鎢絲的重要步驟,傳統(tǒng)的旋鍛工藝雖能獲得較大變形量,但加工后的組織不均勻且耗能較大;三輥軋機(jī)軋制摻雜鎢棒材,軋件咬入能力較弱,且結(jié)構(gòu)復(fù)雜,維護(hù)較為繁瑣。本文通過高速連軋機(jī),采用一火次十道連軋的連軋工藝,將直徑為18.5mm的摻雜鎢燒結(jié)棒連軋為直徑9mm的摻雜鎢桿,研究了摻雜鎢棒的顯微組織及連軋過程的應(yīng)力和應(yīng)變場(chǎng)。利用金相顯微鏡、掃描電子顯微鏡等方法觀察了四道、六道、十道次連軋后摻雜鎢棒材橫截面的組織。結(jié)果發(fā)現(xiàn):摻雜鎢棒材連軋后,顯微組織顯著細(xì)化,道次越多,晶粒細(xì)化越顯著。經(jīng)過十道次連軋后,晶粒平均直徑約為3~5μm,燒結(jié)孔被壓縮甚至閉合,摻雜鎢棒橫截面邊緣區(qū)域晶粒比中心區(qū)域更加細(xì)小。部分連軋后的摻雜鎢棒出現(xiàn)了區(qū)域性的晶粒異常長(zhǎng)大,其內(nèi)部鉀泡及鉀管較多。隨著連軋道次的增加,摻雜鎢棒的顯微硬度明顯提高。通過Abaqus軟件對(duì)摻雜鎢棒的四道次、六道次、十道次連軋過程進(jìn)行有限元模擬,對(duì)模擬后的軋件網(wǎng)格變形、溫度場(chǎng)、應(yīng)力場(chǎng)、應(yīng)變場(chǎng)以及軋制力進(jìn)行了分析。結(jié)果表明,連軋過程中摻雜鎢棒橫截面上心部溫度最高,表面溫度最低。在變形區(qū)內(nèi),軋件表面的等效應(yīng)力和殘余等效應(yīng)力最大,向心部遞減,中心處的等效應(yīng)力和殘余等效應(yīng)力最小;四道次、六道次連軋的軋件心部等效應(yīng)變最大,向表面遞減,經(jīng)過十道次連軋后,軋件等效應(yīng)變的分布為表面最高,心部最低。殘余等效應(yīng)變從軋件表面向中心逐漸減小,最小值出現(xiàn)在約2/5R處,其后又逐漸增大。殘余等效應(yīng)變最小值出現(xiàn)的區(qū)域,與部分連軋后摻雜鎢棒的晶粒異常長(zhǎng)大區(qū)域相符,是導(dǎo)致?lián)诫s鎢棒晶粒異常長(zhǎng)大的主要原因。隨著連軋道次的增加,各道次穩(wěn)態(tài)軋制階段的軋制力波動(dòng)逐漸變大,說明軋制的穩(wěn)定性降低。通過對(duì)不同初軋溫度和摩擦系數(shù)下殘余應(yīng)力、殘余應(yīng)變及軋制力的變化分析,發(fā)現(xiàn)隨著初軋溫度和初軋速度的升高,十道次連軋的軋制力和軋件的殘余應(yīng)力逐漸降低,殘余應(yīng)變?cè)黾?殘余應(yīng)力、殘余應(yīng)變和軋制力均隨著摩擦系數(shù)的增大而增大。
[Abstract]:Doped tungsten has many advantages such as high melting point, low expansion coefficient and good sag resistance at high temperature. It is widely used as cathode material for lighting, gas discharge light source and electron tube. By hot deformation method, it is an important step to obtain fine doped tungsten rod with excellent microstructure and properties. Although the traditional rotary forging process can obtain a large amount of deformation, the microstructure after processing is not uniform and energy consumption is large. The rolling of Tungsten bar by three high rolling mill has weak bite ability, complex structure and complicated maintenance. In this paper, the microstructures and stress and strain fields of doped tungsten bars with diameter 18.5mm are studied by using the continuous rolling process of a high speed continuous rolling mill with ten passes. The doped tungsten sintered bar with diameter 18.5mm has been continuously rolled into doped tungsten rods with diameter 9mm. The microstructures of the doped tungsten bars and the stress and strain fields in the continuous rolling process have been studied in this paper. The microstructure of four, six and ten passes of doped tungsten bar cross section was observed by metallographic microscope and scanning electron microscope (SEM). The results show that after continuous rolling of doped tungsten bar, the microstructure is significantly refined, and the more passes, the more the grain refinement. After ten times of continuous rolling, the average diameter of the grain is about 3 ~ 5 渭 m, the sintered hole is compressed or even closed, and the grain size in the edge of cross section of doped tungsten rod is smaller than that in the center region. After partial continuous rolling, regional grain growth occurs in the doped tungsten rods, and there are more potassium bubbles and potassium tubes in the interiors. The microhardness of doped tungsten rod increases with the increase of continuous rolling pass. The four, six and ten passes continuous rolling process of doped tungsten rod was simulated by Abaqus software. The mesh deformation, temperature field, stress field, strain field and rolling force were analyzed. The results show that the temperature of the top center of the cross section of doped tungsten rod is the highest and the surface temperature is the lowest during the continuous rolling process. In the deformation zone, the equivalent stress and residual equivalent stress on the surface of the rolling piece are the largest, the concentric part decreases, the equivalent stress and the residual equivalent stress at the center are the smallest, and the equivalent strain in the center of the workpiece with four passes and six passes continuous rolling is the largest and decreases to the surface. After ten times of continuous rolling, the distribution of equivalent strain is the highest on the surface and the lowest at the center. The residual equivalent strain decreases gradually from the surface to the center of the workpiece, and the minimum appears at about 2 / 5R, and then increases gradually. The region where the minimum value of residual equivalent strain appears is consistent with the abnormal grain growth region of the doped tungsten rod after continuous rolling, which is the main reason for the abnormal growth of the doped tungsten rod grain. With the increase of continuous rolling pass, the rolling force fluctuates gradually in each pass steady state rolling stage, which indicates that the rolling stability is decreased. By analyzing the variation of residual stress, residual strain and rolling force at different temperature and friction coefficient, it is found that the rolling force and the residual stress of the rolling piece decrease gradually with the increase of the temperature and speed of the first rolling. The residual strain, residual stress, residual strain and rolling force increase with the increase of friction coefficient.
【學(xué)位授予單位】：煙臺(tái)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG146.411;TG335.9

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