本文選題：低活化馬氏體鋼　切入點：真空擴散焊接　出處：《合肥工業(yè)大學(xué)》2017年碩士論文

【摘要】：低活化馬氏體鋼因具有較高的熱導(dǎo)率、較低的輻照腫脹和熱膨脹系數(shù)等優(yōu)良的熱物理性能,被普遍認為是未來聚變示范堆和聚變動力堆的首選結(jié)構(gòu)材料。聚變堆包層模塊(TBM)的結(jié)構(gòu)復(fù)雜、體積龐大、服役環(huán)境較為惡劣,各部件之間需要采用焊接等方法實現(xiàn)穩(wěn)固連接。低活化馬氏體鋼中合金元素含量相對較高,對焊接技術(shù)要求較為苛刻,而傳統(tǒng)熔化焊過程中存在液-固相高溫熱循環(huán)及焊縫區(qū)域的非平衡凝固,通常會引起焊接接頭的組織及性能退化,成為結(jié)構(gòu)的薄弱環(huán)節(jié),從而影響聚變堆的安全可靠運行。以擴散連接為代表的固態(tài)連接技術(shù)因其具有焊接溫度低于母材熔點、尺寸裝配精度高等優(yōu)點,有望取代傳統(tǒng)熔焊工藝并于聚變實驗堆包層模塊的制造領(lǐng)域發(fā)揮重要作用。本文在不同焊接工藝條件(焊接溫度、焊接壓力及保溫時間)下對低活化馬氏體鋼進行真空擴散焊接試驗,通過對擴散焊接試樣進行光學(xué)顯微觀察(OM)、掃描電鏡觀察(SEM)、能譜測試(EDS)以及X射線衍射(XRD)觀測,分析焊縫區(qū)的相組成和組織形態(tài)、加熱及保溫過程中金屬的組織演化規(guī)律等;通過對焊接件進行拉伸及沖擊試驗,比較熱處理前、后焊件力學(xué)性能差異,探究不同工藝參數(shù)對微觀組織和力學(xué)性能的影響規(guī)律,從而對低活化馬氏體鋼的擴散焊接進行工藝優(yōu)化。試驗結(jié)果表明,低活化馬氏體鋼的原始母材顯微組織主要為板條馬氏體,在真空擴散焊接的加熱及保溫過程中,低活化馬氏體鋼會發(fā)生再結(jié)晶及奧氏體化現(xiàn)象。當焊接溫度較高或保溫時間較長時,均會促進奧氏體生長,而粗大的奧氏體晶粒會對擴散焊接接頭的力學(xué)性能帶來損害;保溫時間結(jié)束焊接試樣冷卻至室溫后,焊縫區(qū)顯微組織為馬氏體、殘余奧氏體及數(shù)量較多尺寸較小的析出碳化物;而經(jīng)過焊后熱處理后,殘余奧氏體組織基本消失不見。在焊接溫度為950~1100℃范圍時,隨著焊接溫度的升高,焊件的拉伸強度隨之提高,在1050℃時達到最高值973MPa;當焊接溫度繼續(xù)升高到1100℃時,焊件的拉伸強度則有所下降。在保溫時間為90~180min范圍時,焊件的拉伸強度一直隨著保溫時間的延長而增加,但當保溫時間超過150min后,接頭的抗拉強度基本沒有增強,開始趨于平緩。在10~20MPa的焊接壓力下,焊接件的抗拉強度一直隨焊接壓力提升而穩(wěn)步提高。但限于低活化馬氏體鋼在高溫下的屈服強度,試驗時沒有繼續(xù)選用更高的焊接壓力進行擴散焊接。提高焊接溫度可以通過激活更多原子進行無規(guī)則的擴散遷移提升擴散效果,從而一定程度上提高焊件的拉伸強度;但較高的焊接溫度同樣會促進奧氏體晶粒的吞并、長大,而粗大的奧氏體晶粒冷卻轉(zhuǎn)變后得到的粗晶粒組織會降低焊件的抗拉強度。因此,當達到1050℃時,焊件的抗拉強度會隨著焊接溫度的升高而降低。同樣,保溫時間的延長為良好的擴散效果提供了必要的條件,但當保溫時間過長時,雖然活躍態(tài)原子擴散越充分,但由于粗大的奧氏體晶粒,其抗拉強度反而無明顯提升。而當焊接壓力越大時,焊接面的微觀凸起塑性變形程度越大,焊接面之間實際接觸面積便越大,從而使焊接面附近激活態(tài)原子獲得足夠的擴散通道通過無規(guī)則遷移及跨越界面進行固態(tài)自擴散,使得焊接面結(jié)合狀況更為優(yōu)良。焊件的沖擊韌性主要取決于擴散焊接結(jié)束時焊縫區(qū)的晶粒尺寸,當奧氏體晶粒隨著焊接溫度的升高及保溫時間的延長而越來越大時,焊縫區(qū)的金屬的沖擊韌性則越來越差。
[Abstract]:Because of low activation martensitic steel with high thermal conductivity, excellent thermal physical properties such as coefficient of low irradiation swelling and thermal expansion, is widely regarded as the future fusion demonstration reactor and fusion power reactor. The primary structural materials for fusion reactor blanket module (TBM) complex structure, large volume, harsh service environment between the various components, need to adopt the welding method to achieve stable connection. Low activation martensitic steel alloy element content is relatively high, the more demanding of the welding technical requirements, and the traditional fusion welding process in the presence of liquid - solid heat cycle and the welded zone of non-equilibrium solidification, usually caused by degradation of microstructure and properties of welded joints and become a weak link structure, thus affecting the safe and reliable operation. The fusion reactor as the representative of the solid diffusion bonding connection technology because of its welding temperature is lower than the base metal melting point, high precision assembly size The advantages, play an important role in the field of manufacturing is expected to replace the traditional welding process and blanket module in fusion experiments. In this paper, the welding process in different conditions (welding temperature, welding pressure and holding time) on the low activation martensitic steel welding test of vacuum diffusion, through the sample of diffusion welding of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X ray diffraction (XRD) observation, analysis of weld zone of the phase composition and microstructure, metal heating and heat preservation in the process of microstructure evolution; through tensile and impact test of welding, heat treatment, welding parts the mechanical properties of differences, explore the different influences of process parameters on the microstructure and mechanical properties, diffusion and low activation martensitic steel for welding process optimization. The experimental results show that the original parent material of low activation martensitic steel The microstructure is mainly lath martensite, in vacuum diffusion welding of heating and heat preservation process, low activation martensitic steel and austenitic recrystallization occur phenomenon. When the welding high temperature or holding time is long, will promote the growth of austenite, the mechanical properties of coarse austenite grain will bring on diffusion welded joint damage; holding time end welding specimen after cooling to room temperature, the weld zone microstructure is martensite, residual austenite and carbide precipitates a large number of small size; and after post weld heat treatment, the residual austenite organization basically disappeared. In the welding temperature of 950~1100 range, with the increase of welding temperature, tensile the strength of welds increased, reached the highest value of 973MPa at 1050 DEG C; when the welding temperature continues to rise to 1100 DEG, the tensile strength of weld is decreased. The holding time is 90~18 The range of 0min, the tensile strength of welding has been increased with the prolongation of holding time, but when the holding time is more than 150min, the tensile strength and no enhancement, began to flatten. In the welding pressure of 10~20MPa, the tensile strength of the welded samples with the welding pressure ascension has been improved steadily. But due to the limited yield strength low activation martensitic steel under high temperature, do not continue to use higher welding pressure diffusion welding test. The welding temperature can be activated by more atomic diffusion of irregular migration to enhance the diffusion effect, from a certain extent and increase the tensile strength of welding; welding high temperature but will also promote the annexation. The austenite grain growth, and coarse grain organization to obtain the coarse austenite grain cooling transformation will reduce the tensile strength after welding. Therefore, when reached 1050 degrees, the welding tensile strength The strength will decrease with the increase of the welding temperature. Similarly, the longer holding time for good diffusion provides the necessary conditions, but when the holding time is too long, although active atom diffusion more fully, but because of coarse austenite, the tensile strength but no obvious improvement. When the welding pressure is greater the micro convex welding, plastic deformation degree, the welding surface between the actual contact area is large, so that the welding surface near the activated diffusion channels obtained by enough irregular migration and self diffusion of solid state across the interface, the welding surface combined with the status of more excellent. The impact toughness of weld depends the grain size of the weld zone of diffusion welding at the end, when the austenite grain increased with prolonging holding time and welding temperature is more and more big, the weld metal impact toughness It's getting worse and worse.

【學(xué)位授予單位】：合肥工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG457.11

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