【摘要】：隨著工程中奧氏體鋼與珠光體鋼異質(zhì)材料焊接的廣泛應(yīng)用，異質(zhì)接頭失效的事故也是頻頻的發(fā)生，導(dǎo)致焊接接頭失效的主要原因是珠光體和奧氏體異質(zhì)接頭熔合線兩側(cè)存在碳遷移現(xiàn)象。本文對電廠動力鍋爐系統(tǒng)通過模擬接頭的實際工況制備試件來分析典型的奧氏體與珠光體異質(zhì)接頭，來測定碳遷移情況。分析發(fā)現(xiàn)了在珠光體和奧氏體異質(zhì)接頭中由珠光體鋼一側(cè)的碳元素向奧氏體鋼一側(cè)擴散。為了抑制異質(zhì)接頭中碳遷移的現(xiàn)象，本文選取了A402、A102、Ni317、R307四種常用于異質(zhì)鋼焊接過程中的焊材，制備了焊接試樣，并且將焊接試樣分為焊態(tài)、時效處理、蠕變狀態(tài)三組進行實驗。通過對各試樣進行光學(xué)顯微鏡和掃描電鏡的分析，對各組試樣的組織和碳遷移情況進行對比，發(fā)現(xiàn)了對碳遷移產(chǎn)生影響的因素，，在此基礎(chǔ)上一種抑制碳遷移現(xiàn)象的超低碳新型焊條便誕生了。通過將超低碳新型焊條進行與以上四種常用焊材相同的實驗步驟，得到的實驗結(jié)果與之前四種焊材試樣進行了組織、斷口和碳遷移的比較。結(jié)果表明：影響蠕變斷裂的主要因素是碳遷移，A402、R307、A102焊條所焊試件經(jīng)過蠕變試驗以后，斷裂的位置均發(fā)生在奧氏體與珠光體熔合線附近，通過對斷裂部位的組織及碳分布和斷口進行分析，發(fā)現(xiàn)以上三種試樣在蠕變試驗過程中均存在明顯的碳遷移現(xiàn)象，并且蠕變斷裂的斷口均具有脆性斷裂的特征。發(fā)現(xiàn)在碳遷移層中存在由碳鉻化合物和滲碳體組成的有害硬脆相。但是由Ni317和自主研制的新型超低碳焊條所焊接的試樣幾乎沒有發(fā)生碳遷移現(xiàn)象，并且蠕變斷裂的斷口表現(xiàn)為塑性斷裂的特征，熔合區(qū)部位只存在少量的碳擴散，而這是由于兩側(cè)的碳元素濃度梯度的差異而發(fā)生的。通過對新型超低碳焊條與其它四種焊條所焊的蠕變試樣的比較，發(fā)現(xiàn)新型的超低碳焊條的蠕變斷裂時間要比A402、R307、A102要長，比Ni317的蠕變斷裂時間稍短。由此可知：自行研制的超低碳焊條對碳遷移起到了有效的抑制作用，超過了工程上焊接珠光體和奧氏體異質(zhì)鋼常用焊材的高溫力學(xué)性能，雖然比鎳基材料稍差，但是對于絕大部分工程已經(jīng)可以滿足需要了。由于在價格上比昂貴的鎳基材料要低得多，比常規(guī)的奧氏體焊材的價格還低，性價比高，具有較強的實用性。
[Abstract]:With the wide application of heterogeneous material welding of austenitic steel and pearlite steel in engineering, the failure of heterogeneous joints also occurs frequently. The main reason for the failure of welded joints is the phenomenon of carbon migration on both sides of the fusion line between pearlite and austenite heterogeneity joints. In this paper, the typical austenitic and pearlite heterogeneity joints are analyzed to measure the carbon transport in the power boiler system of power plant by preparing the specimen under the actual working conditions of the simulated joints in order to analyze the typical austenite and pearlite heterojunction. The diffusion of carbon element from the side of the pearlite steel to the side of the austenitic steel was found in the pearlite and austenite heterojunction. In order to restrain carbon migration in heterogeneous joints, four kinds of welding materials, A402, A102 and Ni317R307, which are commonly used in the welding process of heterogeneous steel, are selected in this paper. The welded specimens are prepared, and the welded specimens are divided into three groups: welding state, aging treatment and creep state. Through the analysis of each sample by optical microscope and scanning electron microscope, the structure and carbon migration of each group were compared, and the factors influencing the carbon migration were found. On this basis, a new ultra-low-carbon electrode was born to suppress carbon migration. By using the new ultra-low carbon electrode as the same experimental steps as the above four kinds of common welding materials, the experimental results are compared with those of the previous four kinds of welding materials, such as microstructure, fracture surface and carbon migration. The results show that the main factor affecting creep fracture is that after creep test, the location of fracture occurs near the fusion line between austenite and pearlite. Through the analysis of the structure, carbon distribution and fracture surface of the fracture site, it is found that the above three specimens have obvious carbon migration phenomenon during the creep test, and the fracture surface of the creep fracture has the characteristics of brittle fracture. It is found that there are harmful hard and brittle phases in the carbon transport layer composed of carbochrome compounds and cementites. However, the specimens welded by the new ultra-low carbon electrode developed by Ni317 and developed by ourselves have almost no carbon migration phenomenon, and the fracture surface of creep fracture shows the characteristics of plastic fracture, and there is only a small amount of carbon diffusion in the fusion zone. This is due to differences in carbon concentration gradients on both sides. The creep fracture time of the new ultra low carbon electrode is longer than that of A402C R307 and A102, and is a little shorter than that of Ni317 by comparing the creep specimen of the new ultra low carbon electrode with the other four kinds of electrode. The results show that the creep fracture time of the new type of ultra low carbon electrode is longer than that of the other four kinds of electrode. It can be seen that the ultra-low carbon electrode developed by ourselves has an effective effect on the inhibition of carbon migration, which exceeds the high temperature mechanical properties of the commonly used welding materials of pearlite and austenitic heterogeneity steel in engineering, although it is slightly worse than that of nickel base materials. But for the vast majority of projects can already meet the needs. Because the price is much lower than the expensive nickel base material, the price is lower than the conventional austenitic welding material, the ratio of performance to price is high, and it has strong practicability.
【學(xué)位授予單位】：沈陽工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TG422.1

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