奥氏体钢和珠光体耐热钢专用焊接材料的研制及性能分析

发布时间：2018-07-24 11:57

【摘要】：随着工程中奥氏体钢与珠光体钢异质材料焊接的广泛应用，异质接头失效的事故也是频频的发生，导致焊接接头失效的主要原因是珠光体和奥氏体异质接头熔合线两侧存在碳迁移现象。本文对电厂动力锅炉系统通过模拟接头的实际工况制备试件来分析典型的奥氏体与珠光体异质接头，来测定碳迁移情况。分析发现了在珠光体和奥氏体异质接头中由珠光体钢一侧的碳元素向奥氏体钢一侧扩散。为了抑制异质接头中碳迁移的现象，本文选取了A402、A102、Ni317、R307四种常用于异质钢焊接过程中的焊材，制备了焊接试样，并且将焊接试样分为焊态、时效处理、蠕变状态三组进行实验。通过对各试样进行光学显微镜和扫描电镜的分析，对各组试样的组织和碳迁移情况进行对比，发现了对碳迁移产生影响的因素，，在此基础上一种抑制碳迁移现象的超低碳新型焊条便诞生了。通过将超低碳新型焊条进行与以上四种常用焊材相同的实验步骤，得到的实验结果与之前四种焊材试样进行了组织、断口和碳迁移的比较。结果表明：影响蠕变断裂的主要因素是碳迁移，A402、R307、A102焊条所焊试件经过蠕变试验以后，断裂的位置均发生在奥氏体与珠光体熔合线附近，通过对断裂部位的组织及碳分布和断口进行分析，发现以上三种试样在蠕变试验过程中均存在明显的碳迁移现象，并且蠕变断裂的断口均具有脆性断裂的特征。发现在碳迁移层中存在由碳铬化合物和渗碳体组成的有害硬脆相。但是由Ni317和自主研制的新型超低碳焊条所焊接的试样几乎没有发生碳迁移现象，并且蠕变断裂的断口表现为塑性断裂的特征，熔合区部位只存在少量的碳扩散，而这是由于两侧的碳元素浓度梯度的差异而发生的。通过对新型超低碳焊条与其它四种焊条所焊的蠕变试样的比较，发现新型的超低碳焊条的蠕变断裂时间要比A402、R307、A102要长，比Ni317的蠕变断裂时间稍短。由此可知：自行研制的超低碳焊条对碳迁移起到了有效的抑制作用，超过了工程上焊接珠光体和奥氏体异质钢常用焊材的高温力学性能，虽然比镍基材料稍差，但是对于绝大部分工程已经可以满足需要了。由于在价格上比昂贵的镍基材料要低得多，比常规的奥氏体焊材的价格还低，性价比高，具有较强的实用性。
[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.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG422.1

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