低活化马氏体钢真空扩散焊接工艺研究

发布时间：2018-03-26 15:03

本文选题：低活化马氏体钢　切入点：真空扩散焊接　出处：《合肥工业大学》2017年硕士论文

【摘要】：低活化马氏体钢因具有较高的热导率、较低的辐照肿胀和热膨胀系数等优良的热物理性能,被普遍认为是未来聚变示范堆和聚变动力堆的首选结构材料。聚变堆包层模块(TBM)的结构复杂、体积庞大、服役环境较为恶劣,各部件之间需要采用焊接等方法实现稳固连接。低活化马氏体钢中合金元素含量相对较高,对焊接技术要求较为苛刻,而传统熔化焊过程中存在液-固相高温热循环及焊缝区域的非平衡凝固,通常会引起焊接接头的组织及性能退化,成为结构的薄弱环节,从而影响聚变堆的安全可靠运行。以扩散连接为代表的固态连接技术因其具有焊接温度低于母材熔点、尺寸装配精度高等优点,有望取代传统熔焊工艺并于聚变实验堆包层模块的制造领域发挥重要作用。本文在不同焊接工艺条件(焊接温度、焊接压力及保温时间)下对低活化马氏体钢进行真空扩散焊接试验,通过对扩散焊接试样进行光学显微观察(OM)、扫描电镜观察(SEM)、能谱测试(EDS)以及X射线衍射(XRD)观测,分析焊缝区的相组成和组织形态、加热及保温过程中金属的组织演化规律等;通过对焊接件进行拉伸及冲击试验,比较热处理前、后焊件力学性能差异,探究不同工艺参数对微观组织和力学性能的影响规律,从而对低活化马氏体钢的扩散焊接进行工艺优化。试验结果表明,低活化马氏体钢的原始母材显微组织主要为板条马氏体,在真空扩散焊接的加热及保温过程中,低活化马氏体钢会发生再结晶及奥氏体化现象。当焊接温度较高或保温时间较长时,均会促进奥氏体生长,而粗大的奥氏体晶粒会对扩散焊接接头的力学性能带来损害;保温时间结束焊接试样冷却至室温后,焊缝区显微组织为马氏体、残余奥氏体及数量较多尺寸较小的析出碳化物;而经过焊后热处理后,残余奥氏体组织基本消失不见。在焊接温度为950~1100℃范围时,随着焊接温度的升高,焊件的拉伸强度随之提高,在1050℃时达到最高值973MPa;当焊接温度继续升高到1100℃时,焊件的拉伸强度则有所下降。在保温时间为90~180min范围时,焊件的拉伸强度一直随着保温时间的延长而增加,但当保温时间超过150min后,接头的抗拉强度基本没有增强,开始趋于平缓。在10~20MPa的焊接压力下,焊接件的抗拉强度一直随焊接压力提升而稳步提高。但限于低活化马氏体钢在高温下的屈服强度,试验时没有继续选用更高的焊接压力进行扩散焊接。提高焊接温度可以通过激活更多原子进行无规则的扩散迁移提升扩散效果,从而一定程度上提高焊件的拉伸强度;但较高的焊接温度同样会促进奥氏体晶粒的吞并、长大,而粗大的奥氏体晶粒冷却转变后得到的粗晶粒组织会降低焊件的抗拉强度。因此,当达到1050℃时,焊件的抗拉强度会随着焊接温度的升高而降低。同样,保温时间的延长为良好的扩散效果提供了必要的条件,但当保温时间过长时,虽然活跃态原子扩散越充分,但由于粗大的奥氏体晶粒,其抗拉强度反而无明显提升。而当焊接压力越大时,焊接面的微观凸起塑性变形程度越大,焊接面之间实际接触面积便越大,从而使焊接面附近激活态原子获得足够的扩散通道通过无规则迁移及跨越界面进行固态自扩散,使得焊接面结合状况更为优良。焊件的冲击韧性主要取决于扩散焊接结束时焊缝区的晶粒尺寸,当奥氏体晶粒随着焊接温度的升高及保温时间的延长而越来越大时,焊缝区的金属的冲击韧性则越来越差。
[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.

【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.11

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