【作者】 马广义；

【导师】 吴东江；

【作者基本信息】 大连理工大学 ， 机械制造及其自动化， 2013， 博士

【摘要】 第三代核电站(AP1000)用非能动式核主泵采用屏蔽式电机,而屏蔽式电机中屏蔽套的精密制造是保证核主泵正常工作的基础。套体材料为超薄哈氏合金(HastelloyC-276),制造过程包含对套体进行焊接加工,这是核主泵屏蔽套制造过程的难点和重点。本文针对超薄大长径比Hastelloy C-276合金屏蔽套的焊接要求,采用激光焊接技术,提出焊接参数优化准则,在减小焊接热影响区的基础上,对焊接区域进行显微组织观察分析,并结合原始材料的力学和耐腐蚀性能,对焊接区域进行针对性地性能检测,综合评估激光焊接过程对材料宏观、微观性能的影响,为核主泵屏蔽套的自主制造提供理论基础和工程支撑。主要研究内容及结果如下：(1)使用Nd:YAG脉冲固体激光器实现了0.5mm厚度Hastelloy C-276的焊接成形,讨论了单脉冲能量、焊接速度、脉冲频率、脉冲宽度和离焦量对焊缝上下表面宽度的影响规律,提出了焊接参数优化准则；根据焊缝平整性、内部存在横／纵向轮廓条纹以及特殊轮廓特征,结合浮力效应和玛尔戈尼对流熔池流动理论研究了上述现象与焊接工艺特征的关系；此外,采用X射线无损探伤和逐层抛光的方法分别对焊缝进行了宏观和微观焊接缺陷检测,检测结果说明脉冲激光焊接工艺能够得到近无缺陷的焊接接头。(2)利用扫描电镜、电子探针、X射线衍射仪和微观硬度计分别检测了焊缝微观组织、元素分布、相结构以及显微硬度特征。焊缝处发现了明显的次晶界和枝状晶,晶粒细化现象明显；激光焊接过程并未导致宏观偏析,但微观偏析现象明显;提出了分段修正k值的Brody-Flemings方程,揭示了Cr、Mo、W、Fe元素凝固过程扩散规律,证实了激光焊接工艺有利于抑制脆性相的生成；X射线衍射结果说明母材和焊缝处相组织均以面心立方奥氏体为主；微观硬度结果表明焊缝处微观硬度并未受到影响。(3)通过拉伸试验,发现焊接接头的屈服极限与母材基本相同,仅在室温条件下焊接接头的抗拉强度有所降低；母材断口形貌主要以较浅等轴韧窝断口为主,而焊缝断口呈现出较深细密等轴韧窝断口特征；XRD分析并未在常温焊缝断口处发现脆性相的富集；高温工程应力应变曲线结果表明拉伸试样均表现出均匀的塑性变形过程,高温真实应力应变曲线结果表明焊缝处极限应变与母材相当,具有相同的加工硬化趋势。(4)在王水溶液中母材主要发生均匀腐蚀,而焊缝处呈现出典型晶间腐蚀特征；电化学腐蚀结果说明激光焊接对Hastelloy C-276材料在中性溶液中的耐蚀性影响不大,但母材以选择性腐蚀为主,焊缝以晶间腐蚀为主,焊缝处腐蚀速度低于母材。更多还原

【Abstract】 The canned motor was used in the nuclear reactor coolant pump of AP1000, and in the canned motor, the can, which was Hastelloy C-276alloy, was important to the work of nuclear main pump. During the manufacture of the can, the welding of can was critical. In this paper, based on the welding requirements of thin large draw ratio Hastelloy C-276alloy can, a laser welding method was proposed. Also, the optimized welding parameters were obtained, and the microstructure, mechanics property and corrosion resistant on the weld joint were investigated. Finally, the effect of welding method on the macro/micro characteristics of Hastelloy C-276was evaluated.(1) Using Nd:YAG laser achieved the well weld joint of Hastelloy C-276, and the effects of single energy, welding velocity, repetition and duration on the weld joint were discussed. Then, the optimization criterion of welding parameters was proposed. Aiming at the smooth, contour line and special profile of weld joint, the buoyancy effect and Marangoni convection was applied to explain the phenomena above. In addition, by the X-Ray nondestructive inspection and layer-by-layer polishing, nearly no any welding defect was found. Hence, it was concluded that the laser welding could achieve the well weld joint nearly without welding defect.(2) Using the SEM, EMPA, XRD and micro-sclerometer, the microstructure, element distribution, phase structure and microharness of weld were tested. In the weld, the obvious sub grain boundary and fined dendrite were found, and the macro segregation was not found, but the micro segregation was significant. A Brody-Flemings model with piecewise revised k was proposed to calculate the element distribution under the rapid cooling condition. The distribution of Cr, Mo, W and Fe during the laser welding was revealed, and it was indicated that the laser welding could restrain the forming of brittle phase. The results of XRD and microharness test indicated the phase structure of weld was the same as that of base metal, and the microharness of weld was not influenced by the laser welding.(3) The yield strength of the weld joint was the same as that of the base metal, but at room temperature, the tensile strength of weld joint was a little smaller than that of the base metal. There were many dimples in the fracture of base metal, and in the weld fracture, the tiny deep dimples were observed. In the fracture of weld, it was not found the enrichment of brittle phases by the XRD test. The engineering stress-strain curve showed all stretched samples presented the same plastic forming, and the true stress-strain curve showed the limiting strain and work hardening trend of weld were the same as that of base metal. (4) Under the corrosion of nitrohydrochloric acid condition, the even corrosion was observed in the base metal, and the intergranular corrosion was found in the weld. The electrochemical results indicated, in the neutral solution, the corrosion resistance of Hastelloy C-276was not affected by the laser welding, but the corrosion mechanisms of base metal and weld were different.更多还原