【作者】 朱强；

【导师】 雷玉成；

【作者基本信息】 江苏大学 ， 材料学， 2011， 博士

【摘要】 CLAM钢是用于制造我国聚变反应堆第一壁和聚变反应堆包层的首选结构材料。CLAM钢的焊接技术关系到实验包层模块TBM能否最终成功制造,是CLAM钢走向实际应用的关键技术之一。因此,针对CLAM钢熔化焊行为及其接头在液态锂铅中腐蚀机理进行研究,可以为CLAM钢在聚变示范堆中的实际应用,为提高CLAM钢焊接结构在液态金属腐蚀条件下的性能提供理论基础和技术依据。本课题采用基体材料和自制的9.8Cr2W0.5Ta材料作为填充材料,对5mm厚的CLAM钢进行了TIG焊。对两组试样进行了焊后热处理,并对焊接接头进行了显微硬度测试、拉伸试验、夏比冲击试验,并观察和分析了焊缝显微组织及断口形貌。采用基体材料填充时,随着焊后热处理温度的增加,焊缝区的显微硬度值明显降低,焊接接头的抗拉强度也呈下降趋势,而冲击吸收功则有提升,只有当焊后热处理温度达到760℃/30min时,焊缝才在局部发生韧性断裂,且焊缝冲击吸收功仍远低于母材。焊缝显微组织主要是回火马氏体和块状δ铁素体组织。焊缝中的析出相主要为M23C6相,且M的主要成分为Cr、Fe、W和Mn。采用9.8Cr2W0.5Ta焊丝进行填充时,随着焊后热处理温度增加,焊接接头的力学性能变化规律与基体材料填充时基本一致：焊缝区的显微硬度明显降低,接头的抗拉强度呈下降趋势,且只有当焊后热处理温度达到760℃/30min时,焊缝才在局部发生韧性断裂；但焊缝显微组织中容易引起辐照脆性的块状δ铁素体数量明显较基体材料填充时少,且析出相M23C6颗粒中M的主要成分为Cr、Fe、W和V。采用ANSYS有限元分析软件,建立了CLAM钢TIG焊对接接头三维有限元分析模型,采用双椭球热源模型,通过数值模拟计算分析了整个焊接过程中的瞬态温度分布及熔池变化情况,并对焊接残余应力以及焊后变形情况进行了模拟。对比分析了不同焊接速度下温度分布和熔池变化的情况,分析了焊接过程热效率的取值,亦即有效焊接热输入变化对焊接热循环的影响。通过模拟可知焊速为2mm/s、η取值在0.78～0.85参考范围内时,焊接熔宽和熔深均较合理,与实际焊接情况符合较好。由模拟可知沿焊缝方向,横向残余应力在焊缝中心表现为拉应力,而在焊缝两端表现为压应力；纵向应力均为拉应力。在垂直焊缝方向,横向残余应力主要由纵向应力引起,并在焊缝中心表现为拉应力,而纵向残余应力在近缝区为拉应力,随着离开焊缝距离的增加逐渐转变为压应力。结合焊态下CLAM钢在480℃、0.08m/s液态金属锂铅中的腐蚀情况,对易腐蚀区的形成及其对焊缝腐蚀量的影响规律进行了分析,并建立了基本腐蚀结构模型。研究结果表明：由于焊缝中析出的M23C6碳化物颗粒偏聚于原奥氏体晶界以及马氏体板条,使该区域的Cr含量明显降低,从而形成了易腐蚀区,降低了该区域耐液态锂铅腐蚀的性能。焊态下CLAM钢在480℃、0.08m/s的工况下,腐蚀量较大,经500h、1000h腐蚀时长后,失重分别为0.491mg/cm2(平均腐蚀深度为0.55μm),0.641mg/cm2(平均腐蚀深度为0.72μm),远高于回火态下CLAM钢基体的腐蚀量,随腐蚀时长的增加,试样腐蚀速度下降明显。焊态下CLAM钢经腐蚀后,焊缝区表面元素无明显变化,内部无锂铅元素渗透,腐蚀层较为均匀。更多还原

【Abstract】 CLAM steel is used in the manufacture of China’s fusion reactor first wall and other structural. Welding techniques and processes related to the test blanket module (TBM) can be created successfully, is a key technology for the practical application of CLAM steel. Therefore, researching on the performance of CLAM steel with TIG welding and corrosion behavior of weldment in liquid lithium-lead, is benefit to practical application of CLAM steel, to improve the performance of CLAM steel structure in liquid metal corrosion.In this study, Tungsten Insert Gas (TIG) welding on China Low Activation Martensitic (CLAM) steel (5mm thick) under identical conditions was performed, a) using the original CLAM composition filler metal and b) using the modified composition (9.8Cr2W0.5Ta). Microhardness test, tensile test, Charpy impact test and microstructure measurements were carried out on TIG welded joints after post weld heat-treatment. Using the original CLAM composition filler, the microhardness and ultimate tensile stress of weld metal decreased when the temperature of PWHT increased. Absorbed energy increased with PWHT temperature rising, until PWHT was done at 760℃/30min, the specimen ductile fractured in local area. The microstructure of the weld metal was found to be tempered martensite with a little of delta ferrite. M23C6 particles are the predominant type of carbides, the composition of M is Cr, Fe, W and Mn. Using the modified composition (9.8Cr2W0.5Ta), the mechanical properties of welded joints is consistent with that by using the original CLAM composition filler:the microhardness and ultimate tensile stress of weld metal decreased when the temperature of PWHT increased. Absorbed energy increased with PWHT temperature rising, until PWHT was done at 760℃/30min, the specimen ductile fractured in local area. However, compared with the matrix material filled, the number ofδferrite is less than that by using original CLAM composition filler. The compostion of M is Cr, Fe, W and V.Three-dimensional finite element numerical model of CLAM steel TIG welded butt joint was established using finite element analysis software-ANSYS, double ellipsoid heat source model is chosen for thermal simulation. Transient temperature distribution and weld pool changes in welding process were analysized by numerical simulation, welding residual stress and deformation after welding were also simulated. The temperature distribution under different welding speed and referenced value of the welding process thermal efficiency were caculated, It shows that 2mm/s of welding speed andηreferenced value in the range of 0.78 to 0.85 were reasonable to obtain fine weld width and penetration depth, were good agreement with the actual welding conditions. It also shows that transverse residual stress is tensile stress at the center of joint, is compressive stress at both ends of joint. Along the vertical direction, transverse residual stress is tensile stress at the center of joint and mainly caused by the longitudinal stress. The longitudinal residual stress is tensile stress near joint, with increasing distance from the weld, gradually transformed into compressive stress.Under 480℃,0.08m/s liquid lithium lead corrosion, the easily corrosive areas of CLAM steel joints existenced, its influence on corrosion was analysized, and established a basic structural model. The results show that:as the M23C6 carbides segregated in the original austenite grain boundaries and martensite lath, Cr content significantly reduced in this place, and formed easily corrosive area, reduced the resistance corrosion performance in liquid lithium lead. Under such conditions, CLAM steel joints were seriously corroded, after 500h and1000h corroded, weight loss was respectively 0.491mg/cm2 (average corrosion depth is 0.55μm) and 0.641mg/cm2 (average corrosion depth is 0.72μm), much higher than tempered CLAM steel corrosion. With time increased, the corrosion rate of the sample decreased significantly. By corrosion, the elements in the surface of weld zone did not significant changed, no lithium-lead penetrated is inside, corrosion layer became more uniform.更多还原