Nb、C、Si对15-15Ti与16-15NbSi奥氏体不锈钢焊接接头组织性能影响
发布时间：2019-06-29 14:00
【摘要】：包壳与端塞焊接是我国钠冷快堆堆芯组件制造的重要组成部分。15Cr-15Ni含Ti单相奥氏体不锈钢(15-15Ti),具有良好的高温强度、耐腐蚀性能以及辐照性能,是我国钠冷快堆燃料主要候选包壳材料。该材料在焊接时易出现焊接热裂纹和晶间腐蚀等问题,且目前与其相匹配的端塞材料尚未实现国产化应用。本文针对15-15Ti奥氏体不锈钢焊接中容易出现的问题,在现有文献和资料基础上,设计一种与之相匹配的含Nb、Si的16Cr-15Ni改进型奥氏体不锈钢(16-15NbSi)作为端塞材料,采用氩弧焊(TIG)将6组不同合金成分的16Cr-15Ni与15-15Ti进行自熔焊接,并研究Nb、C、Si含量对焊接接头时效前后组织性能的影响,考察焊接接头的热裂纹敏感性和晶间腐蚀性能,对确定端塞的合金成分范围,实现端塞材料的国产化具有重要意义。本文研究工作与成果如下:(1)采用Thermo-Calc软件对设计的6组16-15NbSi合金成分进行热力学平衡相图计算。结果表明,随着Nb元素的增加,NbC由从γ相中析出,转变为直接从液相中析出。C含量的增加可促进NbC的形成,Si元素可扩大Laves相的析出温度区间,降低σ相的析出温度和析出量。(2)对时效前后焊接接头组织性能进行分析可知,随Nb元素和C元素含量增加,NbC析出量和尺寸均增加,Si元素含量增加使晶界处析出相的析出现象更为显著。时效后焊接接头组织中Nb、C含量较低时NbC析出相的析出量和尺寸几乎无变化,当Nb和C含量分别达到0.9wt.%和0.09wt.%时焊缝组织中析出相尺寸长大严重。时效前后焊接接头的拉伸性能几乎没有变化,其中,0.6wt.%Nb、0.03wt.%C和0.09wt.%C时焊接接头具有较高的抗拉强度和延伸率。时效后焊接接头硬度与时效前相比略有下降,且6组焊接接头中,只有0.6wt.%Nb、0.03wt.%C时效前后焊缝硬度均高于母材硬度。(3)6组焊接接头在热裂纹敏感性试验中未发现裂纹。晶间腐蚀试验中,只有0.6wt.%Nb和0.09wt.%C时发生了晶间腐蚀开裂,其余5组均未发现晶间腐蚀倾向。(4)综合焊接接头时效前后的组织性能,优选出端塞的最佳合金成分范围为:C含量0.02-0.04wt.%,Nb含量0.5wt.%-0.7wt.%,硅含量小于0.4wt.%.
[Abstract]:Shell and end plug welding is an important part of the manufacture of sodium cold fast reactor core assembly in China. 15Cr-15Ni contains Ti single phase Austenite stainless steel (15-15Ti), which has good high temperature strength, corrosion resistance and irradiation performance, and is the main candidate coating material for sodium cooled fast reactor fuel in China. The material is prone to welding hot crack and intergranular corrosion, and the matching end plug material has not yet been made in China. In order to solve the problems in welding of 15-15Ti Austenite stainless steel, based on the existing literature and data, an improved 16Cr-15Ni stainless steel (16-15NbSi) containing Nb,Si was designed as end plug material. Six groups of 16Cr-15Ni and 15-15Ti with different alloy composition were self-fluxing welded by argon arc welding (TIG), and Nb,C, was studied. The effect of Si content on the microstructure and properties of welded joints before and after aging is of great significance to determine the alloy composition range of end plugs and to realize the localization of end plug materials. The research work and results of this paper are as follows: (1) the thermodynamic equilibrium phase diagram of six groups of 16-15NbSi alloys is calculated by Thermo-Calc software. The results show that with the increase of Nb element, NbC precipitates from gamma phase to precipitates directly from liquid phase. The increase of C content can promote the formation of NbC. Si element can expand the precipitation temperature range of Laves phase and decrease the precipitation temperature and precipitation amount of 蟽 phase. (2) the microstructure and properties of welded joints before and after aging show that the precipitation amount and size of NbC increase with the increase of Nb element and C element content. The precipitation of precipitated phase at grain boundary is more obvious with the increase of Si element content. After aging, the precipitation amount and size of NbC precipitated phase were almost unchanged when the content of Nb,C in welded joint was low. When the content of Nb and C reached 0.9wt.% and 0.09wt.%, respectively, the precipitated phase size in weld microstructure grew up seriously. There is little change in the tensile properties of the welded joints before and after aging, in which the welded joints have higher tensile strength and extensibility when 0.6wt.% NB, 0.03wt.% C and 0.09wt.%C. The hardness of the welded joint after aging is slightly lower than that before aging, and only 0.6 wt.% NB in the six groups of welded joints, and the hardness of the weld before and after aging is higher than that of the base metal. (3) No cracks were found in the hot crack sensitivity test of the 6 groups of welded joints. In the intergranular corrosion test, intergranular corrosion cracking occurred only in 0.6wt.%Nb and 0.09wt.%C, and no intergranular corrosion tendency was found in the other five groups. (4) the optimum alloy composition range of end plug was 0.02 wt.%, 0.5 wt.% and 0. 7 wt.%, respectively, and the silicon content was less than 0. 4 wt.%, 0. 02 wt.%, 0. 7 wt.%, and 0. 4 wt.%, 0. 4 wt.%, 0. 02 wt.%, 0. 5 wt.%, 0. 7 wt.% and less than 0.4 wt.%, respectively.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407
本文编号：2507866
[Abstract]:Shell and end plug welding is an important part of the manufacture of sodium cold fast reactor core assembly in China. 15Cr-15Ni contains Ti single phase Austenite stainless steel (15-15Ti), which has good high temperature strength, corrosion resistance and irradiation performance, and is the main candidate coating material for sodium cooled fast reactor fuel in China. The material is prone to welding hot crack and intergranular corrosion, and the matching end plug material has not yet been made in China. In order to solve the problems in welding of 15-15Ti Austenite stainless steel, based on the existing literature and data, an improved 16Cr-15Ni stainless steel (16-15NbSi) containing Nb,Si was designed as end plug material. Six groups of 16Cr-15Ni and 15-15Ti with different alloy composition were self-fluxing welded by argon arc welding (TIG), and Nb,C, was studied. The effect of Si content on the microstructure and properties of welded joints before and after aging is of great significance to determine the alloy composition range of end plugs and to realize the localization of end plug materials. The research work and results of this paper are as follows: (1) the thermodynamic equilibrium phase diagram of six groups of 16-15NbSi alloys is calculated by Thermo-Calc software. The results show that with the increase of Nb element, NbC precipitates from gamma phase to precipitates directly from liquid phase. The increase of C content can promote the formation of NbC. Si element can expand the precipitation temperature range of Laves phase and decrease the precipitation temperature and precipitation amount of 蟽 phase. (2) the microstructure and properties of welded joints before and after aging show that the precipitation amount and size of NbC increase with the increase of Nb element and C element content. The precipitation of precipitated phase at grain boundary is more obvious with the increase of Si element content. After aging, the precipitation amount and size of NbC precipitated phase were almost unchanged when the content of Nb,C in welded joint was low. When the content of Nb and C reached 0.9wt.% and 0.09wt.%, respectively, the precipitated phase size in weld microstructure grew up seriously. There is little change in the tensile properties of the welded joints before and after aging, in which the welded joints have higher tensile strength and extensibility when 0.6wt.% NB, 0.03wt.% C and 0.09wt.%C. The hardness of the welded joint after aging is slightly lower than that before aging, and only 0.6 wt.% NB in the six groups of welded joints, and the hardness of the weld before and after aging is higher than that of the base metal. (3) No cracks were found in the hot crack sensitivity test of the 6 groups of welded joints. In the intergranular corrosion test, intergranular corrosion cracking occurred only in 0.6wt.%Nb and 0.09wt.%C, and no intergranular corrosion tendency was found in the other five groups. (4) the optimum alloy composition range of end plug was 0.02 wt.%, 0.5 wt.% and 0. 7 wt.%, respectively, and the silicon content was less than 0. 4 wt.%, 0. 02 wt.%, 0. 7 wt.%, and 0. 4 wt.%, 0. 4 wt.%, 0. 02 wt.%, 0. 5 wt.%, 0. 7 wt.% and less than 0.4 wt.%, respectively.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407
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