水电站800MPa高强度结构钢焊接工艺研究
发布时间:2018-05-29 09:21
本文选题:水电用钢 + 低合金高强钢 ; 参考:《西南交通大学》2017年硕士论文
【摘要】:某水电站是中国在建的最大水电站工程之一,为了保证大水流量下的正常运行,其压力钢管采用强度级别为800MPa的新型国产高强结构钢。本文针对国产新型800MPa级低合金高强度结构钢的常用焊接方法——焊条电弧焊、富氩气体保护焊以及埋弧焊工艺进行了一系列研究。首先对比了 780CF钢800CF钢埋弧焊的接头组织和性能,两者接头焊缝区都为韧塑性较好的针状铁素体和粒状贝氏体组织,热影响区为贝氏体组织,其中粗晶区和部分相变区为接头薄弱区域。针对780CF钢,采用不同焊接方法、不同焊材及不同线能量下的接头性能进行试验分析。埋弧焊由于焊剂覆盖,在相同线能量下,冷却速度较小,晶粒较焊条电弧焊和富氩气体保护焊稍粗大,但原子扩散更充分,强化质点和第二相的强化效果较好。在都能达到标准要求的前提下,埋弧焊焊接效率更高,焊接过程更稳定,自动化程度高,因此采用埋弧焊作为压力钢管的主要焊接方式。对比不同焊材的接头性能,从焊材化学成分及接头组织等方面进行分析对比,选出综合性能较优焊材。对不同焊接方法设定了大、小两种线能量,两种线能量下都能得到符合标准GB/T 50766-2012《水利水电工程压力钢管制作安装及验收规范》的接头。大线能量下接头加热温度较高,晶粒较粗大,但同时原子扩散能力增强,有利于强化质点的形成和均匀分布,增强接头强度和韧塑性。且大线能量下生产效率更高。因此推荐焊条电弧焊线能量范围在25~35KJ/cm之间;富氩气体保护焊线能量范围25~35KJ/cm之间;埋弧焊线能量范围28~35KJ/cm之间。针对多层多道焊中相邻的两条焊道进行分析,未变再热粗晶区和亚临界再热粗晶区的性能变化不大,与一次粗晶区相似;过临界再热粗晶区晶粒细化,强度及韧塑性提高;临界再热粗晶区形成了晶粒大小和成分不均匀的组织,韧塑性下降,但相比于一次部分相变区性能仍较好。因此焊道间相互作用使焊接温度场重合区域性能较优,接头薄弱区域仍为一次粗晶区和一次部分相变区。
[Abstract]:A hydropower station is one of the largest hydropower projects under construction in China. In order to ensure the normal operation under the heavy water flow, the steel pipe with strength grade 800MPa is adopted as a new type of domestic high strength structural steel. In this paper, the common welding methods of 800MPa low alloy high strength structural steel, such as electrode arc welding, argon rich gas shielded welding and submerged arc welding, are studied in this paper. The microstructure and properties of submerged arc welding (SAW) of 780CF steel 800CF steel were compared at first. The weld zone of both joints was acicular ferrite and granular bainite structure with good ductility and ductility, and the heat affected zone was bainite structure. The coarse-grained region and partial phase transition zone are the weak zone of the joint. The joint properties of 780CF steel under different welding methods, different welding materials and different wire energy were tested and analyzed. Because of flux covering, the cooling rate of submerged arc welding is smaller than that of electrode arc welding and argon-rich gas arc welding, but the atomic diffusion is more sufficient, and the strengthening effect of particle and second phase is better than that of electrode arc welding and argon rich gas welding. On the premise of meeting the standard requirement, submerged arc welding is more efficient, the welding process is more stable, and the degree of automation is high. Therefore, submerged arc welding is used as the main welding method of pressure steel pipe. The joint properties of different welding materials were compared and analyzed from the aspects of chemical composition and joint structure. For different welding methods, two kinds of line energy, large and small, can be obtained under two kinds of line energy. The joints can be obtained according to the standard GB/T 50766-2012 "Specification for production, installation and acceptance of penstock for water conservancy and hydropower engineering". The higher heating temperature and larger grain size of the joints with large wire energy, however, the enhancement of the atomic diffusion ability is beneficial to the formation and uniform distribution of particles and the strengthening of the strength and ductility of the joints. And the production efficiency is higher under the large line energy. Therefore, it is recommended that the energy range of electrode arc welding line is between 25~35KJ/cm, that of argon rich gas shielded welding line is between 25~35KJ/cm and that of submerged arc welding wire is between 28~35KJ/cm. According to the analysis of two adjacent passes in multilayer and multi-pass welding, the properties of coarse grain zone and sub-critical coarse grain region in unreheated and subcritical reheat have little change and are similar to those in primary coarse crystal region, and the grain size is refined and the strength and ductility are improved in the supercritical reheat coarse grain area. In the critical reheat coarse-grained region, the grain size and composition are not uniform, and the ductility is decreased, but the properties are still better than those in the primary phase transition zone. Therefore, the interaction between welding passes makes the performance of welding temperature field coincidence region better, and the weak zone of the joint is still the primary coarse crystal zone and the first partial phase transition zone.
【学位授予单位】:西南交通大学
【学位级别】:硕士
【学位授予年份】:2017
【分类号】:TG457.11;TM622
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