600MPa级高强钢微合金化药芯焊丝研制及电化学特性研究

发布时间：2018-08-17 12:28

【摘要】：海工装备常年处于低温环境并承受海水、大气的共腐蚀作用,因其苛刻的服役条件,海工装备用钢必须兼备高强度、高韧性以及优良的低温冲击韧性和耐海水、大气腐蚀性,而装备服役环境的严酷性对焊接工艺和焊接接头质量又提出了更高的要求。目前,关于向焊缝金属中过渡微合金化元素以期改善其微观组织、力学性能或第二相等研究主要集中于传统焊条药皮方面,与药皮焊条电弧焊等传统焊接手段相比,药芯焊丝焊接过程中熔滴过渡方式有所差异,焊接过程多为大线能量多层多道焊,焊缝成形后组织组成与性能也有所不同,而对于600MPa级高强钢药芯焊丝焊缝金属的相关改性研究试验也比较少见。本课题基于一定的药芯焊丝合金体系,并添加定量混合稀土和Cu元素,拉制出600MPa级海工装备低合金高强钢用药芯焊丝,制备多组焊接接头试样进行试验,以期得出稀土和Cu对焊缝金属性能的影响规律。本课题利用冷轧钢带成形法拉制不同混合稀土和Cu添加量的600MPa级高强钢药芯焊丝,制备成焊接接头后,利用金相显微镜、SEM、EDS、XRD、电化学加速腐蚀以及力学性能试验等手段对焊缝金属微观组织和综合力学性能以及电化学特性进行分析,并根据试验结果总结影响规律,为该级别药芯焊丝的微合金化提供参考。实验结果表明稀土元素的添加对焊缝金属微观组织和力学性能具有明显的影响,金相组织随着添加量的上升呈细化趋势,针状铁素体逐渐增多,但添加过多时,造成组织和晶粒大小均匀性下降。在合适含量范围内,低温冲击韧性、硬度、屈服强度和抗拉强度都有较大程度的提升,Re达到606MPa,Rm达到753MPa,总体呈现先升高后降低的趋势。适宜尺寸的第二相粒子也有一定的增加,从而利于晶粒形核。Cu的添加除了在一定程度上促进针状铁素体的形成,还会造成晶间富集物的产生,其对焊缝金属屈服强度和抗拉强度以及低温冲击韧性等也无明显改善作用,力学性能总体朝着不利的方向发展。在电化学特性方面,两种元素的添加对焊缝金属耐蚀性都有一定提升作用。电化学试验结果显示稀土添加越多,其腐蚀电流越小并且容抗弧半径越大,耐蚀性越好,而Cu的添加存在一个最佳范围,大致为0.28%~0.72%,此时腐蚀电流较小并且总阻抗值较高,耐蚀性较为稳定。因此,在对焊缝金属微合金化过程中,稀土元素对焊缝金属整体性能提升较为明显,而Cu虽然对耐蚀性有一定的促进作用,但作为工程结构材料,焊缝金属的结构性能并没有得到明显的提升。
[Abstract]:Marine engineering equipment is in a low temperature environment all year round and is subjected to the common corrosion of sea water and atmosphere. Because of its harsh service conditions, marine equipment steel must have both high strength, high toughness and excellent low temperature impact toughness and corrosion resistance to sea water and atmosphere. The harshness of equipment service environment requires higher welding process and welding joint quality. At present, the research on the transition of microalloyed elements to weld metal in order to improve its microstructure, mechanical properties or second equivalent is mainly focused on the traditional electrode coating, compared with the traditional welding methods such as flux-coated electrode arc welding, etc. In the process of flux-cored wire welding, the transfer mode of droplet is different, the welding process is mostly multi-layer and multi-pass welding with large wire energy, and the microstructure and properties of the weld are also different after forming. However, relative modification experiments on weld metal of 600MPa grade high strength steel flux-cored wire are rare. Based on a certain flux-cored wire alloy system and the addition of quantitative mixed rare earth and Cu elements, the 600MPa marine equipment low alloy high-strength steel cored wire was produced and many groups of welded joint samples were prepared for test. The effect of rare earth and Cu on the properties of weld metal was obtained. In this paper, 600MPa grade high strength steel flux-cored wire with different amount of mixed rare earth and Cu was fabricated by cold rolled steel strip forming method, and the welding joint was made. The microstructure, comprehensive mechanical properties and electrochemical properties of weld metal were analyzed by means of metallographic microscope (SEM) EDSX XRD, electrochemical accelerated corrosion test and mechanical property test, and the influence rules were summarized according to the experimental results. It provides a reference for the micro alloying of the flux-cored wire. The experimental results show that the addition of rare earth elements has an obvious effect on the microstructure and mechanical properties of weld metal. The homogeneity of microstructure and grain size decreases. In the range of suitable content, the low temperature impact toughness, hardness, yield strength and tensile strength are all increased to a large extent. Re reaches 606 MPa / m to 753 MPA / a, and the overall trend is to increase first and then decrease. In addition to promoting the formation of acicular ferrite to a certain extent, the addition of the second phase particles of suitable size also leads to the production of intergranular enrichment, which is beneficial to the nucleation of the grain and the formation of acicular ferrite. It has no effect on the yield strength, tensile strength and low temperature impact toughness of the weld metal, and the mechanical properties of the weld metal are developing in an unfavorable direction. In terms of electrochemical properties, the addition of two elements can improve the corrosion resistance of weld metal to some extent. The electrochemical test results show that the more rare earth is added, the smaller the corrosion current is and the larger the arc radius of capacitive reactance is, the better the corrosion resistance is. However, the addition of Cu has an optimum range of 0.28% 0.72%, and the corrosion current is smaller and the total impedance value is higher. Corrosion resistance is relatively stable. Therefore, in the process of microalloying the weld metal, the rare earth element can improve the overall properties of the weld metal more obviously, while Cu can promote the corrosion resistance of the weld metal, but it can be used as the engineering structure material. The structural properties of weld metal were not obviously improved.
【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】：TG42

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