【作者】 王晓国；

【导师】 金云学；

【作者基本信息】 江苏科技大学 ， 材料学， 2010， 硕士

【摘要】 21世纪是发展海洋经济的时代,浩瀚的海洋是资源和能源的宝库,也是人类实现可持续性发展的重要基地。据预测,2015年海上石油产量将达到3600～3900万桶油当量/天,到2020年将达到3700～4100万桶油当量/天。海洋探测、海洋石油的资源开发是建立在海洋工程平台及其各项装备技术基础上的。R4s级系泊链钢是目前海洋工程平台固定中应用级别最高的系泊链钢,其性能的好坏对系泊体的安全性具有重要意义,然而闪光焊焊缝区是整个链环中最薄弱的环节,其性能好坏直接影响着整个链条的性能。目前国内外对R4s级系泊链闪光焊焊缝区组织与性能研究很少,因此,研究热处理工艺对R4s级系泊链焊缝区组织与性能的影响具有重要意义,同时也为后续产业化生产提供一定的理论参考。本文主要结合系泊链的实际生产条件,在热处理工艺上进行创新,通过采用新型的循环淬火工艺来获得比普通热处理后性能更好的综合力学性能。研究结果表明:焊缝区经920℃一次淬火和920℃+920℃循环淬火工艺后,性能对比发现,循环淬火后的抗拉强度比一次淬火高出200MPa,所以本实验淬火工艺全部采用循环淬火。闪光焊焊缝区淬火后在低、中、高温回火后,焊缝区的残余应力降低幅度出现不同变化,特别是在600℃高温回火后,焊缝区残余应力降低幅度达到300MPa,所以此试验主要研究了高温回火对焊缝区组织与性能的影响。试样经920℃循环淬火后,在560℃,580℃,600℃,620℃,640℃回火分别保温20min,30min和40min后。焊缝区所得的回火索氏体仍具有板条马氏体位相,原因在于回火过程板条马氏体发生回复过程,再结晶过程未发生或只生成少量的等轴晶,说明这种钢的抗回火稳定性较好。拉伸试验和冲击试验表明,经过调质处理后,抗拉强度均达到1000MPa以上,0℃下冲击功达到100J以上,断口分析表明,试样断口均表现为韧性断裂。特别是在920℃×30min +920℃×30min淬火+600℃×30min调质处理后,焊缝区拥有大量优良的韧窝,促使焊缝区拥有较高的强度和最好的塑性,综合性能配合最好。经过低温冲击试验表明,焊缝区经过调质处理后试样仍具有较高的韧性。随着冲击温度的降低,塑性变形程度也随之下降,断口形貌由初始的完全韧窝形貌转变为准解理断口和韧窝断口的混合形貌,断裂类型由韧性断裂逐步向脆性断裂转变。焊缝区经920℃×30min+920℃×30min淬火+600℃×30min调质处理后,即使在-20℃低温下冲击,其断口形貌仍全部为韧窝形貌,在-40℃时冲击韧性仍达到89J具有较好的韧性。腐蚀挂片试验及电化学试验表明,焊缝区腐蚀形式主要为点蚀与晶界腐蚀。腐蚀机理为电位较低的金属基Fe与电位较高的渗碳体等第二相粒子组成微电池进行腐蚀,阳极不断溶解腐蚀,而阴极得到保护,其中金属基Fe为阳极,而渗碳体等第二相为阴极。调质处理改善了焊缝区组织并在一定程度上提高焊缝区耐蚀性,但不能有效阻止材料的腐蚀。从试样的极化曲线中可以看到,试样并不能形成有效的钝化膜,因此该材料不能采用阳极保护法进行保护。更多还原

【Abstract】 The marine economy will develop faster in the 21st century, the oceans are not only the vast treasure house of resources and energy, but also important base for sustainable development for mankind. It is predicted that offshore oil production will reach 36~39 million barrels per day by 2015, add up to 37~41 million barrels per day by 2020. The sea explorations and the exploitation of ocean resources are mainly based on ocean engineering platform and its equipment technology. Fixation of marine engineering platforms and equipments depends on high-level mooring chain. The R4s grade mooring chain is the highest-ranking marine engineering chain at present, weld joint was the weakest area of the entire chain link, which could affect the integrated performance of the entire chains directly. The properties of the material are depended on chemical compositions and microstructures. And heat treatment is an effective measure to alter microstructures and increase comprehensive properties, under the condition of the chemical composition unchanged. At present, the papers about mechanical properties of R4s level mooring chain flash welding joint are very little at home and abroad. It is very significance to study the properties of weld joint under Heat-Treatment, simultaneously provides the necessary conference for the following industrial production.According to the mooring chain actual working condition, this paper uses the cyclic quenching process to obtain better mechanical properties. The results are as followed: Compared with the normal quenching and tempering, after cycle quenching process, the tensile strength increases by 200MPa. After different tempered, the residual stress had different changing. Especially under 600℃tempered, the residual stress could reduce to 300MPa. With the same quenching temperature (920℃), after tempering at 560℃, 580℃, 600℃, 620℃, 640℃, and respectively tempering for 20min, 30min and 40min,It was found that the weld joint has the best comprehensive mechanics when tempered at 600℃for 30min. It still has tempered lath martensite phase even tempered at 640℃for 40min, which indicts that the material used in this experiment has good tempering stability. Tensile test and impact test showed that,the tensile strength can reach 1000MPa,and the impact energy at 0℃reached 100J. The fracture all contains large fiber zone which is characterized by ductile fracture. Especially under the 920℃×30min+920℃×30min+600℃×30min quenching and tempering treatment, the specimen has a large number of fine dimples, which has the best mechanical performance. Hanging patch test and electrochemical corrosion tests showed that the mainly corrosion of weld joint is pitting and intergranular corrosion. The corrosion mechanism is as followed: the micro-battery corrosion that consist of the low potential Fe-based and high potential second-phase particles happened. The process is constant corrosion with anodic dissolution and the cathodic protection, in which Fe-based as an anode, while the carburizing as the cathode body. Cyclic quenching and tempering treatment makes the organization and the corrosion resistance of the weld joint improved significantly. It also can be found from the polarization curves of the specimen, the material does not form an effective passivation film, so the anode protection law can not be used for this material.更多还原