【作者】 张占伟；

【导师】 李午申；

【作者基本信息】 天津大学 ， 材料加工工程， 2009， 博士

【摘要】 自保护药芯焊丝是一种无需外加保护措施即可进行焊接的新型焊接材料。由于其抗风能力强、焊接设备简便等特点,尤其适合野外、高层建筑等施工场合。应用自保护药芯焊丝进行野外管道建设具有焊接效率高、焊缝质量好等特点,因此可大幅降低长输管线的综合建设成本。本文以BaF₂-Al-Mg渣系为基础渣系,对药芯组分选择、焊丝制作工艺、自保护机理、焊接工艺性能、熔覆金属强韧化等环节进行了系统研究,研制出与X80管线钢相匹配的高强韧性自保护药芯焊丝。BaF₂-Al-Mg渣系通过气、渣、金三元联合的方式保护熔滴和熔池,以气、渣保护降低氮的溶解量,以铝脱氮、固氮消除溶入熔池的氮可能产生的氮气孔、时效脆化等缺陷,强脱氧剂铝、镁脱氧可有效控制焊缝中的氧含量。本研究药粉预处理是将BaF₂、LiF、Fe₂O₃等药粉混合、造粒,经700℃⁸50℃烧结保温30min,粉碎、筛分保留粒度为60目¹50目药粉的工艺流程。经过预处理的混合粉,具有粒度均匀、比重大、流动性好、吸湿性低的特点,保障了混合粉的均匀性和焊丝填充率的稳定性。通过混料回归设计建立了药芯组分中BaF₂、LiF、Fe₂O₃、Al-Mg、Li₂CO₃对熔渣覆盖率、飞溅率、发尘率影响的数学模型,并可通过模型预报和控制药芯组分对上述指标的影响。提出了新的熔滴-熔渣-钢皮结构模型,并借助高速摄影技术提出本研究焊丝熔滴过渡以外摆接触过渡和射流过渡为主,伴有少量的爆炸过渡。研究了Fe₂O₃、Li₂CO₃、Al-Mg对各种熔滴过渡频率的影响,得出它们在药芯中的适用范围。通过热力学分析,提出铝对熔池固氮存在最小临界值。该临界值随熔池中氮含量的提高而降低,铝含量低于临界值时熔池不具有固氮效果,超过临界值后随铝含量的增加熔池固氮能力提高,固氮产物为多面体的AlN。通过正交试验对熔敷金属进行强韧化设计,研究了Ni、Mn、Zr、Ce对熔覆金属强韧性的影响。得出Ni:1.6wt.%、Mn:1.1wt.%、Zr:0.02wt.%、Ce:0.009wt.%为本研究渣系自保护药芯焊丝的最优合金系统。熔敷金属以粒状贝氏体组织为主,抗拉强度为594MPa时,-40℃下Charpy-V冲击韧度平均值达164J。优化的焊丝通过在X80管线钢上进行焊接工艺性能和接头力学性能的综合焊接评定,评定结果满足西气东输二线相关规范对X80管线钢环焊缝的要求。更多还原

【Abstract】 Self-shielded flux cored wire （SSFCW） is a new type welding material, which is capable of providing weld metal free from welding defects when welding in the open air without any intentionally protect. Due to its good wind resistant, simple equipment make it especially suitable for field, high-rise building and other fields. Using self-shielded flux cored wire for field pipeline construction has the characteristics of high efficiency, good weld quality and so on. As a result, long-distance pipeline construction costs can be greatly reduced. In this paper, BaF₂-Al-Mg slag system is selected as basis slag system. Through the study of flux ingredients selection, wire manufacturing process,self-protection mechanism, welding usability, deposited metal strengthening and toughening design in detail, a new kind of self-shielded flux cored wire with high strength and toughness was developed, which can be used for grade X80 pipeline steel welding.For BaF₂-Al-Mg slag system, gas, slag and alloy elements are jointly used to protect the droplet and molten pool from the contamination of air. By gas and slag protection, nitrogen dissolved in weld pool is reduced as much as possible. For the dissolved nitrogen, aluminum is used to form AlN, which is a stable nitride, so that nitrogen porosity and aging embrittlement are eliminated. Aluminum and magnesium both are strong deoxidizer, which can control the oxygen content in the weld effectively.In this paper, flux pretreatment is a process. BaF₂、LiF、Fe₂O₃ flux are mixed and granulated, then sintered at 700℃⁸50℃for 30min, 60 to 150 mesh flux is kept after grinding and sieving. Pretreated flux has the features of uniform particles, increased density, improved flux fluidity and low moisture absorption. As a result, the flux uniformity and wire feed rate are ensured.The effect of flux ingredients （including BaF₂, LiF, Fe₂O₃, Al-Mg, Li₂CO₃） on slag coverage rate, spattering rate and welding fume have been studied by mixture regression design, by which mathematical models were established. The effect of flux ingredients on as mentioned parameters can be predicted and controlled by the mathematical models.A new droplet, molten slag and wire shell relationship mode has been proposed in this paper. The kinds of droplet transfer modes and the effect of Fe₂O₃、Li₂CO₃、Al-Mg flux ingredients on them have been studied by means of high-speed photography technique. Suitable quantity of each ingredient was obtained.Thermodynamic analysis shows that aluminum-nitrogen reaction in the molten pool has a critical value for aluminum content. The critical value is decreased with the increasing of nitrogen content in molten pool. Lower the critical value, the aluminum in molten has no nitrogen-fixation effect. Beyond it, nitrogen-fixation effect is increasing with the increase of aluminum in molten pool.The effect of Ni, Mn, Zr, Ce on the strength and toughness of deposited metal have been studied by orthogonal design. The optimal alloy system for as studied SSFCW was obtained, that is Ni: 1.6wt.%, Mn: 1.1wt.%, Zr: 0.02wt.%, Ce: 0.009wt.%. With this alloying system, the tensile strength and Charpy-V impact value at -40℃are 594MPa and 164J respectively.Welding usability and weld joint mechanical properties of the developed wire have been evaluated by means of welding at X80 pipeline steel. The evaluation results meet the specifications of the second“West-East Gas Transmission”project for grade X80 girth weld requirements.更多还原