【作者】 姚润钢；

【导师】 李午申；

【作者基本信息】 天津大学 ， 材料加工工程， 2006， 硕士

【摘要】 尽管国内外焊接技术人员多年来对低合金高强度钢氢致裂纹问题进行了大量的研究工作,但对于工程结构而言如何避免氢致裂纹的产生仍然是最值得关注的课题。尤其对那些类似于船舶结构的大型复杂结构,较高强度或高强度钢的焊接往往需要苛刻的焊接工艺要求才能保证焊接接头中不产生裂纹。这种苛刻的焊接工艺要求又导致焊工的工作条件恶劣、焊接成本增高。因此,采取各种途径改善低合金高强度钢的焊接性、简化焊接工艺要求是目前大型复杂结构焊接研究工作中追求的目标。11MnNiCrMoV钢是一种屈服强度不低于440MPa级较高强度船舶结构用钢,具有良好的低温韧性和耐海水腐蚀性能。该钢经过成分调整,焊接性得到较为明显的改善,但仍然沿用了初始研制阶段所确定的焊接预热温度要求,焊接工艺较为严格,给船舶建造带来了一定的难度。焊接接头中扩散氢是影响氢致裂纹形成的三大因素之一。在常用的手工焊、埋弧焊和气体保护焊中,手工焊的扩散氢往往较高,且氢致裂纹倾向最大。若采取有效途径降低手工焊条的扩散氢含量,将能够减小焊接结构的氢致裂纹倾向。E5515-G型焊条专门用于11MnNiCrMoV钢的焊接。在钢板焊接性已得以改善的前提下,本文通过研究E5515-G型焊条扩散氢含量的影响因素,提出了适当提高E5515-G型焊条的烘焙温度,有利于降低该焊条的扩散氢含量,而不影响焊条的熔敷金属和对接接头性能。环境温度和相对湿度都是影响E5515-G型焊条扩散氢含量的因素,空气中绝对湿度(含水量)是影响焊条扩散氢含量的唯一环境因素,空气绝对湿度大时,侵入电弧的空气是焊条扩散氢的主要来源。通过研究11MnNiCrMoV钢的淬硬倾向,表明该钢在冷却时间t8/5较小时容易出现裂纹敏感性大的微观组织。在E5515-G型焊条采用400℃烘焙、扩散氢含量较高的情况下,环境温度不高于0℃时需要50～70℃的预热温度才能避免裂纹的产生。将E5515-G型焊条450℃烘焙,能够实现在0℃时的不预热焊接。以本研究结果为基础提出的11MnNiCrMoV钢新的焊接预热温度要求,比该钢原有的焊接预热温度要求有明显简化。更多还原

【Abstract】 Although a lot of researches on the hydrogen-induced cracks (HIC) of high strength low alloy steels (HSLA steels) have been being done over all worlds for many years, how to avoid the occur of HIC for engineering structure still is the most noticeable problem. Cracks would not occur in the weldments only using the rigorous welding processes for welding of high strength steels of large-scaled complicated structures like ship structures. The rigorous welding processes lead to increase of welding cost and worsening of work conditions of welders. Therefore improvement of weldability of the HSLA steels and reduction of the requirements of welding processes by taking the various ways are the pursued aim in the welding research of large-scaled complicated structures.11MnNiCrMoV steel is a high strength ship structural steel which its yield strength is not less than 440MPa. The steel plates possess the good properties of lower temperature toughness and anti-corrosiveness of sea-water. The weldability of the steel had been improved after its chemical composition was modulated, but its requirements of welding processes is the same as the initial requirements of the 11MnNiCrMoV steel in the first stage. The rigorous welding processes produced some difficulties in the ship-building.Diffusible hydrogen of the weldments is one of the three-affecting-factors on formation of HIC. Among the shielding metal arc welding (SMA), submerged arc welding (SAW) and gas shielding welding, SMA possesses more content of diffusible hydrogen and is prone to produce HIC than others. The proneness of HIC would be reduced while the contents of diffusible hydrogen in the SMA electrodes were reduced using the effective ways. E5515-G electrodes are used specially for welding 11MnNiCrMoV steel. Under the weldability of 11MnNiCrMoV steel had been improved, the paper puts forward the conclusion that proper boost of the barking temperature of E5515-G electrodes will be in favor of reduction the contents of diffusible hydrogen of the electrodes and not affect the its properties according to the study of affecting-factors on the diffusible hydrogen of E5515-G electrodes. Environ-ment temperature and relative humidity all affect the contents of diffusible hydrogen of the electrodes. The absolute humidity (water content in the air) in the air is the sole Environmental factor affecting contents of diffusible hydrogen. When the absolute humidity is large, the air intruding the arc becomes the main source of diffusible更多还原