微量Ca对耐候钢耐大气腐蚀行为及机理研究

With the fast development of our country's economy, Strength of steel has been improved continually. The problem of steel atmospheric corrosion has become increasingly prominent and the existing weathering steel has been unable to meet the requirements of use. Therefore, there is an urgent need to study the development of low cost, high strength weathering steel with excellent corrosion resistant performance..Ca and the common corrosion resistant element, rare earth( RE ), have a similar effect in modifying inclusion and purifying the liquid steel aspects, but Ca has obvious price advantage. So the project put forward to use Ca instead of RE as corrosion resistance element, study the atmospheric corrosion resistance effect of trace Ca on carbon steel, weathering steel and Cu-P Si-Al weathering steel Comparatively and study effect of the morphology, size, distribution and composition of inclusions in steel on initial corrosion rate, inclusion corrosion area size, change of pH value in micro area, composition and morphology of generated corrosion product and corrosion uniformity in the follow-up phase, with the metamorphic effect analysis of Ca on inclusions in steel under different levels of O and S. And it also put forward to study the pitting sensitivity of different inclusion, the pinning reinforcement effect of different inclusion on the generated corrosion product and substrate, the rust layer feature evolution law, the rust layer electrochemical characteristics of different corrosion cycle, the mechanism of corrosion resistance of Ca on steel and the synergistic effect mechanism of trace amounts of Ca and Cu-P and Si-Al compound addition.

随着我国经济建设的快速发展，钢材强度不断被提高，钢材的大气腐蚀问题则日益突出，现有耐候钢已无法满足使用要求。因此迫切需要研究开发低成本、优良耐腐蚀性能的高强韧耐候钢。.Ca在改性夹杂、净化钢液方面与常用耐腐蚀元素稀土(RE)具有相似作用，但其却有明显价格优势。因此本项目提出采用Ca替代RE作为耐蚀元素，对比研究微量Ca对普碳钢、Cu-P系耐候钢和Si-Al系耐候钢耐大气腐蚀性能的影响规律，结合不同O、S水平条件下Ca对钢中夹杂物变质效应分析，研究钢中夹杂物形态、尺寸、分布和成分对锈蚀初期腐蚀速率、夹杂物腐蚀区域大小及微区pH值变化、生成锈蚀产物组成和形貌特征以及对后续阶段腐蚀均匀性的影响；研究不同夹杂物的点蚀诱发敏感性及对生成的腐蚀产物与基体的钉扎强化作用；研究锈层特性演变规律及腐蚀不同周期的锈层电化学特征；探讨Ca对钢耐蚀机理及微量Ca与Cu-P和Si-Al复合添加协同效应机理。

随着我国国民经济的迅速发展，迫切需要开发新型高耐蚀性、高强度、低成本耐候钢。金属Ca具有夹杂物变性和净化钢液的作用，且价格优势明显。因此，本项目用Ca替代Re添加到耐候钢中，深入系统地研究了Ca对Cu-Cr-Ni系耐候钢中非金属夹杂物、组织性能和耐工业大气腐蚀性能的影响，并探讨了Ca与其它常用耐腐蚀合金元素对实验钢耐大气腐蚀性能协同作用。. 随Ca含量增加，实验钢中夹杂物形貌主要由长条状硫化锰以及MnS与Al2O3的复合夹杂变质为含Ca-Al-Mn-O-S的球状或和纺锤状夹杂，并且钢中夹杂物数量明显增加，但夹杂趋于弥撒均匀分布。当Ca为0.0029%时，实验钢中夹杂物细化球化效果最好。轧制获得实验钢组织为多边形铁素体和珠光体，且随着Ca含量的增加，实验钢的铁素体晶粒尺寸明显减小，表明Ca夹杂变质效应有利于钢材组织性能的改善，从而保证含Ca耐候钢具有较好的高强韧性能。. 含Ca量为0.0014%的实验钢在各个腐蚀阶段的腐蚀速率均很低。在腐蚀实验的后期，含Ca量为0.0029%的耐候钢的腐蚀速率下降的比其他钢要快，其锈层的稳定化速度很快。含Ca耐候钢锈层都十分致密，裂纹孔洞少，保护性锈层的厚度增加显著，对基体的保护能力好。含Ca量为0.0029%的钢的腐蚀产物中α-FeOOH含量很高并且Fe3O4含量很少，可见耐候钢中的Ca合金可以促进锈层中稳定致密的α-FeOOH相形成，这与CaO与CaS夹杂物在腐蚀的过程中水解，进而提高了电解液薄膜PH值有关。随着Ca含量增加，锈层自腐蚀电位提高，明显提高了实验钢锈层的热力学稳定性，促进了锈层对基体的保护作用。同时，Ca与元素Cr+Ni、P、Ti和Si+Al复合添加对含Cu普碳钢耐工业大气腐蚀性能协同作用效果依次减弱。因此，我们可以在Cu-P-Cr-Ni耐候钢成分基础上，利用微量Ca替代稀土元素来实现低成本地改善钢材耐大气腐蚀性能，为含Ca耐候钢种在耐工业大气腐蚀中的应用提供了一定的实验与理论依据。