新一代稀土耐候钢的耐蚀机理与耐火性能研究

The anticorrosion performance and fire resistance performance of rare earth weathering steel are studied from the view of application in civil engeering. The rare earth weathering steel is developing in the direction of high corrosion resistance and high strength because of the progress of manufacture technology and the increasing requirements of performance. Both the cleanness and the alloy compositions of the new type of rare earth weathering steel vary, so the effect of rare earth and the anticorrosion mechanism of steel accordingly change. Therefore, corresponding research is needed to be developed. Furthermore, the rare earth weathering steel even has greater application value in civil engineering than in traditional application fields because of its excellent anticorrosion performance. However, in order to obtain ideal application effect in civil engineering, the fire resistance problem of rare earth weathering steel must be studied and solved. In this project, the new type of Cu-P and Cu-P-Cr-Ni weathering steel with rare earth is the research object. The influence of rare earth on the steel performance and the microalloying effect are studied. The anticorrosion mechanism of weathering steel is researched using physical, chemical and electrochemical methods, including the composition and protection mechanism of surface corrosion products, the influence and mechanism of rare earth on the origination and development of rust layer, and the influence of the inclusions on the anticorrosion performance. At the same time, the fire resistance performance of the new type of rare earth weathering steel is studied and the constitutive relation model at high temperature is established. The fire resistance performance of construction members using rare earth weathering steel is also simulated and analyzed. From these researches of both anticorrosion and fire resistance performance, it is beneficial and feasible to determine the optimal content of rare earth and develop the new type of rare earth weathering steel with high strength suitable for application in civil engineering. The study results in this project are useful to promoting the development and application of rare earth weathering steel which has Chinese distinguishing feature of natural resources even further.

从工程应用的角度研究稀土耐候钢的耐蚀和耐火性能。由于工艺水平和性能要求的提高，稀土耐候钢进一步向高耐蚀和高强度方向发展，洁净度和合金成分都有所变化，因此稀土的作用和钢的耐蚀机理也发生改变，需要作相应研究。此外由于防腐性能良好，除了传统应用领域，耐候钢在土木工程中有更大的应用前景，但要实现其在工程中的理想应用，就必须要研究解决其耐火问题。本项目针对洁净的Cu-P和Cu-P-Cr-Ni系新一代稀土耐候钢，研究稀土对钢性能的影响及作用机制；从物理、化学、电化学角度研究其耐蚀机理，包括表面腐蚀产物的保护机理，稀土对锈层生成的影响及作用机制，夹杂物对耐蚀性的影响。同时研究新一代稀土耐候钢的耐火性能，建立高温本构关系模型，并对采用稀土耐候钢的结构构件进行抗火性能分析。通过耐蚀与耐火两方面的研究，确定最佳稀土含量，发展适于工程应用的新一代稀土高强耐候钢，推动有中国资源特色的稀土耐候钢的进一步开发和应用。

为适应新一代稀土耐候钢向高洁净、高耐蚀、高强度方向发展的需要，并开发适于土木工程应用的稀土耐候钢，本项目以新一代洁净稀土耐候钢为研究对象，研究稀土在钢中的行为和作用机理、钢的耐蚀机理及其耐火性能。取得了以下研究成果：（1）氧约为0.0020wt%，硫约为0.0040wt%的稀土耐候钢，稀土含量在0.0065~0.01wt%的范围内，氧为0.004~0.007wt%，硫为0.008wt%的稀土耐候钢，稀土含量在0.012~0.023wt%范围内，钢中夹杂物基本上全部变性为细小弥散分布的球状稀土夹杂，85%以上的夹杂物尺寸小于2μm。稀土改变了钢中原有夹杂物的性质，减少其对钢材性能的危害作用，如此细小夹杂可以变为对钢材性能有利的因素，使得钢的组织细化，并且有一定的固溶稀土含量，使得显微组织中珠光体的形貌由片层状变为粒状，晶界得到净化。适量的稀土提高了耐候钢的综合机械性能，即改善材料塑韧性的同时也提高了强度。（2）加稀土前钢液中的氧硫含量是稀土能否发挥有效冶金效果的一个重要前提条件。在低硫低氧的情况下，加入比高氧硫钢少2倍的稀土就可以达到良好变质夹杂的作用，细化球化弥散夹杂物的效果也更好。而且能获得更多的固溶稀土量，起到合金化作用。（3）研究了工业大气和海洋大气环境下稀土耐候钢的耐蚀性及耐蚀机理。从电化学角度给出了试样锈层保护性能的定量结果并揭示了稀土耐候钢耐蚀性优越的原因。（4）耐候钢加入稀土后，通过变质有害夹杂为球状弥散分布的细小稀土氧硫化物，减弱了微区域电化学腐蚀，分散分布的细小夹杂作为腐蚀反应的活化点，有利于促进钢表面发生全面均匀腐蚀以及后期连续均匀致密锈层的生成。稀土促进了合金元素Cu在锈层中的富集，而且使得不稳定保护性差的锈蚀相向稳定的锈蚀产物转变，达到了提高钢耐蚀性能的作用。此外稀土通过细化钢的晶粒组织以及改变珠光体的形貌使得钢基体表面形成的腐蚀微电池分布均匀、锈蚀产物更加细小，从而生成了保护能力更好的致密锈层。（5）综合分析了稀土耐候钢的常温和高温力学性能，结果表明稀土提高了耐候钢的热强性，稀土耐候钢与普通碳钢相比具有更高的强度和相当的塑性性能，用于工程结构中是合理可行的；（6）借鉴已有的研究成果，给出了稀土耐候钢高温下的应力-应变关系模型。对采用稀土耐候钢的钢管混凝土柱的抗火性能进行了数值分析，编制了模拟程序，对稀土耐候钢在工程中的应用进行了尝试性研究。