冷轧复合不锈钢表面自愈膜形成及韧脆性转变机理与调控措施

Hot-roll bonding stainless steel/carbon steel has problems of expensive equipment, complicated preparation process, high production costs and limited size. Besides, the quality and performance of products are difficult to satisfy the higher operating requirements. The project focuses on the problem of the unrealized cold rolled stainless steel/carbon steel clad composites, which results from self-healing feature of ductile oxidation film on the surface of stainless steel. Thus, the new process has been proposed, which combines carbonization on surface of stainless steel and cold-hot rolling technology to prepare stainless steel/carbon steel clad composites. In the meanwhile, the project is based on the principle of the gradient ductility of stainless steel carburized layer along the thickness direction. The researches emphasize on the energy source of atoms diffusion and migration, mechanism of growth and reaction of carburized layer, and mechanism of deformation and cracking of carburized layer in the process of cold-roll bonding. The mainly purpose of the project is to solve the key scientific problems of mechanism of self-healing characteristic of stainless steel oxidation film, interfacial cold-roll bonding mechanism of carburized stainless steel/carbon steel clad composites. Mechanism of self-healing film growth and ductile-to-brittle transition on the surface of stainless steel can be preliminary established and integrated control technology prototype of surface treatment and rolled bonding technologies can be developed. Consequently, it shall be the foundation of developing new theories and techniques for the preparation of stainless steel/carbon steel clad composites and promoting the efficient preparation and wide application of high performance and low cost stainless steel/carbon steel clad composites.

目前采用热轧复合法制备不锈钢/碳钢复合板所需设备价格昂贵、制备工艺繁琐、生产成本高、复合板尺寸受限、产品质量和性能难以满足更高使用要求，针对不锈钢表面韧性氧化膜自愈特性导致冷轧复合法无法实现不锈钢/碳钢复合的问题，本项目基于不锈钢渗碳层的韧脆性沿厚度方向梯度变化的原理，提出将不锈钢表面渗碳处理与冷-热轧复合法相结合制备不锈钢/碳钢复合板的新工艺。重点开展不锈钢表面原子迁移扩散能量源、不锈钢表面渗碳层的生长规律及作用机制、冷轧复合过程中不锈钢表面渗碳层的变形和开裂机制等研究，主要解决不锈钢表面氧化膜自愈机制及与渗碳层的结构关联性、表面渗碳不锈钢/碳钢冷轧复合界面结合机制等关键科学问题，初步建立冷轧复合不锈钢表面自愈膜形成及韧脆性转变机理，开发不锈钢表面处理—轧制复合一体化控制技术原型，为发展不锈钢/碳钢复合板制备新理论与新技术，推动高性能低成本不锈钢/碳钢复合板的高效制备和广泛应用奠定基础。

不锈钢/碳钢复合板兼具不锈钢高强度、耐腐蚀、韧性高和碳钢低成本等优良性能，在交通桥梁、核电设备、船舶运载等行业中具有重要并广泛的应用。高温真空轧制是目前实现不锈钢/碳钢复合的主要方法，由于受到抽真空和轧制设备的限制，不锈钢/碳钢复合板的生产和使用受到严重制约。不锈钢表面在冷轧条件下难以使表面氧化膜发生开裂，无法与碳钢实现粘合，在非真空条件下热轧则界面发生剧烈氧化，不利于不锈钢/碳钢复合。本项目通过低温气体渗碳对不锈钢进行表面改性处理，改善了不锈钢的表面性能，结合数值模拟仿真和表界面宏微观表征分析，揭示了制备工艺-微观组织-界面结合机制间的关系。研究了不锈钢表面氧化膜的生长机制；建立了不锈钢低温表面渗碳有限元模型，分析了不锈钢低温渗碳表面界面性能，提出了不锈钢低温表面渗碳处理控形控性规律和方法；研究了低温气体渗碳不锈钢与碳钢冷轧复合的工艺，揭示了渗碳层在轧制作用下的变形机制，阐明了不锈钢表面渗碳层冷轧过程中的变形和开裂机制。主要研究结果表明：氧化膜的结构主要分成富含氧化铁的外层和富含氧化铬的内层。不同成膜温度下，铁和铬的扩散速度不同，导致不锈钢表面氧化膜的成分和分层在双层和单层间转变。温度对氧化膜的力学性能的影响则是通过改变膜层中各元素的含量和分布来影响氧化膜的力学性能。低温渗碳主要是形成过饱和的奥氏体，内外浓度差的减小和不锈钢奥氏体对碳原子的溶解程度降低，导致表面碳浓度增加的速率随着渗碳过程的进行而减慢。但渗碳层深度变化有限，渗件深处的碳浓度变化不明显。轧制复合界面层的损伤值越高，界面复合效果也就越好，表面处理方式对不锈钢的表面形貌有较大影响，进而影响不锈钢板材表面的开裂行为，具有较大粗糙度且表面形貌呈现规律起伏状态的不锈钢表面有利于轧制复合。本项目研究结果为金属层状复合材料的制备加工、加快高性能金属层状复合材料的低成本高效制备加工和推广应用奠定了良好的基础。