超快速冷却条件下低碳钢中纳米碳化物析出控制及综合强化机理

Steels have been keeping the development towards high strength and high toughness. Nano-precipitation hardening, as an important mechanism besides fine grain strengthening, is one of the important developing directions for steel. At present, although much research of the precipitation law and strengthening mechanism of nano-carbides has been done, there still remain many key scientific issues to solve. The development of advanced techniques such as ultra fast cooling (UFC) and the quantitative characterization of nano-precipitates provides facilities for research of nano-precipitation strengthening. This project intends to carry out research of nano-carbide precipitation control mechanism and process under UFC in low carbon steels and research of the comprehensive strengthening mechanism. The research will focus on nano-carbides quantitative characterization in low carbon steels, nano-carbide precipitation behavior and control mechanism under UFC, comprehensive strengthening mechanism based on nano-carbide precipitation strengthening. Through this project, the control theory and technology of nano-carbides characteristics such as type, size, quantity, distribution and so on in low carbon steels can be formed, precipitation strengthening effect can be fully developed, and comprehensive strengthening mechanism can be improved. The strength of steel will be significantly enhanced with no or less microalloys addition, and it will promote energy saving in the steel industry. This study will provide physical metallurgy supervision for developing precipitation strengthening steels and comprehensive strengthening steels. The resultant theory and technology can be extended to other metal fields.

钢铁材料不断向高强度高韧性方向发展。纳米析出强化作为细晶强化之外的重要强化方式，是钢的重要发展方向之一。目前虽然对纳米碳化物析出规律和强化机理做了较多研究，但仍然存在许多关键科学问题待于解决。超快速冷却、纳米析出物定量表征等先进技术的发展为纳米析出强化的研究提供了条件。本项目拟开展超快冷条件下低碳钢中纳米碳化物析出相的控制机理与工艺的研究以及钢的综合强化机理的研究。重点研究低碳钢中纳米碳化物的定量表征；超快速冷却条件下纳米碳化物析出行为和控制机理；基于纳米碳化物析出强化的综合强化机理。通过本项目研究，形成低碳钢中纳米碳化物类型、尺寸、数量、分布等特征的控制理论与技术，充分发挥析出强化作用，完善钢的综合强化机理，在不添加或少添加微合金元素的条件下显著提高钢材强度，促进钢铁行业的节能降耗。本研究将为发展析出强化型及综合强化型高性能钢提供物理冶金学指导，其理论和技术可推广至其它金属领域。

纳米析出强化作为细晶强化之外的重要强化方式，是钢的重要发展方向之一。超快速冷却、纳米析出物定量表征等先进技术的发展为纳米析出强化的研究提供了条件。.项目围绕超快冷条件下低碳钢中纳米碳化物析出相控制机理与工艺开展研究，建立了复合型合金碳化物析出热力学和动力学模型，得出基体平衡浓度和瞬时浓度、析出相成分、形核率、数量密度、平均半径等随温度或时间的变化规律；计算出Fe-C合金奥氏体的相变驱动力，得出过冷奥氏体分解析出纳米渗碳体规律，且通过超快冷技术实现了普通碳锰钢中渗碳体的纳米级析出，形成显著强化效果；通过对微合金钢的超快冷工艺研究及对析出物的定性、定量统计分析发现，超快冷条件或添加微合金元素，均可促进纳米碳化物的析出强化，进而提高钢的强度；微合金碳化物和纳米渗碳体可同时起到析出强化作用；Ti元素的添加，增加了TiC相间析出数量密度，细化析出粒子尺寸，增强析出强化效果；Nb-V复合析出时，随着等温时间延长，析出物中V的比例逐渐增大，并出现两种形核方式，即置换型和异质形核型复合析出；采用无损电解提取技术，获得了四边形MC类碳化物，以及针状、片状M3C类纳米碳化物；冷速显著提高时，M3C及MC类碳化物的析出强化增量均有所增加。.项目共发表论文65篇，其中SCI收录43篇；申请国家发明专利12项（8项已授权）；研究成果作为创新点之一，获国家科技进步二等奖1项、省部级一等奖5项、二等奖1项。项目所形成的超快冷工艺下纳米碳化物析出相控制理论与技术，可在不添加或少添加微合金元素的条件下显著提高钢材综合性能，为发展析出强化型和综合强化型高性能钢提供物理冶金学指导，完善钢的综合强化机理，亦可推广应用于其它金属材料领域，具有重要的科学意义。项目成果在南钢、宝武韶钢等企业得到应用，实现了低合金钢的减量化生产和普碳钢的升级，促进了钢铁企业“资源节约、节能减排”绿色化发展。