【作者】 束国刚；

【导师】 文习山； 丁辉；

【作者基本信息】 武汉大学 ， 高电压与绝缘技术， 2004， 博士

【摘要】 T91、P91是美国上世纪七十年代研制开发的火力发电厂锅炉蒸汽管道、集热箱、再热器、蒸汽导管等用热强钢，该钢具有高的许用应力，高的持久强度，高的蠕变抗力，高的疲劳强度，高的热导率，良好的焊接性，较好的抗蚀性，以及适中的价格。当今美、欧、日等先进国家的火力发电厂已普遍使用了T91和P91钢，取得了良好的经济效益。我国于“十五”期间引进了该钢种，并进行了国产化研究与生产，10Cr9MolVNb钢就是T91、P91的国产化新钢种，但10Cr9MolVNb钢的研究和生产尚存在诸多问题，钢管质量比先：进国家的T91、P91有较大差距，难以应用到火力发电厂，为解决我国热强钢10Cr9MolVNb性能比先进国家有较大差距这一问题，本文调研和检测了T／P91钢国产化中存在的理论认识、生产工艺、钢管质量、工程应用等的现实状况，开展了该钢的组织结构、强化机理、合金化原理等的应用理论研究，进行了生产工艺的优化研究，并就优化工艺在钢管制造厂实施了工艺实践，对优化工艺生产的钢管进行了组织结构、力学性能、断口等的统计学评价与综合评价，详细研讨了钢在566℃高温时的一些性能特征，并将国产T91钢管在发电厂实施了工程应用和运行检测。 在理论认识上，本文的理论研究明确强调，经正火高温回火热处理的钢为回火板条马氏体组织。本文所作正火高温回火的实验证明，在A1温度以下高温回火时，板条马氏体只发生高温回复而不出现再结晶，这是合金元素Cr、Mo的大量固溶升高了回复与再结晶的温度，以及高温回复时释放了马氏体相变时的应变储存能，再加上高温回复时形成的位错网络的钉轧，致使再结晶的驱动力不足所致。马氏体板条发生高温回复时，板条内碎裂成了多个亚晶，高密度的位错规整为亚稳的位错网，析出的碳化物主要为M₂₃C₆型和MC型，M₂₃C₆型多以短条形在板条界和原奥氏体晶界析出，MC型则多以细短条形在板条内析出，AlN也与碳化物一同参与了钢的弥散析出强化。钢的强化机理除弥散析出强化之外，更以固溶强化、马氏体强化、细晶界面强化、位错强化等复合强化使钢获得满意的热强性。为此热强性目的，钢以Cr、Mo实现固溶强化和马氏体强化，升高马氏体的回复与再结晶温度，提高热强性，形成碳化物M₂₃C₆实现析出强化，但由于Mo和Cr的碳化物形成热小，Mo和Cr在高温时较易从基体固溶态向M₂₃C₆化合态转移从而引起M₂₃C₆的Ostwald熟化，故再以V、Nb固C阻止Mo、Cr向M₂₃C₆中转移。M₂₃C₆的Ostwald熟化是热稳定性的重要标志，界面能是公认的Ostwald熟化的驱动力，本文作者认为，对于热强钢来说，碳化物形成元素例如M。和Cr在基体固溶态和碳化物化合态的化学位是更重要的驱动力，因此碳化物在发生ostwald熟化时，不仅是碳化物尺寸、形态、分布的变化，更重要的是碳化物形成元素由基体向碳化物中迁移所引起的碳化物成分的变化。大量cr在基体中的固溶和马氏体板条发生亚晶碎化与形成亚稳位错网的高温回复，使钢具有高内耗的独特性质，从而提高了钢的抗疲劳能力。钢中N元素的存在，保证了钢在正火的高温加热时不出现Q（6）相，从而保证了钢的马氏体强化效果，同时所出现的AIN的弥散强化更进一步提高了钢的强度。 对原工艺生产的钢管进行的组织、亚结构、断口、强塑性、强韧性等一系列检测表明，钢的组织、亚结构、断口均未达到所希望的标准，马氏体高温回复时位错网密度低，碳化物析出的弥散度不高，M”q型碳化物在原奥氏体晶界显著长大，甚至出现了决不许可的块状铁素体，本文的实验证明，铁素体的出现是回火温度过高，高到了A1点以上所致。组织结构的不当，导致了强塑性和强韧性低，标准偏差大。t统计检验表明，取样位置的影响显著，强塑性和强韧性沿钢管上壁厚的均匀性差，裂纹扩展功小，总破断功小，并出现准解理脆断和放射状准解理断口。这一切均表明制造工艺不佳，调研发现，热处理作业时常常采取提高温度缩短时间的操作，这对于厚壁管显然是不适当的。造成这些问题的原因则是在理论上对钢的组织结构、强化机理、合金化原理等理论问题的认识尚不深入，甚至模糊误解钢的组织为索氏体;在工艺参数上存在不当;在生产作业管理上也待改进。 改进生产工艺的研究除精炼等工艺外，主要研究了钢管的热处理工艺，采用单因素试验法与正交试验法相结合，以室温和高温的强塑性与强韧性共16个力学性能指标的综合力学性能为判据，采用作者所提出的多指标级差量化综合评估法，优选获得了Pgl钢管的优化热处理工艺参数:正火温度1055℃土15℃（1040℃¹070℃）;正火冷却平均速率1000⁸00℃，30℃/min¹00℃/min:800⁶00℃，8℃/min⁵0℃/min;600⁴00℃，4℃/min³0℃/min;或800⁵00℃，7oC/min⁴0℃/min;回火温度765℃士15℃（750℃一780℃），回火冷却自然空冷或风冷。经复试和J积分延性断裂韧度核实，优化工艺可靠。 在成都无缝钢管公司P91钢管的制造中实施了优化工艺，对按优化工艺制造的钢管进行了服、T以、SEM的组织、亚结构、断口分析，用静力拉伸和动力示波冲击法测试了钢管在室温和高温的强塑性与强韧性等力学性能，并对其进行了统计学评价?更多还原

【Abstract】 T91 and P91 are heat resistant steels developed during 1970s in US for boiler components such as steam piping, steam head, reheater, etc in fossil power plants. The steels have higher performance in terms of allowable stress, rupture strength, creep-resistant ability, fatigue strength, and heat conductivity. The steels also have better weld ability and corrosion-resistant ability with a moderate price. Up to now, T91 and P91 have been widely used in fossil plants of the advanced countries and regions such as US, Europe and Japan with good economic benefits achieved. The steels were introduced in China during the 10th 5-year plan period, and the researches on its localization and the productions of the steels have since then been initiated. The 10Cr9MolVNb is a newly localized type of steel imitative of T91 and P91. But there have been many problems with 10Cr9MolVNb in its research and production. The quality of tube made of 10Cr9MolVNb is still substantially lower than that of tube made in advanced countries with as to be applied in power plant. In order to fill the performance gap between 10Cr9MolVNb and T91/P91, this paper carries out investigations on theoretical understanding and practice concerning production process; tube quality and engineering applications of domestically produced T91 and P91 steel. The paper also conducts application researches on theories of its structure, strengthening mechanism, alloying mechanism and optimization of production process. The optimized process has been used in a tube factory for verification need. The tubes manufactured with optimized process are then assessed statistically and comprehensively upon their structures, mechanic properties and fractures etc. The performance properties of the 10Cr9MolVNb under 566C temperature are discussed in detail in this paper. The paper also gives the application experience and testing results of the 10Cr9Mol VNb under operating condition.The paper indicates definitely in theory that the microstructure of the 10Cr9Mo1VNb is tempered martensitic lath when normalized and tempered under high temperature. It is proved by the experiments in this paper that lath martensite only appears high temperature recovery other than recrystallization when tempered below the temperature of A1. This is caused by the lack of driving force of recrystallization due to the elevation of recovery and recrystallization temperature owing to the solid solution of alloying element Cr and Mo, the release of strain energy stored during the phase transformation of martensite and the formation of dislocation network pining. When recovered under high temperature, the inner structure of martensitic lam breaks into several sub-grains. The high-density dislocation transforms into metastable type. The carbide precipitated are mainly type M23C6 and type MC, the former with elliptic shape appearing on grain boundary of martensite lath and austenite, while the latter with fine-short shape precipitated inside of the martensite lath. A1N also participates together with carbide in dispersed precipitation strengthening of steel. Besides dispersed precipitation strengthening, the steel acquires heat-resistant property through some composite strengthening mechanisms such as solution treatment, martensitic strengthening, fined interface surface strengthening, etc. The solution strengthening and martensitic strengthening are realized with the use of Cr and Mo. The precipitation strengthening is acquired through the precipitation of carbide M23C6 due to the elevation of the temperature of recovery and recrystallization. However, Mo and Cr can easily migrate from solid solution matrix to compound M23C6 under high temperature causing the Ostwald ripening of M23C6, thus, V, Nb and solid C are applied to obstruct the migration of Mo and Cr toM23Q5. Ostwald ripening of M23C6 is a significant mark indicating the heat stability of the steel. The interfacing surface energy is widely recognized as the driving force of the Ostwald ripening. However the author of this paper thinks that the更多还原