【作者】 吴红艳；

【导师】 刘相华； 杜林秀；

【作者基本信息】 东北大学 ， 材料加工工程， 2008， 博士

【摘要】 随着国民经济的快速发展,耐候钢作为一种经常大量使用的材料,仅具有良好的耐腐蚀性能已经不能满足生产使用的需要,在降低成本的基础上提高强韧性等综合力学性能是耐候钢发展的方向。超细晶耐候钢是既具有较高的强度和韧性,又具有优良的耐大气腐蚀性能的钢种,日益受到人们的重视。本文结合国家二期973计划项目“工业大气环境下铁素体/珠光体型耐候钢合金化与组织控制理论研究”,进行了低成本Mn-Cu耐候钢热加工过程中的组织变化规律、晶粒细化机制、贝氏体相变强化工艺方面的研究,通过实验室干湿交替加速腐蚀试验、电极化曲线试验研究其耐腐蚀性能,论文主要工作如下：(1)研究了变形温度、变形量和应变速率对耐候钢动态再结晶行为及组织演变的影响。结果表明,在变形温度高、应变速率低时表现出典型的动态再结晶特征,确定了动态再结晶激活能。研究了变形参数对变形抗力的影响规律,回归出了一种较高精度的变形抗力数学模型。(2)研究了耐候钢奥氏体热变形后等温保持时间里的静态再结晶行为,得到了静态软化率曲线,讨论了变形温度、预变形量对静态再结晶行为的影响,确定静态再结晶激活能,建立了相应的静态再结晶动力学模型。(3)采用热膨胀法测定了不同变形量的连续冷却转变曲线,结合金相分析,给出了变形以及冷却速度对耐候钢显微组织的影响规律；研究了变形工艺参数对铁素体相变和贝氏体相变的影响。结果表明,变形扩大了铁素体区和珠光体区,缩小了贝氏体区,促进了铁素体相变；随着变形量的增大,铁素体和贝氏体开始转变温度升高。(4)利用热模拟实验,研究了变形工艺参数对显微组织的影响规律；在此基础上,利用实验轧机进行了热轧实验,对细晶化工艺进行了研究,得到了轧制工艺参数对显微组织和力学性能的影响规律,制定了合理的控轧控冷工艺制度。实验结果表明,随着终轧温度和卷取温度的降低,实验钢的强度提高,屈强比略有提高,延伸率稍有降低；随着锰含量的增加,组织中贝氏体含量增加,铁素体含量减少,晶粒变细,实验钢的强度提高。(5)对实验钢与参比钢SPA-H钢和Q345钢在实验室进行了干湿交替加速腐蚀试验和电化学试验,研究了耐候钢的耐蚀性能及不同晶粒尺寸对耐腐蚀性能的影响,同时对比分析了耐候钢和碳钢锈层结构的差异,分析了合金元素在耐腐蚀性能方面的作用,并讨论了耐候钢的耐腐蚀机理。(6)根据热模拟实验和热轧实验的结果,确定了耐候钢集装箱板的控轧控冷工艺参数,在济钢1700热连轧机组上进行了工业轧制实验,并对轧出的产品进行了耐腐蚀性能、力学性能的检测及显微组织分析,得出了耐腐蚀性良好、各项力学性能均达到要求的耐候钢。结果表明,制定的控轧控冷工艺参数合理可行。更多还原

【Abstract】 With the rapid development of national economy, only good corrosion resistance could not meet the needs as a kind of widely used steel. Improving combination property including the strength and toughness and reducing the cost of production is the new development direction. Ultra-fine grain weathering steel has high strength and toughness, as well as better corrosion resistance, and more and more attention has been paid to them. Under the background of National Secondly 973 Project, which is about the theory research for ferrite and pearlite weathering steel of alloying and microstructure controlling in industry atmospheric environment, the present work is to investigate the microstructure changing, grain refinement, the strengthening of bainite transformation for low cost Mn-Cu weathering steel during hot rolling process, to investigate corrosion resistance by dry/wet cyclic accelerated corrosion experiment and electro-polarization experiment. The main work is as follows:(1) The influence of the deformation temperature, strain value and strain rate of the weathering steel on the austenite dynamic recrystallization behavior and microstructure evolution were investigated. The result indicates that the typical dynamic recrystallization characters are showed when the samples are deformed with small strain rate and high deformation temperature. The activation energy of dynamic recrystallization was obtained. Meanwhile, the influence of deformation parameters on resistance of deformation were investigated and its mathematical model was established.(2) The behavior of austenite static recrystallization of the weathering steel during constant temperature after the hot deformation was investigated and the softening rate curves of the weathering steel were obtained. The influence of deformation temperature and pre-strain value on static recrystallization was discussed. The activation energy of static recrystallization was obtained and the static recrystallization kinetic model was established.(3) The thermal expansion method was taken to test the CCT curves on condition of different stain value. With the metallographic analysis, the influence of strain value and cooling rates on microstructure of the weathering steel was obtained. The influence of deformation parameters on ferrite transformation and bainite transformation was investigated. The results indicate that deformation make ferrite and perlite area be enlarged, bainite area be reduced, promoted the transformation of austenite to ferrite. The starting transformation temperature of austenite to ferrite and bainite increased with increasing strain value.(4) By the thermal simulation experiment, the influence of the deformation parameters on microstructure was investigated. Based on the thermal simulation experiment, the grain refining technology of the steel was investigated through the hot rolling test in the laboratory. The influence of the deformation parameters on the microstructure and mechanical property of the weathering steel was obtained, and the proper TMCP parameters were made. The experiment indicated that the strength and yield ratio of weathering steels increased and elongation percentage decreased a little with decreasing finish rolling and coiling temperature. The results indicate that the volume fraction of bainite increased and ferrite decreased, and the grain is refined and the strength increased with increasing Mn content.(5) Dry/wet cyclic accelerated corrosion experiment and electro-chemistry experiment were conducted on the weathering steels as well as SPA-H steel and Q345 steel, to investigate the corrosion resistance for weathering steels with different grain size. Meanwhile, the difference of rust layer structure between weathering steels and carbon steel was analyzed, so as to have a better understanding of the role of alloying elements on corrosion resistance, and the principle of corrosion resistance of weathering steel was investigated.(6) On the basis of thermal simulation and hot rolling experiment at laboratory, TMCP parameters were determined for container plate of weathering steel, then the industrial experiment was carried out on 1700 hot strip mill. Through analysis on corrosion resistance, the mechanical properties and microstructure of samples obtained under industrial experiment condition, the weathering steel strip was obtained that corrosion resistance and mechanical properties met the requirement. The results indicate that the TMCP parameters are rational schedule.更多还原