【作者】 杨哲；

【导师】 王国栋； 刘振宇；

【作者基本信息】 东北大学 ， 材料加工工程， 2008， 硕士

【摘要】 随着环境保护意识的日益提高,LNG(液态天然气)作为一种清洁能源,占据的比重将越来越大,因此开发具有我国自主知识产权的LNG结构材料——9Ni低温钢已经迫在眉睫。本文以9Ni钢的力学性能为评价指标,通过成分设计、热模拟和轧制工艺、热处理工艺等实验,分析各工序对其组织和力学性能的影响,优化了工艺参数。研究的内容和结果包括：1.参考国内外有关9Ni钢的成分标准,优化其成分参数,为工业生产提供有效依据；2.采用热力模拟试验机开展9Ni钢的高温热变形实验。通过单道次压缩试验,建立了不同温度、不同变形速率条件下的9Ni钢奥氏体的应力—应变关系,推导变形抗力模型；通过连续冷却试验测定9Ni钢静态与动态CCT曲线,结果表明：在1℃/s-30℃/s的冷却条件下仅存在贝氏体转变区域,同静态相比,动态贝氏体转变温度较低,转变结束温度较高,转变速度较高,即贝氏体区域较小；3.模拟模铸和连铸连轧奥氏体区终轧工艺,为达到减量化生产的目的,在其基础上尝试两种新工艺：连铸连轧的双相区终轧工艺和在线热处理工艺。试验结果表明：经两种新的轧制工艺生产出的9Ni钢都表现出良好的力学性能；4.探讨了9Ni钢成分以及终轧温度对其力学性能的影响,结果表明：Ni含量影响显著,过高和过低时力学性能都较差；终轧温度为730℃时,组织细小,力学性能较好；5.通过热处理试验改变各阶段温度参数,优化热处理方案,同时研究分析热处理各阶段温度参数对组织和低温韧性的影响。结果表明：优化调质热处理(QT)工艺参数为800℃淬火+580℃回火,淬火温度影响晶粒度,回火温度影响回转奥氏体的析出量和稳定性；优化两相区热处理(QLT)工艺参数为800℃淬火+670℃中间淬火+580℃回火,淬火温度影响作用不明显,回火温度影响回转奥氏体的析出量和稳定性；经QLT后,9Ni钢的低温韧性更好。更多还原

【Abstract】 With the enhancement of protecting the environment consciousness, the LNG (Liquefied Natural Gas) is used more and more because of being a variety of clean energy. Consequently, it is a critical thing to develop 9Ni constructional material with self-owned intellectual property rights. The mechanical property of 9Ni steel was focused. And the influence of each process on the microstructure and mechanical property was investigated by means of component design, thermal simulation, rolling process and heat treatment process. Moreover, parameters optimization was achieved. The main experiments and conclusions were as follows:1. Referred to domestic and overseas standards of 9Ni steel, effective component scheme was provided though optimizing component parameters.2. The hyperthermia deformation experiments were done by use of the thermal simulation machine. The relationship of austenitic stress-strain under different temperatures and speeds was established by single-pass compression experiment. In addition, model of the resistance to deformation was deduced. And the static and dynamic CCT curves of 9Ni steel were drawn by continuous cooling transformation experiment. The conclusions were as follows:there are only bainite transformation zone. Compared with static CCT curve, the temperature of bainitic starting transformation is lower, conversely its finishing transformation is higher. So it means that the speed of dynamic bainite transformation is higher.3. The die-casting and continuous casting-rolling process were repeated. In order to get 4R(Reduce, Reuse, Recycle, Remanufacture) target, rolling process of finishing temperature at two-phase region and heat treatment online was tried. And mechanical properties of 9Ni steel under both processes were excellent.4. The influences of component of 9Ni steel and finishing rolling temperature on mechanical property were analyzed. The conclusions were as follows:the content of nickel is significant to its mechanical property. Neither lower nor higher of the nickel content is benefit to its mechanical property. Additionally, the microstructure is fine when the finishing rolling temperature is 730℃. 5. The parameters of heat treatment processes were optimized by changing the temperature parameters in every stage. Moreover, the relationship among temperature, microstructure and hypothermia impact toughness was studied. The conclusions were as follows:in the process of quenching and tempering (QT) heat treatment, the optimized temperature parameters are quenching at 800℃and tempering at 580℃. Additionally, the temperature of quenching has a great effect upon grain size, and the temperature of tempering has a great influence on the precipitation and stabilization of reverted austenite. Then in the process of quenching, intermediate quenching and tempering (QLT) heat treatment, the optimized temperature parameters are quenching at 800℃, intermediate quenching at 670℃and tempering at 580℃. But the temperature of quenching has no obvious influence in QLT heat treatment. Similarly, the temperature of tempering has the same effect. Compared two heat treatment process, the hypothermia impact toughness of 9Ni steel is improved by the QLT heat treatment.更多还原