一种新型超（超）临界锅炉用钢的研究- - 具有高密度纳米级孪晶结构高氮奥氏体不锈钢的高温蠕变行为

Based on research and development status of ultra supercritical boiler steel in China, high nitrogen austenitic stainless steel is prepared by using our patent. It is shown that the recrystallization temperature of the experimental material is close to 980℃, and high density nano-twin substructure can be obtained by thermo-mechanical deformation. Such a substructure has high thermal stability and benefits to improve creep rupture strength. In this research, high temperature creep behavior of high nitrogen austenitic stainless steel with high density nano-twin substructure will be investigated, and the interaction between high density nanotwins and dislocations during the high temperature creep process will be discussed. Thermal stability mechanism of nano-twin substructure, nano-twin strenghing mechanism, and the transmission behavior of dislocations under the high temperature creep condition will also be revealed. Based on the above data, a novel economical material which can be used as the ultra supercritical boiler steel will be provided, and its working temperature is over 700℃; A new creep strengthening mechanism under high temperature for high nitrogen austenitic stainless steel will be explored; Furthermore, the method of controlling microstructure of high temperature creep resistance will be found. The theoretical basis will be supplied to develop ultra supercritical boiler steel with independent intellectual property in China.

本项目基于我国超（超）临界锅炉用钢的研究和发展现状，采用专利技术制备高氮奥氏体不锈钢，试验表明，该材料具有较高的再结晶温度（开始再结晶温度980℃），通过热机械变形，能够形成高密度纳米级孪晶亚结构，该结构具有较高的热稳定性，使材料的蠕变断裂强度提高。项目重点通过对具有高密度纳米级孪晶结构高氮奥氏体不锈钢高温蠕变行为的研究，以及高温蠕变过程中位错和孪晶的相互作用、高温蠕变试验条件下纳米级孪晶的变形机制，揭示试验材料在高温状态下生成稳态高密度纳米级孪晶的原因及纳米孪晶的蠕变强化机理。在材料方面，提供一种可以耐700℃、经济的锅炉用钢；在理论方面，探求一种高氮奥氏体不锈钢耐高温蠕变的强化机理；在工艺上，寻求一种具有耐高温蠕变性能显微结构的控制方法，为我国发展具有自主知识产权的超（超）临界锅炉用钢提供理论基础。

基于我国超（超）临界锅炉用钢的研究和发展现状，采用专利技术制备高氮奥氏体不锈钢，该材料具有较高的再结晶温度（开始再结晶温度980℃），通过热机械变形，能够形成高密度纳米级孪晶亚结构，材料的热稳定性和蠕变断裂强度提高。研究表明：高氮奥氏体不锈钢形变强化主导机制受控于形变孪晶的不断细化。一方面，试验钢具有高浓度氮元素固溶在奥氏体晶格间隙位置，提高了电子浓度，显著降低堆垛层错能，利于产生孪晶；另外，氮原子电子结构特点，提高了金属键能，易于形成SRO偏聚畴，产生短程有序结构，使位错运动以平面滑移为主导，位错运动过程中产生的大量肖克莱不全位错1/6 [12 ̅1]，是孪晶的形核源。.通过对固溶处理后的高氮钢进行不同程度的冷变形，发现随变形量的增加，孪晶数目不断提高，孪晶片宽度逐渐减小，形变诱发主孪晶和共轭孪晶（次生孪晶），尺寸细化到10nm左右，形变显微结构形成以孪晶形态为主的微观结构形式。而且，变形导致强度的提高与试验钢孪晶片的细化程度呈线性增长。同时，该材料具有较高的高温蠕变性能。以上研究结果可为我国发展具有自主知识产权的超（超）临界锅炉用钢提供理论基础。