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STRESS ACCELERATION FACTOR, Ω AND STRENGTHENING MECHANISMS CONTROLLING MECHANICAL PROPERTIES OF HIGH NITROGEN HEAT RESISTANT STEELS AT ELEVATED TEMPERATURES

应力加速因子Ω和控制高氮耐热钢高温力学性能的强化机制

基本信息

批准号：
11650717
负责人：
ENDO Takao
金额：
$ 1.41万
依托单位：
YOKOHAMA NATIONAL UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

Forcibly introduced nitrogen has been regarded as the last element for the improvement of heat resistant steels because it improves the mechanical properties without any adverse effect on creep rupture strain. However, the most beneficial effect of nitrogen can be seen when nitrogen is added with a small amount of niobium and/or vanadium. In order to elucidate the combined effect of nitrogen and niobium on creep characteristics, aSUS310S and a 25Cr-20NiNbN steel containing 0.2 mass % of N and 0.45 mass % of Nb were selected for the present study.Creep tests showed that the creep life of the 25Cr-20NiNbN was one hundred times longerthan that of the SUS310S notwithstanding that the chemical compositions were about the same except for a small amount of these additions. In order to describe the stress and temperature dependence of the imaginary strain rate, the constitutive equations for these steels were derived.Although the main substitutional elements in these steels can hardly interact with dislocations, some pieces of evidence were obtained that an atmosphere of Cr-N clusters was formed around moving dislocations in the25Cr-20NiNbN steel. Besides the solid solution hardening due to clustering, it was made clear that the precipitation hardening played an important role in the 25Cr-20NiNbN steel. The analysis of stress relaxation and stress change tests revealed that the fraction of effective stress was about 16% and the threshold stress was about 190 MPa. Using the data on the distribution of particle radius determined by TEM, the threshold stress of about the same magnitude of experimental one was obtained from calculation based on the void strengthening theory.

强制引入的氮被认为是改善耐热钢的最后一个元素，因为它改善了机械性能，而对蠕变断裂应变没有任何不利影响。然而，当氮与少量铌和/或钒一起添加时，可以看到氮的最有益效果。为了阐明氮和铌对蠕变特性的联合作用，本研究选用aSUS 310 S和含N 0.2mass%、Nb 0.45mass%的25 Cr-20 NiNbN钢进行蠕变试验，结果表明，25 Cr-20 NiNbN钢的蠕变寿命比20 NiNbN钢的高，20 NiNbN比SUS 310 S长100倍，尽管除了少量的这些添加物之外，化学成分大致相同。为了描述假想应变率的应力和温度依赖性，推导了这两种钢的本构方程，虽然这两种钢中的主要替位元素几乎不与位错发生相互作用，但在25 Cr-20 NiNbN钢中，运动位错周围形成了Cr-N团簇气氛。结果表明，25 Cr-20 NiNbN钢中除团簇固溶硬化外，沉淀硬化也起着重要作用。应力松弛和应力变化试验分析表明，有效应力分数约为16%，门槛应力约为190 MPa。利用TEM测量的颗粒半径分布数据，根据空穴强化理论计算得到了与实验值相当的临界应力。