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.

强行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，而不会对蠕变破裂应变产生任何不利影响。但是，当添加少量的氮和/或钒时，可以看到氮的最有益作用。为了阐明氮和niobium对蠕变特性的综合作用，AS310s和25cr-20ninbn钢含有0.2个质量为NB的0.2质量％和0.45质量的NB进行本研究。进行本研究。仔细研究。进行的研究表明，25cr-20ninbn的蠕变寿命与SUSS的蠕动寿命相同，而不是SUSS 30s的化学效果。这些添加的少量。为了描述假想应变速率的应力和温度依赖性，得出了这些钢的本构方程。尽管这些钢中的主要替代元素几乎可以与脱位相互作用，但获得了一些证据，表明在25CR-20ninbn钢中，围绕移动的脱位形成了CR-N簇的气氛。除了由于聚类而引起的固体溶液硬化外，还可以清楚地表明，降水硬化在25CR-20ninbn钢中起着重要作用。应力松弛和应力变化测试的分析表明，有效应力的比例约为16％，阈值应力约为190 MPa。使用有关由TEM确定的粒子半径分布的数据，基于空隙强化理论从计算中获得了大约相同幅度的实验级的阈值应力。