Development of Alloy Design and Evaluation Systems for High Temperature Materials Based on Non-Steady-State Creep Concept

高温材料的长期蠕变性能是由短期蠕变试验来评价的。本研究的目的是改善短期蠕变数据的制定和长期性能的评估方法。1.持久寿命预测方法的改进：基于OMEGA方法提出了蠕变方程：ε =（1/OMEGA）{In（1+ zeta）-In（1-etat）}（1）其中ε为蠕变应变，t为时间，OMEGA，zeta和eta为材料常数。2.短期试验的相关条件：根据变形机制图选择短期试验条件，使蠕变机制不因工程设备的使用条件而改变。通过对2.25Cr-1 Mo钢长期蠕变试验数据的分析，阐明了试验条件的选择。发现现有的变形机制图存在一些误解。3.持久寿命预测方法的检验：用10^5h以上的长期蠕变数据对几种持久寿命预测方法进行了检验。在所提议的方法中，提出了更相关的方法。另一个值得一提的发现是固有蠕变强度的概念。也就是说，当试验持续时间足够长时，所有低合金钢的蠕变断裂强度相似。4.组织退化与蠕变寿命消耗的相关性：详细研究了马氏体钢蠕变过程中马氏体板条组织的退化。板条宽度的相对增长与蠕变应变之间存在线性关系。数据库系统的修改：将面向对象的数据库系统修改为适用于蠕变数据的形式。

Long term creep properties of high temperature materials are evaluated from short term creep tests. The objective of the present research is to improve ways of formulation of short term creep data and evaluation of long term properties. The results are summarized as follows :1.Improvement of rupture life prediction : The following creep equation was proposed based on OMEGA method :epsilon=(1/OMEGA){In(1+zetat)-In(1-etat)} (1)where epsilon is the creep strain, t is the time, and OMEGA, zeta and eta are material constants. This equation can predict more accurate rupture life from shorter creep tests.2.Relevant condition of short term tests : Short term test conditions are selected based on deformation mechanism maps so that creep mechanism does not change from service condition of engineering plant. Long term creep data of 2.25Cr-lMo steel was analyzed to clarify how to select the test conditions. It was found that deformation mechanism maps presently available have several misunderstandings. A correct mechanism map of the steel was proposed.3.Examination of prediction methodology : Several methods proposed for rupture life prediction were examined by long term creep date over 10^5h. More relevant methods were suggested among the proposed methods. Another finding to be mentioned is the concept of inherent creep strength. Namely, all the low alloy steels gives similar creep rupture strength when test duration is long enough.4.Correlation between microstructural degradation and creep life consumption : Degradation of martensitic lath structure was studied in detail during creep of martensitic steels. A linear relation was found between relative growth of lath width and creep strain. A nondestructive life assessment method was proposed based on the linear relation.5.Modification of database system : An object-oriented database system was modified to the form applicable to creep data.