9%—12%Cr铁素体耐热钢持久性能评估方法的研究

STUDY ON CREEP-RUPTURE PROPERTY ASSESSMENT METHOD FOR 9%—12%Cr FERRITIC HEAT-RESISTANT STEELS

常规时间-温度参数法（TTP）,如Larson-Miller Parameter（LMP）参数法以及Orr-Sherby-Dorn（OSD）方法对9%—12%Cr铁素体耐热钢进行持久性能预测时存在性能过估,且预测值与实测值之间存在明显差异,本文提出了LMP的分区及其C值优化,以及基于短时实验数据（≤5×10^3h）预测长时（5×10^3—1×10^5h）持久性能的方法.利用已有的持久性能数据,应用所提出的方法进行了应力与持久断裂时间及其相关参量的计算、作图及其比较.结果表明,单区LMP方法的C值随钢种而异;多区LMP方法的C值随钢种及实验应力区而异;基于短时实验数据（≤5×10^3h）预测长时（5×10^3—1×10^5 h）持久性能的预测值与实测值吻合;d[g（σ）]/d（P）随P的变化率可反映不同钢种持久性能的稳定性;LMP分区法及预测函数优化法的计算值与实测值的吻合性很好并进一步克服了利用给定温度下短时持久实验数据外推长时持久性能的过估倾向.

Long-term creep-rupture properties are usually evaluated from short-term data by time-temperature parameter（TTP） method,such as Larson-miller parameter（LMP） and Orr-Sherby-Dorn （OSD） methods.However,the conventional TTP methods sometimes overestimate long-term creep rupture properties if the prediction is based on their short-term test data for 9%-12%Cr ferritic steels.The following concepts/methods are thus proposed in this paper in order to reduce the property overestimation tendency caused by the conventional TTP methods and to obtain a better agreement of the predicted property values with the observed ones.They include the C-value optimization and the multi-C region analysis,the long-term（5×10^3-1×10^5 h） creep rupture property prediction using short term test data（≤5×10^3 h）,the optimization of function used for property prediction,and the effect of d[g（σ）]/d（P） vs P on the stability of steel properties based on the improved LMP method. All the data sets for the 9%-12%Cr steels are from NIMS database for the related calculations and analyses.The results show that the C value in LMP is not only different from steel to steel type but also varies with the multi-region stress levels,and the new approach to rupture life prediction proposes procedures for extrapolations of the short-term results,with rupture time measurements from tests lasting up to only 5×10^3 h providing reasonable estimates of 10^5 h rupture strengths,as well as the variation tendency of d[f（σ）]/d（P） vs P can reflect directly the long-term property stability of the steels investigated.Therefore,the concepts/methods proposed could improve effectively the accordance of predicted property values with observed ones and overcome obviously the overestimation tendency of 10^5 h strengths,which are more suitable and easily realized to assess the long-term creep-rupture properties of the advanced high Cr ferritic steels.