Prediction Of Elevated-temperature Creep Life In 9Cr-1Mo Steel By Different Methods

In the energy and power plants,petrochemical engineering,and aeronautics&astronautics fields,many 9Cr-1Mo heat-resistant steel components are often exposed to elevated temperature and subjected to the long-term sustained loading.Under such service environments,creep damage becomes the most critical factors determining the structural integrity and safe operation of components.In order to guarantee the safe and highly efficient operation of those components,to develop more accurate creep life prediction method had drawn so much attention in the field.Recently,various research results have been obtained and some of them have been applied in engineering at home and abroad.However,there were few reports about the comparative study and comprehensive assessment in creep life prediction methods.The current paper took P91 steel as the research object,the external factors including service temperature and stresses in engineering application were put into comprehensive consideration.On such a basis,the extrapolation accuracy of different TTP parameter methods(LM,OSD,Wilshire model)and the based on creep curve extrapolation methods(?,modified 0,K-R model)were used to estimate the creep rupture life of the present 9Cr-1Mo steel.Compare with the ECCC data,extrapolation accuracy of the above prediction methods can be calculated.Besides,a modified continuum damage mechanics(CDM)model was proposed in this paper and the numerical solution of the modified model was realized.The specific research contents and main conclusions were drawn as follows:It turned out that the accuracy of creep life extrapolation had great relationships with the parameters of the TTP methods such as LM,OSD and Wilshire model.When extrapolating a creep rupture life more than 2 × 105 h,Both LM and OSD parameter methods showed a over-estimation phenomenon.However,Wilshire model showed a preferential accuracy compared with LM and OSD model method.Wilshire model parameter of Qc=314.7kJ·mol-1 could better correlate the creep rupture data for the present 9Cr-1Mo steel.The results showed that the extrapolation methods(? method,modified ? method and K-R model)based on creep curves had high extrapolation accuracy during short-term creep life prediction.Besides,the whole creep strain curves can be easily obtained.When extrapolating the long-term creep rupture life,K-R model had the highest precision and ?parameter method is the worst.By analyzing of creep mechanism under the present creep conditions,a modified CDM model was proposed coupling the traditional continuum damage mechanics.The predicted values of the current model with the numerical calculation were highly consistent with the test data.It indicates that the modified CDM model offers a potential tool to evaluate the creep life of heat-resistant steel.The Wilshire model and the K-R model method showed high extrapolation accuracy and low parameter sensitivity by comparing with the other life extrapolation methods.Besides,the Wilshire model had the highest prediction accuracy.However,these parameter extrapolation methods were based on phenomenological theory which can't reveal the true creep process inside the materials.Thus,it was difficult to select the proper parameters for those models.On the other hand,the modified CDM model can reveal the essence of creep behavior with physical mechanism during creep.Once the quantitative relation between the creep damage variable and the damage degree of the modified CDM model can be established,the model parameters can be reasonably solved.Therefore,the modified CDM model might be the most potential and significant tool for the creep life prediction of metal components in the engineering application.