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As the power density of an engine increases, so does the temperature and stress that the cylinder head is subjected to during operation. Therefore, creep damage prediction needs to consider accurate creep constitutive models and parameters. Aiming at the wide range of temperature and stress working conditions of the compacted graphite cast iron (CGI) cylinder head, CGI creep test was carried out at 450-550 °C and 100-300 MPa. The comparative study of creep constitutive models to characterize the minimum creep rate of CGI under a wide range of temperature and stress was carried out. The research shows that compared with a smaller range of temperature and stress, CGI is more prone to creep damage under wide conditions. and temperature can promote the creep deformation of CGI more than stress. Based on the Norton-Bailey power law model, the Garofalo hyperbolic sine model, and the deformation mechanism-based true stress (DMTS) model respectively, combined with the multi-objective optimization method, the CGI creep constitutive model was constructed. Among them, 73% of the predicted values of the CGI creep model based on the DMTS model are within twice the error range, and the coincidence effect is the best among the three models.

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ASME 2021 code provides constitutive equation for high temperature creep of 316H stainless steel. The paper aims to help engineers and researchers correctly evaluate the strain and creep damage of high-temperature equipment by using the equation. Firstly, the physical mechanism of the items was explained. Secondly, the relationship between crucial parameters with temperature and stress was analyzed. Thirdly, the applicable stress and time range of the 316H creep constitutive equation was briefly introduced. And fourthly, the prediction values of the constitutive equation was compared with the data value from the isochronous stress-strain curve in ASME code. Results show that the constitutive equation is described by three items, in which the first creep stage is described by the rapid initial transient and transient items, and the second creep stage is described by the steady-state creep item. The equation’s applicability of evaluating the strain and creep damage of high-temperature equipment is limited by the starting time of the third creep stage. Moreover the key parameters of the equations, such as εs, εr, decay too rapidly to be accurately predicted at high stress. This research finds that due to item n increases with increasing temperature, the minimum creep rate m and transient creep rate constant r decrease in 1 000-1 075 ℉. Meanwhile, based on contrasting the rapid transient creep rate constants s of the original paper and ASME code, item D of parameter s is incorrect in the latter. Based on comparing predicted strain obtained by equation and data from ASME code isochronous stress-strain curves, the paper finds that predicted values at 950, 1 050 and 1 150 ℉ will agree with isochronous stress-strain curves, but larger than the datum from curve at 1 000 ℉, resulting in a relatively conservative strain prediction. Based on above four research and results, the paper concludes that the high temperature creep constitutive equation of 316H stainless steel in the ASME code can be used to evaluate high-temperature equipment structural integrity at 950, 1 050 and 1 150 ℉, but the result of 1 000 ℉ is conservatism.

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)