Abstract
The present study provides a feasible method to evaluate creep properties for a 9%Cr-Mo-Co-B power plant steel by comparing two sets of data obtained from small punch tests and conventional uniaxial creep tests. The method includes three steps: firstly, conduct a series of small punch tests and conventional creep tests in different load and temperature conditions; secondly, convert the load and central deflection data obtained from the small punch test to stress and strain data; thirdly, determinate the best fit correlation factor by comparing the two sets of data in selected creep models. It is found that two sets of data show a similar trend in stress–rupture time relation, stress–minimum strain rate relation and LMP–stress relation. The correlation factor, ksp, can effectively bridge the gap between the load in small punch test and the stress in conventional creep test. For a high-Cr martensitic heat-resistant steel named as CB2, the ksp value 1.4 can make a good prediction for rupture time, while for minimum creep rate and the Larson–Miller parameter, the ksp value 1.4 will lead a conservative prediction in the low-stress range.
Highlights
In the background of increasing emphasis on energy conservation and pollution reduction all over the world, the operating temperature of components in steam power plants exceeds 600 ◦C and continues to rise in the ultra-supercritical (USC) units in order to achieve the desired overall efficiency and save fuel costs [1,2,3]
As a result of numerous trials in the COST programs, 9Cr-1Co-100ppm Boron composition is selected for the casting steel CB2 and forging steel FB2 that are suited for application at high temperatures up to 620 ◦C
In order to evaluate the creep resistance of a material, a conventional creep test is commonly performed under specific stress and temperature
Summary
In the background of increasing emphasis on energy conservation and pollution reduction all over the world, the operating temperature of components in steam power plants exceeds 600 ◦C and continues to rise in the ultra-supercritical (USC) units in order to achieve the desired overall efficiency and save fuel costs [1,2,3]. In order to evaluate the creep resistance of a material, a conventional creep test is commonly performed under specific stress and temperature. The conventional creep test needs a full-size specimen, which is material consuming and impossible in many cases involving a remaining-life assessment of in-service components. One of the most widely used methods is summarized in the standard CWA 15627: small punch test method for metallic materials [21], in which a correlation factor between SP load and uniaxial creep stress is introduced. Steel CB2 is a potential alloy that will be widely used in USC plant components in China [22]; it is urgent to discover a low-cost assessment method for creep properties that could replace the conventional creep test. By comparing the two sets of data in the creep models, a relationship between the two test methods can be established from the perspective of optimizing the correlation factor
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