Influencing Factors Analysis And Application Study For Small Punch Creep Test

Small punch creep (SPC) test technique is a new method to evaluate the properties of material in high temperature. It's nearly non-destruction makes it be arrested by more and more researchers. However, the work of research has located in the primary phase, and the results came from various research institutions are different. The theory and experiment technology of SPC test still need be improved to apply in engineering well. In this paper, SPC test was researched through Cr5Mo steel in following aspects: improving the FEM of SPC test, discussing the influence of oxidation on the results, and the application of SPC test on life prediction, which has an important meaning for extending and perfecting SPC test. The main work and conclusions are listed as follow: (1) The FEM of SPC test was improved by adding plastic deformation in process of loading and local remeshing on the basis of former FEM. Furthermore, a conclusion was drawn by analyzing the equivalent stress (combination of Von Mises and maximum principal stress) in specimen, that the stress in center on up-surface of specimen can represent the stress of SPC test well. (2) The minimum deflection rate, applied load and fracture time in logarithmic coordinates, two of them have a linear relationship at random on the base the results of FEM. Further, the sensitivity of deflection and equivalent stress at disc center to meshes size was discussed and the conclusion is that the size of meshes in radial direction has a significant on the fracture time. Otherwise, the meshes size in axial direction has no effect in it, and stress is insensitive to size of meshes. (3) A set of SPC tests were carried out to research the influence of oxidation on SPC test at the condition of 550°C-404N and 65CTC-173N with different argon flow. The results show that the fracture times decrease and the thickness of remainder metal increase with the increase of argon flow, and the appropriate Ar flow was determined based on it. The result come from shorter creep test, need be verified by longer creep test. (4) SPC tests for new and in-serviced Cr5Mo steel were carried out at the same condition. The result shows that the fracture times of in-serviced material are shorter than that of the new material, due to the material softing caused by the pearlite spheroidization and the poverty of strengthening elements, such as Cr and Mo. (5) The Monkman—Grant equation about minimum deflection rate and fracture time was established based on the SPC tests at different temperature and applied load. And the relation between minimum deflection rate in SPC test and minimum creep strain rate in uniaxial creep test also was established: sM -2.06 8M1. 108...