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Large Forgings Hydrogen Brittleness Damage Mechanism Research Based On Method Of Crystal Plasticity Finite Element

Posted on:2014-11-02Degree:MasterType:Thesis
Country:ChinaCandidate:J G LiFull Text:PDF
GTID:2251330392464355Subject:Mechanical design and theory
Abstract/Summary:PDF Full Text Request
Heavy forgings is the main basic components of all kinds of necessary, heavy, keyequipment and installations. It is the necessities during the national economic construction,national defense industry and modern science development. If there are white flakes in theheavy forgings, it would make the heavy forgings cracking during the quenching heattreatment and the working process. And it would cause significant accidents and loss. So,the heavy forgings with the white flakes must be scrapped. The white flakes is a kind ofcancer of heavy forgings.White flakes is one of hydrogen embrittlement phenomenon. As the process of heavyforgings cooling down, the solubility of hydrogen in steel decreases. The hydrogen, in theheart of heavy forgings, is not spread out in time, and separate out the internal defect. Theprecipitation of hydrogen pressures on the surrounding metal, and with the internal stresstogether, cause the micro crack propagation. White flakes grow up slowly.In recent years, with the development of science and technology, the crystal plasticityfinite element method has become a very active theory method in materials and plasticforming field about polycrystalline, precipitation, precipitation, grain and crack. Thispaper based on the crystal plasticity finite element method, and the formation mechanismof white flakes was revealed from mesoscopic point by considering hydrogen pressure,microscopic pore, internal stress, the grain boundary and so on.First, Cr5was selected as test materials and simulation parameters was set. Second,the region crystal mesoscopic model of white flakes’ core was set up. Crystal plasticityfinite element and macroscopic finite element were used respectively to simulate to gethydrogen stress field of white flakes’ core under different hydrogen pressure. There was aslip dislocation concentrate region in the microscopic pore tip through the comparison ofsimulation results. The propagation of the crack was made predictions by fracturemechanics. Third, there was different microscopic pore in sizes and shapes within theheavy forgings. Under comparison and analysis of hydrogen stress field, The more flatmicroscopic pore was, the more conducively the white flakes generated. Finally, polycrystal pore model was set up through ABAQUS’ scripting interface. And found thatinternal stress extremum mostly occured at grain boundary under simulation analysis.Under the analysis of the different positions a microscopic pore’s interference of hydrogenstress field, this phenomenon is good for the white flakes growing up, while grainboundary did bad for the white flakes growing up.
Keywords/Search Tags:heavy forgings, white flakes, crystal plasticity finite element method, hydrogen pressure, microscopic pore, polycrystalline pore model
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