| Due to its outstanding creep resistance,good corrosion resistance and high temperature oxidation resistance,P91 heat resistant steel were used in the thermal power and nuclear power plants' piping components.Long-term creep life of pipe material was defined the shape variables were less than 2% when the using time was 105 h in the engineering,then the creep strain rate would below 10-10ms-1.Traditional uniaxial creep tests cannot meet the needs at low stress creep research because of the low strain resolution;on the other hand,P91 heat-resistant would lead to microstructure degradation in service life.The influence of creep properties caused by microstructure degradation was still unknown.The purpose of this study:Using the high strain rate of “the helicoid spring creep test” to investigate the creep properties of P91 heat resistant steel in different conditions of heat aging treatment,revealed the “microstructure degradation factor” of P91 heat resistant steel under high temperature and low stressess.ANSYS finite element simulation were used to analy different screw pitches of P91 helicoid spring samples in mechanics field and got the conclusion:when the length of the screw pitch is as long as 1-3 times of the length of the lateral section,“the helicoid spring creep test” were on the basis of the principle of pure torsional deformation.The X-rd and SEM microstructure observation were carried out on the specimens after aging treatment.Results showed: 1)the precipitated phases are Laves phases,M23C6 phases and MX phases.2)MX phases would get to saturation after aging treatment and mainly disper in the interior of the martensite lath grain.3)M23C6 phases appear in martensite lath grain boundary and the original austenite grain boundary and saturated in 700 h then coarsening.4)Laves phases appeared in the edge of martensite lath and the crystal boundary precipitates in 2100 h and were easily to grow up.The creep properties of P91 heat resistant steel were study under high temperature and low stresses.And got the conclusion: 1)“The helicoid spring creep test” was valid.2)Blackburn's equation can best describe the creep data.3)Uniaxial creep test would oversized the remaining life of the using material.4)Laves phases was the “microstructure degradation factor” of P91 heat resistant steel under high temperature and low stressess.ANSYS finite element simulation,microstructure observation and creep properties under high temperature and low stresses were used to study the creep properties of P91 heat resistant steel.Research results would provide a theoretical support for the next step to carry out the modification of P91 heat resistant steel,the creep data of P91 heat resistant steel under high temperature and low stresses would supply for safety service evaluation of high chromium alloy steel. |
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