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박경동(K. D. Park),안재필(J. P. An) 한국동력기계공학회 2005 한국동력기계공학회 학술대회 논문집 Vol.- No.-
Boiler is one of the most important utilities providing steam to turbine in order to supply mechanical energy in thermal power plant. It is composed of thousands of tubes for high efficient heat transfer. The material for boiler tubes is used in such high temperature and pressure condition as 540℃, 22㎫. The boiler tube material is required to resist creep damage, fatigue cracking, and corrosion damages. 2.25%Cr-IMo steel is used for conventional boiler tubes, and austenitenite stainless steel is used for higher temperature boiler tubes. But the temperature and pressure of steam in power plant became higher for high plant efficiency. So, the property of boiler tube material must be upgaded to fit the plant property. Several boiler tube material was developed to fit such conditions. X20CrMoV12.1 steel is also developed in 1980's and used for superheater and reheater tubes in supercritical boilers. The material has martensite microstructures which is difficult to evaluate the degradation. In this thesis, degrade the X20CrMoV12.l steel at high temperatures in electric furnace, and evaluate hardness with Vickers hardness tester and strengths with Indentation tester.
박경동(K. D. Park),안재필(J. P. An) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-
The lightness of components required in automobile and machinery industry is requiring high strength of components. so this requirement is accomplished as the process of shot-peening method that the compressive residual stress is made on the metal surface. Special research is therefore needed about compressive residual stress on the metal surface in the process of shot-peening method. therefore, in this paper the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in environment condition(temperature) and mechanical condition(shot velocity, stress ratio)was investigated with considering fracture mechanics. by using the methods mentioned above, the following conclusions have been draw. (I) The fatigue crack growth rate(da/dN) of the Shot-peened material was lower than that of the Un-peened material. And in high temperature, fatigue crack growth rate decreases with increasing temperature. while fatigue crack growth rate increases by decreasing temperature in low temperature. (2) Fatigue life shows more improvement in the Shot-peened material than in the Un-peened material. And compressive residual stress of surface on the Shot-peen processed operate resistance force of fatigue crack propagation.