Investigation On Precipitate Of HR3C And Super304H Stainless Steels Aging At High Temperature

In order to make our country remain strong in the international contest, power generation industry must apply sufficient electric energy. At present, burning fossil fuel is the most important way to acquire electric energy in our country. Due to the unprecedented energy crisis and environmental pollution, it is necessary to develop new electric energy generation technology which needs less consumption and provides more output. Therefore, plenty of countries including us give priority to building ultra supercritical power plant with operation temperature more than600℃and operation pressure more than27MPa. Compared with the traditional power plant, ultra supercritical power plant has higher efficiency and lower energy consumption, which is also the mainstream of power technology in the future.HR3C and Super304H, two kinds of heat resistant austenitic stainless steels, with great creep strength, corrosion resistance and steam oxidation resistance, are used into superheater and reheater which are the key components of ultra supercritical power plant. The micro structure changes have direct impact on the stability and reliability of heat resistant material at high temperature high pressure operation condition. Therefore, the study on microstructure variation of HR3C and Super304H in practical working environment becomes an important subject.This paper chooses HR3C and Super304H as research subject, Employing optical metallographic microscope, X-ray diffraction analysis, scanning electron microscope and transmission electron microscope to investigate the characteristics of microstructure in different aging stage; applying Vickers hardness test to judge the mechanical property of two materials and electrochemical workstation system test to evaluate the level of intergranular corrosion resistance. The results indicate that the primary strengthening phases of HR3C are MX phase containing NbC, NbN and Nb (C、N) and Z phase (NbCrN). Cr diffused from matrix to a part of MX phase gradually. Finally, MX phase transforms into Z phase, which improves the property of intergranular corrosion resistance of HR3C by stabilizing Cr element. The primary strengthening phases of Super304H are MX phase, Z phase and Cu-rich phase. The formation of Cu-rich phase depends on Cu and Fe, Cr, Ni elements diffusion bidirectionally. In initial aging stage, Cu-rich segregation area forms in austenitic matrix. Then, the copper content is gradually increasing in Cu-rich segregation areas, and the other elements, such as Fe, Cr and Ni diffuse away from the Cu-rich segregation areas to austenitic matrix with the increasing of aging time. The coactions of Z phase and Cu-rich phase restricts the form of Cr-poor area, and improves the property of intergranular corrosion resistance of Super304H. The comparison for these two stainless steels indicates that HR3C has better strength and corrosion resistance than Super304H, while Super304H, which is qualified for ultra supercritical power plant, is more economic due to the less Ni content.