Research On The Creep Damage Of The High-grade Heat-resistant Steel Welded Joints

From the beginning of the 20th century now, vigorously develop the power industry has been the country's economic construction is the top priority. Thermal power construction in China will mainly develop high-efficiency parameters of ultra-high (Ultra) critical thermal power units. In the course of thermal power technology development, raising the temperature and pressure steam is the effective way to improve the Thermal Power efficient. In order to ensure units run stably at a higher temperature and pressure, material is one of the key factors. At present, in order to develop and apply for the Ultra-supercritical power plant (steam temperature of 650℃, pressure of 25MPa), foreign countries have used a new high temperature alloy steel P92 ferrite, which has high temperature creep strength and lasting anti-steam oxidation at the temperature above 600℃.Through the heat treatment method to simulate the P92 steel welding heat cycle, access to the simulation of heat-affected zone, and prepare the creep simulation sample. Then do the creep test of heat-affected zone, base metal and weld sample together under the temperature 650℃. Through the creep test results, establish a zone of injury creep constitutive equation. By the 650℃sustained high temperature tests, research the sample microstructure after high temperature creep, By Metallographic analysis and TEM analysis, to discuss the mechanism of damage creep and crack cracking mechanism. Conclusions are as follows:With the way of simulation of the heat cycle to simulate the heat-affected zone's microstructure is proved to be effective. By fitting the constitutive equation of considering the damage to creep, found that HAZ, base metal and weld of P92 steel's uniaxial creep properties are different largely at 650℃. After long time and high-temperature creep, the welded joints in all regions have different degrees of damage and performance in the form of creep holes. Especially in fine-grained has the most creep holes, which display that this area is the heaviest damage and the fastest damage growing zone. Through TEM analysis know the reasons for the damage caused are mainly grain boundary carbide precipitation, and with the development of creep, the coarse precipitation makes the grain boundary weaken. At the same time, the dislocation density is also smaller in the process of creep. All these factors make lower anti-creep properties of P92 steel.