Study On The Microstructure And Properties Of T/P91 After Heat Treatment To Strengthen And Its Welded Joints

T/P91 steel is a new martensitic steel, which is improved 9Cr-1Mo steel. Its main advantage is the low thermal expansion, good thermal conductivity, processing, and oxidation resistance, high toughness and detection of surface cracks easily, and at high temperatures creep higher and lasting strength and allowable stress. It is suitable for all kinds of boilers in power plant boiler and gas turbine power unit parts, solving the booster phenomenon which the old boiler of generating units caused because of using 12Cr1MoV or 102 steel, so the T91 steel has become a common concern to countries in the world of steel.Based on orthogonal test, metallographic test and mechanics test, the subject concludes the best heat treatment process: solid solution temperature between 1030℃and 1060℃, solid solution time between 10min and 15min, high temperature tempering process at 820℃within 30min or 760℃within 90min. The results can be T91 tube manufacturers and on-site welding heat treatment process developed to provide reference.This paper by simulating the on-site welding of T91 steel tube compared with the actual operation may occur in several welding processes and solved practical engineering in the post-weld heat treatment problem of low hardness value. The results showed that: the value of welding parameter is proportional to the size of grain in welded seam and the area ratio of columnar grain region, but the mechanical properties meet the requirements; the lower hardness of T91 steel welded seam after heat-treatment due to hardness tester in the pipeline in the field test result on the error is too large; welding process should be strictly in accordance with the standard operation, and welding can be done correctly the case, try to choose a small welding parameters ( the much bigger welding parameters could cause biting edge and other defects) and low layer to layer temperature.In this paper, by means of simulating the welding of P91 steel, the problem of the black shade line in welded seam receives to be analysed, and the reasons for the above problem are denseness of carbides in shade line area and the inconformity of anticorrosion to corrosive liquor between carbides and matrix. The black shade line isn't harmful for the performance of joints at room temperature, but also the long-run influence for product requires further study.