Research On Correlations Between Properties And Microstructure For Valve Inlet Pipe Joint Welded By NG-TIG With Hot Wire

X10CrMoVNb9-1Steel is widely used in superheater，reheater and steam pipeline ofboiler power station for its high temperature creep rupture strength, heat stability and hightemperature creep resistance, but there is still further research on its process adaptabilityand performance evaluation. In this paper, narrow-gap Tungsten Inert Gas (NG-TIG) withhot wire method was taken to weld the X10CrMoVNb9-1valve inlet pipe in all positions,research is focused on the correlations between properties and microstructure of weld joint.Basing on the research on microstructure analysis, tensile (RT.&HT.) test, hardness test,impact test and high temperature creep rupture strength, these results show thatmicrostructure were tempered lath martensite for different areas of weld; for HAZ, coarsetempered martensite microstructure in the coarse grains area, fine tempered martensitemicrostructure in the fine grains. Room and high temperature tensile test results show thetensile failure position appears on base metal side which the samples were taken from thedifferent area of weld joints, it indicate the strength of weld seam is higher than base metal,and compared to yield strength and tensile strength at room temperature, the strengthdrops significantly at high temperature. The hardness of weld seam is about260HV, andthe lowest hardness of base metal is about180HV, the curve of HAZ hardness is droppedfrom weld seam to base metal. Impact test on the different position of weld joints, theimpact toughness of weld seam is equal to base metal, the lower impact toughness appears near the fusion line which between the weld seam and HAZ. Acc.to the report of600℃creep rupture strength, the time increase while the load reduce, the strength limit of1000his122.69MPa with the extrapolation. Otherwise the hardness of weld seam decreases afterstress-rupture test comparison with the hardness before the test, also including HAZ andbase metal. Lots of gathering carbides are found at weld joint especially for the grainboundaries, which could explain the decreasing of hardness after stress-rupture test. Thestudy results could provide reference for the control of weld process parameters anddiscussion on the failure during the service process at high temperature.