After annealed at 800-950 ℃ for 8-48 h,the changes of microstructure and hardness of the hot-rolled 420U6 nitrogen-containing martensitic stainless steel under different annealing processes were studied by means of laser confocal microscope and Vickers hardness tester.The results show that the annealed microstructure is composed of ferrite matrix distributed with carbide,and the size and morphology of the carbide differ obviously under different heat processes.When annealed at 850 ℃ for 16-24 h,the carbide exhibits spheric shape and its size is generally uniform with average diameter of 0.4-0.5 μm.With the increase of annealing temperature and prolonging of holding time,the hardness of the tested 420U6 steel decreases at first and then increases slightly.The occurrence of lamellar carbide is responsible for the increase in hardness.
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