Studies On The Effect Of Laser Surface Melting Treatment On The Microstructure And Properties Of 9Cr-ODS Steel

Oxide dispersion-strengthened steel is a kind of alloy material which is mainly prepared by mechanical alloying to dissolve the nanometer size oxide in the alloy matrix and disperse it to improve the comprehensive performance.However,the traditional method of mechanical alloying combine with subsequent heat treatment is not yet mature,it will lead to many defects such as pores and inclusions in ODS steel,and the distribution of nanoscale oxides is not very evenly,which affects the serviceability of ODS steel.In this paper,laser surface melting combined with different periods of heat treatment is used for surface modification of ODS steel.With the aim of investigating the surface structure,properties and the evolution of nano-oxide dispersion phase of solidified layer using optical microscope,scanning electron microscope,energy dispersive spectrometer,microhardness and electrochemical workstation.The research results are as follows.In the experiment of ODS steel matrix were first laser melting in different scanning speed,followed by heat treatment.Laser surface melting process will change the existing form of nano-oxide dispersion phase,so that the irregular shape of nanoscale particles in the matrix of ODS steel dissolved in sharp corners,into a regular spherical shape.Among them,the laser power,spot size and scanning speed is 3000 W,2 mm×10 mm and 800 mm/min respectively,the shape of the nano-dispersion phase in melted layer is the most structured and most evenly distributed,while the melted layer hardness under this condition is high,and the corrosion resistance is best.After subsequent heat treatment,the size of the nano-dispersed phase in the melted layer was significantly reduced,but a certain degree of aggregation occurred and the hardness of the melted layer was also greatly reduced.In the experiment of ODS steel matrix for the pre-heat treatment,and then the different laser scanning rate of laser melting process,the pre-heat treatment homogenized the microstructure of ODS steel and changed the thermal conductivity of ODS steel so that the depth of the melted layer was generally reduced.The nano-oxide dispersion phase in the melted layer showed a very regular spherical shape with a slight increase in size and distribution.Among them,the solidified layer effect is best when experiment with pre-heat treatment and laser surface melting followed,with the laser power,spot size and scanning speed is 3000 W,2 mm×10 mm and 800 mm/min respectively.in this way,the melted layer shows the higher hardness,and the best corrosion resistance.In these two routes,pre-heat treatment followed by laser surface melting process route with a laser power of 3000 W,a spot size of 2 mm × 10 mm and a scanning speed of 800 mm / min respectively,nano-dispersed phase shape the most structured,most evenly distributed,and the higher the hardness of the melted layer,the best corrosion resistance.Taken together,pre-heat treatment followed by laser melting process route both to adjust the morphology of nano-oxide dispersion phase,but also to ensure the hardness and corrosion resistance of the melted layer,so this process is more suitable for ODS steel surface modification.