Study On Laser Remelting Processing On Nodular Cast Iron Surface

The microstructure of nodular cast iron,simple manufacture technology and low cost,is spheroidal graphite particle with the lowest stress concentration effect,which are evenly distributed on the strength and toughness pearlite or ferrite matrix.Therefore,the nodular cast iron has a comprehensive mechanical property equivalent to carbon steel,which is becoming more and more widely used in industrial production and social life.As the surface failure is the main way of failure of the engineering materials,the requirement of nodular cast iron,especially the surface properties,is becoming higher and higher.In order to meet the needs of industrial application,it is becoming more and more important to research and develop surface strengthening technical for the nodular cast iron.In this paper,by means of laser remelting experiment on surface of nodular cast iron.The influence of laser remelting process on morphology of remelting zone and microstructure and property were studied.The relationship between the laser process parameters and the microstructure and properties of the remelting zone were dicussed.Laser remelting technology,which can effectively eliminate harmful phase such an impurities,pores and compounds in surface layer of nodular cast iron and refine the coarse structure of surface layer of nodular cast iron and improve quality and performance of surface layer of nodular cast iron,were researched.In this paper,the laser remelting experiment on the nodular cast iron was carried out by using fiber laser beam,the laser power was between 0.3KW to 1.4KW,and the scanning speed was between 5mm/sec to 25mm/sec.The effect of geometrical morphology and microstructure of the remelting zone and heat-affected zone were studied by VHX-600 K super depth 3D digital micro analyzer.The microhardness of the remelting area and heat-affected zone were researched.The effect of laser power and scanning speed on the geometrical morphology,microstructure and michardness of remelting zone were discussed.Study on geometrical morphology of remelting zone indicated that the laser power has an important influence on geometrical morphology of remelting zone.When the laser power is less than 0.8KW,there is no deep penetration phenomenon in the remelting zone.When the laser power is greater than 0.8KW,with the increase of laser power,the proportion of deep penetration area is significantly increased.When the laser power is 1.4KW and the scanning speed is 5mm/sec,the depth of the deep penetration area accounts for about 40% of the total area of the remelting zone.In addition,when the laser power increases from 0.3KW to 1.4KW,the geometry of the cross section of the remelting zone also evolves from the flat semi-ellipticity to the standard circular arc.When the power of the laser is constant,the geometrical morphology of laser scanning speed of remeling zone is not obvious,but with the decline of the laser scanning speed,deep penetration area of the remelting zone accounted for a significant increase.Study on microstructure and microhardness of laser remelting zone and heat-affected zone on the surface of nodular cast iron indicated that after laser remelting,the microstructure of the remelting zone is refined,the casting defects disappear and the graphite particles escape to the surface of the molten pool during remelting.The average hardness of the remelting zone is 870 HV,which is 4 times that of the nodular cast iron.Due to the influence of the high temperature of the laser molten pool,the thick quenched structure appeared in the heat-affected zone.The microstructure characteristics of laser remelting zone indicated that with the increase of laser power,the laser scanning speed decreases,and the microstructure in laser remelting zone gradually evolves from fine cellular dendrites to thick dendrites.