Study On Surface Laser Alloying Of Nodular Cast Iron Hot Roller

Metallurgical hot roll is an important tool for steel production,and it is a large consumable component that determines rolling efficiency and rolling quality.However,due to its harsh working conditions,the roll surface cracking,deformation and other problems are easy to appear in the application.In this paper,Fe-based,Ni-based and Co-based alloying layers were prepared on the surface of nodular cast iron hot roller matrix by laser alloying technique.The effects of scanning velocity on microstructure,phase composition,hardness and wear properties of alloyed layers were systematically studied.The results are as follows:The phase compositions of the Fe-based alloyed layer is composed of?-Fe solid solution,Fe₅C₂ phase,Fe₃C phase phase.With the increase of scanning speeds,the content of?-Fe phase decreases and the content of Fe₃C phase increases.The phases of Ni-based alloyed layer is composed of NiCx phase and?-Ni phase,Fe₃C phase.With the increase of scanning speeds,the content of?-Ni phase decreases,wihle the contents of NiCx phase increases obviously.The phase of Co-based alloying layer is composed of CoCx phase,?-Co phase and Fe₃C phase.And with the increase of scanning speeds,the content of?-Co phase decreased and the content of CoCx phase increased.The microstructure of the alloying layer is mainly composed of?-phase dendrites and eutectic carbides.The major solid solution tissues obtained are different depending on the powder compositions to be added.The upper tissue of the alloying layer is obviously more refined than the bottom tissue of the alloying layer.As the scanning speeds are improved,the microstructure of the alloyed layers which prepared by the three different powders are becomes finer,that is,the grain refinement degree is enhanced.Microhardness of the alloyed layer prepared by the three powder systems is 2.5³times higher than that of the substrate.When the laser scanning speeds are between 600mm/min⁹00mm/min,with the increase of the laser scanning speeds,the microhardness of the alloyed layer exhibits an increase trend.After the increase of laser scanning speeds from 900 mm/min to 1350mm/min,the microhardness of alloyed layer decreased to a certain extent.However,when the laser scanning speed is 1350 mm/min,the microhardness of the sample surface is higher than the microhardness of the sample at the scanning speed of 600 mm/min.In Fe-based alloyed layer,when the scanning speeds increases from 600 mm/min to 900 mm/min,the wear resistance at room temperature decreases,while the scanning speeds increases from 900 mm/min to 1350 mm/min,the wear resistance of the alloyed layer at room temperature increases.In the Ni-based alloyed layer,the wear resistance at room temperature decreases with the increase of scanning speed,and the best wear resistance is obtained for the sample prepared at the scanning speed of 600 mm/min.For the Co-based alloyed layer,the wear resistance decreases first and then increases with the increase of scanning speed,and the wear resistance at room temperature is the best when the scanning speed is 1350 mm/min.For the Fe-based alloyed layer,the wear resistance at 700?increases gradually with the increase of scanning speed,and show the higher wear resistance when the scanning speed is 1350 mm/min.For Ni-based alloyed layer,the wear resistance at700?decreases and then increases with the increase of scanning speeds,With the increase of scanning speed,the wear resistance of Co-based alloyed layer at 700?decreases and then increases,and show the better wear resistance at scanning speed of1350 mm/min.