Study On Microstructure Evolution And Properties Of Laser Direct Forming 24CrNiMoY Alloy Steel

As one of the key components of high-speed trains,the brake disc has a complex structure,The toughness,hardness and strength of the forming material are required to be high.At present,Chinese brake discs mainly rely on imports,manufacturing technology is subject to foreign countries,urgent need for independent research and development.Laser direct deposition technology is one of the cutting-edge technologies for preparing high-speed iron braking devices at home and abroad,compared with the traditional manufacturing technology,the laser direct deposition technology is expected to solve the problems of the complicated technology,low material utilization rate,long production cycle and other problems existing in the manufacturing of brake discs by traditional technology.The process of laser direct deposition technology has the characteristics of complex metallurgical reaction and non-equilibrium solidification,the formed samples prepared under different process parameters have different microstructures and properties.Therefore,direct laser deposition technology is used to optimize the process parameters to prepare alloy steel samples with good performance and few defects.The in-depth study of its microstructure evolution and properties has important scientific research significance and wide application value.This experiment uses the 24CrNiMoY alloy steel material prepared by the research group,screening to obtain alloy steel powder with appropriate mesh number,Using the FL-Dlight02-3000W semiconductor laser,24CrNiMoY alloy steel samples with different process parameters and different preheating temperatures were prepared by direct laser deposition technology.Using metallographic,scanning and other characterization methods,the microstructure and morphology of 24CrNiMoY alloy steel samples were studied with laser process parameters and preheating temperature.The microhardness tester,universal material testing machine and other equipment were used to analyze the sample performance.The experimental results show that:24CrNiMoY alloy steel samples with different laser scanning speeds?4 mm/s,5mm/s,6 mm/s,7 mm/s,8 mm/s,9 mm/s?were prepared under the condition that other process parameters were not changed,preheat the substrate to some extent,The tissue properties of its samples are shown below:At the same scanning speed from the top to the bottom,the granular bainite gradually increases,the lath bainite content decreases,the ferrite is refined and the content shows a declining trend.At different scanning speeds in the same sediment depth,lath bainite rise fist then fall,and granular bainite decreases fall first and then rise.When the scanning speed is 7 mm/s,the structure is uniform meanwhile the performance is excellent.The hardness and strength are the highest,which are 450.8 HV_0.2,804.176 MPa,and 1114.73 MPa,respectively.At the 2000W,7mm/s laser forming process parameters and 24CrNiMoY alloy steel samples prepared at different preheating temperatures?25?,100?,150?,200?,250??obtained different bainite structures.The structure of the sedimentary layer gradually changed from a large amount of bainite+a small amount of ferrite+granular bainite to a large number of granular bainite+lath bainite+a small amount of ferrite.When the preheating temperature is 150°C,the sample with the most uniform hardness distribution and the highest hardness value is obtained.Its hardness value is 442.4 HV_0.2.At this time,the tensile strength and yield strength of the samples were 1138.11 MPa and 816.46 MPa,respectively.The comprehensive properties of the samples reached the optimal values.