| The high-speed train brake disc is a key part in the high-speed rail brake system,and its quality and performance determine the operation safety and service life of the high-speed rail.Chinese high-speed rail brake discs still relies on imports at present,and the manufacturing technology is monopolized by foreign countries.Using traditional casting methods,there are some problems such as complicated process,long cycle times and low material utilization.As an advanced manufacturing technology,laser additive manufacturing has become one of the key research technologies at home and abroad.It has a broad application prospect in the manufacturing field of new high-speed brake discs.24CrNiMoY alloy steel is the main material for the manufacture of brake discs,due to the characteristics of laser non-equilibrium metallurgy,there are often complex deformation and cracking problems caused by structural phase transformation and stress in the process of laser additive manufacturing alloy steel brake discs.Preheating is an effective method to improve the structure and properties of alloy steel and eliminate defects.Therefore,the research on the effect of preheating on the structure and properties of 24CrNiMoY alloy steel prepared by laser direct deposition(DLD)has not only important scientific research significance but also significant data application value.In this paper,the method of combining simulation and experiment is adopted.Firstly,the APDL language of ANSYS 15.0 finite element software is used to analyze and research the thermal behavior of the singel and muti-layer samples of 24CrNiMoY alloy steel deposited by DLD at different preheating temperatures(25℃,100℃,150℃,200℃,250℃).Then,using the FL-DLight02-3000W laser,24CrNiMoY alloy steel samples was directly deposited on the Q235 substrate preheated by the DB-XAB preheating plate.By means of OM,SEM,EDS,laser confocal,XRD,TEM,EBSD,microhardness tester,universal material testing machine and other analytical methods,combined with simulation calculation methods,the structure,defects,mechanical properties and evolution mechanisms of alloy steel samples deposited under different preheating conditions were systematically studied.The main structure of 24CrNiMoY alloy steel samples by DLD were lath bainite and granular bainite.With the increase of preheating temperature,the content of LB was reduced from 95.7%to 3.5%,crack and pores of samples were decreased significantly,and the mechanism of preheating temperature on the structure and pores were established.Under the optimized experiment parameters with laser powder of 2000W，scanning speed of 6mm/s and preheating temperature of 200℃,the prepared samples have good strength and toughness,the highest hardness is 414HV0.2,the tensile strength is 1051 MPa,and the elongation is 7.4%.Preheating treatment has a good role in regulating the defects,structure and properties of laser directly deposited alloy steel. |
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