Microstructure And Mechanical Properties Of 17- 4PH Stainless Steel By Laser Solution And Aging

17-4PH martensite precipitation-hardening stainless steel is widely used in turbine blades,aerospace,nuclear waste barrels,etc.due to its high strength,high hardness and good corrosion resistance.Some of these complex and precise key components may cause local failures and lead to overall failures in long-term work,thereby affecting the mechanical efficiency and safe operation.17-4PH stainless steel was used as a substrate to study the application of laser solid solution and aging,and the comprehensive mechanical properties and microstructure of the laser solid solution zone were analyzed.a large number of systematic experiments were conducted to dicuss the influence of the main process parameters of the laser solid solution on the hardness and depth of the laser solid solution hardening layer.The laser input energy gradually increases and the 17-4PH stainless steel is completely dissolved with the laser powe increasing or the scanning speed decreasing,and in this way,the depth and hardness of the hardening layer tend to increase after aging.Blackening treatment and preheating have a certain effect on increasing the depth of the laser solid solution hardening layer,but the preheating makes the stainless steel surface more easily melted.The molten pool is typically parabolic and high preheating temperature leads to a decrease in the hardness of the laser solid solution layer.Finally,the rectangular spot energy distribution is uniform,which is favorable for the laser solid solution with high energy density at a low speed.On this basis,the process parameters of the 25×8mm laser beam spot are further explored.Many different laser solid solution process parameters were used and its comprehensive mechanical properties were tested.With the deepening of the laser solid solution,the comprehensive mechanical properties of the 17-4PH stainless steel solid solution layer have been improved.The depth of the laser solid solution hardening layer gradually increases from 0.89 mm to 2.83 mm,the highest Vickers hardness increases from 430 HV to 500 HV,and the tensile strength improves from 890 MPa of the substrate to 1300 MPa.Moreover,there is a certain increase in the impact toughness and elongation of the laser solid solution hardening layer,while its friction and wear properties are basically the same as those of traditional solid solution and ageing.The comprehensive mechanical properties of laser solid solution fully meet or even partially exceed the effect of conventional solution aging,and it satisfys the strengthening requirements of 17-4PH stainless steel components local solid solution aging.Finally,the microstructure of the 17-4PH laser solid solution hardening layer was studied and the strengthening mechanism was analyzed.It can be deduced that the rapid heating and cooling of laser solid solution is beneficial to the formation of high density dislocation and vacancy.The interactions between the precipitated second phase particle,such as ?-Cu and NbC,and the high density of dislocations would increase the energy of dislocation movement,and therefore improve the hardness and strength of the hardening layer.In addition,the result of EBSD shows that there are lots of retained austenite after laser solid solution aging,and the presence of a suitable amount of retained austenite contributes to the improvement of the toughness.