| Mould is the mother of industry and the most important basic equipment of manufacturing industry.There are some disadvantages in the traditional manufacturing method of mould,such as long production cycle,high cost,complicated process,complex special-shaped mould processing,which can not meet the individualized demand,but using additive manufacturing method to make molds can make up for the shortcomings of traditional manufacturing methods.Therefore,this paper intends to explore the printability of H13 steel and 18Ni300 steel.Through the research on the shape control and the performance control of additive manufacturing,understand the forming laws of H13 steel and 18Ni300 steel,and clarified the solidification process of these two kinds of steel and their influence on phase transformation and properties,so as to provide theoretical and technical guidance for additive manufacturing of H13 steel and 18Ni300 steel.In this paper,the forming rules of H13 steel and 18Ni300 steel were studied by changing the printing parameters,and the best printing parameters were obtained.According to the best parameters,large specimens are printed,which with good surface and internal quality.In order to improve the performance of printing specimens,heat treatment was carried out.The relevant specimens were analyzed by metallography,XRD,SEM,TEM,room temperature tensile and electrochemical corrosion.The influence of solidification cooling rate on the solidification behavior and structure of printing was studied by copper mold suction casting.Many valuable results have been obtained.Both H13 steel and 18Ni300 steel have very good 3D printability.The large specimen obtained has no visible cracks,pores and other defects,the structure is uniform and the surface is smooth.The optimal printing parameters of H13 steel and 18Ni300 steel are laser power P = 2200 W,scanning velocity v = 600 mm / min and laser power P = 2600 W,scanning velocity v = 600 mm / min.The H13 steel printed specimen can be directly applied in the occasions where the toughness requirement is not high.Without heat treatment,high strength,hardness and corrosion resistance can be obtained,tensile strength reached 2081 MPa,Rockwell hardness reached 56.0 HRC.For occasions requiring good toughness and good coordination,the molded parts can be directly tempered at 550 °C for 2h and tempered twice without quenching.At this time,the tensile strength is 2006 MPa,the Rockwell hardness is 55.2 HRC,and the plasticity is high.The best heat treatment process for 18Ni300 steel printed specimens is 840 ? solid solution 1h + 490 ? aging 12 h.Its mechanical properties have been improved,tensile strength reached 1846 MPa,Rockwell hardness reached 52.1 HRC,while still maintaining high plasticity.The corrosion resistance of the specimen decreased after solution aging treatment.The strength and hardness of aged specimens increased with the precipitation of intermetallic compounds,and then decreased with the growth of intermetallic compounds.The strengthening methods of the two kinds of hot die steels are different,and their additive manufacturing and heat treatment process are different.The solidification cooling rate in the additive manufacturing process has a great influence on the solidification behavior and structure of H13 steel.The change of solidification cooling rate was simulated with different size specimens by copper mold suction casting method,and the influence law of solidification cooling rate on solidification behavior and microstructure of H13 steel was obtained.There is no equiaxed dendrite when the solidification rate is slower.When the cooling rate is fast,there are equiaxed dendrites,and columnar dendrites and cellular crystalline regions become smaller.The rapidly solidified H13 steel is only composed of supersaturated ? phase,which is martensitic structure.The hardness of the suction casting specimen is higher and more uniform than that of the additive manufacturing,and the corrosion resistance of the specimens is similar. |
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