Additive manufacturing technology has become an indispensable tool for manufacturing complex geometries that are often difficult to manufacture by conventional techniques. The process offers cost reduction, product an‎d process redesign, lead time reduction, an‎d flexibility to manufacture parts with desired material properties. The purpose of the present study is to investigate the effect of the type of protective gas used during the manufacturing process an‎d to investigate the effect of homogenization heat treatment an‎d optimal solution treatment in terms of temperature an‎d holding time on the mechanical properties an‎d microstructure of 17-4 PH steel fabricated by laser powder-bed fusion process. For this purpose, cubic samples were produced on two separate build platforms with identical parameters under argon an‎d nitrogen atmospheres. The porosity an‎d surface density were determined by image analysis. The aforementioned samples were subjected to different heat treatment cycles. In general, the cycles performed consisted of additional homogenization at 1200°C for 4 hours, solution treatment at 1150 an‎d 1040°C for 1 hour, an‎d aging at 480°C for 1 an‎d 4 hours. The microstructure, hardness, an‎d tensile properties of the samples were examined before an‎d after various heat treatments. The microstructure was characterized using optical an‎d scanning electron microscopy. Microstructural studies showed that the melt pools in the samples produced under nitrogen gas atmosphere were deeper an‎d the amount of porosity formed was less than in the samples produced under argon atmosphere. Also, the use of nitrogen atmosphere caused the formation of small amounts of nitride compounds in the structure. The use of nitrogen gas resulted in an increase in the amount of austenite phase in the samples compared to argon gas. In the as-built condition, Proeutectoid ferrite particles were observed in the form of grain boundary Allotriomorphs. The results of mechanical tests showed that first, the hardness an‎d tensile properties of the samples produced under the nitrogen gas atmosphere were better than those produced under the argon atmosphere, an‎d second, the application of the proposed heat treatment consisting of additional homogenization at 1200 °C along with solution treatment at 1150 °C an‎d aging for 4 hours at 480 °C resulted in better mechanical properties than the stan‎dard heat treatment for Wrought parts. This heat treatment provided properties beyond ASTM stan‎dards by providing a yield strength of 1113 MPa, a UTS of 1257 MPa, an‎d an elongation of 9.83%. Finally, it was determined that applying direct aging for one hour at 480°C would result in a severe decrease in mechanical properties due to the formation of nitride phases with needle-shaped morphology.

احمد كرمانپور

محسن بدرسماي

بهزاد نيرومند , حبيب الله رستگاري