A hybrid additively manufactured martensitic-maraging stainless steel with superior strength and corrosion resistance for plastic injection molding dies

Abstract The customization of plastic injection molding dies is technologically and economically limited by conventional manufacturing processes. Recent advances in hybrid additive manufacturing (HAM) have provided more geometrical freedom for the manufacturing of parts with desired properties. In this paper, we report manufacturing of a hybrid 420/Corrax stainless steel with a reliable interface that can be applied in the manufacturing of next-generation geometrically complex plastic injection molding dies with enhanced strength and corrosion resistance. AISI 420 martensitic stainless steel is used as a cost-effective substrate, and a maraging stainless steel grade, known as Corrax, is printed on top of it using laser powder bed fusion (LPBF). A hybrid heat treatment cycle is applied to improve metallurgical properties and to enhance mechanical compatibility between the martensitic and the maraging stainless steels. Tensile tests coupled with scanning electron microscopy are carried out for analysis of failure, which show the development of shear bands in the microstructure of the 420 stainless steel substrate while a limited amount of deformation occurs in the interface region and Corrax microstructure. Void nucleation, growth, and coalescence are found at the 420/Corrax interface due to mechanical incompatibility and decohesion; however, microstructural instability mainly occurs along the shear bands on the 420 side and leads to fracture, which is quantified using high-resolution X-ray computed tomography. Nanoindentation tests show that the maximum level of hardness occurs at the interface due to the existence of sub-micron grains and the formation of AlN nanoparticles. Also, the formation of β-NiAl precipitates enhances the Corrax strength after heat treatment. In addition to a high strength, elevated corrosion resistance of the cooling channels is essential to extend the service life of plastic injection molding dies. Potentiodynamic corrosion testing at the interface shows that Corrax has remarkable corrosion resistance compared to 420. Therefore, additive manufacturing of the critical die areas such as the cooling channels using Corrax increases the service life of the mold.