Microstructure, Phase Composition, and Mechanical Properties of a Layered Bimetallic Composite ER70S-6-ER309LSI Obtained by the WAAM Method

Abstract

Currently, additive manufacturing technologies for materials and products are being implemented and improved. This is due to the possibility of creating workpieces with complex geometric shapes and specified functional gradient properties. The materials with the most complex functional properties demanded by the military–energy industry include bimetals of the “low-alloyed carbon steel—stainless chromium-nickel steel” type. One of the promising ways to obtain bimetallic products is the WAAM (Wire Arc Additive Manufacturing) technology. Despite the large scientific groundwork, the composition, structure, and properties of bimetallic composites produced by WAAM have not been sufficiently studied. The aim of the current work is to study the effect of WAAM parameters and the subsequent heat treatment on the composition, structure, and physical and mechanical properties of the bimetallic composite “ER70S-6-R309LSI”. Spectral, metallographic, and X-ray diffraction studies were carried out, as were mechanical tests of the samples obtained under various WAAM modes. In order to improve the composites’ properties, various types of heat treatments were applied. It is shown that the WAAM modes, the building strategy, and heat treatment determine the structure of layers and transition zones, as well as the mechanical characteristics of the composite. The structure of ER70S-6 in the composite is represented by the ferrite and the ferrite–cementite mixture (pearlite), and ER309LSI is represented by different ratios of austenite, δ-ferrite, carbide, and intermetallic phases. From the point of view of the mechanical properties, the most promising mode of surfacing is “Double Pulse”, followed by heat treatment by way of austenitization and normalization annealing. In this case, there is a decrease in the content of the δ-ferrite, a leveling of microhardness values, and a 40% increase in the tensile strength of the composite.