Microstructure and Properties of ER50-6 Steel Fabricated by Wire Arc Additive Manufacturing

In this paper, ER50-6 steel was fabricated by wire arc additive manufacturing (WAAM) with an A-W GTAW system. The microstructure, mechanical properties, and corrosion behaviors of ER50-6 steel by WAAM were studied. The results showed that, with the GMAW current increased, from the bottom to the top of the sample, the microstructure was fine ferrite and granular pearlite, ferrite equiaxed grains with fine grains at grain boundaries, and columnar ferrite, respectively. The average hardness in the vertical direction of samples 1# and 2# was 146 and 153 HV, respectively. The hardness of sample 2# increased because of the refinement of grain. The pores in the sample increased as the bypass current increased. The higher bypass current also has a deterioration effect on the corrosion behavior of ER50-6 steel.

Improving Strength of Structural Steels by Preheating in an Oxygen-Containing Medium

The results of the preliminary heat treatment effecting in a medium with a high oxygen content on the microstructure and mechanical properties of structural steels are presented. It is shown that the usage of preheating in the glass mass in the range of (Ac130°C) – Ac1for steels of grades 50 and 40H leads to the formation of a structure with dispersed granular pearlite and crushed excess ferrite precipitates. Such a structure, when heated for quenching, provides rapid formation of a homogeneous austenite and a delay in the growth of austenite grain, which provides the best combination of strength and plasticity after the final heat treatment. It is established that the tensile strength increases 1.2-1.3 times while maintaining the plasticity characteristics. The reliability of the obtained estimates of the mechanical property characteristics is confirmed by the results of a statistical analysis.

Effect of Co Addition on the Microstructure of Matrix in Tungsten Carbide Reinforced Surface Composite

WC-Co surface reinforced composite was formed by V-EPC (vacuum-expendable pattern casting), and the microstructure of the matrix in the composite was investigated. The results show that the Co addition caused the appearance of granular pearlite and troostite in the matrix, therefore the brittle tendency of the composite was lighten. After the molten steel infiltrating into the preform, the component diffusion in matrix decreased from the substrate to the surface of composite, the composition of the matrix became more uneven, and the formation of the granular pearlite and troostite were facilitated. When the atomic concentration of W and C in the matrix increased, Co3W3C, η type carbide, was easier to separate out. Before the temperature of the composite drop to 1200°C, Co3W3C could precipitate in the interface reaction between the matrix and the tungsten carbide particles, the hardness of the matrix would be increased, and then the abrasive resistance of the composite could be improved.

Magnetic Field-Induced Granular Pearlite at Early Stages of Phase Transformation

ffects of high magnetic fields (HMF) up to 19.81T on pearlite phase transformation are studied by examination of the microstructures of a Fe-0.47C-2.3Si-3.2Mn (wt %) alloy partially isothermally processed above the eutectoid temperature. The results show that granular pearlite (GP) can be obtained at earlier transformation stages. The evolution of the granular pearlite is always accompanied by the formation of lamellar pearlite. TEM analysis reveals the existence of sub-grain boundaries within GP colonies and indicates that the nucleation of ferrite matrix in GP belongs to multiple nucleation mechanism. Most of carbides at the early stage of pearlite formation are found to precipitate at the α/γ interface--the growing front of ferrite phases, and some of coarse carbides can further develop into thin lamellar cementite.