The Influence of the Hot Working Tool Steel Substrate Material on the Element Distribution, Microstructure and Hardness of Gas Metal Arc Welding Hardfaced Layers

The paper presents the results of gas metal arc welding (GMAW) hardfacing testing performed on three grades of hot working tool steels, namely: 55NiCrMoV7, X37CrMoV5-1 and modified X38CrMoV5-3 grade. Metallographic investigations, mainly microstructural ones, were carried out and hardness profiles were analyzed. The chemical composition was investigated in each individual layer of the hardfaced deposits and the substrate material, in order to obtain a profile representation. The obtained results of profilometric evaluation of the chemical composition showed clear differences in the content of basic and alloying elements in the subsequent weld layers. The diversity of the chemical composition of the substrate material caused that the uniform chemical composition for all tested materials was achieved only in the third, upper weld layer. Despite the variable content of alloying elements and carbon, as well as slight differences in microstructure occurring for individual weld layers, a substantially stable and high hardness was maintained over the entire cross-section of the obtained hardfaced coatings. In the area of the heat-affected zone (HAZ), a decrease in hardness was observed, which is associated with the decomposition of the high-temperature tempered martensite and the spheroidization of the microstructure.