This article discusses the influence of Tungsten Inert Gas (TIG) surfacing of duplex cast steel on its hardness and structure. The samples of 24Cr-5Ni-2.5Mo ferritic-austenitic cast steel were subjected to single-overlay processes with the use of solid wire having the chemical composition similar to that of the duplex cast steel. As a result of the surfacing, the welds were obtained that had no welding imperfections with a smooth transition to the base material. In the test without the heat treatment, directly below the fusion line, we observe a ferrite band with a width of approximately 200 m without visible austenite areas. Some of the samples were then solution treated (1060°C). Both variants, without and after solution heat treatment, were subjected to testing. Significant changes in the microstructure of the joint were observed after the heat treatment process (heat affected zone and weld microstructure changes). In both areas, an increase in the austenite volume fraction after solution heat treatment was observed. Changes in the microhardness of the ferrite in the HAZ area directly below the fusion line were also observed.
Effects of solution treatment on room temperature mechanical properties were studied in cast AZ91 (Mg-9%Al-1%Zn-0.2%Mn) and AZ91-0.5%Ca alloys. In as-cast state, the Ca addition contributed to the suppression of discontinuous β phase precipitation and the formation of Al2Ca phase. After solution treatment, the AZ91 alloy had only a small amount of Al8Mn5 particles, while β and Al2Ca phases were still present in the Ca-containing alloy. In as-cast state, the AZ91-0.5%Ca alloy showed better yield strength and hardness than the AZ91 alloy. The solution treatment increased the elongation in both alloys, which eventually led to the increase in ultimate tensile strength. The solution treatment resulted in a marked decrease in yield strength and hardness in the AZ91 alloy, whereas the decrements in those values were relatively negligible in the Ca-containing alloy due to the residual phases and solution hardening effect of Ca.