Experimental selection of the initial dissolution treatment temperature range for the subsequent cold rolling of IN907 superalloy sheet

The present study aims to determine the optimal temperature range of the dissolution treatment for the cold rolling of the IN907 superalloy. Samples of the IN907 superalloy hot-rolled sheet, after phase characterization by x-ray diffraction (XRD) and simultaneous thermal analysis (STA) experiments, were subjected to dissolution treatment in the temperature range of 940 °C–1000 °C, followed by cooling in air. The samples were then examined for microstructure, microhardness, tensile properties, and plane strain compression (PSC). Unlike the XRD test, the STA curve of the alloy showed two exothermic peaks, the first peak in the 750–950 °C temperature range associated with the intragranular laves phase and the second peak in the 1100–1175 °C temperature range associated with the oxide phase. The results showed that with increased temperature of the initial dissolution treatment from 980 °C to 1000 °C, the complete dissolution of the grain boundary laves phase led to an increase in the average grain size from 45μm to 57μm and a decrease in the yield and tensile strength by 42 MPa. The microhardness test showed that increasing the temperature of the initial dissolution treatment had little effect on the microhardness. Also, the flow stress diagrams and the normalized work hardening rate of the PSC test showed a similar behavior despite the observation of shear bands in the microstructure center of the compressed sample.