Microstructure Evolution During Solution Treatment and Its Effects on the Properties of Ni-Fe-Cr Alloy

Ni-Fe-Cr alloys have been widely used for petrochemical, chemical and nuclear application due to their superior corrosion resistance and good workability. Nowadays, Ni-Fe-Cr alloys with higher strength are demanded for the engineering application. Increasing the carbon content could enhance the strength of Ni-Fe-Cr alloys due to the solid-solution strengthening effect of interstitial carbon atoms. However, an increase in the carbon content would promote the precipitation of carbides, which would reduce the corrosion resistance. In order to optimize the carbon content and determine the solution treatment, microstructure evolution during solution treatment and its effects on the properties of Ni-Fe-Cr alloys with different carbon content were investigated using OM and SEM. The results show that variation in carbon content affects the carbide dissolution and grain size during solution treatment, which affects the mechanical properties and intergranular corrosion susceptibility of Ni-Fe-Cr alloys. For the Ni-Fe-Cr alloy with carbon content of 0.010%, M23C6 carbides produced during the hot-working process do not exist after solution treatment at 950 degrees C. For the alloy with carbon content of 0.026%, M23C6 carbides are dissolved into the matrix when the solution temperature increases to 1000 degrees C. An increase in the carbon content from 0.010% to 0.026% results in an increased tensile strength and has slightly observable effect on the elongation. The alloys with the carbon content in the range of 0.010%similar to 0.026% have lower intergranular corrosion susceptibility. As the carbon content increases to 0.056%, M23C6 carbides could not be dissolved even at the solution temperature of 1050 degrees C, and inhomogenous grain-size distribution is observed. The presence of undissolved M23C6 carbide weakens the solid-solution strengthening effect of carbon atoms, and significantly increases the susceptibility to intergranular corrosion.