Effect Of Hot Extrusion On Microstructure And Properties Of Inconel625 Alloy

Inconel625, a Nb and Mo-Modified, is a solid solution strengthened nickel base superalloy. With excellent corrosion resistance and high oxidation resistance, Inconel625 has both good tensile and fatigue properties from low temperature to 980 ℃, and resistance to salt spray atmosphere stress corrosion. But limited to the range of forming temperature of nickel alloy was narrow and the intrinsic properties such as large deformation resistance, the actual production of large diameter pipe bar molding technology is also imperfect. The large diameter inconel625 alloy tube bar are obtained in this paper by the method of hot extrusion, and the influence of different forming parameters on the formability is analyzed, and the reasonable hot extrusion process parameters are obtained. The microstructure and properties of the materials were studied by various analytical tools, mechanical samples and electrochemical experiments.The microstructure and properties of Inconel625 alloy before and after hot extrusion were studied. It was found that the existence of Nb segregation existed before and after extrusion. By means of SEM and TEM analysis, there was M23C6 carbide found at the grain boundary in the heating process before hot extrusion. After hot extrusion, the microstructure of the material was uniform by perfect recrystallization, but there were still some carbide retained at the grain boundary. The texture density of extrusions was obviously decreased, the mechanical properties were improved, and the corrosion resistance was better.As the extrusion ratio increases, actual extrusion temperature increased resulting from the thermal deformation, the average grain size was significantly increased, but texture density was decreased. High temperature made carbide at the grain boundary dissolute and secondary cracks on fracture surface reduce, strength was increased by enhancement of solid solution strengthening. The elongation was decrease. Corrosion resistance also showed a downward trend.When the extrusion ratio and extrusion speed were improved at the same time. The deformation heat were more, but the high speed extrusion made that the second phase had little time to dissolve and recrystallization grains had not enough time to grow up. Compared with the increase of extrusion ratio, the recrystallization grain size also showed an increasing trend, but the amplitude was smaller. The dissolution rate of crystalline carbide was significantly reduced, and the fracture surface was increased. Corrosion resistance was improved.