Study On Intergranular Precipitation And Cavitation Erosion Behavior Of Hastelloy G30

Hastelloy G30 is a Ni-Cr-Fe nickel-based alloy with good corrosion resistance,high strength and long service life,which is widely used in petroleum,chemical and energy fields,etc.Hastelloy G30 will face intergranular precipitation in the weld heat affected zone during welding,and the alloy will also suffer from intergranular precipitation after long-term service in high temperature environment.In addition,Hastelloy G30 is susceptible to cavitation problems after long-term service in a flowing liquid environment,which can lead to material failure in severe cases.In this paper,the molar fraction of each equilibrium phase of Hastelloy G30 at different temperatures was calculated by thermodynamic method and used to determine the aging treatment temperature.The intergranular precipitation behavior of Hastelloy G30 was studied by scanning electron microscopy,transmission electron microscopy and electron backscatter diffractometer.The cavitation tests were carried out by ultrasonic cavitation device and the cavitation damage mechanism of Hastelloy G30 was investigated by scanning electron microscopy.The following main findings were obtained:The Hastelloy G30 precipitation at the grain boundaries was observed to be both continuous and discontinuous under SEM,and the continuous precipitation was observed to be short rod-like and the discontinuous precipitation was irregularly granular under TEM.The discontinuous precipitations are not completely isolated from each other,but are connected by tiny precipitations.The following bitwise relationships were found between the σ-phase in the(?)crystal direction and the matrix phase:(?)_σ//[011],(?)_σ//(?)and(?)_σ//(?),(?)_σ//(?).The following site-directed relationships exist between the[113]crystal orientation and the matrix phase:[113]_σ//[001],(?)_σ//(020).The σ-phase was determined to be semi-co-grained to the matrix by transmission electron microscopy highresolution maps.EBSD analysis revealed that the Σ1 grain boundary of Hastelloy G30 is highly immune to σ-phase precipitation,with 95%of the Σ1 grain boundaries immune to precipitation.Σ3 grain boundaries are also more resistant to σ-phase precipitation,with no precipitation occurring on about 95%of the Σ3 grain boundaries.Σ9 grain boundaries are less resistant to precipitation,with precipitation occurring on about 90%of the grain boundaries.Σ27 grain boundaries and random large-angle grain boundaries are less immune to σ-phase precipitation,with precipitation occurring on about 95%of the grain boundaries.Σ27 grain boundaries and random large-angle grain boundaries are less immune to the precipitation phase,with precipitation occurring on about 95%of the boundaries.Hastelloy G30 has good resistance to cavitation and the cavitation incubation period is about 5 h.The initial damage of cavitation occurs mainly at the grain boundaries and twin boundaries,and with the growth of cavitation time,the damage will also occur at the internal slip zone of the grain.Selective cavitation is the main damage mechanism of Hastelloy G30.