The retaining ring is installed on the generator rotor through a thermal sleeve and plays a role in fixing, protecting and preventing deformation, displacement and eccentricity of the rotor end windings. In the past, the materials used in turbine engine unit retaining rings were 50Mn18Cr4, 50Mn18Cr4WN, 50Mn18Cr5, etc. However, these materials are very sensitive to moist air and often suffer from stress corrosion cracking. Nowadays, 1Mn18Cr18N austenitic stainless steel is commonly used. This material has excellent corrosion resistance due to its low carbon and high chromium composition. At the same time, the addition of nitrogen expands the austenite phase zone at room temperature, making it difficult to Ferromagnetism appears. In order to understand the effect of heat jacketing temperature on the structure and properties of 1Mn18Cr18N retaining ring steel, high-temperature (100°C) tensile tests and room temperature impact tests of retaining ring steel were conducted under different heat treatment systems, and the fracture surfaces were examined with the help of scanning electron microscopes and metallographic microscopes. and microstructure were analyzed to study the crack initiation and propagation fracture mechanism of retaining ring steel.
The 1Mn18Cr18N austenitic stainless steel used in the test was taken from the tangential part of the guard ring produced by a company. Its main chemical composition (mass) was measured using an infrared carbon and sulfur meter (CS800), a plasma spectrometer (ICAP6300) and a direct reading spectrometer (Metal75-80). Fraction, %) is C0.079, Si0.21, Mn18.54, P0.017, S0.005, Cr18.82, Ni0.14, N0.62, and the balance is Fe.
The samples were heated in the furnace (SGH28-92A box-type resistance furnace) to 100, 200, 300, 400, 500, 550 and 600°C respectively, and kept for 1 hour, followed by air cooling. The microstructure of the sample was observed using OLYMPUS-PMG3 metallographic microscope and S-3700 high-resolution scanning electron microscope. After the samples were ground with sandpaper (200, 400, and 600 mesh) and mechanically polished (diamond spray with a particle size of 2.5 μm), they were electrolytically etched with 10% supersaturated oxalic acid solution. A SHIMADZUAG-1 universal electronic tensile testing machine was used to conduct a high-temperature tensile test at 100°C. The tensile specimen was taken from the tangential part of the middle ring of the retaining ring. It was an M10 threaded tensile specimen with a diameter of Φ5mm and a gauge length of 25mm. The impact test was carried out on the JB300D impact testing machine. The impact sample was taken from the tangential part of the retaining ring and was a standard Charpy impact V-notch impact sample with a size of 10mm×10mm×55mm.
The results show that as the heating temperature increases, there are fewer slip lines inside the grains. At 500°C to 600°C, the grain boundary and slip line precipitates precipitate from point-like or chain-like to semi-reticular or full-reticular forms; precipitates The generation of 1Mn18Cr18N steel has a significant impact on the mechanical properties of 1Mn18Cr18N steel. When the heating temperature is increased to 500℃ (550℃), the dispersion distribution of the precipitated phase plays a certain strengthening role in the impact (tensile) performance. When the heating temperature is increased to 600℃, the entire The network precipitated phase weakens the grain boundaries and causes the tensile and impact properties of 1Mn18Cr18N steel to drop sharply. Fracture analysis shows that as the heating temperature increases, the fracture mode of 1Mn18Cr18N steel changes from ductile fracture to quasi-cleavage fracture and brittle fracture.
