Papers by Keyword: 9Cr18

Abstract: Formed in the semi-solid state, materials can obtain unconventional microstructures and properties compared with traditional method. In this paper, semi-solid billet of 9Cr18 steel was obtained through a wavelike sloping plate. Microstructure analysis of the semi-solid billet was conducted through scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). X-ray diffraction (XRD) test and microhardness test were also used to analyze the properties. The results showed that the structure of 9Cr18 semi-solid billet contained globular primary austenite and secondary austenite-Cr₇C₃ eutectic. Globular primary austenite grains were first formed during partial solidification in the sloping plate, and then the rest liquid metal formed secondary austenite and Cr₇C₃ eutectic structure surrounding the primary grains. Cr atoms had a concentration in the rest liquid side, which along with C atoms contributed to the formation of the Cr₇C₃ carbide. Hardness in the primary solid grain area and the eutectic area was about 330 HV and 650 HV, respectively. These specific properties were important for subsequent thixoforming of the functional graded materials.

Abstract: An experimental equipment with inclined plate cooling and shearing had been developed to prepare semi-solid 9Cr18 martensitic stainless steel slurry. The effects of inclined plate angel and length on microstructures refinement and spheroidization in semi-solid 9Cr18 alloy was investigated. The results show that when the molten alloy is flowing along the plate surface, the microstructure of the alloy involves from coarse dendrite to fine spherical grains, the sloping plate can provide sufficiently the undercooling for nucleation and lay a foundation for heterogeneous nucleation to form lots of nuclei of crystal internally and on the sloping plate surface, thus causing the melt to nucleate eruptively. Sloping plate angle and sloping plate length can affect the shear strength and shear time of the flow alloy on the sloping plate and thus influence alloy microstructure. Fine spherical grain in the semi-solid 9Cr18 slurry can be obtained at α=45°and L=600mm, the major grain equivalent diameters are less than 55μm and more than 40% of the grain shape factor is in 0.75, exhibiting better grain fine degree and roundness. Using energy dispersive spectrometer (EDS) to investigate the liquid and solid phase in the 9Cr18 semi-solid slurry, iron content is lower and carbon and chromium content is higher in the liquid phase than in the solid phase which makes it possible to prepare the FGM (functional gradient material) with a high wear resistance in the surface and a good strength and toughness in the center.

Abstract: 9Cr18 is a type of martensite stainless steel. It has high hardness, chemical stability, fine anticorrosion, wearable and quench stability. It has been used in different areas with high-anticorrosion and high polishing surface as mirror. So it requires for the high level surface quality after lapping and polishing. In this paper, the surface quality (surface roughness and flatness) of 9Cr18 is discussed with lapping parameters which include velocity, load and time distribution of two lapping steps(rough lapping and Ultra-precision lapping). In order to optimize those parameters, an optimization experiment for lapping 9Cr18 with Al2O3 was designed by Taguchi method. Finally, the optimum condition of each factor can be determined that speed: 80rpm, load:3.0kPa, and time distribution: rough lapping time=15min, Ultra-precision lapping time＝45min are the optimum conditions for both Ra and Wt.