Effect of Additives on Structure and Properties of High Chromium Refractories

Table 1 Chemical Composition of Raw Materials (w) % Item Industrial chromium oxide zirconia □ Zhang Hui Zhang Hong Yang Bin Luoyang Institute of Refractory Materials Luoyang 471039 The samples were molded by high pressure and fired at high temperature. Bulk density, apparent porosity and normal temperature flexural strength, normal temperature compressive strength were measured according to national standards or the original Ministry of Metallurgical standards. The thermal shock resistance test is to heat the 25mmX25mmX125mm specimens to 600C, 800°, 1000°, and 1200°, respectively, to insulate the 30-jaw shears and rapidly quench once in flowing water, and measure the residual flexural strength after thermal shock to residual The flexural strength retention rate indicates how well the material resists thermal shock. The microstructure of the sample was observed with an optical microscope and an electron microscope.

2 Results and discussion 2.1 Effect of AI2O3 on the normal temperature performance of the material The influence of AI2O3 on the normal temperature compressive strength and apparent porosity of high chromium materials is given. Compared with the sample without Al23, the addition of Al23 promoted the sintering of high-chromium materials, and the apparent porosity decreased significantly. At the same time, the compressive strength of the material at room temperature was greatly increased. When the addition of Al2O3 was 4a%, the room temperature resistance The compressive strength can reach over 120MPa and the apparent porosity decreases to 13%. The effect of AI2O3 on the properties of high-chromium materials is closely related to the microstructure of the material. The microstructure features of high-chromium materials are given. The formation of continuous solid solution of Al23 and Cr23 can significantly promote the sintering of Cr23, and can significantly increase the degree of close bonding between matrix and particles. In the presence of Al23, the microstructure of the high-chromium material is characterized by the continuous structure of the Cr 3 Al 3 solid solution sintered from the matrix part Cr 23, and a layer of (Cr, Al) 3 solid solution is formed around the Cn 3 particles. Directly combined with the matrix, this continuous structure of the particles and the matrix directly makes the strength of the material significantly improved, 2a% of AI2O3 added amount to obtain better results.

Effects of Al23 and Zr2 on the microstructure of high-chromium materials 2.2Zr2 Effects on the properties of normal temperature and thermal shock resistance of materials The relationship between the properties of high-chromium materials at room temperature and the addition of Zr2 is shown in Table 2. It can be seen from Table 2 that with the addition of Z1O2 With the increase of the amount, the apparent porosity of the sample increases, and the bulk density decreases. When the Zr2 addition amount is less than 2b%, the normal temperature compressive strength and the normal temperature flexural strength decrease as the Zr2 content increases, and when the Zr2 content exceeds 2b%, Start to rise.

The main reason for the decrease of the strength after adding Zr2 is that the phase change of Zr2 occurs during the sintering process of the material and microcracks occur. The influence of the amount of stomatal surface 2Zr2 added on the performance of the sample is eight. 3) The apparent porosity /% normal temperature flexural strength / MPa normal temperature compressive strength / MPa rate increased, the direct bonding of particles and matrix due to the influence of Zr2 decreased. However, after the addition of Zi2 exceeds a certain level, the dispersion strengthening of the Zr2 grains in the grain boundary and (Cr,Al)23 solid solution will play a major role and the strength will increase significantly.

The relationship between the retention of residual strength after thermal shock and the amount of Zr2 added can be seen. It can be seen that at the initial stage of Zr2 addition, the residual strength retention of the material increases as the amount of Zr2 is added. This is related to the toughening effect of the microcracks produced by the phase transition of Zr2. This can also be seen from (C). However, when the amount of Zr2 was added to a certain extent, with the increase of the amount of Zi2 added, the residual strength retention of the material decreased. This is mainly due to the fact that when Zr2 is added in large amounts, under large thermal shock temperature differences, the mismatch between Zi2 and the matrix on the thermal expansion rate and elastic modulus causes a large internal stress, and at the same time micro-cracks are formed to make the energy disperse. Reduced, so that the proportion of intensity reduction after heat shock increases. The appropriate amount of Zi2 added is 2b%~3b%. The high-chromium refractories researched and developed by our institute are run on the 6.5MPa coal-water slurry gasifier of Luohe Chemical Fertilizer Plant, with a maximum service life of 16000 hours and an average service life of 13,000 hours. 3 Conclusions Added a % ~ 3b%, the high chromium material has good overall performance.

The close combination of particles and matrix, the coexistence of granular (Cr,Al)23 solid solution and the microstructure characteristics of uniform distribution of toughening phase Zr2 make the high-chromium refractories have better comprehensive performance.

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