Aluminothermic centrifugation is a new process for preparing wear-resistant ceramic-lined steel pipes. Improving the compactness of ceramic layers is an important issue in the development of ceramic-lined steel pipes. The pores in the ceramic layer are composed of pores and shrinkage cavities. The self-propagation reaction of single Al-Fe23 system has large heat release and high temperature. Although the volatile impurities and gas in the system can be mostly removed under the action of centrifugal force, due to the rapid cooling of the system, the Al23 ceramic phase condensation fund project: Hebei Provincial Education Commission The funded project (98213) has a high solid temperature and a large solidification shrinkage. The self-propagating reaction product has a short residence time in the molten state, resulting in the formation of more pores and crater porosity in the final inner liner layer generally up to 10% 25%. The additive adjusts the composition of the inner liner and changes the solidification process, which can effectively improve the microstructure of the ceramic layer, thereby improving the quality of the composite pipe. The additives studied have Si2, feldspar, etc. 1. This work studied the addition of dehydration in the Al-Fe23 system. The effect of borax, Na2B47 additive (abbreviated as NB) on the microstructure of the ceramic layer.
2 Test materials and methods Powder material: dehydrated borax and Fe23 powder mixed ball milled to a 100 mesh and then added a 100 mesh Al powder. The homogeneous powder, Sun Shiqing, etc.: The final material of the spinel-boron glass-lined steel pipe is placed in a 6mmX4mmX100mm hot-rolled seamless steel pipe test piece, and the aluminum heat centrifugal test is carried out on a self-made centrifugal test machine. The centrifugal force is 280G (G is the acceleration of gravity).
The metallographic method was used to analyze the ceramic pores and microstructure, and the phase composition of the ceramic layer was identified by X-ray diffraction analysis.
3 Test results and analysis 3.1 Compared with the ceramic-lined steel pipe prepared by the single A-Fe23 system, the composite tube composition and microstructure can be made more uniform in thickness of the ceramic layer, especially the inner surface is smoother and smoother, and the ceramic layer is free. Cracks and flaking occur.
The metallographic observation of the cross section of the polished and polished test piece shows that the composite steel pipe is composed of an outer steel pipe, an intermediate transition metal layer and an inner layer ceramic.
The transition metal layer and the steel tube achieve a good metallurgical bond, and the transition metal layer exhibits a dendritic form (). The ceramic layer has a clear interface with the transition metal layer. There are some small circular pores in the ceramic layer with a diameter of 1040m, which are distributed in the glass phase of the matrix, and the middle arrow refers to the pores. Quantitative metallographic analysis showed that the porosity of the ceramic layer was the porosity of the 250X ceramic layer of the dendritic structure of the transition metal layer. 50XFig. The matrix indentation is often cracked, indicating that the matrix is ​​a brittle glass phase composed of B2O3, Na2O and FeO. .
The effect of the ceramic layer microstructure 250X 3.2Na2B47 additive was first analyzed for the effect of Na2B47 additive on the self-propagation process. From the actual aluminothermic centrifugation process, the proper amount of NB can make the aluminothermic reaction tend to be stable, prolong the burning time, and control the smoke injection phenomenon, which improves the safety of the centrifugal self-propagation test. This shows that NB hinders the contact probability and contact area of ​​Al powder and Fe23 powder, reduces the reaction speed, and acts as a diluent.
The ceramic main crystal phase of the single Al-Ftt3 system self-propagating reaction product is AI2O3, and also contains 10% 30% FeAl24. After adding NB additive, the ceramic main crystal phase is FeAl24, and Al23 is the secondary crystal phase. Since the melting point of FeAl24 (760*C) is lower than the melting point of Al23 (2050*C), NB causes the crystallization temperature range of the molten ceramic to be greatly lowered, and the fluidity is improved.
B23 and Na2 in NB have a strong tendency to vitrify, and the ceramic product is easy to form a glass phase due to the rapid cooling rate during the preparation of the composite tube. From the pores distributed in the base glass phase, it can be determined that the glass phase has a lower solidification temperature than FeAl24. Thus, the solidification temperature range of the entire ceramic layer is significantly reduced, and under the action of strong centrifugal force, there is more time to remove the gas; and the glass phase solidification shrinkage is smaller than the crystal phase, which reduces the possibility of shrinkage formation. Therefore, the density of the ceramic layer is significantly improved, and the inner surface is also smoother and smoother.
In the self-propagation process, NB can react with the rust of the inner wall of the steel pipe (mainly Fe23): the inner wall of the pipe is easily welded with the liquid metal Fe formed in the self-propagating reaction of the aluminum, and the metallurgical bond between the transition metal layer and the steel pipe is achieved.
It is known from the X-ray line (editor) that the ceramic main crystal phase is iron-aluminum spinel (FeAk4) and the secondary crystal phase is corundum (Al23). Combined with the microstructure observation, it can be determined that the medium-white bulk phase is FeAk4 and the acicular phase is Al23. It is found that the microhardness test shows that the Na2B47 additive promotes the perfect metallurgical bond between the transition metal layer and the steel pipe matrix. (Continued on page 28) Pan Jing, et al: The study of bonded Fe+SiC magnetic abrasives shows that the surface texture after grinding is very deep, and the surface after grinding has only a very shallow processing texture. Moreover, the lower the hardness of the material, the shallower the processed texture, which corresponds to the measured surface roughness value.
No traces of plastic deformation and microcracks were observed between the parallel-arranged textures on the T10A and 45 steel surfaces. This indicates that the sharp-hard SiC particles cut the surface of the material, and the inductive magnetic lines at the surface protrusions are relatively dense. Grinding is also faster, resulting in a rapid decrease in surface roughness. At the same time, the abrasive brush arranged along the magnetic lines during the magnetic grinding process is flexible, and a small amount of relative displacement can occur between the abrasives, the stress on the surface of the workpiece is low, and there is no strong impact stress, so the surface is not caused. Microcracks. In addition to the shallow parallel arrangement of the cutting texture on the ground surface of the 30CrMnSiA steel, a small amount of uniform fine pits can be seen. This is because the steel quenched hardness (28HRC) is lower than the first two. When the SiC particles cut the surface, the stress sometimes exceeds the yield strength of the material, causing local plastic deformation and forming a crater. Therefore, in general, the magnetic grinding of the surface of T10A, 45, 30CrMnSiA by bonded Fe+SiC magnetic abrasive is a low-stress abrasive grinding process. This process provides a high surface quality for the workpiece.
4 Conclusion The particle size has a significant effect on the surface roughness of the grinding. Under certain process conditions, they all have the best value.
A method of obtaining a magnetic abrasive by bonding Fe and SiC particles with an adhesive is feasible. The heat resistance and toughness of the adhesive and proper cooling are important factors in extending the service life of the abrasive.
The magnetic grinding mechanism of 30CrMnSiA steel is the low stress abrasive grinding of SiC particles on the surface of the material.
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