PDF《博士学位论文公示材料》

3000 元/t;

20Mn23AlV 钢连铸生产工艺的综合成材率由 68.4%提高至 83.7%,吨钢成本降低

1660 元/t. ―2― 论文摘要(英文) High manganese steel has a wide range of applications due to its good wear resistance and non-magnetic properties. Mn13 wear-resistant steel and 20Mn23AlV non-magnetic steel are two typical high-manganese steels. Due to their high alloying element content, wide two-phase zone and strong thermal sensitivity, the die casting production process is widely used at home and abroad. The use of continuous casting technology instead of die casting technology has become the development direction of high manganese steel production technology. In this thesis, the evolution behavior, generation mechanism and control method of inclusions in high manganese steel smelting process were studied systematically with Mn13 steel and 20Mn23AlV steel. The solidification structure, elemental segregation and carbide precipitation behavior of high manganese steel under different continuous casting conditions were analyzed. A new type of CaO-Al2O3 based mold flux for high manganese steel continuous casting was designed and developed. Based on the research results, the cleanliness control technology, solidification structure control technology, carbide control technology and the new mold flux were widely used in the industrial continuous casting process of high manganese steel, and have achieved good application results. Under the conditions of this paper, the following important research results have been obtained. 1. The evolution behavior and control mechanism of inclusions in high manganese steel during smelting process were clarified, and the cleanliness of high manganese steel and the stability control of inclusions were realized. The evolution of inclusions in Mn13 steel smelting process was: Al2O3→MgO(MnO)・ Al2O3→ CaO-Al2O3 inclusions. The formation of spinel inclusions in the smelting process of Mn13 steel was unavoidable, and the increase of manganese content can effectively promote the precipitation of spinel inclusions. A suitable calcium treatment can modify the spinel inclusions in the Mn13 steel into CaO-Al2O3 based inclusions. There was no spinel inclusion in the 20Mn23AlV steel continuous casting slab, and the main inclusions were AlN. A small amount of MgO inclusions were also present. 2. The solidification structure change of high manganese steel under different continuous casting process conditions was clarified, which provided an important guide for the optimization of high manganese steel continuous casting secondary cooling process. Under the same cooling water flow conditions and electromagnetic stirring, with the increase of the casting speed, the proportion of the columnar crystal region of the continuous casting slab gradually decreased, the proportion of the equiaxed crystal region gradually increased, and the secondary dendrite spacing of the columnar crystal region gradually increases. The solidification heat transfer model for Mn13 steel continuous casting process was established. The equation between the secondary dendrite spacing and cooling rate of Mn13 steel continuous casting slab was . 3. The carbon and manganese segregation and carbide precipitation behavior of high manganese steel continuous casting slab under different process conditions were revealed, which provided a control method for carbide precipitation of high manganese steel continuous casting slab. Carbon had a certain degree of negative segregation in the cross-dendritic region, and the degree of segregation in the central equiaxed crystal region was obviously aggravated. The flaky carbides were precipitated in a large amount, and were distributed in a needle-like or block-like manner along the grain boundary. The main component was (Mn,Fe)3C cementite. Manganese element was mainly segregated in the columnar crystal region, and was mainly segregated at the grain boundary in the equiaxed crystal region. There was no obvious macrosegregation phenomenon, but there was a certain composition fluctuation phenomenon. The results of the carbide precipitation simulation experiments show that the temperature was below 550° C, the precipitation of carbides increased significantly ―3― as the cooling temperature and cooling rate decreasd. In order to avoid a large amount of precipitation of carbides, the Mn13 steel continuous casting slab should be cooled quickly after it was taken off the line to reduce its residence time in the low temperature section in industrial production process. 4. Based on the analysis and evaluation of traditional CaO-SiO2 based mold flux, a new CaO-Al2O3 based mold flux for 20Mn23AlV high manganese steel continuous casting was developed, which provided a solution for the continuous casting problem of 20Mn23AlV high manganese steel. Compared with CaO-SiO2 based mold flux, the reactivity of the new CaO-Al2O3 based mold flux and 20Mn23AlV steel was significantly reduced, the composition and properties both remain relatively stable, and the metallurgical function were better played. 5. The developed inclusion control technology, solidification structure control technology, carbide control technology and new mold flux were integrated into the industrial continuous casting production of high manganese steel, which realized the smooth production process and product quality improvement, and good application effect was obtained. Compared with the die casting production process, the comprehensive yield rate of Mn13 steel continuous casting process was increased from 85% to 95%, the cost per ton of steel was reduced by 3,000 yuan/t;