High-carbon hard wire steel was a high-strength steel widely used in steel wire ropes and steel strands. With the rapid development of automotive high-speed rail and electronic products related technologies, higher requirements were put forward for the performance of metal materials in its auxiliary industries. The size distribution of inclusions became an important criterion for determining the properties of steel. Class B non-metallic inclusions in steel (mainly alumina) were the main types of common inclusions in various high-quality steels. In view of the present situation and existing problems in the modification process of alumina inclusions in high carbon hard wire steel, the modification process of B-type inclusions was systematically studied to explore the evolution process of inclusions. Use an intermediate frequency induction furnace to test in an alumina crucible. In this work, industrial pure iron, recarburizer and Fe-68%Mn alloy were added into the test furnace to prepare high-carbon hard wire steel samples with different contents of rare earth lanthanum, and then the steel ingot through wire cutting to take the target sample (10 mm×10 mm×10 mm) at the center of the cylindrical steel ingot was took. The prepared samples were characterized by metallurgical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) and chemical composition testing to clearly understand the type, number, size distribution and other information of inclusions, and analyze the mechanism of rare earth lanthanum on the cleaning of molten steel. Afterwards, combined with Factsage thermodynamic calculations, the evolution of inclusions before and after the addition of lanthanum was inferred, which could provide a better reference for purifying irregular-sized alumina inclusions in molten steel. The effects of different additions of lanthanum (within the range of 0~0.0360%) on the composition, morphology, size and spacing of alumina inclusions were studied by SEM and EDS. The results were as follows: (1) From a macroscopic point of view, before and after adding rare earth lanthanum, the morphology of the inclusions changed from polygonal alumina inclusions to nearly spherical rare earth lanthanum composite inclusions. With the addition of rare earth lanthanum, the number density of 3~5 μm inclusions decreased significantly, the number density of 1~3 μm inclusions increased significantly, and the average inclusion size of impurities decreased by 5.9~7.7 μm. (2) From a microscopic point of view, the evolution of inclusions before and after the addition of rare earth lanthanum was calculated through data statistics. Before lanthanum was added, the interfacial spacing between inclusions was mainly in the range of 10~100 μm. With the addition of lanthanum, the interfacial spacing between inclusions was mainly in the range of 100~500 μm, and the distribution of inclusions could be found to be more diffuse. (3) Before lanthanum was added, the surface density of alumina inclusions accounted for the largest proportion. With the increase of lanthanum addition, the proportion of the maximum areal density of inclusions decreased successively. The proportion of the four samples according to the maximum areal density from small to large was as follows: Sample S4< Sample S3< Sample S2< Sample S1. (4) The possible inclusions of high carbon steel during 1873 K and solidification were calculated by Factsage software to further verify the experimental phenomena observed during the test. The transition path of inclusions in steel at 1873 K was: Al2O3 → LaAlO3 + La2O3·11Al2O3 → LaAlO3 + La2O2S → La2S3 + La2O3, and La2S3 precipitated during the curing process. By increasing the amount of lanthanum added, the way to modify Al2O3 inclusions in steel was as follows: Al2O3 →LaAlO3 + La2O3·11Al2O3+ La2S3 →LaAlO3 + La2O2S + La2S3→La2S3 + La2O3. From the results of experiments and calculations, it was found that the addition of rare earth lanthanum to high carbon steel containing alumina inclusions could optimize the size, morphology, and number density of inclusions, and from the perspective of inclusions, it could improve the quality of high carbon steel. Thereby improving the drawing performance of high-carbon steel wire. By comparing with the previous work of adding rare earth cerium to high carbon steel, it was found that the modification effect of rare earth lanthanum was better than that of rare earth cerium. The later work arrangements would go deep into the atomic level, explore the specific internal reactions between inclusions, and observe the movement of inclusions in real-time under high temperature in-situ conditions, and perform real-time statistics to analyze specifically why alumina inclusions were in rare earths. Through the use of simulation software and existing detection methods, it provided a better theoretical basis for better explaining the movement of inclusions in molten steel. © 2022, Youke Publishing Co., Ltd. All right reserved.
