High-speed steel rolls have excellent properties such as long service life, smooth surface and uniform thickness of rolled materials. At present, the centrifugal casting method is mostly used in industry to prepare the roll rings of high-speed steel rolls. The preparation process is simple and low-cost. However, because the high-speed steel materials used for rolls contain high alloying elements such as Cr, V, W, and Mo, they solidify. During the process, under the action of centrifugal force, component segregation easily occurs, making the performance of the outer layer (working layer) of the roller ring lower than that of the inner layer (non-working layer).
The electro-slag remelting method is used to prepare high-speed steel roll materials, and appropriate modifiers are used to improve the structure. Use recycled scrap high-speed steel as raw material, configure M2 high-speed steel roll material, use yttrium-based heavy rare earth composite modifier, and cast consumable electrode rods through a vacuum medium frequency induction furnace. The modifier is added during the casting process, and the weight of the modifier is according to the high speed. The steel weight is 1%, and then the prepared electrode rod is electro-slag remelted, and CaF2-Al2O3-CaO ternary slag is used to prepare a high-speed steel roll ingot of Ф110mm×300mm. High-speed steel roll ingots undergo heat treatment: annealing at 800°C + quenching at 1050°C + tempering at 550°C twice.
Metallographic examination found that the high-speed steel sample without a modifier added had a fishnet-like structure. Its eutectic carbides are enriched at the grain boundaries and are mainly fishbone-shaped, with only a small amount of granular eutectic carbides distributed within the grains; in high-speed steel samples with modifiers added, eutectic carbides The morphology of the material has changed, and at the same time, the eutectic carbides in the grains have increased, and the grains have become smaller. After annealing, quenching, and tempering heat treatment, the eutectic carbide network structure of the sample with modifier added was further interrupted; compared with the high-speed steel sample without modifier added, the eutectic carbide became finer and the particles The number of eutectic carbides increases, the distribution is even, and the network structure breaks. Correspondingly, the impact toughness increases from the original 8.7J/cm2 to 9.8J/cm2.
High-speed steel materials are prepared using the electro-slag remelting method. During the smelting process, the water-cooled crystallizer is cooled and takes away heat, so its cooling rate is much faster than ordinary centrifugal casting, which refines the primary grains and simultaneously causes multiple dendrites. The decrease in branching and dendrite spacing caused some of the eutectic carbide network structures in the high-speed steel samples to break.
After adding the modifier, the nucleation particles increase, which plays a role in purifying the molten steel. In the subsequent solidification process, it can reduce the generation of eutectic carbides at the grain boundaries and achieve the purpose of refining the eutectic carbides at the grain boundaries. In addition, the M7C3 type eutectic carbides at the grain boundaries in the sample with modifier added are divided into fine M2C and M6C type eutectic carbides after heat treatment. Therefore, the eutectic carbide network structure of the sample is formed after heat treatment. Further fractures occur.