Search

The Ti element plays a role in pinning grain boundaries but also has a good binding ability to C and N, forming large primary carbides. Therefore, the effect of Ti content on primary carbides&rsquo, behavior in H13 ingots was comprehensively studied. A non-aqueous electrolysis method was used to determine the three-dimensional (3D) characteristics of primary carbides. We found a great difference between the two-dimensional (2D) and the three-dimensional characteristics of primary carbides. When performing 2D analyses, the density of the primary carbides appeared high, while their size was small. The actual characteristics of primary carbides can be obtained only by 3D observation. The primary carbide showed a typical dendritic structure, whose center consisted of Ti&ndash, V-rich carbide wrapped by V-rich carbide. As the Ti content increased, the size of the primary carbide increased from 24.9 &mu, m to 41.3 &mu, m, and the number density increases from 25.6 per/mm2 to 43.9 per/mm2. The Ti4C2S2 phase precipitated first, then changed into Ti&ndash, V-rich carbide, and finally further partly transformed into V-rich carbide. The addition of elemental Ti promoted the precipitation and transformation of primary carbides, resulting in an increase of the number density and size.

Phosphorus is undesirable in steel for it greatly decreases ductility and causes embrittlement in most cases. The kinetic behavior of phosphorus transfer was investigated during electroslag remelting (ESR) of G20CrNi2Mo bearing steel. Four heat treatments were carried out using an industrial furnace with a capacity to refine 2400 kg ingot. It was found the P content in the four ingots were all higher than that in the electrodes, indicating rephosphorization occurs during ESR. A kinetic model based on film and penetration theory was developed to elucidate the variation of phosphorus from metal film to droplet and metal pool. The model indicates that the rate-determining step of phosphorus transfer is at the slag side. Rephosphorization mainly occurs in the metal film and falling droplet. In addition, the effect of P in the slag and electrode, as well as the temperature of the slag pool on the P content in the metal pool were discussed. In order to achieve a low-P ingot of no more than 0.015%, the corresponding maximum P content in slag under the condition of a certain P content in the electrode was proposed.