What are the influencing factors of forging exposure?
作者：admin 来源：本站 发布时间：2019-06-04 11:13:10 浏览量：
The quenching layer almost burns in forging heating because of its high degree of supercooling and rapid solidification of the initial molten steel on the ingot surface. After the formation of chilling layer, grain begins to form columnar crystals along the die wall vertically. This is partly due to the choice of crystal solidification under large temperature gradient and the low concentration of solute in solidification front and the easy washout of solidification front in circulation. Therefore, inclusions and segregation defects are very small and can be considered as pure columnar crystals. Depending on the pouring temperature and the size of columnar crystals, the thickness of ingots is generally about 50 mm 120 mm ~. Dendritic columnar crystals, where the direction of the crystal deviates from the growth direction of the columnar crystal, form segregation in this type of region.
At a certain stage, the dendrite branch achieves supercooling and solidification in the central region of molten steel at the same time and to the same degree, and eventually forms a huge equidistant. The deposition cone enriches at the bottom of the ingot with non-metallic inclusions, creating a core defect rather than acting as a defect. From the above analysis, the A-type segregation of backup roll and exposure due to poor crystal quality of ingot branches is the surface area exposed to forgings, which is also a scattered band with axial leakage. At the same time, combined with the change of temperature and concentration gradient density in the solid and liquid phases of McDonald's and hunting type, the separation theory is induced, resulting in unstable and solidified molten steel not driving the molten steel circulation. The flow of molten steel will gradually circulate through heating the center of the ingot, which can make the local dendrite remelting. The remelting can increase the liquid fraction, reduce the flow resistance, further increase the flow rate and accelerate the remelting. This unstable phenomenon forms a series of small pipe flows in the solid and liquid phases. The solid phases in the pipe flow form grooves. Of course, the higher the flow rate, the higher the melting rate. The dendritic liquid flow with high concentration was obtained by expanding the cell.
The circulation must carry a large number of non-metallic inclusions in molten steel. With the decrease of temperature, the non-metallic inclusions in molten steel with viscous flow are blocked and remain in the areas where dendritic pipe flow is further concentrated and difficult to remove. The blocked pipe current merges to form a type of isolation. It is not difficult to see from the above analysis that under the same casting conditions, molten steel is pure, and more difficult is to produce a kind of isolation. According to the above analysis, the distribution of inclusions can be reduced by increasing the purity of molten steel and leaking the ingot core as much as possible in the dendritic zone.
