The process of producing ultra-low carbon steel in heat treatment vacuum furnace

1. Process of production of ultra-low carbon steel in heat treatment vacuum furnace:

Converter of the molten steel – steady oxygen measurement sampling – light processing measured again seven minutes to steady oxygen to 8 minutes of deep decarburization process, steady oxygen measurement sampling – aluminium deoxidizing and alloying – cycle after 3 minutes to steady oxygen measurement sampling, 5 minutes after the steel net cycle.
For this process, the difficulty control mainly has two aspects, the first, how to take the carbon to the lowest range in 15 minutes; Second, how to determine the residual oxygen content in the molten steel after 15 minutes of decarbonization, the aluminum can be put in place at one time, which can ensure aluminum deoxidization and aluminum alloy. That way, the smelting time can be controlled between 25 and 30 minutes. Otherwise, the vacuum processing time will be greatly extended. Smelting in the process of production of ultra-low carbon steel, as the extension of time, the contact between refractory material and steel liquid will lead to carbon steel back, in addition, the amount of ultra-low carbon steel because of the addition of aluminum is larger, a lot of Al2O3 inclusions produce, so the aluminum to join the sooner, the more conducive to Al2O3 inclusions floatation, the more conducive to the process after the operation and improve the quality of our products.

2. Carbon control:
Ultra-low carbon steel production, the converter molten steel is not directly after deoxidization on decarburization process of vacuum furnace, so the converter of molten steel, we need to know the content of carbon and oxygen in molten steel. According to practical experience, 100 PPM of carbon requires about 150 PPM of oxygen. If you want to remove the carbon to extremely low range, you must also ensure that there is more than 200 PPM of oxygen in the steel water. For example, the carbon in the converter is 300 parts per million, and the amount of oxygen needed to get the carbon to a very low range is 3 x 150+200 = 650 PPM.
Surplus oxygen content is higher, of course, the more conducive to decarburization, however, high surplus oxygen content will need more aluminum to DNA, which will cause waste of raw materials, will also affect the purity of molten steel. It is the change curve of carbon content in the vacuum decarburization process in the production process of ultra-low carbon steel. As we can see, in the first six minutes of decarbonising, the carbon content drops rapidly, and in the subsequent nine minutes, the carbon is reduced by less. But it can go down to about 15ppm. For the sake of analysis, we divided the 15-minute decarbonization process into two phases, the first six minutes to light and the last nine minutes to decarbonizing.