Elimination of casting porosity in stainless steel butterfly valve body and control of melting and pouring temperature

After SAF2507 is smelted to 1 670 ~ 1 700 ℃, turn off the power supply and let it stand for 2 min. during this period, no slag removal operation is carried out (i.e. no slag removal agent is needed), and then turn on the power supply. At this time, the slag will continuously float up to the liquid level. When the temperature is low, the slag will not float up automatically. After the slag floats fully, sprinkle stainless steel slag forming degassing agent on it, and then remove the slag. The reason why molten steel is melted to such a high level is that in addition to the need for slag, the melting temperature also directly affects the pouring temperature.

Generally speaking, if the pouring temperature is too high, it is easy to produce shrinkage cavity and porosity defects. If the pouring temperature is too low, the defects of casting pores are easy to occur. According to long-term production experience, the pouring temperature of butterfly valve casting is 1590 ~ 1650 ℃. After slag removal, the molten steel shall be still, and then poured into the large ladle. After contacting with the ladle, the temperature will decrease. It takes nearly 10 minutes from the stop of heating of the molten steel to the entry of the molten steel into the mold cavity. The molten steel in 1 ton ladle is cooled by 6.4 ℃ every minute. It is very necessary to control the pouring temperature and strictly control the discharge temperature of the molten steel. The tapping temperature of molten steel should be 1670 ~ 1700 ℃.