Ductile iron has high strength, good toughness, oxidation resistance and high temperature resistance. It can be cast instead of forging and iron instead of steel. It can be used in slag pot products. It not only maintains the excellent characteristics of cast iron slag pot which is not easy to deform and stick, but also has high strength, high toughness and heat fatigue resistance. It can replace cast steel slag pot with economical price, The slag pot also has the characteristics of impact resistance, high temperature resistance and chilling and heating resistance.However, it is difficult to control the production process of ball milled cast iron slag pot, especially when the casting weight is more than 20t, it is necessary to prevent the decline of nodular graphite, the segregation of components, the floating of graphite, and the stress crack of the casting. All these factors must be strictly controlled. Because the temperature of steel slag is generally 920-1340 ℃, the slag pot is seriously oxidized in use, especially at the bottom of the slag pot because of the repeated quenching and heating of steel slag, the cracks on the inner wall of the slag pot will be more and deeper, resulting in the slag pot sticking and then failure.
1. Factors affecting service life of slag pot and causes of cracks
There are cracks on the trunnion of slag pot wall and deformation on the trunnion of slag pot bottom.
After being used, the slag pot with large residual stress appears cracks quickly after quenching and heating; when the user operates improperly, steel leakage occurs when slag is discharged, water is drawn on the liquid steel, and the casting is uneven in cold and heat, which leads to transverse cracks; the slag pot sticks to the slag pot, and cracks are caused by repeated strong hammering and slag cleaning.
2. Basic parameters and technical requirements of ductile iron slag pot
The casting of slag tank is 19500kg in weight, 3380mm in outer diameter, 2550mm in height, and 100-105mm in wall thickness. Trunnions are forged and cast in.
Material: QT500-7; spheroidization rate is more than 85%, graphite size is 5-7 grade, matrix is pearlite + ferrite, pearlite content ≥ 65%. The castings shall be tested by 100% ultrasonic testing according to DIN en12680-3 standard, and above grade 3.
3. Characteristics of hengin's ductile iron slag pot
3.1 the spheroidal graphite ductile iron slag pot is mainly treated by rare earth alloying to refine the grain and improve the strength; because rare earth has the function of refining the molten iron and eliminating the harmful influence of impurity elements, it can effectively eliminate the harm of trace impurity elements to the casting and improve the casting quality, The casting crack tendency caused by trace impurity elements was eliminated; the wire feeding process was adopted to add qrmg8res nodularizing agent and casife inoculation treatment to ensure the nodularizing grade and inoculation effect.
3.2 when the content of CE and w (CR) is high, the slag has good strength and less carbide.
3.3 Cr and Mo are added to form Cr2O3and Mo2O3 respectively. Cr2O3and Mo2O3are both dense passive films, which are evenly coated on the surface of the casting to prevent the penetration of O atoms into the cast iron, so that the pot body has a strong oxidation resistance at high temperature, so as to prolong the service life of ductile iron slag pouring.
3.4 the slag pot made of heat-resistant nodular cast iron has the characteristics of good thermal conductivity, high-temperature oxidation resistance and heat-resistant fatigue, and its service life is much better than that of cast steel slag pot.
