|
In this paper, thick cross-section of the high toughness of cast ductile iron blast furnace stave often leaking, burning, cracks, fracture, short life, using optical microscopy, scanning electron microscopy and tensile testing machine experiment equipment, by casting observation of the state high toughness thick Ductile Iron Stave microstructure, tensile strength and elongation properties of the test to study the Si content, the breeding process, wall thickness, and cooling rate thick section spheroidal graphite cast high toughness cast iron the Stave organization and performance, and study the its graphite variability; ductile iron blast furnace stave CAE solidification simulation, solidification time, solidification process graphite variation. Underwrite bred an iron trough bred and stream inoculation inoculation, change gave birth dose found added to underwrite bred 0.9%, gave birth to an iron trough of 0.5%, 0.1% inoculation program stream inoculation. The sample cooling wall attached cast studies have shown that ball rate reached 90% the ferrite amount of 88 to 90%, no carbides appear the average reached 24.8% elongation, tensile strength of about 400MPa . High toughness Thick Ductile Iron Stave attached cast sample, when the carbon content of about 3.5%, a silicon content of 2.3 to 2.9%, the matrix microstructure of ferrite does not appear carbide and pearlite, with significantly increasing the content of silicon, graphite, deterioration, reduced elongation. The silicon content of 2.3%, the the spheroidization level reaches 2, the graphite size reaches 7, 25.9% elongation, tensile strength of 406MPa. Analysis of wall thickness of 250mm and 300mm high toughness thick section ductile iron cooling wall organization and performance analog sample found that with the increase in the wall thickness, spheroidization level reduced from two to three, graphite ball size from 7 reduced to six. The same time as the wall thickness increases, the elongation phenomenon of decline, the wall thickness of 250mm specimen elongation is up to 26.39%. Select high toughness ductile iron the Stave analog test block cooling water pipe between the two layers of the sample, with the reduction of the cooling rate, the first to appear chunky or vermicular graphite, graphite ball then gradually rounded, and finally reappears fragments like graphite. Spheroidization level up to 2 to 3, a minimum of only six, the graphite ball is best for 7, the worst four. Elongation and tensile strength also presents the trend of increased and then decreased with the decrease of the cooling rate. Maximum tensile strength of 397MPa, a minimum of 311MPa, elongation up to 19%, a minimum of 4% in the core part. CAE solidification simulation results show that: the liquid metal filling is smooth, no eddy current phenomenon of loss in the temperature of the liquid metal in the casting process is about 40 ℃, the cooling pipes around metal liquid temperature dropped to about 70 ℃. Finally, with the solidification order by after prolonged clotting time, graphite ball gradually grow from small rounded flowering, chunky deformity graphite. In the first solidification region castings ball level 2 to 3, the graphite size 7, only six final solidification ball area level, the graphite size of 4. The distribution of the liquid phase of the CAE simulation also explains the reason for this graphite distortion, liquid distribution and Niyama the Shrinkage criterion also shows the the casting solidification final distribution in the liquid phase is prone to shrinkage porosity, shrinkage tendency.
|