The inoculant used in the production of nodular cast iron piston rings is a special mixed inoculant, which is composed of customized s inoculant and M inoculant in a certain proportion. The inoculation effect of single double piece nodular cast iron piston ring is obviously better than the commonly used fesi75 inoculant. The composition of s inoculant used in the test is: 73% ～ 78% Si, 0.7% ～ 1.0% Sr, 0.6% ～ 1.0% Ca, Al ≤ 1.0%. M inoculant composition: 43% ～ 47% Si, 1.0% ～ 1.5% Mg, 0.6 ～ 0.9% Ca, Al ≤ 1.0%.
The biggest feature of the mixed inoculant is that it can not only prevent the as cast white mouth, promote the formation of ferrite and fine fossil graphite balls, and reduce casting defects, but also the micro supplement of the unique spheroidizing elements mg, Sr and Ca under the condition of relatively low molten iron temperature can not only significantly increase the number of graphite balls, but also stabilize spheroidization and make the balls more round. The results of inoculation of qualified molten iron after spheroidizing treatment with different amount of inoculant. ① The pass rate of ball count is counted on the basis of spheroidization; ② When the amount of inoculant is less than 0.4%, the graphite core decreases gradually, the graphite ball becomes larger, the number decreases, the roundness becomes worse, and free cementite appears; ③ When the inoculant dosage is 0.5%, the number of balls does not increase, but the total graphite content increases, the ball diameter increases, and there is flowering phenomenon; ④ When the addition amount is 0.6%, the graphite ball blooms seriously. Due to the increase of relative silicon content and high carbon equivalent, graphite floats.
In a word, proper amount of inoculant and instantaneous inoculation and rapid pouring can not only ensure the matrix structure, but also effectively eliminate the free cementite, disperse the phosphorus eutectic, reduce the final silicon content and improve the toughness. The optimum amount of mixed inoculant is 0.4%.