Development and production of Bainite Ductile Iron grinding ball (3)

3.Microstructure and mechanical properties of bainite ductile iron

According to GB9441-88, the spheroidizing grade of each furnace number sample and grinding ball is above 1 ~ 2 grade, the size of spheroidal graphite is above 7 ~ 8 grade (100 times Figure 2), the number of graphite balls is more, and the distribution is uniform, the matrix structure (1000x Figure 3) of the cast waste heat graded isothermal quenching is lower bainite with a small amount of martensite, retained austenite and carbide, and the bainite structure is uniform and fine. The properties of this structure are characterized by high strength and hardness; it also has a high degree of toughness. The test results of the impact specimen: hardness ≥52HRC, impact toughness ≥14J/CM2(as shown in Table 3).

BAINITE DUCTILE IRON GRINDING BALL
BAINITE DUCTILE IRON GRINDING BALL 2

Grinding ball performance test results (see Table 4 and Figure 4): different diameter of the grinding ball using wire cutting machine, cutting along the diameter direction, hardness along the diameter, the matrix structure distributed evenly (50 ~ 55HRC) from the surface to the center is dominated by lower bainite more than 80%.

4.Production validation

Two hundred tons of grinding balls were produced in batches, and the grinding balls were put into industrial operation for five months in a cement plant, excellent performance, its outstanding feature is to achieve a high hardness and high toughness of good coordination, relative wear resistance slightly lower than high chromium ball, far higher than other types of grinding ball, its service life is forged steel ball 8 ~ 10 times. 2 ~ 4 times as much as medium manganese pellets. That’s one to three times the size of the world, and the breakage rate is low (less than 0.5%) . Compared with high chromium ball, its quality level is the same as high chromium ball, but the production cost is only 0. 7 ~ 0. Eight times, with a crushing rate one-fifth that of a high-chromium ball. The economy is better than high chromium ball, which is forged steel ball 5 ~ 6 times. To produce a ton of cement with an annual output of 500,000 tons of cement, bainite ductile iron grinding ball than forged steel ball can save 2. 26 CNY, so a year can save as much as 1.13 million CNY it can be seen that the use of this process of production of bainite ball, iron grinding ball its significant economic benefits.

5.Conclusion

The low alloy bainite ductile iron grinding ball can be melted and produced by cupola with proper sand mold casting technology, and the heat treatment technology of as-cast residual heat classification isothermal quenching is adopted by adding proper amount of alloy elements Mo, Mn, Cu, Cr, etc. , ductile iron with lower bainite and a little martensite, retained austenite and carbide as matrix can be obtained, and the comprehensive properties of grinding ball of bainite ductile iron produced by this process are better than those by other processes, and the lower bainite is uniform and fine, the spheroidizing rate is 1 ~ 2 grade, the size of spheroidal graphite is 7 ~ 8 grade, the hardness is ≥52hrc, the impact toughness is ≥14J/CM2, the hardness is evenly distributed along the cross-section of grinding ball diameter (50 ~ 55hrc) ; The bainite ductile iron grinding ball produced by this process has the advantages of low cost, good wear resistance, simple process and good effect after put into production.