At present, many measures to improve the strength of gray cast iron often have an adverse impact on its machinability. Studies have shown that the machinability of gray cast iron is improved after inoculation treatment.
Inoculation treatment can not only reduce the white tendency at the thin wall, refine the grain, improve the microstructure of gray iron castings, but also improve the strength of gray iron castings . Some studies have shown that the amount of graphite in gray iron castings treated with fesi75 + Sr composite inoculation is significantly increased, the graphite is shorter, the tip is smoother, and the pearlite has smaller sheet spacing, which improves the mechanical properties of gray iron.
Xu Guifang et al. Used 60% basi + 40% SIFE compound inoculant to inoculate the gray cast iron cylinder block, and then added an appropriate amount of alloy elements, which can stabilize the tensile strength of gray cast iron above 250Mpa. Zhou Yongshou used antimony containing compound inoculant to improve the strength and hardness. The production and application verification shows that the compound inoculant can make the tensile strength of gray cast iron castings with chemical composition in the range of 3.87% – 3.94% Ce, 0.25% – 0.49% Cr and 0.43% – 0.52% Cu reach 290.5-335mpa and the hardness reach more than 210hb.
Aravind vadiraj et al. studied the effect of mixed rare earth inoculation on alloy gray cast iron. The results show that all gray cast iron has uniformly distributed A-type graphite structure, and the addition of rare earth elements can refine graphite and microstructure, The alloy gray cast iron without mixed rare earth elements has higher volume fraction pearlite (89%) and lower volume fraction flake graphite (11%), while the gray cast iron inoculated with mixed rare earth elements has higher volume fraction flake graphite (15%) with pearlite with volume fraction of 85% as the matrix, due to the increase of graphite volume fraction by 40% – 60%, the tensile strength of alloy gray cast iron will be reduced from 344mpa to 300mpa and the hardness will be reduced from 247 vhn to 221 vhn, but the wear resistance of gray cast iron can be improved When the amount of Ba inoculant is 0.5% – 0.6%, the tensile strength of gray castbody can reach more than 300mpa, and it is pointed out that Mo has a significant effect on improving the tensile strength of gray cast iron casting body. For the influence of different inoculants on the machinability of gray cast iron for cylinder block,
Wang Kui introduced that the tensile strength of gray cast iron treated with rare earth inoculant can be stable at about 300 MPa and has a good quality coefficient. The gray cast iron for cylinder block inoculated with strontium has excellent machinability and small section sensitivity. When inoculated with 60% fesi75 + 40% RE, the tensile strength of gray cast iron is about 295mpa, with good hardness and quality; When inoculated with 20% fesi75 + 80% Sr, gray cast iron has the best machinability, the lowest section sensitivity and microhardness; When 40% rare earth + 60% 75 ferrosilicon compound inoculant is selected, the tensile strength of gray castings is greater than 295mpa; The gray iron castings for cylinder block treated with 20% rare earth + 80% 75 ferrosilicon composite inoculant have the best machinability, minimum section sensitivity and hardness difference; After 75sife inoculation treatment, the mixture containing rare earth, chromium, manganese, silicon and iron is alloyed in a certain proportion or alloyed with pure copper. The gray cast iron alloyed with the mixed additive has better processability than the gray cast iron alloyed with copper.