Research Of Improvement On Diesel Engine Casting's Uniformity In Different Wall Thickness(615 Cylinder Block)

The effects of pig iron amount in cupola melting, Cu element, inoculation on the microstructure and mechanical properties were investigated to improve and stabilize materials properties of WD615 diesel cylinder block, and the experiments had been done during producing in the workshop.The results show that the austenite amount is increased and the matrix is strengthened, while improving the Si/C ratio by decrease pig iron amount because the cutting effect of flake graphite on the matrix is minished via graphite amount decreasing and Si strengthens the matrix via solid solution hardening. So the mechanical properties of castings are improved by this way, and ultimate tensile strength reached 300MPa when pig iron addition amount is lower than 21%.Cu element can depress the critical temperature of austenite transformation, refine and increase the pearlite amount of matrix. Because of some amounts of Cr and Sn elements existed in molten iron, the pearlite content change of casting matrix was not distinct by the addition of Cu. But the thickness of pearlite flake was refined obviously, adding up to 0.5% of Cu from 0.2% wt pct. Because the effect of Cu on refining pearlite is finite, Cu content was increased to 0.5%, the pearlite and tensile strength of separat testing bar decrease a little. In addition, the wall thickness sensibility of casting got better by Cu alloying. The hardness difference between thick section and thin was decreased from 50HB to 27HB, because of Cu content from 0.0% to 0.5%.The inoculation effect of 75ferrosilicon fade quickly, and the form of graphite is bad, tensile strength is low, using SiBa alloy can improve graphite morphology and tensile strength. The bad effects of lead can be eliminate by rare earth element; but high property industry steel scrap is used in cupola melting, the effects of rare earth is not as good as multi-inoculation.The mechanical properties of casting was influenced significantly by the absorption of inoculant alloy which was affected directly by adding method and time. The experiment results indicated it was not beneficial to the absorption it that the inoculant alloy was placed in the ladle,The graphite morphology and tensile strength of casting was bad and low produced by this method. The absorption can be improved by adding to the tapping stream, the graphite morphology and tensile strength were improved. The inoculation effect was best when the adding time was 25 seconds after 1/3 tapping amount. If the adding time increased to 35s, the last inoculant alloy can't be absorbed because of floating on the surface of molten iron.Casting's wall thickness sensitivity is the same with tensile strength, the best adding time is 25 seconds after 1/3 tapping amount. Hardness difference of the 1# and 4# step block decrease from 38HB to 26HB.