The original material of zc170 cylinder head is HT300, the technical requirements are WCu = 0.5% ~ 0.8%, WCR = 0.2% ~ 0.4%, WMO = 0.2% ~ 0.35%, and the hardness of the body should be more than 190hbw. The overall dimension of cylinder head is 355mm × 230mm × 209mm, the weight of the blank is 65kg, the main wall thickness is 8 ~ 10m m, and the maximum hot spot diameter is about 60mm.
The vermicular graphite cast iron is Ru T300, the matrix is mainly ferrite, the vermicular rate is more than 50%, the elongation is more than 2%, the tensile strength is more than 300mpa, and the hardness is more than 140hbw.
Main equipment and test conditions: 7T induction furnace. The fast analysis equipment in front of furnace mainly includes spectrometer, carbon sulfur analyzer, tensile testing machine, Brinell hardness tester and microscope.
- Second trial production
1) The ingredients and treatment process remain unchanged, but the amount of vermicularizing agent is reduced to 0.35% of the treated liquid iron, i.e. 1.75kg. The test results show that WS, wla, WCE and WMG of the treated liquid iron are 0.013%, 0.006%, 0.017% and 0.015%, respectively, reaching the expected target composition. The spectrum shows that the creep rate is 85% (see Figure 1), the tensile strength is 363mpa and 370mpa, the elongation is 3.39% and 4.46%, the hardness is 154hbw, and the properties meet the requirements of RuT300.
2) In the second batch, 70 cylinder heads were poured and 67 cylinder heads were machined. After machining, 8 pieces were still loose, leading to air leakage, and there was looseness at the place about 30mm above the tappet hole and the place where the threaded holes were concentrated. Then the idea of reducing the hot spot as much as possible was improved. The tappet hole lap diameter was 40mm, the height was about 130mm, and the hot spot was large. A sand core bulge was made at the tappet hole of the upper cover core to reduce the hot spot. In addition, a chill is added at the threaded hole (see Fig. 2), and a gate cup is set on the basis of the original gate, which increases the height of the sprue (pressure head) by about 120mm and enhances the feeding capacity (see Fig. 3).
- The third trial production
The third trial production was carried out according to the second trial production and some improvement methods to reduce the hot spot. The trial production results were satisfactory. The creep rate of several metallographic samples reached more than 80%, and no obvious porosity was found in the casting.
After two times of trial production, carburizer and recycled material were used in the middle. The results were not very ideal, and some loose phenomenon occurred. The main reason is that the sulfur mainly comes from the carburizer during the induction furnace melting, the sulfur content of the original molten iron is uncontrollable, and there are many impurities in the return material, which makes the original molten iron have more uncertain factors, and there is no advanced vermicular iron detection equipment in front of the furnace, so it is impossible to accurately adjust according to the changes of various elements in the molten iron. For this reason, the second trial production process was used in the later production to ensure the relative stability of the elements in the original molten iron. It was verified that it can meet the needs of production and can be stably mass produced, with the yield of more than 92%. Because the alloy in the original gray cast iron is eliminated, the casting cost is obviously reduced, and the cylinder head made of vermicular graphite cast iron has certain toughness, so the risk of cracks in the process of use is greatly reduced.