Research On The Vermicular Graphite Cast Iron Vermicularization Process, Structure And Performance Of Engine Cylinder Head

Vermicular graphite iron material not only has the characteristics of good thermal conductivity and good shock absorption performance,but also has high mechanical properties.In recent years,it has gradually been applied to the production of important parts of automobile engines,replacing the gray cast iron materials with lower strength.Although vermicular graphite cast iron materials have been used for a long time,the theoretical research on vermicular graphite cast iron materials is not deep enough,and the production is more dependent on experience.In order to ensure that the vermicularization rate of each batch of vermicular cast iron castings is stabl e,many production companies have strict requirements on the vermicularization process and the quality of raw materials,but in the actual production process,due to fluctuations in the composition of raw materials,the vermicularizing agent is replaced.Lots of vermicular failures.For this problem,this article focuses on the production of multi-cylinder small-diameter diesel engine cylinder heads of vermicular cast iron materials,focusing on the effects of vermicularization techniques,vermicular elemen ts,and charge composition on vermicularity,microstructure,and mechanical properties.For a long time,the raw materials for the production of vermicular cast iron are mainly high-quality pig iron.In recent years,the price of pig iron has been rising continuously.In order to reduce the production cost of vermicular cast iron castings,the experimental steel scrap was used in this thesis,and the recarburizing agent and some steels were added during smelting.A synthetic pig iron is prepared from the alloy and this synthetic pig iron is used to prepare the vermicular cast iron.After testing and analysis,it can be seen that the use of this synthetic pig iron can produce vermicular cast iron materials,and its microstructure and mechanical properties are almost no different from vermicular cast iron produced from pig iron.In this paper,by investigating different kinds of vermicularizers and inoculants,the effects of vermicularization and inoculation of elements and ratios on the microstructure and graphite morphology of vermicular cast iron were investigated.According to the laws obtained from the experiment,magnesium and rare earth are elements that promote the vermicularization of graphite.The ability of magnesium to promote the vermicularization o f graphite is stronger than that of rare earth elements.Therefore,the greater the proportion of magnesium in vermicularizers,the greater the rate of vermicularization.The more sensitive the addition of vermicularizing agent,the worse the stability of vermicularization,but during the vermicularization reaction,the magnesium element will violently burn when it encounters high temperature iron fluid and the deflagration agent will detonate.The explosion reaction will play a stirring role and make the c reep The chemical elements are more evenly distributed within the processing package and do not need to be mixed with the molten metal after the vermicularization reaction.Calcium is also an element that promotes the vermicularization of graphite.Since t he absorption of calcium by the molten metal is weak,most of the calcium forms a scum on the surface of the solution after the vermicularization is completed.The experimental use of inoculant mainly contains silicon,barium and calcium,and the inoculant can play a role in increasing the number of nucleation of graphite in the molten metal.According to some data,it is easy to inoculate using only a single silicon element as an inoculant.The phenomenon of recession,while calcium and strontium have the ability to prolong the appearance of recession,so the inoculants used in the experiment are considered long-term inoculants.Experiments show that the role of calcium in the promotion of graphite spheroidization is greater than its role in the fertility o f iron.When the proportion of calcium in the vermicular and inoculant is high,the inoculation is insufficient and the graphite spheroidization is severe.Phenomenon,which will lead to the presence of carbides in the vermicular cast iron organization,th is organization has a greater impact on all aspects of the material properties.Magnesium also has the ability to increase the sensitivity of the tissue's white mouth.The smaller the content of magnesium in the vermicularizer is,the less likely the carbi des in the vermicular graphite iron matrix are.Inoculants increase the amount of nucleation of graphite.With the addition of inoculants,the amount of ferrite in the matrix increases,and carbide defects also improve.Through analysis,it can be seen tha t the microstructure of vermicular graphite cast iron obtained by using rare earth magnesium vermicularizer and calcium cerium inoculant is better,and the vermicularization rate can reach more than 80%.When the wall thickness is greater than 10 mm,there is no carbide in the matrix.When the rare earth magnesium alloy is added in an amount of 0.25% by weight of the treated iron liquid,the amount of the calcium-niobium alloy added is 0.5% by weight of the treated iron liquid.The content of alloying eleme nts will affect the amount of ferrite in the vermicular graphite cast iron.With the increase of Cu,Cr,Mn content,the content of carbon in the vermicular graphite cast iron decreases gradually,and the tensile strength of the material also increases.Th e wall thickness also has a certain influence on the vermicularity and the amount of ferrite in the structure.The wall thickness will affect the cooling rate.The smaller the wall thickness,the greater the cooling rate,the more serious the spheroidizing of the graphite,the lower the vermicularization rate,and the faster the cooling rate.It will also lead to a decrease in the amount of ferrite in the vermicular graphite cast iron.Summarizing the experimental rules,the diesel engine cylinder head of Y NF40 type vermicular cast iron material was trial-produced.In the trial production process,the alloy composition of the molten iron was adjusted to improve the pouring temperature and structure of the pouring system.Finally,the cylinder head sample was successfully prepared and tested.The prepared cylinder head casting vermicularity and mechanical properties can meet the design requirements.