Effect Of Nb And Sb On Microstructure And Mechanical Properties Of Ductile Iron

As an important engineering material,nodular cast iron is widely used in industrial production.However,with the economic and social changes,people have put forward new requirements for the mechanical properties of nodular cast iron,and the research on new highperformance ductile iron is urgent.At present,the production of high-performance ductile iron is mainly achieved by heat treatment and alloying,unlike heat treatment,using alloying to obtain high-performance nodular cast iron in the as-cast state has more process and cost advantages.There are various alloying elements,such as Si,Mn,Cu,Ni,Mo and these elements have been studied in depth.Although Nb,Sb and some elements are also considered to be effective elements for strengthening ductile iron,little research has been done on the role and mechanism of these elements in nodular cast iron,and there are many opinions that make it difficult to form a system.Therefore,it is necessary to carry out research on the influence of Nb and Sb on ascast nodular cast iron.Based on QT450-10 without adding other alloying elements,this thesis first discusses the effects of Nb and Sb alloying elements on the microstructure and mechanical properties of ascast ductile iron respectively,and reveals the action rules and mechanism of Nb and Sb on ductile iron.On this basis,the compound effects of different contents of Nb and Sb elements on ductile iron were also studied.The main findings are as follows:(1)Ferro-niobium is added to the induction furnace along with other raw materials.When the Nb content is 0.05 wt.%-0.21 wt.%,In addition to the solid solution in the structure of the ductile iron,Nb will also exist in the form of massive NbC particles.These particles have different shapes,most of which are below 10 ?m,and are distributed in graphite and matrix structures.When the Nb content increased,the spheroidization rate and number of graphite structure decreased,and the size of graphite sphere increased;meanwhile,the ferrite content in the matrix structure decreased,the pearlite content increased,and the pearlite structure was refined.As the Nb content increases,the tensile strength of the sample increases.When the Nb content is 0.21 wt.%,the tensile strength reaches a maximum of 504 MPa,which is 11.3% higher than when no alloying element is added.However,the elongation rate keeps decreasing.(2)The antimony metal is added to the nodular cast iron by the in-package punching method.When the Sb content is 0.006 wt.%-0.025 wt.%,the Sb elements are all dissolved in the ductile iron structure,and are distributed in large amounts on the boundary between the graphite balls and the matrix structure,thereby forming an antimony-rich layer with a high Sb content.With the increase of Sb content,the spheroidization rate,number of graphite structure and precipitated graphite area ratio showed a parabolic trend,and reached the peak when the Sb content was 0.013 wt.%,after which these data began to decline;when the Sb content increased,the ferrite content in the matrix decreases,the pearlite content increases,and the pearlite layer spacing gradually decreases.The tensile strength of the sample increases with the increase of Sb content.When the Sb content is 0.025 wt.%,the tensile strength reaches a maximum of 521 MPa,which is 15.1% higher than that of the sample without alloying elements.The elongation of the sample is continuously decreasing.For the composition of nodular cast iron designed in this experiment,the Sb content should not exceed 0.013 wt.%.(3)When Nb and Sb elements are added to the molten iron at the same time,the pearlite content of the alloyed nodular cast iron sample is significantly increased,and the tensile strength value is greatly increased.When the contents of Nb and Sb are 0.21 wt.% and 0.013 wt.%,respectively,the tensile strength of the obtained alloyed ductile iron reaches a maximum of 578 MPa,which is 27.6% higher than that without alloying elements,but its elongation will also be affected and reduced.Therefore,in actual production,the amount of the two alloying elements should be reasonably selected according to the needs,so that the strength and plastic toughness of the ductile iron can be kept at a high level.