Study On Microstructures And Properties Of Horizontal Continuous Casting Ductile Iron Bars For Plunger Pump

In this paper,the two different grades(LZQT500-7 and LZQT600-3)of horizontal continuous casting ductile iron dense bars(HCCDIBs)were researched.The effects of horizontal continuous casting production process on the as-cast microstructure,mechanical properties and corrosion resistance of different HCCDIBs were studied,and the microstructure(number,diameter and shape factor of Graphite nodules,number and interlamellar spacing of pearlite.)were quantitatively analyzed by Image J software.On this basis,the microstructure,mechanical properties and corrosion resistance of different parts of corresponding austempered ductile irons(ADI)were studied,and quantitative statistical analysis of ADI microstructure(bainitic ferrite length and thickness,retained austenite)was carried out.In addition,the influence of 0.3%Cu on the microstructure and properties in different parts of HCCDIBs and their corresponding ADI were discussed.The main conclusions are as follows:(1)The as-cast microstructures in different parts of LZQT500-7 and LZQT600-3 HCCDIBs are composed of ferrite,pearlite and graphite nodule.(2)According to the position of the cast iron dense bars produced in horizontal continuous casting,the number of graphite nodule is reduced,the spheroidization is worse,the graphite nodule diameter is increased,the content of pearlite is increased,and the interlamellar spacing is decreased from the surface to the center on the left side of LZQT500-7 HCCDIBs.The hardness in horizontal direction is basically symmetrical about the center of the HCCDIBs,the vertical direction is obviously asymmetrical,and the hardness on the lower side is slightly higher than the same location on the upper side.The tensile and torsional strength of surface and 1/2R on the left side of the HCCDIBs are superior to the center.The change trend of microstructure and mechanical properties of LZQT600-3 HCCDIBs from the surface to center on the left side has the same tendency as the LZQT500-7 HCCDIBs.However,the addition of copper element,the number of graphite nodule increases,the diameter of the graphite nodule decreases,the number of pearlite increases,the interlamellar spacing of the pearlite decreases,and the tensile and torsional strength of different parts are improved,the section sensitivity is lowered.(3)The corrosion resistance of LZQT500-7 and LZQT600-3 HCCDIBs gradually deteriorates from the surface to center.However,the addition of copper element increases the amount of pearlite and reduces the corrosion resistance(4)The ADI microstructures in different parts of LZQT500-7 and LZQT600-3 HCCDIBs are composed of bainitic acicular ferrite,retained austenite and graphite nodule(5)The size of acicular ferrite becomes lengther and thicker,the content of retained austenite decreases from the surface to the center on the left side of the LZQT500-7 ADI.The LZQT500-7 ADI strength and torsional strength of surface and 1/2R on the left side are superior to the center.The change of acicular ferrite size and retained austenite content of LZQT600-3 ADI from the surface to center on the left side is the same as that of LZQT500-7 ADI.However,the addition of copper element,the acicular ferrite is remarkably refined,shortened and thinned,the content of retained austenite increases,and the tensile strength and torsional strength are improved(6)The corrosion resistance of LZQT500-7 and LZQT600-3 ADI gradually deteriorates from the surface to center.However,the addition of copper element increases the amount of retained austenite and improves corrosion resistance(7)The microstructure and mechanical properties of the LZQT500-7 HCCDIBs and its ADI from the lower surface to center has the same tendency as the left side.Due to gravity,the microstructure in the lower 1/2R is the finest,the best properties,which is better than the lower surface.(8)The fracture mechanisms of tensile specimens of LZQT500-7 and LZQT600-3 HCCDIBs and their corresponding ADI are all micropore aggregation and cleavage hybrid fracture.The fracture mechanism of torsion specimens is pure shear fracture.