| Wind power industry has developed rapidly in recent years. The development of wind power will be in the single and large scale, high reliability, to the sea and scale. For this situation, the low temperature high-ductility corrosion resistance ductile cast iron was developed. In this paper,1.2% to 1.8% nickel and 2.0% to 2.5% silicon were added into low temperature high-ductility corrosion resistance ductile iron, then as-cast samples were annealed. Microstructure observation, scanning electron microscopy, spectrum analysis, X-ray diffraction analysis, tensile strength test, brinell hardness test, low-temperature iMPact toughness test, and corrosion resistance test were done to research the effect of nickel and silicon on the microstructure and mechanical properties of low-temperature high-ductility corrosion resistance ductile iron.The results show that the as-cast microstructure of low-temperature high-ductility corrosion resistance ductile iron was constituted of spheroidal graphite, pearlite, ferrite and little cementite. The graphite size class of each sample was six to eight degree, and the spheroidization class was one to three degree.The Graphite size and morphology was not influenced by nickel and silicon. Pearlite of occurred in matrix increased in value with the increase of nickel, but decreased with the increase of silicon. When the Si content was 2.03%, Ni content was 1.78%, the amount of cementite was highest in the cast sample, up to 10%.After graphitization annealing process, the amount of pearlite decreased, the amount of ferrite increased, and cementite completely eliminated. When the silicon content was constant, with the increase of nickel, the brinell hardness and tensile strength increased, and elongation decreased; when the nickel content was constant, with the increase of silicon, the brinell hardness and tensile strength increase, and elongation decreases. When the Si content was 2.01%, Ni content was 1.20%, the tensile strength of samples was 458MPa, the elongation was up to 23.0%. The morphology of tensile fracture had a large number of dimples, and showed the ductile fracture characteristics.With increase of nickel, the iMPact energy decreased, and the brittle fracture characteristics of iMPact fracture increased; with increase of silicon, the iMPact energy decreases, and the brittle fracture characteristics of iMPact fracture increased. When the Si content was 2.01%, Ni content was 1.20%, it had the highest iMPact energy at 20℃,-20℃,-40℃, respectively,18.8J,16.3J,13.6J.Corroding through sodium chloride etching solution showed that the corrosion started in the grain boundary and ferrite-graphite interface, the width of the interface corrosion increased over time, the matrix erosion deepened, showing the uneven phenomenon due to graphite and matrix with varying corrosion degrees were more evident. When silicon content was constant, corrosion rate decreased with the increase of nickel; when nickel content was constant, corrosion rate decreased with the increase of silicon. Corrosion rate of samples were less than 0.1g.m-2.h-1, corrosion level was all one degree. The lowest corrosion rate was 0.04286gm-2.h-1 in the 3.5% sodium chloride etching solution. Corrosion produced Fe3O4 corrosion product, traces Fe3O4 remain within the matrix and formed within a layer of Fe3O4 rust layer. The rust layer had strong adhesion, high density, and played a certain barrier role to chloride ions and dissolved oxygen spreading within the matrix, and the corrosion reaction can became passivation.In short, in order to make the low-temperature iMPact energy of the low-temperature high-ductility corrosion resistance ductile iron more than 12J at-20℃or at -40℃, and make intensify tensile strength greater than 400MPa and corrosion resistance less than 0.1g.m-2.h-1, so the amount of ferrite must was greater than 95% in matrix organization, Ni content can not exceed 1.5%, Si content can not exceed 2.3%, but not less than 1.9%. |
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