Selected malleable iron pipe fittings casting chemical composition
Effect of chemical composition on the malleable including obtaining vermicular graphite and on the substrate, both of which in turn affect the mechanical properties and other properties of compacted graphite cast iron, the chemical composition of these effects should choose according malleable.
(1) carbon, silicon and carbon equivalent compacted graphite iron production in the general vicinity of the eutectic composition, in order to help improve the performance and reduce the chilling tendency casting, commonly used carbon equivalent of taking 4.3% -4.6%.
Effect of Carbon on malleable tensile strength similar to gray iron and ductile iron, with increasing carbon content, malleable tensile strength will increase due to graphite, pearlite decrease and decline, but this effect is smaller than gray cast iron was many. In order to reduce the chilling tendency, carbon content and generally 3.6% -3.8%, thin pieces take the upper limit, thick bulky take the lower limit.
Silicon inhibits the chilling tendency malleable, silicon also strongly promote the formation of ferrite elements, the strength of the decline; but only by reducing the silicon content is difficult to prevent the formation of ferrite surrounding graphite. Therefore, to prevent produce white, compacted graphite iron end silicon content is generally controlled between 2.4% -2.8%. Taking into account the creep process to bring large amount of silicon, so the mass fraction of iron melt silicon is generally controlled at between 1.5% -1.8%.
(2) Manganese play a stabilizing role in the pearlite malleable, but because the more branches vermicular graphite, manganese role greatly reduced. For hybrid Magang can adjust the manganese content to obtain the corresponding mechanical properties, manganese content is generally controlled between 0.4% -0.7%. For the ferrite compacted graphite iron manganese content should be strictly controlled in order to increase the matrix ferrite content, manganese best quality control scores below 0.4%.
(3) Linlin no creep of impact, but is formed in the substrate phosphorus eutectic greatly reduce mechanical strength and impact toughness, produced in the casting shrinkage and cold cracking. Thus, in addition to wear Magang, the phosphorus content is generally controlled at 0.08% or less.
(4) sulfur and sulfur vermicularizing alloy affinity, consume more vermicularizing, both increased material consumption and production costs, while a large number of iron sulfide will affect the flow of the liquid, acceleration of creeping recession. Therefore, malleable sulfur content should be strictly controlled, the general control of the mass fraction 0.07% or less.
(5) the addition of rare earth elements rare earth elements in liquid iron from the first purification to remove iron liquid sulfur, oxygen, hydrogen, nitrogen. Purified liquid iron, rare earths play the remaining graphite metamorphism, creep is the main agent of Magang. To make degenerates into worm-like graphite, rare earth iron liquid residues should be controlled 0.045% -0.075% (by mass). Below the critical mass, the resulting flake graphite; exceeds the upper limit, the resulting spherical graphite, reduce creep rate.
(6) Magnesium with rare earths, is another important component vermicularizing deterioration of Magang. Research and practice show that, to get a good vermicular graphite, magnesium content in general should be controlled 0.015% -0.03%. Below the lower limit or above the upper limit can not obtain adequate creep rate of Magang.
(7) The main alloying elements alloying elements used to adjust the malleable ferrite content of the matrix, in order to achieve improved creep agent added to expand the scope and purpose of the mechanical properties.
Malleable commonly used alloying elements mainly Cu, Mn, Sb, Sn, Ni, Cr, Mo, V, Ti, B and so on. Addition of alloying elements can be added a single element to be added a variety of complex elements, achieve the purpose of improving performance.
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