DJM Technical Introduction

    Smelting of high chromium cast iron

    Smelting of high chromium cast iron
    1 high chromium cast iron chemical composition (see table below)
    In addition, still need copper and scrap electrode block (for adjusting the carbon content).
    3 smelting process requirements
    (1) the melting temperature of high chromium cast iron is higher than that of general cast iron. It is about 1200 degrees Celsius, the temperature is about 1500 degrees Celsius, and the intermediate frequency induction furnace is used for smelting.
    (2) lining using acidic or alkaline lining can be, lining ratio, knotting, drying and sintering were carried out according to the conventional process.
    (3) charging general according to the normal sequence of feeding, the first gray iron, molybdenum iron refractory iron alloy into the bottom and scrap according to collapse under the tight loose the principle of loading ().
    (4) send electric melting furnace power transferred to the maximum melting, due to CR melting loss of larger (about 5% ~ 15%), so the ferrochrome should at last, usually adding roasted red iron scrap melting all.
    (5) - to metal charge all melted and raise the temperature to 1480 DEG C, adding ferromanganese, ferrosilicon and aluminium deoxidation.
    (6) pouring in medium frequency induction furnace melting, the temperature can not be too high, when the temperature reaches the 1480 DEG C can be baked, liquid iron in the package internal stay for a period of time for sedation, depending on the size of the workpiece different in 1380 to 14.1 DEG C pouring.
    Two, production process
    (1) high chromium cast iron casting performance is poor, its thermal conductivity is low, poor plasticity, high shrinkage and hot crack and cold cracking tendency, in the casting process to consider the combination of the characteristics of cast steel and cast iron, we must give full attention to the casting of the feeding problem, its principle and cast steel pieces of the same (with riser and chill and follow the principle of sequential solidification). Due to the high chromium content in the alloy, easy on the surface of the molten iron conjunctiva, so it looks like the molten iron flow difference, but actually better mobility.
    (2) modeling should be used water glass sand and other high strength and permeability of sand, paint should adopt high refractoriness, high alumina or magnesia powder and alcohol mixing. In addition, in order to obtain the fine grain structure and good surface quality, in the shape of castings is not too complex, metal mold casting has been widely adopted.
    (3) of high chromium cast iron shrinkage and cast steel are similar, and making the appearance the linear shrinkage rate can be calculated by 1. 8% to 2%. In sand production and the riser size can be calculated according to the provisions of the carbon steel, and pouring system according to grey cast iron calculation, but need to put the cross-sectional area increased 20% to 30%. The riser should pay attention to two aspects: one is to ensure the casting belt (the use of the site) the quality of; the second is to try to improve the rate of finished products of the castings.
    (4) due to the high chromium casting riser is not easy to be removed, thus modeling in the form of riser should use side riser or knock off.
    (5) in specific parts of the casting process design, it is necessary to pay attention to not let casting hindered contraction, so as to avoid cracking. In addition, after pouring out of the box temperature too high is also very easy to cause cracking in castings, 540 DEG C under slow cooling is necessary, should make casting in the mold is cooled sufficiently, and then out of the box sand cleaning, or out of the box after the first not clear sand pile in together (casting, gating and Risering system) around the dry sand slow cooling. Out of the box surrounding environment must be kept dry, not wet water, otherwise easily cause casting crack.
    (6) pouring temperature is low, is advantageous to refining dendrite and eutectic structure and avoid because of too high temperature caused by the shrinkage defects and surface adhering sand. Pouring temperature general than the liquidus (1290 - 1350 DEG C) about 55 DEG C, light a small piece of general control of in 1380 to 1420 DEG C, wall thickness 100mm above the heavy control in 1350 to 1400 DEG C.

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