Preparation process of high-carbon iron powder for powder metallurgy

Abstract

The present invention relates to a preparation process of high-carbon iron powder for powder metallurgy. The graphite powder used in this process is a mixture of two particle sizes, with D50 being 3 - 10 μm and D50 being 10 - 30 μm respectively; and low-temperature micro-powder wax bonding is adopted, and the softening temperature point of the micro-powder wax is not higher than 80°C. First, prepare water atomized steel powder containing carbon, and then, after mixing the graphite powder in a certain proportion, prepare high-carbon water atomized steel powder by means of adhesive mixing and attachment. During the use of the high-carbon iron powder of the present invention in powder mixing, there is no need to additionally add graphite powder, and it can be directly used, which can ensure the stability of the mixed powder while preventing the generation of sintering holes and maintaining the consistency of the physical properties of the product parts.

Description

Technical Field

[0001] The present invention relates to the field of powder metallurgy, and particularly to a preparation process of high-carbon iron powder for powder metallurgy. Background Art

[0002] Water atomized iron powder is commonly used as the basic raw material for preparing parts of powder metallurgy products. However, during the use process, alloy auxiliary materials such as graphite and copper powder (electrolytic copper powder, atomized copper powder, etc.) often need to be added to improve various properties of the final product parts of the product to achieve its best use effect.

[0003] Currently, graphite powder is often added during the process of mixing and powder making. Generally, it is added directly or by adhesive mixing. However, there are the following limitations: 1. When added directly, the cost is relatively low. However, if the amount of graphite powder added is large, segregation is likely to occur, resulting in poor sintering size stability and large performance deviation of the product parts after sintering. In severe cases, holes will appear on the surface of the product parts. 2. The adhesive mixing technology can effectively bond graphite to the surface of the base powder and improve the problem of large sintering size fluctuations. However, the particle size of graphite powder is extremely different from that of the base powder, which easily causes large fluctuations in the loose bulk density of the mixed finished powder and is not conducive to the production of multi-step product parts. 3. Through the above two methods, the maximum addition amount of graphite powder is ≤2.0%. For those with a carbon content higher than this value, segregation of graphite is likely to occur, ultimately affecting the sintering performance and mechanical properties of the product parts. Summary of the Invention

[0004] The present invention provides a preparation process of high-carbon iron powder for powder metallurgy. First, water atomized iron powder containing carbon is prepared, and then after mixing graphite powder in a certain proportion, high-carbon water atomized iron powder is prepared by the way of adhesive mixing and attachment. During the use process of the high-carbon iron powder of the present invention in mixing and powder making, there is no need to add graphite powder additionally and it can be used directly, which can ensure the stability of the mixed powder, prevent the generation of sintering holes, and maintain the consistency of the physical properties of the product parts.

[0005] In order to achieve the above object, the present invention is realized by adopting the following technical solutions:

[0006] A preparation process of high-carbon iron powder for powder metallurgy. The graphite powder used in this process is a mixture of two kinds of graphite powder with D50 being 3 - 10 μm and D50 being 10 - 30 μm respectively; and low-temperature micro powder wax adhesion is adopted. The softening temperature point of the micro powder wax is not higher than 80 °C, which can make the graphite adhere to the surface of the iron powder particles to ensure the compressibility and sintering size stability of the iron powder.

[0007] It includes smelting, atomization, reduction, adhesive stirring, and mixing processes;

[0008] Smelting: Using scrap steel and pig iron as the main raw materials, molten steel with uniform and stable composition and less impurities is obtained through electric furnace smelting. The carbon content in the steel is 0.4% - 1.0% according to the process requirements, and the tapping temperature is 1620 - 1850 °C;

[0009] Atomization: The atomization pressure is 8 - 13 Mpa, the starting atomization temperature is 1580 - 1750 °C, the ending atomization temperature is 1570 - 1700 °C, and the molten steel flow diameter is 14 - 28 mm;

[0010] Reduction: The as-atomized coarse powder is reduced in a reduction furnace. The preheating section temperature of the reduction furnace is 550 - 750 °C, with a length of 4 - 6 m; the high-temperature section temperature is 750 - 900 °C, with a length of 6 - 10 m; the cooling section temperature is 100 - 750 °C, with a length of 4 - 10 m;

[0011] Bonding and mixing: The reduced finished powder is crushed, screened, and batch-mixed, then low-temperature micro-powder wax is added, and graphite powder of two particle sizes is added, and the mixture is made into a semi-finished product;

[0012] Mixing: The uniformly mixed semi-finished product is heated to 70 - 90 °C and continuously mixed and stirred with a mixer.

[0013] In the above reduction step: The hydrogen flow rate is 60 - 180 m 3 / h, the running speed is 90 - 300 mm / min; the thickness of the material layer is 25 - 40 mm, and the carbon content of the finished powder is controlled at 0.02% - 0.1%.

[0014] The addition amount of the low-temperature micro-powder wax accounts for 0.1% - 2.0% of the reduced finished powder by mass ratio, and the addition amounts of the graphite powder of the two particle sizes account for 3% - 20% of the reduced finished powder by mass ratio.

[0015] In the above bonding and mixing step, the rotation speed of the mixer is controlled at 10 - 20 r / min, and the mixing time is controlled at 10 - 30 min.

[0016] In the above mixing step, the rotation speed of the mixer is controlled at 10 - 20 r / min, and the mixing time is controlled at 10 - 60 min.

[0017] The atomized iron powder prepared by the above process has the following chemical composition by weight percentage: C 3% - 20% (composed of the carbon content of the finished powder and the addition amount of graphite powder), Si ≤ 0.030%, Mn ≤ 0.15%, P ≤ 0.015%, S ≤ 0.015%, and the rest is Fe and unavoidable impurities.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. The compressibility of the product of the present invention (under 600 MPa) ≥ 6.80 g / cm3 ;

[0020] 2. A high proportion of graphite is directly attached to the surface of iron powder particles, without graphite segregation, and the base powder itself has a relatively high carbon content, which is beneficial to enhancing the mechanical properties of the sintered parts;

[0021] 3. During the preparation process of the mixed powder, it can be directly used without additional addition of graphite powder. At the same time, the generation of sintering holes is eliminated, and the physical properties of the product parts are maintained consistent. Specific Embodiments

[0022] The specific embodiments of the present invention will be further described below in conjunction with the embodiments: The indicators of each embodiment are shown in Table 1; the process parameters of the embodiments are shown in Tables 2 - 4.

[0023] Table 1 Embodiment Indicators

[0024]

[0025] Table 2 Smelting and Atomization Process Parameters of the Embodiment

[0026] Number Tapping temperature (°C) Atomization pressure (MPa) Atomization start temperature (°C) Atomization end temperature (°C) Molten steel flow diameter (mm) 1 1690 9 1640 1600 15 2 1710 10 1680 1665 27 3 1780 12 1720 1680 20 4 1780 11 1680 1610 18 5 1730 8 1690 1650 25 6 1700 13 1640 1580 22

[0027] Table 3 Reduction Process Parameters of the Embodiment

[0028]

[0029] Table 4 Binder and Mixing Process Parameters of the Embodiment

[0030]

[0031]

[0032] The mixed powder used in the embodiment for preparation, taking the common grade FC0208 as an example, its composition is mainly: 0.8% C, 2.0% Cu, and the rest are iron elements and other trace impurity elements. The comprehensive properties of the powder metallurgy products are shown in Table 5 (including the comparative example). The comparative example is the mixed iron powder with directly added graphite powder in the prior art.

[0033] Table 5 Comprehensive Properties of the Powder Metallurgy Products Prepared in the Embodiment

[0034]

[0035] Note: The sintering size data is the average value of 5 test results.

[0036] Through the above comparison, the mixed powder based on the base powder of the present invention is significantly superior to the mixed powder produced by other methods in terms of compressive properties, sintering size stability, physical properties, etc.

Claims

1. A preparation process of high-carbon iron powder for powder metallurgy, characterized in that, the graphite powder used in this process is a mixture of two kinds of graphite powders with D50 of 3 - 10μm and 10 - 30μm respectively; and low-temperature micro-powder wax bonding is adopted, and the softening temperature point of the micro-powder wax is not higher than 80°C; specifically including smelting, atomization, reduction, bonding and stirring, and mixing processes; Smelting: Using scrap steel and pig iron as the main raw materials, molten steel is obtained through smelting. The carbon content in the steel is 0.4% - 1.0% according to the process requirements, and the tapping temperature is 1620 - 1850°C; Atomization: The atomization pressure is 8 - 13 Mpa, the starting temperature of atomization is 1580 - 1750°C, the ending temperature of atomization is 1570 - 1700°C, and the diameter of the molten steel flow is 14 - 28 mm; Reduction: The as-atomized raw powder is reduced in a reduction furnace. The temperature of the preheating section of the reduction furnace is 550 - 750°C and the length is 4 - 6 m, the temperature of the high-temperature section is 750 - 900°C and the length is 6 - 10 m, and the temperature of the cooling section is 100 - 750°C and the length is 4 - 10 m; Bonding and stirring: The reduced finished powder is crushed, screened, and batch-mixed, then low-temperature micro-powder wax is added, and then two kinds of graphite powders with different particle sizes are added, and the mixture is made into semi-finished products; Mixing: The uniformly mixed semi-finished products are heated to 70 - 90°C, and the mixture is continuously stirred with a mixer; The addition amount of the low-temperature micro-powder wax accounts for 0.1% - 2.0% of the reduced finished powder by mass ratio, and the addition amounts of the two kinds of graphite powders with different particle sizes account for 3% - 20% of the reduced finished powder by mass ratio.

2. The preparation process of high-carbon iron powder for powder metallurgy according to claim 1, characterized in that, in the above reduction step: the hydrogen flow rate is 60 - 180 m³ / h, the running speed is 90 - 300 mm / min; the thickness of the material layer is 25 - 40 mm, and the carbon content of the finished powder is controlled at 0.02% - 0.1%.

3. The preparation process of high-carbon iron powder for powder metallurgy according to claim 1, characterized in that, in the above bonding and stirring step, the rotation speed of the mixer is controlled at 10 - 20 r / min, and the mixing time is controlled at 10 - 30 min.

4. The preparation process of high-carbon iron powder for powder metallurgy according to claim 1, characterized in that, in the above mixing step, the rotation speed of the mixer is controlled at 10 - 20 r / min, and the mixing time is controlled at 10 - 60 min.

5. The preparation process of high-carbon iron powder for powder metallurgy according to claim 1, characterized in that, for the atomized iron powder prepared by the above process, its chemical composition by weight percentage is as follows: C 3% - 20%, Si ≤0.030%, Mn ≤0.15%, P ≤0.015%, S ≤0.015%, and the rest is Fe and inevitable impurities.

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