CN112111693B - 420 stainless steel powder for MIM and water-gas combined atomization powder preparation method thereof - Google Patents
420 stainless steel powder for MIM and water-gas combined atomization powder preparation method thereof Download PDFInfo
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Abstract
The invention discloses a water-gas combined atomization powder preparation method of 420 stainless steel powder for MIM, which belongs to the field of alloy materials, and comprises the following elements in percentage by weight: c: 0.5-0.6%, Si is less than or equal to 1.0%, Mn: 0.7-1.5%, N: 0.1-0.7%, Cr: 12.0 to 14.0%, Ni: 1.0-3.0%, Mo: 0.5-1.5%, Co: 0.1-0.5%, Nb: 0.5-1.5%, and the balance of Fe and impurities. Smelting by adopting a medium-frequency induction furnace, pouring the medium-frequency induction furnace, and enabling molten steel to flow into a tundish and flow out of a leakage hole; high-pressure water is sprayed out from a nozzle of the spray disk, is focused on a molten steel flow, breaks the molten steel into fine particles, and is cooled into metal particles in the flight process; filtering, vacuum drying and sieving to obtain fine powder with particle size smaller than 400 mesh. The invention has the beneficial effects that: the alloy powder prepared by the process has good sphericity. The good sphericity can make the powder obtain enough fluidity in the process of entering the die cavity in the injection of MIM process, can fully fill the die cavity, obtain the injection blank with high density, and has small size fluctuation.
Description
Technical Field
The invention relates to the field of alloy materials, in particular to 420 stainless steel powder and a water-gas combined atomization powder preparation method thereof.
Background
The 420 stainless steel belongs to martensitic stainless steel, and can be classified into 420J1 (national standard GB 2Cr13) and 420J2 (national standard GB 3Cr13) according to the carbon content. 420J1(2Cr13) does not meet the performance requirements of the cutting tool because of low hardness and tensile strength. The commonly used 420 at present refers to 420J2(3Cr 13). The martensitic stainless steel features that its matrix is martensitic and magnetic, and its mechanical properties can be regulated by heat treatment. The american iron and steel association designates martensitic stainless steels as numbers 410, 420 and 440. Martensite has an austenite structure at high temperature, and the austenite structure can be transformed into martensite (quenched) when cooled to room temperature at an appropriate rate. The 420 stainless steel has high hardness and good corrosion resistance, and is a stainless steel material widely applied to mechanical parts, valves, turbine blades and cutter blades.
The composition and mechanical properties of the conventional 420(3Cr13) stainless steel are shown in Table 1.
TABLE 1 composition and mechanical Properties of conventional 420(3Cr13) stainless Steel
Note: the hardness and tensile strength values are measured after quenching and tempering.
The traditional 420 stainless steel cannot be used as a material of a high-end cutter tool because the hardness of the traditional 420 stainless steel is only HRC53 at most after heat treatment, and the traditional 420 stainless steel cannot bear hacking and hacking of harder frozen meat, beef bones and pork bones, and easily causes edge curling and edge collapsing of the cutter tool. And because the hardness is soft, the knife edge part is not wear-resistant. Secondly, the traditional 420 stainless steel has insufficient corrosion resistance, is easy to generate pitting corrosion phenomenon and brings risks to human health.
Metal Injection Molding (MIM) technology is currently phased out of the traditional foundry processing industry. The metal injection molding is characterized in that metal powder is mixed with an organic polymer material to form a powder material wrapped by the organic polymer material, the powder material is heated, pressurized and injected into a mold cavity through an injection molding machine, and an injection blank with a required shape is obtained after cooling and demolding. And then the blank is degreased in a degreasing furnace to form a degreased blank, and finally the blank is sintered in a sintering furnace to form a part. The method has the advantages that the generation of waste materials and leftover materials is avoided by one-step forming, the shape can keep the required shape after sintering, and machining such as cutting is not needed, so that the MIM technology is called as a net machining technology, and a large amount of manpower and energy are saved. In addition, because the MIM sintered part has uniform metal structure and less component segregation, and the grains are fine and have a fine grain strengthening effect, the mechanical property can reach the level of a part processed by a casting machine, even exceeds that of the part processed by the traditional casting machine. Therefore, the metal injection molding technique has been widely used in the manufacture of mechanical parts, automobile parts, art ornaments, household devices, and electric appliance parts.
Because of the inexpensive and superior properties of 420 stainless steel, the MIM manufacturing industry desires to use powdered 420 stainless steel to manufacture various cutter tools and other components by MIM. However, the current method for manufacturing 420 stainless steel powder is mainly a water atomization method, but the 420 stainless steel powder prepared by the water atomization method cannot meet the requirements of MIM manufacturing. The main reasons are:
the water atomized powder of 420 stainless steel has poor sphericity and more irregular particles, which causes poor powder fluidity, so the density of an injection pressed compact is low, and the sintering density is low.
The poor flowability of 420 stainless steel powder can also affect the dimensional stability of an injection blank, the fluctuation of sintering shrinkage rate is large, and the dimensional precision of a sintered part is poor.
The water atomized 420 stainless steel powder has poor sintering shape retention, and parts have more deformation after high-temperature sintering.
The water atomized 420 stainless steel powder sintered parts had low hardness (heat treated temper hardness only HRC45-48), low tensile strength (about 600MPa), and still low sintered density, the main reason being.
In conclusion, 420 stainless steel (3Cr13) is widely used in the industries of machine manufacturing, tool and cutting tool manufacturing, and the like. However, in the tool and cutting tool industry, the conventional 420 stainless steel (3Cr13) cannot be used as a raw material of high-end stainless steel tools due to the defects of insufficient hardness, poor strength, insufficient corrosion resistance and the like. Meanwhile, the emerging MIM manufacturing industry urgently needs 420 stainless steel powder which is suitable for MIM manufacturing process characteristics and is used for manufacturing cutter blades with higher hardness, higher strength and better corrosion resistance.
Disclosure of Invention
Aiming at the problem that 420 stainless steel powder prepared by a water atomization method in the prior art cannot meet the requirements of MIM manufacturing, the invention provides 420 stainless steel powder and a water-gas combined atomization powder preparation method thereof, and provides novel 420 stainless steel powder which is suitable for MIM manufacturing process and has high hardness, high strength and high corrosion resistance for the MIM manufacturing industry. The specific technical scheme is as follows:
420 stainless steel powder for MIM comprises the following elements in percentage by weight: c: 0.5-0.6%, Si is less than or equal to 1.0%, Mn: 0.7-1.5%, N: 0.1-0.7%, Cr: 12.0 to 14.0%, Ni: 1.0-3.0%, Mo: 0.5-1.5%, Co: 0.1-0.5%, Nb: 0.5-1.5 percent, and the balance of Fe and impurities, wherein the content of the impurities is less than 0.02 percent.
Preferably, the impurities are mainly S and P, and the content of each impurity does not exceed 0.01%.
Preferably, the 420 stainless steel powder has a particle size of less than 400 meshes, an average particle size of only 8-10 mu m and an oxygen content of less than or equal to 2000 ppm.
Preferably, the laser particle size D10 of the 420 stainless steel powder is 2.6-2.9 μm, D50 is 8-9 μm, and D90 is 20-21 μm.
Preferably, the 420 stainless steel powder has a loose packed density of 3.02g/cm3 and a tap density of 4.78g/cm 3.
In the process of actual mass research and verification, the research and analysis of the effect of different element contents of the stainless steel powder are more refined, and a plurality of surprising and novel development results are obtained.
Wherein, the Cr content is 12.0-14.0% to play a role in corrosion resistance, and generally speaking, the Cr content is higher than 10% to have better corrosion resistance. When the Cr content reaches 13%, the 420 stainless steel can be ensured to have oxidation resistance and corrosion resistance.
The sintering temperature of the powder 420 stainless steel can be effectively reduced by adding 1.0-3.0% of Ni. The vacuum sintering temperature of the water atomized 420 stainless steel powder is 1350-1380 ℃. The addition of Ni lowers the melting point of the powder, so the sintering temperature is lowered, and the sintering at the temperature of 1250-1280 ℃ can obtain a higher sintering density of 7.6g/m 3. The addition of Ni not only can improve the sintering density, but also Ni is a strong austenite forming element, and the significance of Ni is that the solubility of austenite to N is higher. Ni is also a strong carbide forming element, and can form relatively fine NiC which is uniformly distributed in the tempering process of heat treatment, play a role in pinning dislocation motion and improve the strength of the sintered part. The toughness and the wear resistance of Ni are good, and the toughness and the wear resistance of metal can be improved by adding Ni.
The addition of 0.1-0.7% of N plays an important role in improving the strength of 420 stainless steel. N is an effective solid solution strengthening element, and the effect of fine crystal strengthening is increased. N is also an austenite stabilizing element, and the amount of Ni used can be reduced. N has higher solid solubility than C, and can reduce precipitation under a given strength condition. N can improve the pitting corrosion resistance of the 420 stainless steel, reduce the corrosion sensitivity of a grain boundary and improve the corrosion resistance. The addition of N can improve the yield strength and tensile strength of the stainless steel during annealing. The strengthening mechanism of the stainless steel by the N is two, wherein the N is used as interstitial atoms to strengthen a matrix, and the N causes a certain dragging effect on dislocations when migrating along the dislocations through crystal lattices to strengthen the metal. The interstitial solid solution strengthening effect of N is much larger than that of carbon, so that the strength of the steel is greatly improved, and good toughness and plasticity are maintained. Meanwhile, the addition of N plays a role in improving the corrosion resistance of the 420 stainless steel. The corrosion of the stainless steel is divided into two stages, the first stage is not a corrosion induction period, or inoculation period, the corrosion degree of the stainless steel is relatively light, and the corrosion is independent of the grain size; the second stage is a stable corrosion period, with the material being corroded from the surface at a fixed rate. The addition of N can refine the grains, resulting in increased grain boundaries. The propagation of corrosion is hindered by a large number of grain boundaries, thereby suppressing the rate of corrosion. In addition, the increase of the grain boundary reduces the precipitation of chromium carbide, thereby reducing the loss of Cr, reducing the sensitivity of the grain boundary and improving the intergranular corrosion resistance of the alloy.
Surprisingly, the wear resistance of 420 stainless steel can be improved by adding 0.5-1.5% of Mo. Mo is an element with strong corrosion resistance except Cr, and particularly has good effect of improving the high-temperature corrosion resistance of stainless steel. Secondly, the addition of Mo improves the hardenability of the 420 stainless steel, namely, the phase transformation depth of quenching can be improved, and the capability of obtaining a martensite structure of the 420 stainless steel, namely, the depth of a hardening layer of the 420 stainless steel is improved.
Wherein, the Co addition has the same effect as Ni, and has the effects of reducing sintering temperature and improving sintering density. More importantly, the simultaneous addition of Co and Mo can ensure that the 420 powder stainless steel obtains high hardness and good comprehensive mechanical property in the tempering treatment process of heat treatment. Co alone reduces the hardenability of the steel and therefore must be added simultaneously with Mo. Because the carbon ratio of 420 powder stainless steel is higher, belonging to hypereutectoid steel, the addition of Co can improve the hardness, yield point and tensile strength of the steel in a tempered or normalized state, in other words, the steel is made to be stronger and suitable for the use requirement of cutter blades.
In the stainless steel powder, the addition of Nb mainly plays a role in refining grains, and according to the Holl-Petch formula, the steel can obtain the effect of double high strength and toughness as the grain size becomes smaller. During sintering of the powder 420 stainless steel, Nb is firstly dissolved into austenite to form a solid solution, and Nb exists in a fine carbide form during quenching and is distributed very dispersedly, so that the nucleation energy is reduced, namely, the nucleation of crystal grains is promoted, and the growth of the crystal grains is hindered. Therefore, the Nb has very obvious fine grain strengthening effect, and the hardness and the impact toughness of the steel are obviously improved. Meanwhile, Nb increases the tempering stability of the 420 powder stainless steel and has secondary strengthening effect.
The addition of Si can play a certain role in deoxidation and slagging in the smelting process of 420, the bonding force of Si and O is strong, the Si and O are commonly used deoxidizing agents in metallurgy, and in molten metal liquid steel, the Si and O form SiO2 and exist in a semi-molten solid particle state. The SiO2 can be adhered to the wall of the smelting furnace under the stirring of molten steel. Because the specific gravity of the SiO2 is light, the SiO2 gradually floats to the surface of the molten steel to form slag to be removed. From the viewpoint of the microstructure properties, the addition of Si narrows the austenite region, and improves the hardenability of 420 powder stainless steel. Si atoms and Fe form an interstitial solid solution, so that the hardness and tensile strength of the Fe matrix can be improved. Meanwhile, Si is also a strong carbide forming element, and can form very fine silicon carbide dots to form a dispersion strengthening effect on the Fe matrix. However, when the mass ratio of Si exceeds 3%, the plasticity and toughness of the steel are significantly reduced. Therefore, in the 420 powder stainless steel, the mass fraction of Si is designed to be less than or equal to 1%.
It was found that the addition of Mn improved the strength of 420 stainless steel. As the Mn and the Fe are infinitely dissolved in the solution, the influence on the shaping is small while the strength is improved. Mn is also a strong oxidizing element, has very strong bonding force with O, is a commonly used deoxidizer in metallurgy, and can reduce the oxygen content in the smelting process of 420 powder stainless steel. Mn improves hardenability of steel and hot workability of steel. Mn improves the tempering stability of the 420 powder stainless steel. Mn delays the martensite decomposition and the transformation of residual austenite in the tempering process of 420 powder stainless steel, increases the recrystallization temperature of ferrite, makes chromium carbide difficult to aggregate and grow and keeps larger dispersion, thereby improving the resistance of the steel to temper softening, namely improving the tempering stability of the steel. So that the steel can be tempered at a higher temperature to obtain better toughness, which plays an important role in preventing the 420 powder stainless steel from edge breakage when used in a cutter tool. However, the higher the content of Mn, the lower the formability and weldability of the steel.
The invention also provides a water-gas combined atomization powder preparation method of 420 stainless steel powder, which comprises the following specific steps:
step one, smelting, namely smelting in a medium-frequency induction furnace, wherein the highest temperature in the smelting process is controlled at 1620 ℃ and 1650 ℃, the smelting time is 45-65 minutes, and the smelting time comprises 40-50 minutes of feeding and melting time and 5-10 minutes of heat preservation and deoxidation time; the capacity of the intermediate frequency furnace can be used from 100 to 500kg, and the maximum output power is 300 KW. The lining material is high-purity magnesite mixed with sodium metasilicate aqueous solution (sodium silicate) and boric acid in a certain proportion.
Step two, atomizing, namely, dumping the medium-frequency induction furnace by using a hydraulic machine, and enabling molten steel to flow into a tundish and flow out from a leakage hole of the tundish; the upper part of the atomizing tower is provided with a spray disk, and high-pressure water is sprayed out from a nozzle of the spray disk, is focused on a molten steel flow, breaks the molten steel into fine particles and is cooled into metal particles in the flying process;
filtering, mixing the atomized metal powder with water, settling at the bottom of the atomizing tower, installing a powder storage tank at the bottom of the atomizing tower, allowing the metal powder to be completely settled in the powder storage tank, and arranging a porous partition plate at the bottom of the powder storage tank, wherein the porous partition plate is provided with 1000-mesh filter cloth; connecting a water outlet at the bottom of the storage tank with a water suction pump in a suction filtration mode, and starting the water suction pump to discharge water in the storage tank until no clear water is above the powder;
and step four, vacuum drying, namely pouring the filtered wet powder into a double-cone rotary vacuum dryer. After the powder inlet is closed, starting a vacuum pump, heating simultaneously, and waiting for the powder to be completely dried;
and step five, screening, namely screening the powder after vacuum drying by using a vibrating screen with 400 meshes to obtain fine powder with the particle size of less than 400 meshes.
In the first step, in order to reduce the oxidation caused by the contact time of the metal and the air at high temperature, the input sequence of raw materials is designed in the smelting and feeding process. Firstly, putting a pure Fe ingot into a cooling furnace, starting to transmit power and heat until the Fe ingot is completely melted; then adding Cu, Ni, Mo and Co, keeping the power of the intermediate frequency furnace at 300kW until the intermediate frequency furnace is completely melted, and controlling the furnace temperature at 1600 ℃; adding Mn, Si and chromium iron nitride alloy, observing the added metal to be melted, and entering a heat preservation stage.
Preferably, after the heat preservation stage in the step one, the power of the intermediate frequency furnace is 300kW, the temperature of the molten steel is measured every 2 to 3 minutes, the temperature of the furnace is kept at the state of 1620 ℃ and 1650 ℃ for 5 to 10 minutes, and finally, the power is reduced to 60 to 80kW to prepare atomization.
Preferably, in the second step, in the whole atomization process, nitrogen is filled into the atomization tower, a nitrogen inlet is arranged above the spray plate, the nitrogen flows through the spray plate along with the metal liquid, 8-nozzle spray plates are adopted, the diameter of each nozzle is 1.5-2.0mm, water is sprayed out through the nozzles and then is sprayed in a fan shape, atomized water sprayed out through the 8 nozzles is converged at one focus, the diameter of the ceramic leakage hole of the tundish is 3-8mm, the atomized water flow is 150L/min, the atomized pressure is 110-.
Preferably, in the fourth step, the vacuum degree of the vacuum dryer is set to be less than 0.09MPa, and the heating temperature is 150 ℃. The water-gas combined atomization process provided by the invention can be used for preparing the alloy powder with the median diameter D50 being 8-10um and the oxygen content being less than or equal to 2000 ppm.
The technical scheme of the invention has the following beneficial effects:
(1) the alloy powder prepared by the process has good sphericity. The good sphericity can make the powder obtain enough fluidity in the process of entering the die cavity in the injection of MIM process, can fully fill the die cavity, obtain the injection blank with high density, and has small size fluctuation.
(2) The alloy powder prepared by the process has good low-temperature sintering temperature performance, and can be sintered at the temperature of 1250-Sintered density 7.6g/m3。
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is an SEM photograph of powder 420 stainless steel produced by combined water and gas atomization according to the present invention;
FIG. 2 is a feed made of stainless steel 420 powder of the present invention mixed with a binder;
figure 3 is a three pack MIM process sintered coupon according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings of the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
According to the embodiment, on the basis of 420(3Cr13) stainless steel, by adding Cu, N, Nb, Ni, Mo and Co metal and nonmetal trace elements, the hardness, strength and corrosion resistance of the sintered powder are improved, and novel 420 stainless steel powder with high hardness, high strength and high corrosion resistance suitable for an MIM manufacturing process is provided for the MIM manufacturing industry.
The powder 420 stainless steel manufactured according to the embodiment is prepared by high-temperature smelting of raw materials, high-pressure water atomization, vacuum drying and sieving according to a formula designed by components to obtain product powder. Sintering the product powder into a sample block in an MIM mode, and testing the mechanical property and the corrosion resistance after heat treatment.
A100 kg medium frequency induction smelting furnace is used, the maximum power is 300kW, and the furnace lining is made of a high-purity magnesia furnace lining. The powder 420 stainless steel was designed to have the following composition:
TABLE 2 powdered 420 stainless Steel composition
| Element(s) | Fe | Cr | Ni | Mo | Mn | N | Co | Nb | C |
| Designed content wt% | Balance of | 13.0 | 1.5 | 0.5 | 1.2 | 0.6 | 0.3 | 1.5 | 0.55 |
Wherein, N is put into the medium-frequency induction furnace in a chromium nitride alloy mode.
In the embodiment, the method for preparing 420 stainless steel powder by water-gas combined atomization comprises the following specific steps:
smelting: preheating the medium frequency furnace to 1000 ℃, firstly putting a pure Fe ingot into the furnace, and starting to heat until the Fe ingot is completely melted. Adding Cu, Ni, Mo and Co, keeping the power of the intermediate frequency furnace at 300kW until the medium frequency furnace is completely melted, and controlling the furnace temperature at 1600 ℃.
Adding Mn, Si and chromium iron nitride alloy, observing the added metal to be melted, and entering a heat preservation stage. The power of the intermediate frequency furnace is 300kW, the temperature of the molten steel is measured every 2 to 3 minutes, and the furnace temperature is kept at 1620 ℃ and 1650 ℃ for 5 to 10 minutes. And finally, reducing the power to 60-80kW, removing slag on the surface of the melt, and preparing for atomization.
Atomizing: and (3) pouring the medium-frequency induction furnace by using a hydraulic machine, wherein molten steel flows into the tundish and flows out from the leakage hole of the tundish. The upper part of the atomizing tower is provided with a spray disk, and high-pressure water is sprayed out from a nozzle of the spray disk, is focused on a molten steel flow, breaks the molten steel into fine particles, and is cooled into metal particles in the flight process. In the whole atomization process, nitrogen is filled into the atomization tower, and a nitrogen inlet is arranged above the spray disk, so that the nitrogen flows through the spray disk along with the metal liquid. Nitrogen flow rate by float type N2The gas flow meter is used for controlling, and the set flow is 10L/min. A spray disk with 8 nozzles is adopted, the diameter of each nozzle is 1.5mm, the diameter of a ceramic leakage hole of a tundish is 4mm, and the atomized water flow is set to be 200L/min. The atomization pressure is 125 MPa. And (4) completely pouring the molten steel in the intermediate frequency furnace.
And (3) filtering: and precipitating the atomized water-powder mixture into a powder storage tank at the bottom of the atomization tower, taking down the powder storage tank, connecting the powder storage tank with a water pump, and performing suction filtration until no clear water exists on the surface of the powder layer.
And (3) vacuum drying: and (4) putting the wet powder into a vacuum drier for vacuum drying. The vacuum degree of the vacuum drier is set to be less than 0.09MPa, and the heating temperature is 150 ℃. After about 4 hours, the drying was stopped and the dryer was opened to take out the powder.
Screening: and sieving the powder after vacuum drying by using a vibrating screen with 400 meshes to obtain fine powder with the granularity of less than 400 meshes.
The powder test results are shown in table 3:
TABLE 3 characteristics of 420 stainless steel powder produced by water-gas combined atomization
The microscopic morphology of the particles of the 420 stainless steel powder is shown in figure 1, and the 420 stainless steel powder manufactured by water-gas combined atomization has fine particle size, the average particle size is only 8-10 mu m, and the powder has good spherical shape, so that the powder has good flow and meets the requirements of MIM manufacturing process on the powder.
A mixture of Polyoxymethylene (POM), Polyethylene (PE) and Stearic Acid (SA) was used as a binder for 420 stainless steel powder, and a feed (feed stock) was prepared after heating, stirring and mixing in an internal mixer, the feed size being 4-5mm, and the diameter being 2-3mm, as shown in FIG. 2.
Injecting the feed into a die cavity by using a metal injection machine, taking out and cooling the feed, degreasing the feed in a degreasing furnace, and sintering the feed in a vacuum sintering furnace at the maximum sintering temperature of 1280 ℃ for 1 hour. The sintered test block size was 50mm × 8mm × 5 mm.
And (4) heat treatment, namely heating the sintered blocks in a heat treatment furnace to 1080 ℃, preserving heat for 1 hour, taking out and air-cooling. And tempering at 250 deg.c for 1 hr, and cooling in the furnace.
And (3) carrying out mechanical property test on the three groups of sintered blocks, wherein the test result is shown in Table 3, the hardness is measured to be 56HRC, a universal mechanical testing machine is used for carrying out tensile test on the sintered blocks, the tensile strength is 832-plus 903MPa, and the three-point bending strength of the tested sintered blocks is 1830-plus 1880 MPa.
TABLE 4420 mechanical Properties of stainless steel powder MIM agglomerates
| 1# | 2# | 3# | Conventional 420(3Cr13) agglomerate | |
| Hardness HRC | 56 | 57 | 56 | 46 |
| Tensile strength sigma b MPa | 854 | 832 | 903 | 623 |
| Bending strength sigma bb MPa | 1850 | 1880 | 1830 | 1450 |
The corrosion resistance of the sintered blocks is tested by using a salt spray tester, wherein the salt water mixture ratio is 5 wt% NaCL solution, and the temperature is 35 ℃. The test results are shown in Table 5, and it can be seen that the corrosion resistance in salt spray starts to increase with the passage of time, and the corrosion rate decreases after 96 hours. The MIM sintered part made of the powder 420 stainless steel has better corrosion resistance.
TABLE 5420 salt spray Corrosion resistance of stainless steel powder MIM agglomerates
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A420 stainless steel powder water-gas combined atomization powder preparation method is characterized in that the contents of all elements are as follows by weight percent: c: 0.5-0.6%, Si is less than or equal to 1.0%, Mn: 0.7-1.5%, N: 0.1-0.7%, Cr: 12.0 to 14.0%, Ni: 1.0-3.0%, Mo: 0.5-1.5%, Co: 0.1-0.5%, Nb: 0.5-1.5%, the balance of Fe and impurities, and the content of the impurities is lower than 0.02%, and the method comprises the following specific steps:
step one, smelting, namely smelting by adopting a medium-frequency induction furnace, wherein the temperature in the smelting process is controlled at 1620 ℃ and 1650 ℃, the smelting time is 45-65 minutes, and the smelting time comprises 40-50 minutes of feeding and melting time and 5-10 minutes of heat preservation and deoxidation time;
step two, atomizing, namely, dumping the medium-frequency induction furnace by using a hydraulic machine, and enabling molten steel to flow into a tundish and flow out from a leakage hole of the tundish; the upper part of the atomizing tower is provided with a spray disk, and high-pressure water is sprayed out from a nozzle of the spray disk, is focused on a molten steel flow, breaks the molten steel into fine particles and is cooled into metal particles in the flying process;
filtering, mixing the atomized metal powder with water, settling at the bottom of the atomizing tower, installing a powder storage tank at the bottom of the atomizing tower, allowing the metal powder to be completely settled in the powder storage tank, and arranging a porous partition plate at the bottom of the powder storage tank, wherein the porous partition plate is provided with 1000-mesh filter cloth; connecting a water outlet at the bottom of the storage tank with a water suction pump in a suction filtration mode, and starting the water suction pump to discharge water in the storage tank until no clear water is above the powder;
step four, vacuum drying, namely pouring the filtered wet powder into a double-cone rotary vacuum dryer; after the powder inlet is closed, starting a vacuum pump, heating simultaneously, and waiting for the powder to be completely dried;
and step five, screening, namely screening the powder after vacuum drying by using a vibrating screen with 400 meshes to obtain fine powder with the particle size of less than 400 meshes.
2. The method as claimed in claim 1, wherein the impurities are mainly S and P, and the contents of S and P are not more than 0.01%.
3. The method as claimed in claim 1, wherein the 420 stainless steel powder has a particle size of less than 400 mesh, an average particle size of 8-10 μm, and an oxygen content of 2000ppm or less.
4. The method as claimed in claim 3, wherein the laser particle size D10 of the 420 stainless steel powder is 2.6-2.9 μm, D50 is 8-9 μm, and D90 is 20-21 μm.
5. The method as claimed in claim 4, wherein the 420 stainless steel powder has a bulk density of 3.02g/cm3Tap density of 4.78g/cm3。
6. The method for preparing 420 stainless steel powder according to any one of claims 1-5 by water-gas combined atomization, wherein in step one, pure Fe ingot is put into a cold furnace, and power is supplied to heat up until the Fe ingot is completely melted; then adding Cu, Ni, Mo and Co, keeping the power of the intermediate frequency furnace at 300kW until the intermediate frequency furnace is completely melted, and controlling the furnace temperature at 1600 ℃; adding Mn, Si and chromium iron nitride alloy, observing the added metal to be melted, and entering a heat preservation stage.
7. The method as claimed in claim 6, wherein the power of the IF furnace is 300kW after the heat preservation stage in the step one, the temperature of the molten steel is measured every 2-3 minutes, the furnace temperature is maintained at 1650 ℃ in 1620 ℃ for 5-10 minutes, and finally the power is reduced to 60-80kW to prepare for atomization.
8. The method as claimed in any one of claims 1 to 5, wherein in step two, during the entire atomization process, nitrogen is charged into the atomization tower, the nitrogen inlet is located above the spray disk, so that the nitrogen flows through the spray disk with the metal liquid, 8-nozzle spray disks are adopted, the diameter of each nozzle is 1.5-2.0mm, the water is sprayed out through the nozzles and is sprayed in a fan shape, the atomized water sprayed out from 8 nozzles is converged at one focus, the diameter of the ceramic eyelet of the tundish is 3-8mm, the atomized water flow rate is 150-.
9. The method for pulverizing 420 stainless steel powder according to any of claims 1-5, wherein in step four, the vacuum drier is set to have a vacuum degree of less than 0.09MPa and a heating temperature of 150 ℃.
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