Reduced iron powder, method for its production and use
By optimizing the particle size distribution of reduced iron powder through a three-layer annular fabric and multiple screening processes, the problem of poor formability of iron powder in thin-walled parts was solved, enabling the production of high-strength and low-cost thin-walled parts.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MA STEEL POWDER METALLURGY CO LTD
- Filing Date
- 2023-11-08
- Publication Date
- 2026-07-24
AI Technical Summary
Existing iron powder has poor formability when pressing thin-walled parts, and the green strength is insufficient, which easily leads to cracks or fractures in the thin-walled areas, resulting in material waste and increased production costs.
Reduced iron powder is prepared by a three-layer annular fabrication method. By controlling the mass ratio and particle size of iron oxide and reducing additives, combined with reduction reaction, annealing treatment and multiple sieving, the particle size distribution and physical properties are optimized, thereby improving the strength and formability of the green body.
The prepared reduced iron powder has good compact strength and formability, which can effectively improve the strength of thin-walled parts, reduce the risk of fracture, increase material utilization and reduce production costs.
Smart Images
Figure BDA0004536623620000071 
Figure BDA0004536623620000081 
Figure BDA0004536623620000082
Abstract
Description
Technical Field
[0001] This invention belongs to the field of powder metallurgy technology, specifically relating to a reduced iron powder, its preparation method, and its application. Background Technology
[0002] With the development of powder metallurgy technology, more and more parts can be manufactured using powder metallurgy. In the past, when manufacturing thin-walled parts (thickness of 1-3mm), most manufacturers would first press them into thicker blanks, sinter them, and then machine them to shape the thin-walled parts.
[0003] However, based on considerations such as reducing processing costs and increasing material utilization, manufacturing companies prefer to directly press thin-walled parts into one piece. This reduces the amount of powder used during the pressing process, as well as material waste in subsequent cutting processes, thereby increasing powder utilization and significantly reducing production costs.
[0004] Currently, the commonly used iron powder has poor formability and insufficient green strength when pressing thin-walled parts, making it easy for cracks to form at thin walls or even break directly. Summary of the Invention
[0005] The purpose of this invention is to provide a reduced iron powder, its preparation method, and its application. The reduced iron powder prepared by this invention has good compaction strength and formability. When used to produce thin-walled parts, it can effectively improve the strength of the thin-walled parts, making them less prone to breakage.
[0006] To achieve the above objectives, the present invention provides the following technical solution:
[0007] This invention provides a method for preparing reduced iron powder, comprising the following steps:
[0008] Iron oxide and reducing additives are distributed in a three-layer annular pattern and then subjected to a reduction reaction to obtain the first reduction product. The three-layer annular pattern consists of an inner core and an outer layer of reducing additives, with iron oxide in the middle layer. The reducing additives include semi-coke, coke powder, and limestone, with a mass ratio of (33-35):(28-30):5. The mass ratio of iron oxide to reducing additives is 150:(64-68).
[0009] The first reduction product is subjected to a first pulverization to obtain a primary reduction powder; the particle size of the primary reduction powder is: the volume percentage of the primary reduction powder ≤100 mesh is 100%, and the volume percentage of the primary reduction powder ≤200 mesh is 40-52%.
[0010] The primary reduction powder is annealed in a flowing hydrogen atmosphere to obtain a second reduction product.
[0011] The second reduction product is subjected to a second pulverization to obtain a secondary reduction powder; the secondary reduction powder is subjected to a first sieve to obtain a first undersize; the first undersize is subjected to a second sieve to obtain a second undersize; the mesh size of the sieve during the first sieve is smaller than the mesh size of the sieve during the second sieve.
[0012] The first sieve undersize and the second sieve undersize are mixed to obtain reduced iron powder; during the mixing, the mass ratio of the first sieve undersize and the second sieve undersize is (60-65):(35-40).
[0013] Preferably, the three-layer annular fabric consists of a cylindrical inner core, an annular intermediate layer, and an annular outer layer nested together in sequence; the outer edge diameter of the cylindrical inner core is 168cm, the outer edge diameter of the annular intermediate layer is 275cm, and the outer edge diameter of the annular outer layer is 426cm.
[0014] Preferably, the reduction reaction is carried out at a temperature of 1155–1160°C for 122 hours.
[0015] Preferably, the first powder preparation is carried out using a Raymond mill, and the operating current of the Raymond mill is ≤75A.
[0016] Preferably, before the annealing process is performed on the first powder obtained by the first powder preparation, the method further includes: magnetically separating the first powder to obtain a primary reduced powder, wherein the mass content of acid-insoluble matter in the primary reduced powder is ≤0.32%.
[0017] Preferably, the annealing treatment is performed at a temperature of 925–930°C for 3–3.5 hours; the hydrogen flow rate is 45–50 m³ / h. 3 / h.
[0018] Preferably, the second grinding is carried out in a hammer crusher, wherein the bottom plate aperture of the hammer crusher is 4-6 mm.
[0019] Preferably, the mesh size of the sieve is 90 mesh during the first screening and 100 mesh during the second screening.
[0020] This invention provides reduced iron powder prepared by the preparation method described above, wherein the reduced iron powder contains TFe ≥ 98.75% and has a loose bulk density of 2.75–2.8 g / cm³. 3 Compressibility at 500 MPa ≥ 6.74 g / cm³ 3 The volume percentage of reduced iron powder with a mesh size of ≤200 is 45-48%, the acid-insoluble content is ≤0.25% by mass, the hydrogen loss value is ≤0.25%, and the Latola value is ≤0.1%.
[0021] This invention provides the application of the reduced iron powder described in the above technical solution in the preparation of thin-walled parts.
[0022] This invention provides a method for preparing reduced iron powder, comprising the following steps: iron oxide and reducing additives are distributed in a three-layer annular arrangement and then subjected to a reduction reaction to obtain a first reduction product; the three-layer annular arrangement consists of an inner core and an outer layer of reducing additives, with an iron oxide sandwiched in the middle; the reducing additives include semi-coke, coke powder, and limestone, wherein the mass ratio of semi-coke, coke powder, and limestone is (33-35):(28-30):5; the mass ratio of iron oxide to reducing additives is 150:(64-68); the first reduction product is subjected to a first pulverization to obtain primary reduction powder; the particle size of the primary reduction powder is: ≤100 mesh, with the volume of the primary reduction powder accounting for... The volume percentage of primary reduction powder (≤200 mesh) is 40-52% (100%). In a flowing hydrogen atmosphere, the primary reduction powder is annealed to obtain a second reduction product. The second reduction product is then subjected to a second pulverization to obtain secondary reduction powder. The secondary reduction powder is first sieved to obtain a first undersize. The first undersize is then second sieved to obtain a second undersize. The mesh size of the sieve used in the first sieve is smaller than that used in the second sieve. The first and second undersizes are mixed to obtain reduced iron powder. During mixing, the mass ratio of the first and second undersizes is (60-65):(35-40). The preparation method provided by this invention, by strictly controlling the mass ratio of raw materials during the reduction reaction, enables iron oxide to be fully reduced in the reduction reaction stage without severe carburization. By strictly controlling the particle size distribution of the primary reduction powder in the first pulverization stage, this invention enables the reduced iron powder product to have a high stability in dimensional change rate, improving the compact strength and formability of the reduced iron powder product. This invention further increases the elemental iron content in reduced iron powder through annealing. Finally, by subjecting the second reduction product to a second powdering process followed by two sievings and controlling the mass ratio of the first and second sieve undersizes during merging, the invention effectively avoids damaging the formability of the reduced iron powder, resulting in a more uniform particle size distribution and more stable physical properties such as bulk density across the entire batch, thus ensuring consistent performance across each batch. In summary, the reduced iron powder produced by the method provided by this invention exhibits good green strength and dimensional change rate. Using it to produce thin-walled parts can effectively improve the strength of the thin-walled sections, making them less prone to breakage.
[0023] Furthermore, in this invention, before the annealing process to obtain the first powder from the first powder preparation, the method further includes: magnetically separating the first powder to obtain a primary reduced powder, wherein the mass content of acid-insoluble matter in the primary reduced powder is ≤0.32%. Preferably, this invention uses magnetic separation after the first powder preparation to reduce the content of acid-insoluble matter in the reduced iron powder product, thereby giving the reduced iron powder product better green strength and dimensional change rate. Using it to produce thin-walled parts can effectively improve the strength of the thin-walled sections of the parts, making them less prone to breakage. Detailed Implementation
[0024] This invention provides a method for preparing reduced iron powder, comprising the following steps:
[0025] Iron oxide and reducing additives are distributed in a three-layer annular pattern and then subjected to a reduction reaction to obtain the first reduction product. The three-layer annular pattern consists of an inner core and an outer layer of reducing additives, with iron oxide in the middle layer. The reducing additives include semi-coke, coke powder, and limestone, with a mass ratio of (33-35):(28-30):5. The mass ratio of iron oxide to reducing additives is 150:(64-68).
[0026] The first reduction product is subjected to a first pulverization to obtain a primary reduction powder; the particle size of the primary reduction powder is: the volume percentage of the primary reduction powder ≤100 mesh is 100%, and the volume percentage of the primary reduction powder ≤200 mesh is 40-52%.
[0027] The primary reduction powder is annealed in a flowing hydrogen atmosphere to obtain a second reduction product.
[0028] The second reduction product is subjected to a second pulverization to obtain a secondary reduction powder; the secondary reduction powder is subjected to a first sieve to obtain a first undersize; the first undersize is subjected to a second sieve to obtain a second undersize; the mesh size of the sieve during the first sieve is smaller than the mesh size of the sieve during the second sieve.
[0029] The first sieve undersize and the second sieve undersize are mixed to obtain reduced iron powder; during the mixing, the mass ratio of the first sieve undersize and the second sieve undersize is (60-65):(35-40).
[0030] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.
[0031] This invention involves distributing iron oxide and reducing additives in a three-layer annular pattern for reduction reaction to obtain a first reduction product. The three-layer annular pattern consists of an inner core and outer layer of reducing additives, with iron oxide in the middle layer. The reducing additives include semi-coke, coke powder, and limestone, with a mass ratio of (33-35):(28-30):5. The mass ratio of iron oxide to reducing additives is 150:(64-68). In this invention, the volume percentage of iron oxide with a particle size ≤100 mesh is preferably 100%, and the volume percentage of iron oxide with a particle size ≤200 mesh is 46%. Before distributing the reducing additives, the iron oxide is preferably pretreated, which preferably includes drying and grinding sequentially. The drying is preferably carried out in a drying drum at a temperature of 700-800°C. After drying, the moisture content of the obtained dried iron oxide is preferably ≤0.1%. The grinding is preferably carried out using a ball mill sieving system. This invention does not have special requirements for the specific implementation process of the grinding and screening. In this invention, the particle size of the semi-coke is preferably ≤5mm. The particle size of the coke powder is preferably ≤5mm. The particle size of the limestone is preferably ≤1mm. Before the material is applied, this invention preferably uses a four-roll mill to grind the semi-coke and coke powder to make them finer. The mass ratio of the semi-coke, coke powder and limestone is preferably 33:30:5. The mass ratio of the iron oxide and the reducing agent is preferably 150:68. This invention preferably mixes the semi-coke, coke powder and limestone evenly in a mixer to obtain the reducing agent. The three-layer annular material is preferably a cylindrical inner core, an annular intermediate layer and an annular outer layer nested in sequence; the outer edge diameter of the cylindrical inner core is preferably 168cm, the outer edge diameter of the annular intermediate layer is preferably 275cm, and the outer edge diameter of the annular outer layer is preferably 426cm. The three-layer annular material is preferably: the reducing agent is applied to the cylindrical inner core and the annular outer layer; the iron oxide is applied to the annular intermediate layer. The three-layer annular fabric is preferably used to place iron oxide and reducing agents in the reaction mold. The reaction mold is preferably made of SiC and preferably includes a cylindrical core reaction zone, and an intermediate sandwich reaction zone and an outer reaction zone arranged concentrically with the cylindrical core reaction zone. Specifically, the three-layer annular fabric arrangement preferably involves arranging the reducing agents in the cylindrical core reaction zone and the outer reaction zone of the reaction mold, and arranging iron oxide in the intermediate sandwich reaction zone of the reaction mold. Before placing the materials in the reaction mold, the present invention preferably coats the bottom of each of the three reaction zones of the reaction mold with a small amount of reducing agent. After the reaction mold is filled, the present invention preferably covers the surface of the iron oxide with a small amount of reducing agent to completely cover the surface of the iron oxide.
[0032] In this invention, the reduction reaction is carried out in a tunnel furnace. The preferred temperature for the reduction reaction is 1155–1160°C, and the preferred time is 122 hours. After the reduction reaction is completed, the reacted material is preferably cored and unloaded to obtain a first reduction product, which is a ring-shaped cylindrical sponge iron.
[0033] After obtaining the first reduction product, the present invention performs a first pulverization on the first reduction product to obtain primary reduction powder; the particle size of the primary reduction powder is: 100% by volume for primary reduction powder ≤100 mesh, and 40-52% by volume for primary reduction powder ≤200 mesh. In the present invention, the first pulverization is preferably carried out using a Raymond mill, and the operating current of the Raymond mill is preferably ≤75A. In the present invention, before performing the Raymond milling, the first reduction product is preferably subjected to a jaw crusher and a hammer crusher in sequence. The present invention does not have special requirements for the specific implementation process of the jaw crusher and hammer crusher.
[0034] In this invention, before the annealing process to obtain the first powder, the process preferably further includes: subjecting the first powder to magnetic separation to obtain a primary reduced powder, wherein the mass content of acid-insoluble matter in the primary reduced powder is ≤0.32%. This invention does not have specific requirements for the specific implementation process of the magnetic separation.
[0035] After obtaining the primary reduced powder, the present invention anneales the primary reduced powder in a flowing hydrogen atmosphere to obtain a second reduced product. In the present invention, the annealing temperature is preferably 925–930°C, the annealing time is preferably 3–3.5 h, and the hydrogen flow rate is preferably 45–50 m³ / h. 3 / h, more preferably 46-48m 3 / h. The mass content of elemental iron (TFe) in the second reduction product is preferably ≥98.75%.
[0036] After obtaining the second reduction product, the present invention further processes the second reduction product into a second powder to obtain a secondary reduction powder; the secondary reduction powder is then subjected to a first sieve to obtain a first undersize; the first undersize is then subjected to a second sieve to obtain a second undersize; the mesh size of the sieve used in the first sieve is smaller than that used in the second sieve. In this invention, the second powdering is carried out in a hammer crusher, and the bottom plate aperture of the hammer crusher is preferably 4-6 mm. The first and second sieves are preferably performed using a circular vibrating screen. The mesh size of the sieve used in the first sieve is preferably 90 mesh; the mesh size of the sieve used in the second sieve is preferably 100 mesh.
[0037] After obtaining the first and second sieve undersizes, the present invention mixes the first and second sieve undersizes to obtain reduced iron powder; during mixing, the preferred mass ratio of the first and second sieve undersizes is (60-65):(35-40). The preferred mixing time is 20 minutes.
[0038] This invention provides reduced iron powder prepared by the preparation method described above, wherein the reduced iron powder contains TFe ≥ 98.75% and has a loose bulk density of 2.75–2.8 g / cm³. 3 Compressibility at 500 MPa ≥ 6.74 g / cm³ 3 The volume percentage of reduced iron powder with a mesh size of ≤200 is 45-48%, the acid-insoluble content is ≤0.25% by mass, the hydrogen loss value is ≤0.25%, and the Latola value is ≤0.1%.
[0039] This invention provides the application of the reduced iron powder described above in the preparation of thin-walled parts. The reduced iron powder prepared by this invention has good compaction strength and formability. Using it to produce thin-walled parts can effectively improve the strength of the thin-walled sections, making them less prone to fracture. This invention does not specify any particular requirements for the specific implementation process of the application.
[0040] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0041] Example 1
[0042] (1) Dry the iron oxide scale at 750℃ and ball mill it. The resulting iron oxide scale has a moisture content of ≤0.1%, and the volume percentage of iron oxide with a particle size greater than 40 mesh is 0%, while the volume percentage of iron oxide with a particle size less than 200 mesh is 46%.
[0043] (2) The coke powder and semi-coke are ground by a four-roll mill. The particle size of the coke powder and semi-coke is controlled to be below 5 mm. They are weighed with limestone (particle size ≤ 1 mm) in a mass ratio of 33:30:5. After weighing, they are mixed evenly in a mixer to obtain the reducing auxiliary material.
[0044] (3) First, put a portion of the mixed reducing agent (about 2 kg) from step (2) into the bottom of each layer of the neatly stacked SiC tank. Then, put 150 kg of iron oxide scale into the middle interlayer of the SiC tank. Then, put the mixed reducing agent from step (2) into the innermost core and outermost layer of the mold, totaling 64 kg. When laying the material, the outer edge diameter of the inner core of the cylinder is 168 cm, the outer edge diameter of the middle interlayer of the ring is 275 cm, and the outer edge diameter of the outer layer of the ring is 426 cm. Finally, cover the iron oxide scale with the mixed agent from step (2).
[0045] (4) The loaded material is put into the tunnel kiln for reduction reaction. The reduction temperature is 1155℃ and the reduction time is 122h.
[0046] (5) After the reduction is completed, the core is cleaned and the ingot is unloaded to obtain the first reduction product, which is a ring-shaped cylindrical sponge iron. The first powder making is then carried out. The first reduction product is subjected to jaw crusher, hammer crusher, Raymond mill and magnetic separation in sequence. During the process, the Raymond mill current is 73A. The relevant properties of the primary reduction powder are shown in Table 1.
[0047] Table 1 Performance of Primary Reducing Powder
[0048]
[0049] (6) Anneal the primary reduced powder at a temperature of 930℃ and a hydrogen flow rate of 48 m³ / h. 3 The material is annealed for 3 hours, then subjected to a second grinding process in a hammer crusher with a bottom plate aperture of 4 mm. The first undersize material is obtained by passing it through a first circular vibrating screen, and the second undersize material is then passed through a second circular vibrating screen to obtain a second undersize material. The first circular vibrating screen has a 90-mesh aperture, and the second circular vibrating screen has a 100-mesh aperture. The relevant properties of the first and second undersize materials are shown in Tables 2 and 3, where compressibility is the compressive mass per unit volume under 500 MPa conditions, expressed in g / cm³. 3 The loose ratios in Tables 2 to 4 refer to the loose bulk density, with units of g / cm³. 3 .
[0050] Table 2 Properties of the first undersize material obtained from the first vibrating screen.
[0051]
[0052] Table 3. Properties of the second undersize material obtained from the second vibrating screen.
[0053]
[0054] (7) 60 wt% of the first sieve undersize and 40 wt% of the second sieve undersize were mixed together for 20 min. The final reduced iron powder product properties are shown in Table 4.
[0055] Table 4 Performance of Reduced Iron Powder for Thin-Walled Materials
[0056]
[0057] Table 4 shows that the reduced iron powder obtained by the preparation method provided in the above embodiments has a compact strength of 12.8–13.5 MPa (obtained according to ISO 3995:2023 "Metal powders, determination of green strength by transverse fracture of rectangular compacts"). The formability of the reduced iron powder, as determined by the Lattor value reaction, remains stable below 0.1%. This indicates that the reduced iron powder prepared by this invention has good compact strength and formability. Using it to produce thin-walled parts can effectively improve the strength of the thin-walled sections, making them less prone to fracture.
[0058] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.
Claims
1. An application of reduced iron powder in the preparation of thin-walled parts, characterized in that, The thickness of the thin-walled part is 1~3mm, and the method for preparing the reduced iron powder includes the following steps: Iron oxide and reducing additives are distributed in a three-layer annular pattern and then subjected to a reduction reaction to obtain the first reduction product. The three-layer annular pattern consists of an inner core and an outer layer of reducing additives, with iron oxide in the middle layer. The reducing additives include semi-coke, coke powder, and limestone, with a mass ratio of (33-35):(28-30):
5. The mass ratio of iron oxide to reducing additives is 150:(64-68). The first reduction product is subjected to a first pulverization to obtain a primary reduction powder; the particle size of the primary reduction powder is: the volume percentage of the primary reduction powder ≤100 mesh is 100%, and the volume percentage of the primary reduction powder ≤200 mesh is 40~52%. The primary reduction powder is annealed in a flowing hydrogen atmosphere to obtain a second reduction product. The second reduction product is subjected to a second pulverization to obtain a secondary reduction powder; the secondary reduction powder is subjected to a first sieve to obtain a first undersize; the first undersize is subjected to a second sieve to obtain a second undersize; the mesh size of the sieve during the first sieve is 90 mesh; the mesh size of the sieve during the second sieve is 100 mesh. The first sieve undersize and the second sieve undersize are mixed to obtain reduced iron powder; during the mixing, the mass ratio of the first sieve undersize and the second sieve undersize is (60-65):(35-40); The loose bulk density of the reduced iron powder is 2.75–2.8 g / cm³. 3 The volume percentage of reduced iron powder with a mesh size of ≤200 is 45-48%, and the Latola value is ≤0.1%.
2. The application according to claim 1, characterized in that, The three-layer annular fabric consists of a cylindrical inner core, an annular intermediate layer, and an annular outer layer, which are nested together in sequence. The outer edge diameter of the cylindrical inner core is 168cm, the outer edge diameter of the annular intermediate layer is 275cm, and the outer edge diameter of the annular outer layer is 426cm.
3. The application according to claim 1 or 2, characterized in that, The reduction reaction was carried out at a temperature of 1155–1160 °C for 122 h.
4. The application according to claim 1, characterized in that, The first powder preparation is carried out using a Raymond mill, and the operating current of the Raymond mill is ≤75A.
5. The application according to claim 1 or 4, characterized in that, Before the annealing process, the first powder preparation process further includes: magnetically separating the first powder to obtain a primary reduced powder, wherein the mass content of acid-insoluble matter in the primary reduced powder is ≤0.32%.
6. The application according to claim 1, characterized in that, The annealing treatment is performed at a temperature of 925–930°C for 3–3.5 hours; the hydrogen flow rate is 45–50 m³ / h. 3 / h.
7. The application according to claim 1, characterized in that, The second grinding process is carried out in a hammer crusher, wherein the bottom plate aperture of the hammer crusher is 4-6 mm.
8. The application according to claim 1, characterized in that, The reduced iron powder contains ≥98.75% TFe and has a compressibility ≥6.74 g / cm³ under 500 MPa conditions. 3 The acid-insoluble content is ≤0.25% by mass, and the hydrogen loss value is ≤0.25%.