Preparation method for improving tensile property of powder metallurgy iron-based part

Abstract

The invention provides a preparation method for improving the tensile property of a powder metallurgy iron-based part, and relates to the technical field of low alloy preparation through powder metallurgy. According to the method, the preparation process is divided into the boronizing process and the diffusion process, the boronizing structure and the thickness of the boronizing structure can be controlled according to different heating temperatures and time in the boronizing process, and the boronizing thickness can be adjusted between more than ten micrometers and hundreds of micrometers. After the diffusion process, the boronizing layer can keep a Fe2B single-phase boronizing layer between more than ten micrometers and hundreds of micrometers, the surface quality of the surface layer is high, and the hardness, strength and ductility of the powder metallurgy iron-based part are effectively improved. According to the method, through boriding and diffusion heat treatment, a single-layer dense 60-95 [mu] m Fe2B infiltrated layer can be finally obtained in the powder metallurgy low alloy steel, surface layer hole looseness is small, subsequent grinding treatment is not needed, and the hardness, the strength and the ductility can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of powder metallurgy preparation of low alloys, and in particular to a preparation method of powder metallurgy iron-based parts with improved tensile properties. Background Art

[0002] Powder metallurgy is a process that uses metal powder as raw material to produce mechanical parts through a process of mixing, compacting, and sintering. It boasts a range of advantages, including high efficiency, low energy consumption, high material utilization, and uniform material structure. It is widely used in industries such as aviation, aerospace, and automobiles. However, problems such as porosity and surface roughness severely restrict the tensile properties of powder metallurgy materials. Fatigue failure of powder metallurgy materials is a major issue in engineering applications, and improving their fatigue behavior is currently a key task in this field.

[0003] Boriding can achieve a surface structure with high hardness and excellent resistance to high-temperature oxidation and corrosion. However, since boriding generally results in a dual-layer structure of FeB and Fe2B, the FeB layer is relatively brittle. Only a single-phase Fe2B layer can achieve good toughness. Post-boriding cooling often results in transverse cracks in the borided layer due to the combined effects of thermal stress and phase transformation stress. Furthermore, the surface of the borided layer can exhibit significant porosity, which can severely affect surface hardness and negatively impact its practical engineering applications. In practice, the desired borided structure is a single-phase Fe2B layer with a dense, fine-grained layer and minimal porosity.

[0004] Chinese patent CN109487314A discloses a boronizing method for improving the wear resistance of steel surfaces. The method achieves this goal through pretreatment of the steel surface, preparation of an electrolytic solution, and boronizing treatment. The resulting boronized layer is mainly composed of a single Fe2B phase and needs to be prepared under the preparation conditions of additives and electrolytic solution. The prepared boronized layer is thin, brittle, and has poor tensile properties.

[0005] Chinese patent CN108796426A discloses a metal surface superhardening process, which involves quenching, cleaning, tempering, boiling in boiling water for 2-3 days for cleaning, and TD treatment after boronizing. However, the process is complex, the operation is difficult, and the production efficiency is low. Although the hardness of the prepared product is very high, the tensile properties are not effectively improved.

[0006] Chinese patent CN113481503A discloses a method for preparing a boron particle-reinforced metal matrix composite material, a composite material, and its application. The method uses a resonant ball milling method to prepare a uniformly mixed boron-metal micron powder, and then uses a supersonic low-pressure cold spray method to spray a composite coating on a metal substrate in an additive manufacturing manner to form a composite material. Obviously, the preparation process is costly and inefficient, does not form FeB and Fe2B structures, and does not undergo heat treatment to improve tensile properties. Summary of the Invention

[0007] In order to solve the technical problems existing in the prior art, such as the fact that powder metallurgy iron-based parts only focus on adding boron to increase the surface hardness and thus improve the wear resistance, but do not pay attention to the formation of Fe2B single-phase structure and the improvement of tensile properties, and the prepared surface boronized layer is either too thin or the structure distribution is uneven, without the diffusion of the structure, and some only prepare a coating on the surface of the material, which cannot improve the overall tensile properties of the parts; the present invention proposes a preparation method for powder metallurgy iron-based parts to improve the tensile properties that can solve the above problems. The technical solution is as follows:

[0008] A method for preparing a powder metallurgy iron-based part to improve tensile properties, the method comprising the following steps:

[0009] S1. Sample processing: clean the oil stains on the surface of the powder metallurgy iron-based parts sample, and grind and polish the sample surface to obtain a smooth surface iron-based parts sample;

[0010] S2. Initial powder coating of the sample surface: B powder is used to cover the smooth surface of the iron-based part sample in S1, and it is coated and compacted with tantalum foil to obtain a B powder-coated iron-based part sample;

[0011] S3. Preparation of boronized layer on sample surface: Place the iron-based part sample coated with B powder in S2 in a tube furnace, introduce hydrogen to prevent oxidation, heat and keep warm to obtain an iron-based part sample with a surface boronized layer;

[0012] S4. Diffusion treatment of samples: The iron-based part samples with the surface boronized layer in S3 are cleaned to remove the remaining boron powder, and then subjected to diffusion heat treatment, and then air-cooled to room temperature to obtain powder metallurgy iron-based parts with improved tensile properties.

[0013] Optionally, the alloy composition of the powder metallurgy iron-based part sample in S1 is C≤0.81wt.%, Cu≤2.07wt.%, Ni≤2.44wt.%, Mo≤0.53wt.%, Mn≤0.17wt.%, P≤0.45wt.%, and the rest is Fe.

[0014] Optionally, the surface roughness Ra of the iron-based part sample with a smooth surface in S1 is 0.8-2 μm.

[0015] Optionally, the B powder in S2 is industrial B powder of 1-3 μm, the B powder completely covers the powder metallurgy parts, the B powder thickness is about 3-5 mm, the tantalum foil thickness is 0.10±0.05 mm, and the pressure is 200 MPa.

[0016] Optionally, the heating rate in S3 is 5-10°C / min, the temperature is heated to 850-950°C, the holding time is 4-8h, and the thickness of the surface boronized layer is 30-160μm.

[0017] Optionally, the surface hardness of the iron-based part sample with the surface boronized layer in S3 is 1440-1600 HV 0.5 The surface porosity is 5%-20%, the surface roughness is 0.8-3.0μm, the yield strength is 265-300MPa, the tensile strength is 265-380MPa, the elongation is 2.3-4.5%, and the strength-plasticity product is 0.61-1.71GPa·%.

[0018] Optionally, in the surface boronized layer of the iron-based part sample with the surface boronized layer in S3, the Fe2B has a sawtooth distribution shape, a thickness of about 15-60 μm, is distributed in the subsurface layer, and grows closely with the matrix.

[0019] Optionally, the heating rate of the diffusion heat treatment in S4 is 5°C / min, the temperature is heated to 950-1000°C, the holding time is 2-4h, and the thickness of the surface boronized layer is 60-95μm.

[0020] Optionally, the surface hardness of the powder metallurgy iron-based parts for improving tensile properties in S4 is 1182-1230HV 0.5 The surface porosity is 5%-10%, the surface roughness is 0.8-2.0μm, the yield strength is 100-130.3MPa, the tensile strength is 150-220.9MPa, the yield strength ratio is 0.452-0.869, the elongation is 7.8-12.4%, and the strength-plasticity product is 1.17-2.74GPa·%.

[0021] Optionally, in the surface boronized layer of the powder metallurgy iron-based part for improving tensile properties in S4, the Fe2B has a serrated shape, a thickness of about 40-70 μm, and is relatively uniformly distributed on the surface.

[0022] Technical principle of the present invention:

[0023] The method first coats the sample surface with boron powder. High-temperature heating causes the boron powder to melt and penetrate the sample surface. Diffusion occurs at grain boundaries and defects. Initially, at high temperatures, boron atoms penetrate the steel surface, reacting with iron to form two borides, FeB and Fe2B. Due to the boron concentration gradient, the surface is FeB, while the subsurface is Fe2B. Further diffusion annealing is then performed, causing boron atoms to diffuse from high-concentration areas (FeB) to low-concentration areas (Fe2B and the matrix). This reduces the boron concentration in the FeB, leading to a gradual, and ultimately complete, transformation of the FeB into Fe2B. This complete transformation into Fe2B results in a surface with higher hardness and improved toughness, while also avoiding the brittleness of FeB and significantly improving wear resistance and tensile properties.

[0024] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0025] The above scheme, the present invention proposes a preparation method for powder metallurgy iron-based parts to improve the tensile properties, which can solve the technical problems existing in the prior art. For example, powder metallurgy iron-based parts only focus on adding boron elements to increase the surface hardness, thereby improving wear resistance, and do not pay attention to the generation of Fe2B single-phase structure and the improvement of tensile properties. In addition, the prepared surface boronized layer is either too thin or the structure distribution is uneven, and the structure is not diffused. Some only prepare a coating on the surface of the material, which cannot improve the overall tensile properties of the parts.

[0026] The preparation method of the present invention is simple, uses a single B powder as raw material instead of a composite slurry, has low production cost, and the thickness of the diffusion layer can be adjusted according to the holding time and temperature, can significantly improve the density and room temperature mechanical properties of powder metallurgy materials, and can be easily promoted to other metal material fields.

[0027] The present invention coats the sample surface with initial powder so that the infiltration B powder is evenly coated on the sample surface, effectively avoiding the problem of uneven infiltration layer.

[0028] The present invention prepares a boronized layer on the surface of a sample, so as to obtain a FeB+Fe2B double-layer boronized layer, thereby significantly improving the yield strength, tensile strength, surface hardness and wear resistance.

[0029] The present invention further improves the density of the powder metallurgy material and increases the proportion of Fe2B through diffusion treatment of the sample, thereby improving the plasticity and enhancing the comprehensive performance.

[0030] The surface hardness of the powder metallurgy iron-based parts with improved tensile properties prepared by the present invention is 1182-1230HV 0.5The surface porosity is 5%-10%, the surface roughness is 0.8-2.0μm, the yield strength is 100-130.3MPa, the tensile strength is 150-220.9MPa, the yield strength ratio is 0.452-0.869, the elongation is 7.8-12.4%, and the strength-plasticity product is 1.17-2.74GPa·%.

[0031] In summary, compared with other traditional methods, the method of the present invention can obtain a single-layer, dense Fe2B-plated layer with a thickness of 60-95μm in powder metallurgy low-alloy steel through boronizing and diffusion heat treatment, and the surface layer has few loose pores and no subsequent grinding processing is required, which can greatly improve the hardness, strength and elongation; this method is simple and easy to operate, green and environmentally friendly, low cost, short process, high efficiency, and is conducive to large-scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 This is a SEM micrograph of a cross-sectional diffusion layer in a method for preparing a powder metallurgy iron-based part to improve tensile properties, which has not been subjected to diffusion heat treatment, in Example 1 of the present invention;

[0034] Figure 2 This is a cross-sectional SEM micrograph of a method for preparing a powder metallurgy iron-based part to improve tensile properties according to Example 1 of the present invention after diffusion heat treatment;

[0035] Figure 3 : This is an XRD pattern of a boronized layer in a method for preparing a powder metallurgy iron-based part to improve tensile properties according to Example 1 of the present invention; wherein, the pattern marked 900-8B-1000-6DA is subjected to a boronizing treatment at 900°C for 8 hours, air cooling, and then a diffusion homogenization treatment at 1000°C for 6 hours; the pattern marked 900-4B-1000-6DA is subjected to a boronizing treatment at 900°C for 4 hours, followed by air cooling and then a diffusion homogenization treatment at 1000°C for 6 hours; the pattern marked 900-8B-1000-4DA is subjected to a boronizing treatment at 900°C for 8 hours, followed by air cooling and then a diffusion homogenization treatment at 1000°C for 4 hours; (a) is an overall XRD phase analysis pattern of the three patterns, and (b) is a partial enlarged view of (a);

[0036] Figure 4 This is a hardness distribution curve from the surface to the interior of the boronized layer in a method for preparing a powder metallurgy iron-based part to improve tensile properties according to Example 1 of the present invention;

[0037] Figure 5 This is a tensile mechanics curve of the material prepared in the preparation method for improving the tensile properties of a powder metallurgy iron-based part in Example 1 of the present invention; wherein PM is the room temperature tensile property of the original sample, 900-4B is the sample treated by boronizing at 900°C for 4 hours, 900-6B is the sample treated by boronizing at 900°C for 6 hours, 900-8B is the sample treated by boronizing at 900°C for 8 hours, 900-4B-1000-4DA is the sample treated by boronizing and then diffusion annealing at 1000°C for 4 hours, 900-6B-1000-4DA is the sample treated by boronizing and then diffusion annealing at 1000°C for 6 hours, and 900-8B-1000-4DA is the sample treated by boronizing and then diffusion annealing at 1000°C for 8 hours. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0039] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as an "exemplary" in the present invention should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of the word "exemplary" is intended to present concepts in a concrete manner. Furthermore, in the embodiments of the present invention, "and / or" can mean both or either of the two.

[0040] In the embodiments of the present invention, “image” and “picture” may sometimes be used interchangeably. It should be noted that when the distinction between them is not emphasized, the meanings they intend to express are the same.

[0041] In the embodiments of the present invention, sometimes a subscript such as W1 may be written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0042] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0043] A method for preparing a powder metallurgy iron-based part to improve tensile properties, the method comprising the following steps:

[0044] S1. Sample processing: clean the oil stains on the surface of the powder metallurgy iron-based parts sample, and grind and polish the sample surface to obtain a smooth surface iron-based parts sample;

[0045] S2. Initial powder coating of the sample surface: B powder is used to cover the smooth surface of the iron-based part sample in S1, and it is coated and compacted with tantalum foil to obtain a B powder-coated iron-based part sample;

[0046] S3. Preparation of boronized layer on sample surface: Place the iron-based part sample coated with B powder in S2 in a tube furnace, introduce hydrogen to prevent oxidation, heat and keep warm to obtain an iron-based part sample with a surface boronized layer;

[0047] S4. Diffusion treatment of samples: The iron-based part samples with the surface boronized layer in S3 are cleaned to remove the remaining boron powder, and then subjected to diffusion heat treatment, and then air-cooled to room temperature to obtain powder metallurgy iron-based parts with improved tensile properties.

[0048] In particular, the alloy composition of the powder metallurgy iron-based part sample in S1 is C≤0.81wt.%, Cu≤2.07wt.%, Ni≤2.44wt.%, Mo≤0.53wt.%, Mn≤0.17wt.%, P≤0.45wt.%, and the rest is Fe.

[0049] In particular, the surface roughness Ra of the smooth-surfaced iron-based part samples in S1 is 0.8-2 μm.

[0050] In particular, the B powder in S2 is industrial B powder of 1-3 μm, the B powder completely covers the powder metallurgy parts, the B powder thickness is about 3-5 mm, the tantalum foil thickness is 0.10±0.05 mm, and the pressure is 200 MPa.

[0051] In particular, the heating rate in S3 is 5-10°C / min, the temperature is heated to 850-950°C, the holding time is 4-8h, and the thickness of the surface boronized layer is 30-160μm.

[0052] In particular, the surface hardness of the iron-based part sample with the surface boronized layer in S3 is 1440-1600 HV 0.5 The surface porosity is 5%-20%, the surface roughness is 0.8-3.0μm, the yield strength is 265-300MPa, the tensile strength is 265-380MPa, the elongation is 2.3-4.5%, and the strength-plasticity product is 0.61-1.71GPa·%.

[0053] In particular, in the surface boronized layer of the iron-based part sample in S3, the Fe2B has a zigzag distribution shape, a thickness of about 15-60 μm, is distributed in the subsurface layer, and grows closely with the matrix.

[0054] In particular, the heating rate of the diffusion heat treatment in S4 is 5°C / min, the temperature is heated to 950-1000°C, the holding time is 2-4h, and the thickness of the surface boronized layer is 60-95μm.

[0055] In particular, the surface hardness of the powder metallurgy iron-based parts in S4 that improve tensile properties is 1182-1230HV 0.5The surface porosity is 5%-10%, the surface roughness is 0.8-2.0μm, the yield strength is 100-130.3MPa, the tensile strength is 150-220.9MPa, the yield strength ratio is 0.452-0.869, the elongation is 7.8-12.4%, and the strength-plasticity product is 1.17-2.74GPa·%.

[0056] In particular, in the surface boronized layer of the powder metallurgy iron-based parts in S4 that improves tensile properties, the Fe2B has a serrated shape, a thickness of about 40-70 μm, and is relatively uniformly distributed on the surface.

[0057] In the following examples, the hardness of the prepared powder metallurgy iron-based parts was measured using an MHV-1000Z / V3.0 fully automatic micro-Vickers hardness tester, selecting a test force of HV-0.5 and holding the pressure for 10 seconds.

[0058] The room temperature tensile test is carried out in accordance with GB / T228.1-2021. The standard tensile specimen is dog-bone shaped, with a gauge length of 15 mm, a diameter of 2.5 mm, and a total length of 40 mm. The room temperature tensile test is carried out on an electronic universal testing machine GNT300 equipped with an extensometer, with a tensile rate of 0.5 mm / min.

[0059] Example 1

[0060] A method for preparing a powder metallurgy iron-based part to improve tensile properties, the method comprising the following steps:

[0061] S1. Sample processing: The alloy composition of the powder metallurgy iron-based part sample is C 0.71wt.%, and the rest is Fe. Clean the oil stains on the surface of the powder metallurgy iron-based part sample, and grind and polish the sample surface to obtain a smooth surface iron-based part sample. The surface roughness of the smooth surface iron-based part sample is Ra ≤ 2μm.

[0062] S2. Initial powder coating of the sample surface: 1-3 μm industrial pure B powder is used to cover the surface of the smooth iron-based part sample in S1. The B powder coating thickness is about 3-5 mm. The sample is then coated and compacted with tantalum foil. The thickness of the tantalum foil is 0.10 mm and the compaction pressure is 200 MPa. The iron-based part sample coated with B powder is obtained.

[0063] S3. Preparation of boronized layer on sample surface: The iron-based part sample coated with B powder in S2 was placed in a tube furnace, hydrogen was introduced to prevent oxidation, and the sample was heated and kept warm at a heating rate of 5°C / min to a temperature of 900°C and kept warm for 4 hours to obtain an iron-based part sample with a surface boronized layer; Figure 1The dark grey near the top is FeB, which is also serrated. The light grey below, which is connected to the matrix, is Fe2B, which is also serrated. The thickness of the boronized layer on the surface is 30±8μm.

[0064] The surface hardness of the iron-based part sample with a surface boronized layer is 1440±5HV 0.5 , the surface porosity is about 8%, the surface roughness is 1.5μm, the yield strength is 275MPa, the tensile strength is 375MPa, the yield strength ratio is 0.734, the elongation is 3.0%, and the strength-ductility product is 1.13GPa;

[0065] In the surface boronized layer of the iron-based part sample with a surface boronized layer, Fe2B is distributed in a zigzag shape, closely combined with the matrix, and has a thickness of about 15±3μm;

[0066] S4. Diffusion treatment of samples: The iron-based part samples with a surface boronized layer in S3 were cleaned to remove the remaining boron powder, and then subjected to diffusion heat treatment. The heating rate of the diffusion heat treatment was 5°C / min, and the temperature was heated to 900°C for 4 hours. After that, the samples were air-cooled to room temperature to obtain powder metallurgy iron-based parts with improved tensile properties. The thickness of the surface boronized layer was 61.4±6μm.

[0067] Figure 2 It can be seen that after the diffusion homogenization treatment, FeB is completely dissolved to obtain a uniform Fe2B phase. The light gray ones are all Fe2B. The outermost surface contains some boride particles that have not been cleaned up. They can be regarded as foreign matter or dirt in this field of view, not a phase structure.

[0068] Figure 3 As can be seen in the figure, 900-8B-1000-4DA was borided at 900℃ for 8 hours, followed by air cooling and then a diffusion homogenization treatment at 1000℃ for 4 hours. 900-4B-1000-6DA was borided at 900℃ for 4 hours, followed by air cooling and then a diffusion homogenization treatment at 1000℃ for 6 hours. 900-8B-1000-6DA was borided at 900℃ for 8 hours, air cooled, and then a diffusion homogenization treatment at 1000℃ for 6 hours. The XRD phase analysis of the three samples is shown in the overall image and the enlarged detail on the right. It can be seen that the borided layer of 900-8B-1000-4DA is Fe2B phase. Therefore, for the borided sample at 900℃ for 8 hours, the optimal diffusion condition is 1000℃ for 4 hours, which just achieves a complete Fe2B phase.

[0069] Figure 4 The Vickers hardness distribution diagram from the surface to the middle, Figure 4 It can be seen that the hardness gradually decreases with increasing depth; when it reaches a depth of 50μm, the hardness is 587HV 0.5; When the depth reaches 100μm, the hardness is 488HV 0.5 ; When the depth reaches 150μm, the hardness is 460HV 0.5 When the depth reaches 200μm, the hardness is 350HV 0.5 ;

[0070] The surface hardness of the powder metallurgy iron-based parts with improved tensile properties prepared in this embodiment is 1440±5HV 0.5 , surface porosity ≤8%, surface roughness Ra ≤ 1.5μm, yield strength 133.1MPa, tensile strength 194.8MPa, yield strength ratio 0.683, elongation 12.40%, and strength-ductility product 2.416GPa·%.

[0071] from Figure 5 It can be seen that the room temperature tensile properties of the original sample are yield strength of 148.3±2MPa, tensile strength of 194.7±2MPa, and elongation of 0.32±0.10%.

[0072] After boriding at 900℃ for 8h, the yield strength increased to 288.8±2MPa, the tensile strength was 376.9±2MPa, and the elongation was 3.89±0.15%.

[0073] After boronizing at 900℃ for 6h and then diffusion at 1000℃ for 4h, its yield strength is 133.1±2MPa, tensile strength is 194.27±2MPa, and elongation is 9.20±0.15%.

[0074] After boronizing for 900-4h, diffusion was performed at 1000℃ for 4h. The elongation increased from 0.32%±0.10% to 12.4±0.10%. The elongation increased significantly, but the tensile strength decreased slightly to 165.7±2MPa.

[0075] In the surface boronized layer of the powder metallurgy iron-based part with improved tensile properties prepared in this embodiment, the Fe2B is serrated and embedded in the matrix, with a thickness of about 50 μm and a relatively uniform distribution.

[0076] Example 2

[0077] A method for preparing a powder metallurgy iron-based part to improve tensile properties, the method comprising the following steps:

[0078] S1. Sample processing: The alloy composition of the powder metallurgy iron-based part sample is C 0.71wt.%, Cu 2.0wt.%, and the remainder is Fe. Clean the oil stains on the surface of the powder metallurgy iron-based part sample, and grind and polish the sample surface to obtain a smooth surface iron-based part sample; the surface roughness of the smooth iron-based part sample is Ra ≤ 2μm;

[0079] S2. Initial powder coating of the sample surface: 1-3 μm industrial pure B powder is used to cover the surface of the smooth iron-based part sample in S1. The B powder coating thickness is about 3-5 mm. The sample is then coated and compacted with tantalum foil. The thickness of the tantalum foil is 0.10 mm and the compaction pressure is 200 MPa. The iron-based part sample coated with B powder is obtained.

[0080] S3. Preparation of the boronized layer on the sample surface: The iron-based part sample coated with the B powder of S2 was placed in a tube furnace, hydrogen was introduced to prevent oxidation, and the sample was heated and kept warm at a heating rate of 5°C / min to a temperature of 900°C. The temperature was kept warm for 4 hours to obtain an iron-based part sample with a surface boronized layer. The thickness of the surface boronized layer was 30±8μm.

[0081] The surface hardness of the iron-based part sample with a surface boronized layer is 1440±5HV 0.5 , the surface porosity is about 8%, the surface roughness is 1.5μm, the yield strength is 275MPa, the tensile strength is 375MPa, the yield strength ratio is 0.734, the elongation is 3.0%, and the strength-ductility product is 1.13GPa·%;

[0082] In the surface boronized layer of the iron-based part sample with a surface boronized layer, Fe2B is distributed in a zigzag shape, closely combined with the matrix, and has a thickness of about 15±3μm;

[0083] S4. Diffusion treatment of samples: The iron-based part samples with a surface boronized layer in S3 were cleaned to remove the remaining boron powder, and then subjected to diffusion heat treatment. The heating rate of the diffusion heat treatment was 5°C / min, and the temperature was heated to 950°C for 4 hours. After that, the samples were air-cooled to room temperature to obtain powder metallurgy iron-based parts with improved tensile properties. The thickness of the surface boronized layer was 65.4±6μm.

[0084] The surface hardness of the powder metallurgy iron-based parts with improved tensile properties prepared in this embodiment is 1250±5HV 0.5 , surface porosity ≤8%, surface roughness Ra ≤ 1.5μm, yield strength 146.1MPa, tensile strength 204.8MPa, yield strength ratio 0.713, elongation 8.8%, and strength-ductility product 1.802GPa·%.

[0085] In the surface boronized layer of the powder metallurgy iron-based part with improved tensile properties prepared in this embodiment, the Fe2B is serrated and embedded in the matrix, with a thickness of about 60 μm and a relatively uniform distribution.

[0086] Example 3

[0087] A method for preparing a powder metallurgy iron-based part to improve tensile properties, the method comprising the following steps:

[0088] S1. Sample processing: The alloy composition of the powder metallurgy iron-based part sample is C 0.50wt.%, Cu 1.50wt.%, Ni 1.75wt.%, Mo 0.50wt.%, Mn 0.13wt.%, and the remainder is Fe. Clean the oil stains on the surface of the powder metallurgy iron-based part sample, and grind and polish the sample surface to obtain a smooth surface iron-based part sample; the surface roughness of the smooth surface iron-based part sample is Ra ≤ 2μm;

[0089] S2. Initial powder coating of the sample surface: 1-3 μm industrial pure B powder is used to cover the surface of the smooth iron-based part sample in S1. The B powder coating thickness is about 3-5 mm. The sample is then coated and compacted with tantalum foil. The thickness of the tantalum foil is 0.10 mm and the compaction pressure is 200 MPa. The iron-based part sample coated with B powder is obtained.

[0090] S3. Preparation of the boronized layer on the sample surface: The iron-based part sample coated with the B powder of S2 was placed in a tube furnace, hydrogen was introduced to prevent oxidation, and the sample was heated and kept warm at a heating rate of 5°C / min to a temperature of 900°C. The temperature was kept warm for 4 hours to obtain an iron-based part sample with a surface boronized layer. The thickness of the surface boronized layer was 30±8μm.

[0091] The surface hardness of the iron-based part sample with a surface boronized layer is 1440±5HV 0.5 , the surface porosity is about 8%, the surface roughness is 1.5μm, the yield strength is 275MPa, the tensile strength is 375MPa, the yield strength ratio is 0.734, the elongation is 3.0%, and the strength-ductility product is 1.13GPa·%;

[0092] In the surface boronized layer of the iron-based part sample with a surface boronized layer, the Fe2B is distributed in a zigzag shape, is closely integrated with the matrix, and has a thickness of about 15±3μm;

[0093] S4. Diffusion treatment of samples: The iron-based part samples with a surface boronized layer in S3 were cleaned to remove the remaining boron powder, and then subjected to diffusion heat treatment. The heating rate of the diffusion heat treatment was 5°C / min, and the temperature was heated to 900°C for 6 hours. After that, the samples were air-cooled to room temperature to obtain powder metallurgy iron-based parts with improved tensile properties. The thickness of the surface boronized layer was 60.2±2μm.

[0094] The surface hardness of the powder metallurgy iron-based parts with improved tensile properties prepared in this embodiment is 1182±8HV 0.5 , surface porosity ≤8%, surface roughness Ra ≤ 1.5μm, yield strength 165.5MPa, tensile strength 188.8MPa, yield strength ratio 0.877, elongation 9.90%, and strength-ductility product 1.869GPa·%.

[0095] In the surface boronized layer of the powder metallurgy iron-based part with improved tensile properties prepared in this embodiment, the Fe2B is serrated and embedded in the matrix, with a thickness of about 68 μm and a relatively uniform distribution.

[0096] Example 4

[0097] A method for preparing a powder metallurgy iron-based part to improve tensile properties, the method comprising the following steps:

[0098] S1. Sample processing: The alloy composition of the powder metallurgy iron-based part sample is C 0.73wt.%, Cu 2.07wt.%, Ni 1.75wt.%, Mo 0.53wt.%, Mn 0.17wt.%, and the remainder is Fe. Clean the oil stains on the surface of the powder metallurgy iron-based part sample, and grind and polish the sample surface to obtain a smooth surface iron-based part sample; the surface roughness of the smooth iron-based part sample is Ra ≤ 2μm;

[0099] S2. Initial powder coating of the sample surface: 1-3 μm industrial pure B powder is used to cover the surface of the smooth iron-based part sample in S1. The B powder coating thickness is about 3-5 mm. The sample is then coated and compacted with tantalum foil. The thickness of the tantalum foil is 0.10 mm and the compaction pressure is 200 MPa. The iron-based part sample coated with B powder is obtained.

[0100] S3. Preparation of the boronized layer on the sample surface: The iron-based part sample coated with the B powder of S2 was placed in a tube furnace, hydrogen was introduced to prevent oxidation, and the sample was heated and kept warm at a heating rate of 5°C / min to a temperature of 900°C. The temperature was kept warm for 8 hours to obtain an iron-based part sample with a surface boronized layer. The thickness of the surface boronized layer was 30±8μm.

[0101] The surface hardness of the iron-based part sample with a surface boronized layer is 1580±5HV 0.5 , the surface porosity is about 8%, the roughness is ≤1.5μm, the yield strength is 275MPa, the tensile strength is 375MPa, the yield strength ratio is 0.73, the elongation is 4.0%, and the strength-ductility product is 1.5GPa·%;

[0102] In the surface boronized layer of the iron-based part sample with a surface boronized layer, Fe2B is distributed in a zigzag shape, closely combined with the matrix, and has a thickness of about 15±3μm;

[0103] S4. Diffusion treatment of samples: The iron-based part samples with a surface boronized layer in S3 were cleaned to remove the remaining boron powder, and then subjected to diffusion heat treatment. The heating rate of the diffusion heat treatment was 5°C / min, and the temperature was heated to 1000°C for 4 hours. After that, the samples were air-cooled to room temperature to obtain powder metallurgy iron-based parts with improved tensile properties. The thickness of the surface boronized layer was 73.5±6μm.

[0104] The surface hardness of the powder metallurgy iron-based parts with improved tensile properties prepared in this embodiment is 1182±8HV 0.5 , surface porosity ≤8%, surface roughness Ra ≤ 1.5μm, yield strength 120.3MPa, tensile strength 155.4MPa, yield strength ratio 0.774, elongation 8.05%, and strength-ductility product 1.251GPa·%.

[0105] In the surface boronized layer of the powder metallurgy iron-based part with improved tensile properties prepared in this embodiment, the Fe2B is serrated and embedded in the matrix, with a thickness of about 50 μm and a relatively uniform distribution.

[0106] Example 5

[0107] A method for preparing a powder metallurgy iron-based part to improve tensile properties, the method comprising the following steps:

[0108] S1. Sample processing: The alloy composition of the powder metallurgy iron-based part sample is C 0.72wt.%, Cu 0.98wt.%, Ni 2.44wt.%, and the remainder is Fe. Clean the oil stains on the surface of the powder metallurgy iron-based part sample, and grind and polish the sample surface to obtain a smooth surface iron-based part sample; the surface roughness of the smooth iron-based part sample is Ra ≤ 2μm;

[0109] S2. Initial powder coating of the sample surface: 1-3 μm industrial pure B powder is used to cover the surface of the smooth iron-based part sample in S1. The B powder coating thickness is about 3-5 mm. The sample is then coated and compacted with tantalum foil. The thickness of the tantalum foil is 0.10 mm and the compaction pressure is 200 MPa. The iron-based part sample coated with B powder is obtained.

[0110] S3. Preparation of the boronized layer on the sample surface: The iron-based part sample coated with the B powder of S2 was placed in a tube furnace, hydrogen was introduced to prevent oxidation, and the sample was heated and kept warm at a heating rate of 5°C / min to a temperature of 900°C. The temperature was kept warm for 8 hours to obtain an iron-based part sample with a surface boronized layer. The thickness of the surface boronized layer was 30±8μm.

[0111] The surface hardness of the iron-based part sample with a surface boronized layer is 1580±5HV 0.5 , the surface porosity is about 8%, the roughness is ≤1.5μm, the yield strength is 275MPa, the tensile strength is 375MPa, the yield strength ratio is 0.73, the elongation is 4.0%, and the strength-ductility product is 1.5GPa·%;

[0112] In the surface boronized layer of the iron-based part sample with a surface boronized layer, Fe2B is distributed in a zigzag shape, closely combined with the matrix, and has a thickness of about 15±3μm;

[0113] S4. Diffusion treatment of samples: The iron-based part samples with a surface boronized layer in S3 were cleaned to remove the remaining boron powder, and then subjected to diffusion heat treatment. The heating rate of the diffusion heat treatment was 5°C / min, and the temperature was heated to 1000°C for 4 hours. After that, the samples were air-cooled to room temperature to obtain powder metallurgy iron-based parts with improved tensile properties. The thickness of the surface boronized layer was 73.5±10μm.

[0114] The surface hardness of the powder metallurgy iron-based parts with improved tensile properties prepared in this embodiment is 1220±5HV 0.5 , surface porosity ≤8%, surface roughness Ra ≤ 1.5μm, yield strength of 138.1MPa, tensile strength of 204.6MPa, yield strength ratio of 0.675, elongation of 9.40%, and strength-ductility product of 1.923GPa·%.

[0115] In the surface boronized layer of the powder metallurgy iron-based part with improved tensile properties prepared in this embodiment, the Fe2B is serrated and embedded in the matrix, with a thickness of about 65 μm and a relatively uniform distribution.

[0116] Example 6

[0117] A method for preparing a powder metallurgy iron-based part to improve tensile properties, the method comprising the following steps:

[0118] S1. Sample processing: The alloy composition of the powder metallurgy iron-based part sample is C 0.81wt.%, and the rest is Fe. Clean the oil stains on the surface of the powder metallurgy iron-based part sample, and grind and polish the sample surface to obtain a smooth surface iron-based part sample. The surface roughness of the smooth surface iron-based part sample is Ra ≤ 2μm.

[0119] S2. Initial powder coating of the sample surface: 1-3 μm industrial pure B powder is used to cover the surface of the smooth iron-based part sample in S1. The B powder coating thickness is about 3-5 mm. The sample is then coated and compacted with tantalum foil. The thickness of the tantalum foil is 0.10 mm and the compaction pressure is 200 MPa. The iron-based part sample coated with B powder is obtained.

[0120] S3. Preparation of the boronized layer on the sample surface: The iron-based part sample coated with the B powder of S2 was placed in a tube furnace, hydrogen was introduced to prevent oxidation, and the sample was heated and kept warm at a heating rate of 5°C / min to a temperature of 900°C. The temperature was kept warm for 8 hours to obtain an iron-based part sample with a surface boronized layer. The thickness of the surface boronized layer was 30±8μm.

[0121] The surface hardness of the iron-based part sample with a surface boronized layer is 1580±5HV 0.5 , the surface porosity is about 8%, the roughness is ≤1.5μm, the yield strength is 275MPa, the tensile strength is 375MPa, the yield strength ratio is 0.73, the elongation is 4.0%, and the strength-ductility product is 1.5GPa·%;

[0122] In the surface boronized layer of the iron-based part sample with a surface boronized layer, Fe2B is distributed in a zigzag shape, closely combined with the matrix, and has a thickness of about 15±3μm;

[0123] S4. Diffusion treatment of samples: The iron-based part samples with a surface boronized layer in S3 were cleaned to remove the remaining boron powder, and then subjected to diffusion heat treatment. The heating rate of the diffusion heat treatment was 5°C / min, and the temperature was heated to 1000°C for 4 hours. After that, the samples were air-cooled to room temperature to obtain powder metallurgy iron-based parts with improved tensile properties. The thickness of the surface boronized layer was 72.6±4μm.

[0124] The surface hardness of the powder metallurgy iron-based parts with improved tensile properties prepared in this embodiment is 1230HV 0.5 , surface porosity ≤8%, surface roughness Ra ≤ 1.5μm, yield strength 138.1MPa, tensile strength 165.7MPa, yield strength ratio 0.833, elongation 10.20%, and strength-ductility product 1.690GPa·%.

[0125] In the surface boronized layer of the powder metallurgy iron-based part with improved tensile properties prepared in this embodiment, the Fe2B is serrated and embedded in the matrix, with a thickness of about 50 μm and a relatively uniform distribution.

[0126] Example 7

[0127] A method for preparing a powder metallurgy iron-based part to improve tensile properties, the method comprising the following steps:

[0128] S1. Sample processing: The alloy composition of the powder metallurgy iron-based part sample is C 0.73wt.%, Cu 2.01wt.%, Mo 0.45wt.%, and the remainder is Fe. Clean the oil stains on the surface of the powder metallurgy iron-based part sample, and grind and polish the sample surface to obtain a smooth surface iron-based part sample; the surface roughness of the smooth iron-based part sample is Ra ≤ 2μm;

[0129] S2. Initial powder coating of the sample surface: 1-3 μm industrial pure B powder is used to cover the surface of the smooth iron-based part sample in S1. The B powder coating thickness is about 3-5 mm. The sample is then coated and compacted with tantalum foil. The thickness of the tantalum foil is 0.10 mm and the compaction pressure is 200 MPa. The iron-based part sample coated with B powder is obtained.

[0130] S3. Preparation of the boronized layer on the sample surface: The iron-based part sample coated with the B powder of S2 was placed in a tube furnace, hydrogen was introduced to prevent oxidation, and the sample was heated and kept warm at a heating rate of 5°C / min to a temperature of 900°C. The temperature was kept warm for 8 hours to obtain an iron-based part sample with a surface boronized layer. The thickness of the surface boronized layer was 30±8μm.

[0131] The surface hardness of the iron-based part sample with a surface boronized layer is 1580±5HV 0.5 , the surface porosity is about 8%, the roughness is ≤1.5μm, the yield strength is 275MPa, the tensile strength is 375MPa, the yield strength ratio is 0.73, the elongation is 4.0%, and the strength-ductility product is 1.5GPa·%;

[0132] In the surface boronized layer of the iron-based part sample with a surface boronized layer, Fe2B is distributed in a zigzag shape, closely combined with the matrix, and has a thickness of about 15±3μm;

[0133] S4. Diffusion treatment of samples: The iron-based part samples with a surface boronized layer in S3 were cleaned to remove the remaining boron powder, and then subjected to diffusion heat treatment. The heating rate of the diffusion heat treatment was 5°C / min, and the temperature was heated to 1000°C for 6 hours. After that, the samples were air-cooled to room temperature to obtain powder metallurgy iron-based parts with improved tensile properties. The thickness of the surface boronized layer was 94.2±10μm.

[0134] The surface hardness of the powder metallurgy iron-based parts with improved tensile properties prepared in this embodiment is 1158±8HV 0.5 , surface porosity ≤8%, surface roughness Ra ≤ 1.5μm, yield strength 166.0MPa, tensile strength 208.4MPa, yield strength ratio 0.797, elongation 10.20%, and strength-ductility product 2.126GPa·%.

[0135] In the boronized layer on the surface of the powder metallurgy iron-based part with improved tensile properties prepared in this embodiment, the Fe2B is serrated and embedded in the matrix, with a thickness of about 45 μm and a relatively uniform distribution.

[0136] The above scheme, the present invention proposes a preparation method for powder metallurgy iron-based parts to improve the tensile properties, which can solve the technical problems existing in the prior art. For example, powder metallurgy iron-based parts only focus on adding boron elements to increase the surface hardness, thereby improving wear resistance, and do not pay attention to the generation of Fe2B single-phase structure and the improvement of tensile properties. In addition, the prepared surface boronized layer is either too thin or the structure distribution is uneven, and the structure is not diffused. Some only prepare a coating on the surface of the material, which cannot improve the overall tensile properties of the parts.

[0137] The preparation method of the present invention is simple, uses a single B powder as raw material instead of a composite slurry, has low production cost, and the thickness of the diffusion layer can be adjusted according to the holding time and temperature, can significantly improve the density and room temperature mechanical properties of powder metallurgy materials, and can be easily promoted to other metal material fields.

[0138] The present invention coats the sample surface with initial powder so that the infiltration B powder is evenly coated on the sample surface, effectively avoiding the problem of uneven infiltration layer.

[0139] The present invention prepares a boronized layer on the surface of a sample, so as to obtain a FeB+Fe2B double-layer boronized layer, thereby significantly improving the yield strength, tensile strength, surface hardness and wear resistance.

[0140] The present invention further improves the density of the powder metallurgy material and increases the proportion of Fe2B through diffusion treatment of the sample, thereby improving the plasticity and enhancing the comprehensive performance.

[0141] The surface hardness of the powder metallurgy iron-based parts with improved tensile properties prepared by the present invention is 1182-1230HV 0.5The surface porosity is 5%-10%, the surface roughness is 0.8-2.0μm, the yield strength is 100-130.3MPa, the tensile strength is 150-220.9MPa, the yield strength ratio is 0.452-0.869, the elongation is 7.8-12.4%, and the strength-plasticity product is 1.17-2.74GPa·%.

[0142] In summary, compared with other traditional methods, the method of the present invention can obtain a single-layer, dense Fe2B-plated layer with a thickness of 60-95μm in powder metallurgy low-alloy steel through boronizing and diffusion heat treatment, and the surface layer has few loose pores and no subsequent grinding processing is required, which can greatly improve the hardness, strength and elongation; this method is simple and easy to operate, green and environmentally friendly, low cost, short process, high efficiency, and is conducive to large-scale industrial production and promotion.

[0143] It should be understood that the term "and / or" as used herein simply describes a relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A alone, A and B together, or B alone. A and B can be singular or plural. Furthermore, the character " / " as used herein generally indicates an "or" relationship between the associated objects, but it may also indicate an "and / or" relationship. For specific understanding, please refer to the context.

[0144] In this disclosure, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" can mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or plural.

[0145] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0146] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing powder metallurgy iron-based parts to improve tensile properties, characterized in that: The preparation method of the powder metallurgy iron-based parts with improved tensile properties comprises the following steps: S1. Sample processing: clean the oil stains on the surface of the powder metallurgy iron-based parts sample, and grind and polish the sample surface to obtain a smooth surface iron-based parts sample; S2. Initial powder coating of the sample surface: B powder is used to cover the smooth surface of the iron-based part sample in S1, and it is coated and compacted with tantalum foil to obtain a B powder-coated iron-based part sample; S3. Preparation of boronized layer on sample surface: Place the iron-based part sample coated with B powder in S2 in a tube furnace, introduce hydrogen to prevent oxidation, heat and keep warm to obtain an iron-based part sample with a surface boronized layer; S4. Diffusion treatment of samples: The iron-based part samples with the surface boronized layer in S3 are cleaned to remove the remaining boron powder, and then subjected to diffusion heat treatment, and then air-cooled to room temperature to obtain powder metallurgy iron-based parts with improved tensile properties.

2. The method for preparing powder metallurgy iron-based parts with improved tensile properties according to claim 1, characterized in that: The alloy composition of the powder metallurgy iron-based parts sample in S1 is C≤0.81wt.%, Cu≤2.07wt.%, Ni≤2.44wt.%, Mo≤0.53wt.%, Mn≤0.17wt.%, P≤0.45wt.%, and the rest is Fe.

3. The method for preparing powder metallurgy iron-based parts with improved tensile properties according to claim 1, characterized in that: The surface roughness Ra of the smooth iron-based part samples in S1 is 0.8-2 μm.

4. The method for preparing powder metallurgy iron-based parts with improved tensile properties according to claim 1, characterized in that: The B powder in S2 is industrial B powder with a particle size of 1-3 μm. The B powder completely covers the powder metallurgy parts. The thickness of the B powder is about 3-5 mm. The thickness of the tantalum foil is 0.10±0.05 mm. The pressure is 200 MPa.

5. The method for preparing powder metallurgy iron-based parts with improved tensile properties according to claim 1, characterized in that: The heating rate in S3 is 5-10°C / min, the temperature is heated to 850-950°C, the holding time is 4-8h, and the thickness of the surface boronized layer is 30-160μm.

6. The method for preparing powder metallurgy iron-based parts with improved tensile properties according to claim 1, characterized in that: The surface hardness of the iron-based parts sample with the surface boronized layer in S3 is 1440-1600HV 0.5 The surface porosity is 5%-20%, the surface roughness is 0.8-3.0μm, the yield strength is 265-300MPa, the tensile strength is 265-380MPa, the elongation is 2.3-4.5%, and the strength-plasticity product is 0.61-1.71GPa·%.

7. The method for preparing powder metallurgy iron-based parts with improved tensile properties according to claim 1, characterized in that: In the surface boronized layer of the iron-based part sample S3 with a surface boronized layer, the shape of Fe2B is zigzag distributed, with a thickness of about 15-60μm, distributed in the subsurface layer, and grows closely with the matrix.

8. The method for preparing powder metallurgy iron-based parts with improved tensile properties according to claim 1, characterized in that: The heating rate of the diffusion heat treatment in S4 is 5°C / min, the temperature is heated to 950-1000°C, the holding time is 2-4h, and the thickness of the surface boronized layer is 60-95μm.

9. The method for preparing powder metallurgy iron-based parts with improved tensile properties according to claim 1, characterized in that: The surface hardness of the powder metallurgy iron-based parts with improved tensile properties in S4 is 1182-1230HV 0.5 The surface porosity is 5%-10%, the surface roughness is 0.8-2.0μm, the yield strength is 100-130.3MPa, the tensile strength is 150-220.9MPa, the yield strength ratio is 0.452-0.869, the elongation is 7.8-12.4%, and the strength-plasticity product is 1.17-2.74GPa·%.

10. The method for preparing powder metallurgy iron-based parts with improved tensile properties according to claim 1, characterized in that: In the surface boronized layer of the powder metallurgy iron-based parts in S4 that improves tensile properties, the Fe2B has a serrated shape, a thickness of about 40-70 μm, and is relatively evenly distributed on the surface.

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