CN112974801A

CN112974801A - Preparation method of powder metallurgy part

Info

Publication number: CN112974801A
Application number: CN202110158592.XA
Authority: CN
Inventors: 包崇玺; 王佳峰; 曹红斌
Original assignee: Mbtm New Materials Group Co ltd
Current assignee: Mbtm New Materials Group Co ltd; NBTM New Materials Group Co Ltd
Priority date: 2021-02-04
Filing date: 2021-02-04
Publication date: 2021-06-18

Abstract

The invention relates to a preparation method of a powder metallurgy part, which is characterized by comprising the following steps: the method comprises the following steps: designing material components, pressing, sintering, annealing, ultrasonic end face densification and heat treatment. The preparation method of the powder metallurgy part realizes the effect on the axial surfaceCompared with the traditional powder metallurgy process, the densification treatment has higher density of the product, and the local density can exceed 7.60g/cm³Close to the level of powder forging, and the surface relative density can reach more than 99 percent, and the surface densification is basically realized.

Description

Preparation method of powder metallurgy part

Technical Field

The invention belongs to the field of powder metallurgy, and particularly relates to a preparation method of a powder metallurgy part.

Background

Powder metallurgy is the technical discipline of manufacturing metal powders and of manufacturing materials or articles starting from metal powders (including the incorporation of non-metal powders) in the basic process of shaping and sintering. In a broad sense, it also includes a technique of producing a material or a product by a form-sintering method using a powder of a non-metallic compound such as an oxide, a nitride, or a carbide as a raw material. The powder metallurgy process is a technological process of adding raw material powder into a certain die cavity, then pressing and forming, and sintering under a certain condition or sintering in a specific die to obtain a product. With the development of industry, powder metallurgy is a technology capable of manufacturing parts with complex shapes, can save raw materials, save energy and labor, and is suitable for mass production.

Powder metallurgy is an efficient process for producing parts of high strength and complex shape. At present, iron-based parts can be produced by powder metallurgy process through high-compressibility powder, forming, sintering and special post-processing, and the density of the iron-based parts exceeds 7.4g/cm³The parts of (1). For more than 7.6g/cm³The current major manufacturing techniques include injection molding, powder forging. The density level of the re-pressing and re-sintering technology is approximately 7.4 to 7.6g/cm³In the meantime. In addition, there are surface densification techniques in which the tooth-shaped part is rolled (rolled) laterally to achieve local densification of the gear surface.

Powder metallurgy parts tend to have poorer surface contact fatigue strength than cast-rolled steel due to the presence of pores. By the surface densification treatment, the surface with which the teeth are in contact is almost fully densified. The dimensional accuracy of the gear can be further improved by surface densification. The surface densification depth exceeds 0.7mm, and the surface contact fatigue strength of the gear can be greatly improved. In addition, the surface roughness of the gears meets the "mirror" criterion, with the result that the gears run quietly less. After proper heat treatment, the bending fatigue strength and the contact fatigue strength of the gear with no pore on the surface completely reach the level of 8620 carburizing steel. The process of manufacturing the helical gear comprises the following steps: molding (high density), sintering (control of cooling rate), machining, surface densification, heat treatment (control of heat treatment deformation).

The advantages of surface densification are as follows: the tooth part has no pore; a good surface; the wear resistance is increased; noise is reduced; the corrosion resistance is improved; the gear has high dimensional precision; the fatigue characteristics of the parts are improved. However, the surface densification technique is only suitable for a few parts such as external gears, and the application range is limited. In addition, in the case of a part having a carbon content of more than 0.3%, rolling (densification) of the surface is difficult due to high hardness, and the surface density is difficult to increase.

The above techniques all have certain limitations. The density of the primary molding sintering is difficult to increase due to the influence of light raw materials such as lubricant and graphite. For the injection molding process, it is only suitable for the parts with complex shapes, and the cost performance is too poor for the parts with simple shapes and larger sizes. The precision of powder forging is lower, and the die loss is larger. For the re-pressing and re-sintering process, the product density is 7.4-7.6 g/cm³In the meantime. In order to avoid or slow down the diffusion of carbon, more ferrite is reserved, the pre-sintering temperature is usually about 780-850 ℃, the diffusion of carbon is increased along with the increase of the pre-sintering temperature, and the proportion of structures such as pearlite is obviously increased. As the pearlite content increases, the pressure of the repressing increases, and the die loss also increases.

For example, chinese patent No. ZL201410156417.7 (publication No. CN105014077B) of "method for manufacturing powder metallurgy gear and sprocket" of the present applicant's prior application discloses a method for manufacturing powder metallurgy gear and sprocket, and proposes a method for realizing densification of tooth portions or other portions by optimizing a die and changing the dimension in the diameter direction. However, the above-mentioned production method is mainly directed to a portion having a high requirement for radial strength, and cannot achieve surface densification in the axial direction (end face).

Therefore, further improvements to existing methods of making powder metallurgy parts are needed.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a method for preparing a powder metallurgy part, which aims to realize surface densification in the axial direction so as to achieve the purpose of improving hardness, aiming at the current situation of the prior art.

The technical scheme adopted by the invention for solving the technical problems is as follows: the preparation method of the powder metallurgy part is characterized by sequentially comprising the following steps of:

1) designing the components of the material: mixing carbon, iron, chromium, molybdenum, copper and nickel into mixed powder according to the following mass percent, wherein the mixed powder comprises the following components in percentage by mass: carbon: 0.1-1.5%, copper: 0-4%, nickel: 0-5%, molybdenum: 0-2%, chromium: 0.0 to 6%, not more than 2% of unavoidable impurities, 0.1 to 1% of a lubricant, iron: the balance;

2) pressing: pressing the mixed powder in the step 1) into a powder with the density of 6.6-7.4 g/cm³The green body of the powder metallurgy part has the pressing pressure of more than 400 MPa;

3) and (3) sintering: sintering the green body obtained in the step 2) at the temperature of 1000-1350 ℃;

4) ultrasonic end face densification: carrying out ultrasonic impact densification treatment on the axial end face of the part, wherein the average diameter of shot used for impact is 0.2-15 mm, and the impact time is 1-500 s;

5) and (3) heat treatment: and (3) carrying out heat treatment on the densified part in the step 4).

Preferably, in the step 1), chromium, molybdenum, copper and nickel are added in the form of iron alloy or master alloy, carbon is added in the form of graphite, and then 0.1-1% of lubricant by mass percent is added.

In order to machine the surface of the asperities to a certain flatness after impact, the densified regions are machined between step 4) and step 5).

And annealing the sintered part in a non-oxidizing atmosphere between the step 3) and the step 4). Wherein, for the powder metallurgy parts with the carbon content of less than 0.5 percent and the molybdenum, chromium and other alloy content of less than 2 percent and the powder metallurgy parts with low requirement on densification depth, annealing treatment is not required between the step 3) and the step 4).

Preferably, in step 4), the pellet is one of a round steel wire cut pellet, a bearing steel pellet and a tungsten carbon pellet.

In order to improve the roughness of the densified surface, in step 4) the densification is first carried out using pellets with a diameter d1 and then using pellets with a diameter d2, where d1 > d 2.

Preferably, in the step 4), the annealing temperature is 750-1080 ℃, the annealing heat preservation time is 5-200 min, and cooling is carried out at a cooling speed of less than 1.5 ℃/S between the annealing temperature and 300 ℃ after annealing. The annealing temperature is greater than the austenite temperature of the material for which it is designed. The yield strength of the annealed material is reduced, so that plastic deformation and densification are facilitated. Therefore, the annealing cooling speed is too high, so that the yield strength is too high, the plastic deformation is not facilitated, and the densification is not facilitated; and if the annealing cooling speed is too slow, the annealing time is longer, which is not beneficial to mass production, so the cooling speed is kept to be less than 1.5 ℃/S.

Preferably, in the step 3), the sintering time is 5-180 min, and the sintering atmosphere is vacuum or a mixed gas of nitrogen and hydrogen is adopted, wherein the nitrogen: the volume ratio of the hydrogen is 1-75%.

Specifically, in the step 6), the quenching temperature is 750-1250 ℃, the heat preservation time is 30-45 min, the tempering temperature is 150-600 ℃, and the heat preservation time is 5-200 min. The quenching temperature can ensure that the material and the part are fully austenitized, the crystal grains are fine, and the tissues of overheating or overburning are not generated. If the heat preservation time is too short and is less than 5min, insufficient austenitizing and nonuniform temperature can occur; if the heat preservation time is too long, for example, more than 200min, the problems of coarse grains and low efficiency can occur; if the tempering temperature is too low, for example, lower than 150 ℃, the problems of insufficient tempering and increased brittleness of parts can occur; the tempering temperature is too high, such as higher than 600 ℃, the martensite structure of the part is decomposed, the hardness is reduced, the strength is reduced, and the like; if the tempering heat preservation time is too low, the problem of insufficient tempering may occur, the brittleness is increased, and if the tempering heat preservation time is too long, the efficiency is reduced.

Preferably, the depth of the hardened layer of the part with the carbon content of more than 0.4% after sintering after heat treatment is 0.2-5 mm. Because the depth of the hardened layer is too shallow, the support is insufficient, and the strength is lower; if the depth is too deep, the brittleness of the material is increased, and the perfect matching of the strength and the toughness is not realized, so that the adoption of the depth of the hardening layer is beneficial to ensuring that the part has enough support, the material strength is higher, and meanwhile, the material has higher impact toughness.

Specifically, the part is one of an iron-based part, an aluminum-based part, a titanium-based part, a copper-based part, a nickel-based part and a cobalt-based part.

Compared with the prior art, the invention has the advantages that: the preparation method of the powder metallurgy part realizes densification treatment on the axial surface, and compared with the traditional powder metallurgy process, the density of the product is higher, and the local density can exceed 7.60g/cm³The surface relative density can reach more than 99 percent and basically realizes surface densification; the manufacturing process of the preparation method is simple, the occupied space of the equipment is small, only a simple tool is needed without a die, the densification depth is uniform, burrs are avoided, the problem that the die is easy to crack due to high temperature in the forging process is effectively solved, the problem of die abrasion in the extrusion densification process is solved, the production cost is reduced, and the production efficiency is improved.

Drawings

FIG. 1 is a schematic view of ultrasonic densification of a powder metallurgy part according to a first embodiment;

FIG. 2 is a graph showing the effect of densification in example two;

FIG. 3 is a graph showing the effect of the third densification of the example;

FIG. 4 is a graph showing the effects of the sixth densification of the example;

FIG. 5 is the graph showing the effect of eight densification in the example

FIG. 6 is a graph showing the effect of the ninth embodiment on densification;

FIG. 7 is a graph showing the effect of ten densification effects of the example.

Detailed Description

The invention is described in further detail below with reference to the accompanying examples.

The first embodiment is as follows:

1) preparing raw materials, and adopting sintered steel, such as mixed powder of iron, copper and carbon, wherein the mixture ratio is as follows: atomized iron powder accounts for 96.8 percent, carbon accounts for 0.70 percent and copper powder accounts for 2 percent, and then 0.5 percent of lubricant is added;

2) pressing the mixed powder under 600MPa to obtain a powder with a density of 7.10g/cm³The powder metallurgy part green compact of (1);

3) and (3) sintering: sintering the powder metallurgy part at the sintering temperature of 1200 ℃ for 20 minutes in a vacuum sintering furnace;

4) annealing: annealing the sintered part in the step 3) in a non-oxidizing atmosphere at 750 ℃ for 5 min;

5) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The surface roughness Ra after densification was 1.1 μm, the hardness of the densified regions was 93HRB, the hardness of the undensified regions (before densification) was 77HRB, and the surface roughness Ra was 0.6 μm, after 60s of impact with a bearing steel shot having a diameter of 4mm and then 60s of impact with a bearing steel shot having a diameter of 2 mm. It can be seen that the hardness is significantly increased after ultrasonic densification.

6) And (3) heat treatment: and (3) carrying out heat treatment on the parts densified in the step 5), wherein the quenching temperature is 750 ℃, the heat preservation time is 30min, the tempering temperature is 150 ℃, and the heat preservation time is 60 min.

As shown in fig. 1, the ultrasonic impact peening apparatus of the present embodiment includes a variable amplitude vibration rod 4, a transducer 5, a joint 3, a shot bin 2 and a power supply 6 for supplying power to the transducer 5, the transducer 5 is located on a support, the lower end of the variable amplitude vibration rod 4 is connected to the transducer 5, the joint 3 is installed at the upper end of the variable amplitude vibration rod 4, and the shot bin 2 with an open upper end is arranged above the joint 3, when the part 1 needs to be peened, the part 1 is placed on the shot bin 2 and is open towards the upper end of the shot bin 2, and the working principle of the ultrasonic impact peening apparatus of patent No. CN201621053252.1 (publication No. CN205990431U) is referred to, and details will not be repeated in this embodiment.

Example two:

1) preparing raw materials, and adopting sintered steel, such as mixed powder of iron, copper and carbon, wherein the mixture ratio is as follows: the atomized iron powder is 96.8%; 0.70% of carbon and 2% of copper powder, and then adding 0.5% of lubricant;

3) and (3) sintering: sintering the powder metallurgy part at the temperature of 1120 ℃ for 25 minutes in a vacuum sintering furnace;

4) annealing: annealing the sintered part in the step 3) in a non-oxidizing atmosphere at 1000 ℃ for 60 min;

5) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The surface was densified to a depth of 250 μm by first blasting with a 3mm diameter bearing steel shot for 120s and then with a 2mm diameter bearing steel shot for 60s, with a surface roughness Ra of 1.3 μm after densification, a hardness of 95HRB in the densified regions and a hardness of 76HRB in the undensified (pre-densification) regions, and a surface roughness of 0.6 μm. Wherein the densified region has a pore distribution as shown in figure 2.

6) And (3) heat treatment: and (3) carrying out heat treatment on the parts densified in the step 5), wherein the quenching temperature is 850 ℃, the heat preservation time is 45min, the tempering temperature is 600 ℃, and the heat preservation time is 5 min.

Example three:

1) preparing raw materials, namely mixed powder of iron, copper and carbon, wherein the mixture ratio is as follows: the atomized iron powder is 96.8%; 0.70% of carbon and 2% of copper powder, and then adding 0.5% of lubricant;

3) and (3) sintering: sintering the powder metallurgy part at the temperature of 1120 ℃ for 25 minutes in a mesh belt sintering furnace;

4) annealing: annealing the sintered part in the step 3) in a non-oxidizing atmosphere at 950 ℃ for 200 min;

5) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The densification was carried out for 120s with a 4mm diameter bearing steel shot with a densification depth of 320 μm, a surface roughness Ra of 1.5 μm after densification and a hardness of 100HRB in the densified regions, while a hardness of 76HRB in the undensified regions (before densification) and a surface roughness of 0.6. mu.m. The densified region pore distribution is shown in figure 3.

6) And (3) heat treatment: and (3) carrying out heat treatment on the parts densified in the step 5), wherein the quenching temperature is 900 ℃, the heat preservation time is 40min, the tempering temperature is 300 ℃, and the heat preservation time is 200 min.

Example four:

1) preparing raw materials, namely mixed powder of iron, nickel and carbon, wherein the mixture ratio is as follows: the atomized iron powder is 96.8%; 0.70% of carbon and 2% of nickel powder, and then adding a lubricant with the content of 0.5%;

2) pressing the mixed powder under 700MPa to obtain a powder with a density of 7.20g/cm³The powder metallurgy part green compact of (1);

4) annealing: annealing the sintered part in the step 3) in a non-oxidizing atmosphere at 1080 ℃ for 60 min;

5) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The surface roughness Ra of the densified steel sheet was 1.2 μm, the hardness of the densified region was 94HRB, the hardness of the undensified region was 74HRB, and the surface roughness Ra of the undensified region was 0.6 μm, after densification, the steel sheet was impacted with a bearing steel shot having a diameter of 4mm for 60s and then with a bearing steel shot having a diameter of 2mm for 60 s.

6) And (3) heat treatment: and (3) carrying out heat treatment on the parts densified in the step 5), wherein the quenching temperature is 1050 ℃, the heat preservation time is 40min, the tempering temperature is 300 ℃, and the heat preservation time is 200 min.

Example five:

3) and (3) sintering: sintering the powder metallurgy part at 1200 ℃ for 25 minutes in a push rod sintering furnace;

5) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The surface roughness Ra of the densified steel sheet was 1.2 μm, the hardness of the densified region was 93HRB, the hardness of the undensified region was 74HRB, and the surface roughness Ra of the undensified region was 0.6 μm, after densification, the steel sheet was impacted with a 2mm diameter bearing steel shot for 120s and then with a 2mm diameter bearing steel shot for 60 s.

6) And (3) heat treatment: and (3) carrying out heat treatment on the parts densified in the step 5), wherein the quenching temperature is 950 ℃, the heat preservation time is 40min, the tempering temperature is 300 ℃, and the heat preservation time is 200 min.

Example six:

4) annealing: annealing the sintered part in the step 3) in a non-oxidizing atmosphere at 800 ℃ for 80 min;

5) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The surface roughness Ra after densification was 1.6 μm, the densification depth was 330 μm, the hardness of the densified regions was 100HRB, and the hardness of the undensified regions was 75HRB, with a surface roughness Ra of 0.6 μm, with 120s impact with a 4mm diameter bearing steel shot. Wherein the densified region has a pore distribution as shown in figure 4.

Example seven:

1) preparing raw materials, namely mixed powder of iron, copper and carbon, wherein the mixture ratio is as follows: the atomized iron powder is 97.2%; 0.30% of carbon and 2% of copper powder, and then adding 0.5% of lubricant;

2) pressing the mixed powder under 600MPa to obtain a powder with a density of 7.00g/cm³The powder metallurgy part green compact of (1);

4) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The bearing steel shot with the diameter of 4mm is firstly used for impacting for 60s, and then the bearing steel shot with the diameter of 2mm is used for impacting for 60s, the surface roughness Ra1.6 mu m after densification, the hardness of a densified area is 97HRB, the hardness of an undensified area is 60HRB, and the surface roughness Ra is 0.6 mu m. .

5) And (3) heat treatment: and (3) performing carburizing heat treatment on the parts densified in the step 5), wherein the quenching temperature is 880 ℃, the heat preservation time is 40min, the tempering temperature is 300 ℃, and the heat preservation time is 200 min.

Example eight:

4) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The surface roughness Ra of the densified steel sheet was 1.5 μm, the depth of the densified region was 290 μm, the hardness of the densified region was 83HRB, the hardness of the undensified region was 60HRB, and the surface roughness Ra of the undensified region was 0.6 μm. Wherein the densified region has a pore distribution as shown in figure 5.

5) And (3) heat treatment: and (3) carrying out heat treatment on the parts densified in the step 5), wherein the quenching temperature is 880 ℃, the heat preservation time is 40min, the tempering temperature is 300 ℃, and the heat preservation time is 200 min.

Example nine:

5) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The surface roughness Ra after densification was 1.6 μm, the depth of the densified region was 390 μm, the hardness of the densified region was 94HRB, and the hardness of the undensified region was 60HRB, the surface roughness Ra being 0.6 μm, by 120s impact with a 4mm diameter bearing steel shot. The densified region pore distribution is shown in figure 6.

Example ten:

1) preparing raw materials, and adopting sintered steel, such as mixed powder of iron-nickel-copper-molybdenum partially-alloyed powder and carbon, wherein the iron-nickel-copper-molybdenum partially-alloyed powder accounts for 98.6%, and the mixture ratio of the mixed powder is as follows: 1.5 percent of copper, 1.75 percent of nickel, 0.5 percent of molybdenum, 94.85 percent of iron powder and 0.80 percent of carbon, and then adding a lubricant with the content of 0.6 percent;

5) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The surface roughness Ra after densification was 1.7 μm, the depth of the densified region was 290 μm, the hardness of the densified region was 104HRB, and the hardness of the undensified region was 88HRB, with a surface roughness Ra of 0.6 μm, by 120s impact with a 4mm diameter bearing steel shot. Wherein the densified region has a pore distribution as shown in figure 7.

Example eleven:

1) preparing raw materials, namely mixed powder of iron-nickel-copper-molybdenum partially-alloyed powder and carbon, wherein the iron-nickel-copper-molybdenum partially-alloyed powder accounts for 98.6%, and the mixed powder comprises the following components in percentage by weight: 1.5 percent of copper, 1.75 percent of nickel, 0.5 percent of molybdenum, 94.85 percent of iron powder and 0.80 percent of carbon, and then adding a lubricant with the content of 0.6 percent;

5) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The surface roughness Ra of the densified regions was 1.4 μm, the hardness of the densified regions was 105HRB, the hardness of the undensified regions was 88HRB, and the surface roughness Ra of the undensified regions was 0.6 μm, as determined by 60s blasting with a 4mm diameter bearing steel shot and 60s blasting with a 2mm diameter bearing steel shot.

Example twelve:

3) and (3) sintering: sintering the powder metallurgy part at the temperature of 1120 ℃ for 25 minutes in a mesh belt sintering furnace; wherein, nitrogen gas: the volume ratio of the hydrogen is 60 percent;

5) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. Impacting 120s by using a bearing steel shot with the diameter of 3mm, impacting 60s by using a bearing steel shot with the diameter of 2mm, wherein the surface roughness Ra is 1.1 mu m after densification, the densification depth is 290 mu m, the hardness of a densified area is 105HRB, the hardness of an undensified area is 88HRB, and the surface roughness Ra is 0.6 mu m;

6) and (3) heat treatment: and (3) carrying out heat treatment on the part densified in the step 5), wherein the quenching temperature is 950 ℃, the heat preservation time is 40min, the tempering temperature is 300 ℃, the heat preservation time is 200min, and the depth of the measured hardened layer is 0.2 mm.

Example thirteen:

1) preparing raw materials, namely mixed powder of iron-nickel-molybdenum-chromium partially-alloyed powder and carbon, wherein the iron-nickel-molybdenum-chromium partially-alloyed powder accounts for 99.8%, and the mixed powder comprises the following components in percentage by weight: 0.10% of carbon, 5% of nickel, 2% of molybdenum, 2% of chromium and 90.8% of iron, and then adding a lubricant with the content of 0.1%;

2) pressing the mixed powder under 600MPa to obtain a powder with a density of 6.6g/cm³The powder metallurgy part green compact of (1);

3) and (3) sintering: sintering the powder metallurgy part at 1250 ℃ for 5 minutes in a mesh belt sintering furnace; wherein, nitrogen gas: the volume ratio of the hydrogen is 75 percent;

4) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The surface roughness after densification was Ra1.1 μm with a bearing steel shot of 3mm diameter for 120s and then with a bearing steel shot of 2mm diameter for 60s, the densification depth was 290 μm, the hardness of the densified regions was 105HRB, the hardness of the undensified regions was 88HRB, and the surface roughness Ra was 0.6. mu.m.

5) And (3) heat treatment: and (3) carrying out heat treatment on the parts densified in the step 5), wherein the quenching temperature is 1000 ℃, the heat preservation time is 40min, the tempering temperature is 150 ℃, and the heat preservation time is 100 min. The depth of the hardened layer was measured to be 3 mm.

Example fourteen:

1) preparing raw materials, namely mixed powder of iron-copper-nickel-molybdenum-chromium partially-alloyed powder and carbon, wherein the iron-nickel-molybdenum-chromium partially-alloyed powder accounts for 97.5%, and the mixed powder comprises the following components in percentage by weight: 1.5% of carbon, 4% of copper, 5% of nickel, 2% of molybdenum, 6% of chromium and 80.5% of iron, and then adding a lubricant with the content of 1%;

2) pressing the mixed powder under 600MPa to obtain a powder with a density of 7.4g/cm³The powder metallurgy part green compact of (1);

3) and (3) sintering: sintering the powder metallurgy part at 1330 ℃ for 25 minutes in a mesh belt sintering furnace; wherein, nitrogen gas: the volume ratio of the hydrogen is 1 percent;

4) annealing: annealing the sintered part in the step 3) in a non-oxidizing atmosphere at 850 ℃ for 5 min;

5) ultrasonic end face densification: and adopting ultrasonic impact shot blasting equipment to densify the end face. The surface roughness after densification was Ra1.1 μm with a bearing steel shot of 3mm diameter for 120s and then with a bearing steel shot of 2mm diameter for 60s, the densification depth was 290 μm, the hardness of the densified regions was 105HRB, the hardness of the undensified regions was 88HRB, and the surface roughness Ra was 0.6. mu.m. The densified regions are then machined to a roughness and dimensional requirement to machine the bumpy surface to a certain flatness after impact.

6) And (3) heat treatment: and (3) carrying out heat treatment on the parts densified in the step 5), wherein the quenching temperature is 1250 ℃, the heat preservation time is 40min, the tempering temperature is 150 ℃, and the heat preservation time is 200 min. The depth of the hardened layer was measured to be 5 mm.

In summary, the sintering temperature of the above embodiment is 1120-1330 ℃.

Claims

1. The preparation method of the powder metallurgy part is characterized by sequentially comprising the following steps of:

2. The method of claim 1, wherein: in the step 1), chromium, molybdenum, copper and nickel are added in the form of iron alloy or master alloy, carbon is added in the form of graphite, and then a lubricant with the mass percent of 0.1-1% is added.

3. The method of claim 1, wherein: and annealing the sintered part in a non-oxidizing atmosphere between the step 3) and the step 4).

4. The method of claim 1, wherein: in the step 4), the pill adopts one of round steel wire cut pill, bearing steel pill and tungsten carbon pill.

5. The method of claim 1, wherein: in step 4), densification is first carried out with pellets of diameter d1 and then with pellets of diameter d2, where d1 > d 2.

6. The production method according to claim 3, characterized in that: the annealing temperature is 750-1080 ℃, the annealing heat preservation time is 5-200 min, and cooling is carried out at the cooling speed of less than 1.5 ℃/S between the annealing temperature and 300 ℃ after annealing.

7. The method of claim 1, wherein: in the step 3), the sintering time is 5-180 min, and the sintering atmosphere is vacuum or mixed gas of nitrogen and hydrogen is adopted, wherein the nitrogen: the volume ratio of the hydrogen is 1-75%.

8. The method of claim 1, wherein: in the step 5), the quenching temperature is 750-1250 ℃, the heat preservation time is 30-45 min, the tempering temperature is 150-600 ℃, and the heat preservation time is 5-200 min.

9. The method of claim 8, wherein: the depth of a hardening layer of the part with the carbon content of more than 0.4% after sintering after heat treatment is 0.2-5 mm.

10. The method of claim 1, wherein: the part is one of an iron-based part, an aluminum-based part, a titanium-based part, a copper-based part, a nickel-based part and a cobalt-based part.