Powder metallurgy bar billet and preparation method thereof

Abstract

The invention provides a powder metallurgy bar blank and a preparation method thereof, and belongs to the technical field of powder metallurgy. The preparation method of the powder metallurgy bar blank comprises the following steps that mixed powder is formed, and a pressed blank with the oval cross section is obtained; the long axis of the cross section of the pressed blank is perpendicular to the horizontal plane, half of the pressed blank is buried into sand to be sintered, and a blank is obtained; and the blank is subjected to heat treatment, and the powder metallurgy bar blank is obtained. According to the method, the pressed blank with the oval cross section is prepared in the forming process, then the long axis of the cross section of the pressed blank is perpendicular to the horizontal plane, half of the pressed blank is buried into sand to be sintered, the pressed blank can deform under the action of gravity in the sintering process, the long axis tends to the short axis, and the short axis tends to the long axis; therefore, the powder metallurgy bar billet with the circular or nearly circular cross section is obtained, the problem of deformation of the circular bar billet is solved, the product allowance design is reduced, the material utilization rate is increased, and the method has good economic benefits and wide application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy, and in particular relates to a powder metallurgy rod blank and a preparation method thereof. Background Art

[0002] In order to obtain better material properties, powder metallurgy round billets need to be fully alloyed during sintering. However, under the action of gravity, round billets often become elliptical billets, and in order to avoid excessive deformation of the billets, the sintering temperature needs to be strictly controlled. Therefore, the billet deformation problem must be considered when designing the margin, and the product margin is often designed to be large, which is not conducive to process design and enterprise cost control requirements. Therefore, how to solve the deformation problem of round billets and reduce the product margin design has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0003] The object of the present invention is to provide a powder metallurgy rod blank and a preparation method thereof. The rod blank prepared by the preparation method provided by the present invention is a round or nearly round rod blank, and the product surplus design is reduced, thereby improving the material utilization rate.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing a powder metallurgy rod blank, comprising the following steps:

[0006] (1) forming the mixed powder to obtain a compact having an elliptical cross section;

[0007] (2) burying half of the green compact obtained in step (1) in sand for sintering with the major axis of the cross section perpendicular to the horizontal plane to obtain a green compact;

[0008] (3) heat treating the blank obtained in step (2) to obtain a powder metallurgy rod blank.

[0009] Preferably, the method for preparing the mixed powder in step (1) is:

[0010] The raw material powders of each component are ball-milled and mixed to obtain mixed powder.

[0011] Preferably, the Fass particle size of the raw material powder of each component is independently 2 to 10 μm.

[0012] Preferably, the ball-to-material ratio of the ball milling mixing is (1-5):5, and the ball milling mixing time is 2-24 hours.

[0013] Preferably, in step (1), the ratio of the major axis to the minor axis of the ellipse is (1.05-1.25):1.

[0014] Preferably, the molding pressure in step (1) is 100 to 300 MPa, and the molding holding time is 30 to 300 s.

[0015] Preferably, in step (2), the sintering temperature is 1400-1600° C., and the sintering time is 20-60 min.

[0016] Preferably, the roundness value of the blank in step (2) is 0.95-1.0.

[0017] Preferably, the holding temperature of the heat treatment in step (3) is 700 to 1300° C., and the holding time of the heat treatment is 30 to 180 min.

[0018] The present invention also provides a powder metallurgy rod blank prepared by the preparation method described in the above technical solution.

[0019] The present invention provides a method for preparing a powder metallurgy rod blank, comprising the following steps: molding a mixed powder to obtain a compact with an elliptical cross section; burying half of the compact in sand for sintering with the long axis of the compact cross section perpendicular to the horizontal plane to obtain a blank; and heat treating the blank to obtain a powder metallurgy rod blank. The present invention prepares a compact with an elliptical cross section from the mixed powder during molding, and then buries half of the compact in sand for sintering with the long axis of the compact cross section perpendicular to the horizontal plane. During sintering, the compact will deform under the action of gravity, so that the long axis tends to the short axis, and the short axis tends to the long axis, thereby obtaining a powder metallurgy rod blank with a circular or nearly circular cross section, which effectively solves the problem of circular rod blank deformation, reduces product margin design, and improves material utilization. Experimental results show that the roundness value of the blank prepared by the preparation method provided by the present invention is 0.96 to 0.98. DETAILED DESCRIPTION

[0020] The present invention provides a method for preparing a powder metallurgy rod blank, comprising the following steps:

[0021] (1) forming the mixed powder to obtain a compact having an elliptical cross section;

[0022] (2) burying half of the green compact obtained in step (1) in sand for sintering with the major axis of the cross section perpendicular to the horizontal plane to obtain a green compact;

[0023] (3) heat treating the blank obtained in step (2) to obtain a powder metallurgy rod blank.

[0024] The preparation method provided by the present invention is applicable to powder metallurgy billets of any material, and is preferably applicable to tungsten powder metallurgy billets.

[0025] The invention molds the mixed powder to obtain a compact with an elliptical cross section.

[0026] The present invention has no particular limitation on the source of the mixed powder, and commercially available products known to those skilled in the art may be used.

[0027] In the present invention, the method for preparing the mixed powder is preferably:

[0028] The raw material powders of each component are ball-milled and mixed to obtain mixed powder.

[0029] In the present invention, the Fass particle size of the raw material powder of each component is independently preferably 2 to 10 μm; the ball-to-material ratio of the ball milling mixing is preferably: (1 to 5): 5; and the time of the ball milling mixing is preferably 2 to 24 hours. The present invention has no special limitation on the rotation speed of the ball milling mixing, and the operation familiar to those skilled in the art can be adopted. The present invention adopts ball milling mixing to make the raw material powders of each component mixed more uniformly.

[0030] As an implementation manner, the ball-to-material ratio of the ball milling mixing may be: (2-4):5; the ball milling mixing time may be 5-20 hours, or may be 15-18 hours.

[0031] In the present invention, the ball milling mixing is preferably carried out in a ball mill. The present invention has no particular limitation on the model of the ball mill, and any equipment well known to those skilled in the art can be used.

[0032] In the present invention, the mixed powder is preferably placed in a rubber sleeve with an elliptical cross section before molding, and then covered with an outer shell with an elliptical cross section. In the present invention, placing the mixed powder in a rubber sleeve with an elliptical cross section is conducive to processing into a compact with an elliptical cross section; in order to prevent the elliptical rubber sleeve from deforming during pressing, an outer shell with an elliptical cross section is covered.

[0033] The present invention has no special limitation on the material of the rubber sleeve, and any rubber sleeve well known to those skilled in the art can be used.

[0034] In the present invention, the material of the housing is preferably plastic or steel. The present invention has no particular limitation on the specific types of the plastic and steel, and any plastic and steel well known to those skilled in the art can be used.

[0035] In the present invention, the ratio of the major axis to the minor axis of the ellipse is preferably (1.05-1.25): 1. As an embodiment, the ratio of the major axis to the minor axis of the ellipse may be (1.10-1.20):1.

[0036] The present invention has no special limitation on the operation of loading the mixed powder into the rubber sleeve with an elliptical cross section and then putting on the outer shell with an elliptical cross section, and the operation well known to those skilled in the art can be adopted.

[0037] In the present invention, the molding is preferably cold isostatic pressing; the molding pressure is preferably 100-300 MPa; the molding holding time is preferably 30-300 s. The present invention limits the molding pressure and holding time within the above ranges to facilitate molding.

[0038] As an implementation mode, the molding pressure may be 120-240 MPa, or 150-200 MPa; the molding holding time may be 60-240 s, or 100-150 s.

[0039] After the molding is completed, the present invention preferably removes the outer shell and the rubber sleeve of the molded product in sequence to obtain a compact with an elliptical cross section.

[0040] The present invention has no special limitation on the operation of removing the outer shell and the rubber sleeve, and the operation well known to those skilled in the art can be adopted.

[0041] In the present invention, the ratio of the major axis to the minor axis of the ellipse is preferably (1.05-1.25): 1. As an embodiment, the ratio of the major axis to the minor axis of the ellipse may be (1.10-1.20): 1. The present invention limits the ratio of the major axis to the minor axis of the ellipse to the above range, which is conducive to obtaining a circular or nearly circular blank.

[0042] After obtaining a compact with an elliptical cross section, the present invention buries half of the compact in sand for sintering with the major axis of the compact cross section perpendicular to the horizontal plane to obtain a blank. The present invention buries half of the compact in sand for sintering, and during sintering, the compact will deform under the action of gravity, so that the major axis tends to the minor axis, and the minor axis tends to the major axis, thereby obtaining a powder metallurgy rod blank with a circular or nearly circular cross section, which effectively solves the problem of circular rod deformation, reduces product margin design, and improves material utilization.

[0043] In the present invention, the sand is preferably aluminum oxide or zirconium oxide. The present invention has no particular limitation on the particle size of the sand, and any sand well known to those skilled in the art can be used.

[0044] The present invention has no particular limitation on the operation of burying half of the green compact in the sand, and the operation well known to those skilled in the art may be adopted.

[0045] In the present invention, the sintering temperature is preferably 1400-1600° C. and the sintering time is preferably 20-60 min. The present invention limits the sintering temperature and time within the above ranges to enable the compact to be fully alloyed.

[0046] As an implementation mode, the sintering temperature may be 1400-1465° C., or 1445-1450° C.; the sintering time may be 30-50 min.

[0047] In the present invention, the sintering is preferably carried out in a push rod type sintering furnace. The present invention has no special limitation on the type of the push rod type sintering furnace, and any equipment well known to those skilled in the art can be used.

[0048] In the present invention, the roundness value of the blank is preferably 0.95 to 1.0. As an embodiment, the roundness value of the blank can be 0.96, 0.965 or 0.98.

[0049] After obtaining the blank, the present invention performs heat treatment on the blank to obtain a powder metallurgy rod blank.

[0050] In the present invention, the heat treatment temperature is preferably 700-1300°C; the heat treatment time is preferably 30-180 minutes. As an embodiment, the heat treatment temperature can be 800-1000°C; the heat treatment time can be 60-120 minutes.

[0051] The present invention prepares the mixed powder into a compact with an elliptical cross section during molding, and deforms it into a round or nearly round blank after sintering and alloying, which reduces the blank surplus, improves material utilization and improves the problem of round blank deformation.

[0052] At present, the rubber sleeve is a round rubber sleeve, and a round pressed blank is obtained. Theoretically, the blank should also be round. However, under the action of gravity, the blank often becomes an elliptical blank, and in order to avoid excessive deformation of the rod blank, the sintering temperature needs to be strictly controlled. Therefore, the deformation of the blank must be considered when designing the margin. A large amount of margin needs to be removed by machining, and the product margin is often designed to be large. The present invention directly prepares an elliptical pressed blank from the opposite direction. The elliptical pressed blank will deform under the action of gravity, so that the major axis tends to the minor axis, and the minor axis tends to the major axis. In this way, a round or nearly round blank is obtained. There is no need to design a large margin, and less material is removed by machining. The deformation problem of the round rod blank is effectively solved, the product margin design is reduced, and the material utilization rate is improved.

[0053] The present invention also provides a powder metallurgy rod blank prepared by the preparation method described in the above technical solution.

[0054] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Example 1

[0056] The preparation method of φ30×150mm tungsten powder metallurgy rod blank is as follows:

[0057] (1) Tungsten powder, nickel powder, iron powder, cobalt powder and manganese powder are selected as raw materials, wherein the Fischer-Strauss particle size of tungsten powder is 2.5-3.5 μm, the Fischer-Strauss particle size of nickel powder is 2.5-4.0 μm, the Fischer-Strauss particle size of iron powder is 4.5-6.5 μm, the Fischer-Strauss particle size of cobalt powder is between 1.5-2.5 μm, and the Fischer-Strauss particle size of manganese powder is 6-8 μm; the raw materials are weighted according to the ratio of W (wt%): Ni (wt%): Fe (wt%): Co (wt%): Mn (wt%) = 89.8: 7: 3: 0.15: 0.05, and are loaded into a ball mill and mixed for 5 hours to prepare a mixed powder; wherein the ball-to-material ratio is 3:5;

[0058] (2) putting the mixed powder obtained in step (1) into a rubber sleeve with an elliptical cross section, and then putting on an outer shell with an elliptical cross section, using a cold isostatic press, pressing at a pressure of 120 MPa, holding the pressure for 240 seconds, and then removing the outer shell and the rubber sleeve in turn to obtain a compact with an elliptical cross section; wherein the outer shell is a steel shell; and the ratio of the major axis to the minor axis of the ellipse is 1.2:1;

[0059] (3) with the major axis of the cross section of the green compact obtained in step (2) perpendicular to the ground, bury half of the green compact in sand and sinter in a push rod type sintering furnace at a sintering temperature of 1450° C. and a sintering time of 60 min / boat to obtain a green compact with a roundness value of 0.96; wherein the sand is alumina sand;

[0060] (4) heat treating the blank obtained in step (3) to obtain a powder metallurgy rod blank; wherein the heat treatment is carried out at a holding temperature of 1000° C. and a holding time of 60 min.

[0061] The blank prepared in Example 1 was observed to have an obvious metallic luster on its surface.

[0062] The feed in Example 1 is 2.30 kg. If the cross-section of the pressed blank in step (2) is circular, the feed is 2.50 kg. Example 1 reduces the feed by 8%.

[0063] The powder metallurgy rod blank prepared in Example 1 was subjected to mechanical property tests. The test standards were GB228, GB229 room temperature performance, d5 specimens. The test results were: tensile strength of 950 MPa, yield strength of 640 MPa, elongation of 25%, and impact toughness of 200 J / cm 2 .

[0064] Example 2

[0065] The preparation method of φ50×200mm tungsten powder metallurgy rod blank is as follows:

[0066] (1) Tungsten powder, nickel powder, iron powder, cobalt powder and manganese powder are selected as raw materials, wherein the Fischer-Strauss particle size of tungsten powder is 2.5-3.5 μm, the Fischer-Strauss particle size of nickel powder is 2.5-4.0 μm, the Fischer-Strauss particle size of iron powder is 4.5-6.5 μm, the Fischer-Strauss particle size of cobalt powder is 1.5-2.5 μm, and the Fischer-Strauss particle size of manganese powder is 6-8 μm; the raw materials are weighted according to the ratio of W (wt%): Ni (wt%): Fe (wt%): Co (wt%): Mn (wt%) = 93.5: 4.3: 2.0: 0.15: 0.05, and are loaded into a ball mill and mixed for 18 hours to prepare a mixed powder; wherein the ball-to-material ratio is 4:5;

[0067] (2) putting the mixed powder obtained in step (1) into a rubber sleeve with an elliptical cross section, and then putting on an outer shell with an elliptical cross section, using a cold isostatic press, pressing at a pressure of 200 MPa, holding the pressure for 100 seconds, and then removing the outer shell and the rubber sleeve in turn to obtain a compact with an elliptical cross section; wherein the outer shell is a steel shell; and the ratio of the major axis to the minor axis of the ellipse is 1.16:1;

[0068] (3) with the major axis of the cross section of the green compact obtained in step (2) being perpendicular to the horizontal plane, half of the green compact is buried in sand and sintered in a push rod type sintering furnace at a sintering temperature of 1465° C. and a holding time of 35 min / boat to obtain a green compact having a roundness value of 0.965; wherein the sand is zirconium oxide;

[0069] (4) heat treating the blank obtained in step (3) to obtain a powder metallurgy rod blank; wherein the heat treatment is carried out at a holding temperature of 1250° C. and a holding time of 30 min.

[0070] The blank prepared in Example 2 was observed to have an obvious metallic luster on its surface.

[0071] The feed weight in Example 2 is 8.2 kg. If the cross-section of the pressed blank in step (2) is circular, the feed weight is 8.8 kg. Example 2 reduces the feed weight by 6.82%.

[0072] The powder metallurgy rod blank prepared in Example 2 was subjected to mechanical property tests. The test standards were GB228, GB229 room temperature performance, d5 specimens. The test results were: tensile strength of 980 MPa, yield strength of 680 MPa, elongation of 20%, and impact toughness of 100 J / cm 2 .

[0073] Example 3

[0074] The preparation method of φ25×180mm tungsten powder metallurgy rod blank is as follows:

[0075] (1) Tungsten powder, nickel powder, iron powder, cobalt powder and manganese powder are selected as raw materials, wherein the Fischer-Strauss particle size of the tungsten powder is 2.5-3.5 μm, the Fischer-Strauss particle size of the nickel powder is 2.5-4.0 μm, the Fischer-Strauss particle size of the iron powder is 4.5-6.5 μm, the Fischer-Strauss particle size of the cobalt powder is 1.5-2.5 μm, and the Fischer-Strauss particle size of the manganese powder is 6-8 μm; the raw materials are weighted according to the ratio of W (wt%): Ni (wt%): Fe (wt%): Co (wt%): Mn (wt%) = 95: 3.0: 1.6: 0.35: 0.05, and are loaded into a ball mill and mixed for 20 hours to prepare a mixed powder; wherein the ball-to-material ratio is 2:5;

[0076] (2) putting the mixed powder obtained in step (1) into a rubber sleeve with an elliptical cross section, and then putting on an outer shell with an elliptical cross section, using a cold isostatic press, pressing at a pressure of 240 MPa, holding the pressure for 60 seconds, and then removing the outer shell and the rubber sleeve in turn to obtain a compact with an elliptical cross section; wherein the outer shell is a steel shell; and the ratio of the major axis to the minor axis of the ellipse is 1.1:1;

[0077] (3) with the major axis of the cross section of the green compact obtained in step (2) being perpendicular to the horizontal plane, half of the green compact is buried in sand and sintered in a push rod type sintering furnace at a sintering temperature of 1480° C. and a holding time of 25 min / boat to obtain a green compact having a roundness value of 0.98; wherein the sand is alumina;

[0078] (4) heat treating the blank obtained in step (3) to obtain a powder metallurgy rod blank; wherein the heat treatment is carried out at a holding temperature of 1000° C. and a holding time of 60 min.

[0079] The blank prepared in Example 3 was observed to have an obvious metallic luster on its surface.

[0080] The feed in Example 3 is 1.95 kg. If the cross-section of the pressed blank in step (2) is circular, the feed is 2.10 kg. Example 3 reduces the feed by 7.14%.

[0081] The powder metallurgy rod blank prepared in Example 3 was subjected to mechanical property tests. The test standards were GB228, GB229 room temperature performance, d5 specimens. The test results were: tensile strength of 1000 MPa, yield strength of 745 MPa, elongation of 12%, and impact toughness of 60 J / cm 2 .

[0082] It can be seen from the above embodiments that the powder metallurgy billet prepared by the preparation method provided by the present invention is a round or nearly round billet, and the product margin design is reduced, thereby improving material utilization.

[0083] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a powder metallurgy rod blank, comprising the following steps: (1) forming the mixed powder to obtain a compact having an elliptical cross section; (2) burying half of the green compact obtained in step (1) in sand for sintering with the major axis of the cross section perpendicular to the horizontal plane to obtain a green compact; (3) heat treating the blank obtained in step (2) to obtain a powder metallurgy rod blank.

2. The preparation method according to claim 1, characterized in that: The preparation method of the mixed powder in step (1) is: The raw material powders of each component are ball-milled and mixed to obtain mixed powder.

3. The preparation method according to claim 2, characterized in that: The Fass particle size of the raw material powder of each component is independently 2 to 10 μm.

4. The preparation method according to claim 2, characterized in that: The ball-to-material ratio of the ball milling mixing is (1-5):5, and the ball milling mixing time is 2-24 hours.

5. The preparation method according to claim 1, characterized in that: In the step (1), the ratio of the major axis to the minor axis of the ellipse is (1.05-1.25):

1.

6. The preparation method according to claim 1, characterized in that: The molding pressure in the step (1) is 100 to 300 MPa, and the molding holding time is 30 to 300 s.

7. The preparation method according to claim 1, characterized in that: In the step (2), the sintering temperature is 1400-1600° C., and the sintering time is 20-60 minutes.

8. The preparation method according to claim 1, characterized in that: The roundness value of the blank in the step (2) is 0.95-1.

0.

9. The preparation method according to claim 1, characterized in that: The heat treatment in step (3) is carried out at a holding temperature of 700 to 1300° C. and for a holding time of 30 to 180 minutes.

10. Powder metallurgy rod blank prepared by the preparation method according to any one of claims 1 to 9.