CN114427058B

CN114427058B - Hard alloy and manufacturing method thereof

Info

Publication number: CN114427058B
Application number: CN202210011110.2A
Authority: CN
Inventors: 西川昌範; 钟海彬; 林兴
Original assignee: Sichuan Shengong Tungsten Steel Tools Co ltd
Current assignee: Sichuan Shengong Tungsten Steel Tools Co ltd
Priority date: 2022-01-06
Filing date: 2022-01-06
Publication date: 2023-11-21
Anticipated expiration: 2042-01-06
Also published as: CN114427058A

Abstract

The application discloses a hard alloy, which comprises 3.2 to 4.3 weight percent of Ni according to the weight percent (wt%); 9.2 to 10.5wt% of Co;0.5 to 2.0wt% of Cr ₃ C ₂ And/or Cr; the remainder is WC; wherein the total carbon distribution ratio of the WC is 4.80-5.40wt%. The beneficial effects of the application are as follows: according to the hard alloy composition disclosed by the application, good crack resistance can be achieved, and meanwhile, the corrosion resistance is also remarkably improved. Since submicron WC powder is used, co and Ni are used as binding phase, certain solid solution amount of W in Co and Ni is maintained, corrosion resistance is improved, and Cr or Cr is added ₃ C ₂ The corrosion resistance is further improved by uniformly diffusing in the liquid phase, and the distribution state of Co and Ni in the hard alloy is inclined by adopting a special sintering method, so that the crack resistance is improved.

Description

Hard alloy and manufacturing method thereof

Technical Field

The application belongs to the field of hard alloy research and development, and particularly relates to a hard alloy with super corrosion resistance and super crack resistance, a manufacturing method and application thereof.

Background

With the increasing speed and life of forming when forming dies are used, cemented carbides capable of withstanding crack initiation and crack propagation are becoming increasingly important. Further, since some special processing environments of cemented carbide, especially EDM (electric discharge machining) process, use cutting fluid and cutting oil, the cutting fluid and cutting oil may cause corrosion of the processed cemented carbide, and at the same time, the cooling fluid used may cause corrosion of the cemented carbide.

Such corrosion is characterized by the inclusion of nanoscale abrasion resistant metal particle oxides (e.g., znO and SiO 2) in the corrosion process, which abrade the machined surface and also cause corrosion such as microcracking. The erosion damage results in binder dissolution, and reduced resistance of the machined surface to deformation and initial cracking, thus resulting in reduced life of the cemented carbide EDM (electric discharge machining) product.

It is currently a critical need in the art to extend the life of cemented carbides used in EDM (electrical discharge machining) as much as possible.

Disclosure of Invention

The application aims to solve the problem that the corrosion resistance and the crack resistance of the used hard alloy are improved simultaneously by technical means.

In order to solve the problems, the technical scheme of the application is that,

there is provided a cemented carbide, in weight% (wt%), comprising,

3.2 to 4.3wt% of Ni;

9.2 to 10.5wt% of Co;

0.5 to 2.0wt% of Cr ₃ C ₂ And/or Cr;

the remainder is WC; wherein the total carbon distribution ratio of the WC is 4.80-5.40wt%.

Further, the WC content is 83.2-87.1 wt%; preferably, the WC content is 84.8wt%.

Further, the WC average particle diameter is less than 0.7 μm; preferably, the WC average particle size after sintering is 0.6. Mu.m.

Further, the Ni content was 4.0wt%.

Further, the Cr ₃ C ₂ And/or Cr content of 1.2wt%; preferably, the Cr ₃ C ₂ The content of (2) was 1.2% by weight.

Further, the Co content was 10.0wt%.

A method for manufacturing a hard alloy, which comprises the steps of,

placing the powder composed of the above described formula, lubricant, anticoagulant and solvent into a wet ball mill for grinding to obtain a uniform mixture with 50% peak diagram reaching 0.50-0.600 miron;

granulating the mixture into spheres by spraying through a spray dryer;

the dry spherical powder is subjected to a hydraulic forming machine at a speed of about 0.8 to 1.2ton/cm ² Is pressed into a green body;

the green body is subjected to wet CIP treatment under the conditions of a pressure of 150MPa for 5 minutes, a pressure of 90MPa for 2.5 minutes and a pressure of 30MPa for 1 minute, and then sintered;

the sintering temperature is set at two stages of 370 ℃ (180 minutes) and 450 ℃ (90 minutes), 7-10L/min Ar gas is used for dewaxing, then vacuum sintering is carried out until 1350 ℃ (60 minutes), and then the temperature is kept for 1 hour from 1350 ℃ to 1420-1460 ℃ to finish;

finally, ar gas is subjected to high-pressure treatment of 3.0-5.0MPa, and the structure is naturally cooled to 800-600 ℃ after being compact;

and (3) after 800-600 ℃, a forced cooling fan is started for cooling.

Further, it is characterized in that: the lubricant is paraffin wax.

Further, it is characterized in that: the anticoagulant is folic acid.

Further, the solvent is ethanol.

The beneficial effects of the application are as follows: according to the hard alloy composition disclosed by the application, good crack resistance can be achieved, and meanwhile, the corrosion resistance is also remarkably improved. Since submicron WC powder is used, co and Ni are used as binding phase, certain solid solution amount of W in Co and Ni is maintained, corrosion resistance is improved, and Cr or Cr is added ₃ C ₂ The corrosion resistance is further improved by uniformly diffusing in the liquid phase, and the distribution state of Co and Ni in the hard alloy is inclined by adopting a special sintering method, so that the crack resistance is improved.

Drawings

FIG. 1 is a simulated binary state diagram in the practice of the present application;

FIG. 2 is a graph of elemental surface profiles of Co, cr, ni, W for various samples in the practice of the application, where 2-a is sample A, 2-B is sample B, and 2-c is an example of the application;

FIG. 3 is a graph of corrosion resistance versus pH in buffers for certain different alloys;

FIG. 4 is a comparison of the initial oxidation dead times of WC-Ni and WC-Co alloys;

fig. 5 is a view of the particle size of the tungsten carbide sintered in the present example, respectively, for A, B, C three fields of view at 7500 x-ray of the reflected electron image of the electron microscope;

FIG. 6 is a comparative graph of the acidic solution soaking test of the present example;

FIG. 7 is a view showing a partial structure of a section of each sample of the corrosion test of the present embodiment after grinding;

FIG. 8 is a graph showing the comparison of the alkaline solution corrosion test performed on each sample with a sodium hydroxide solution of pH10 in this example;

fig. 9 is a comparative graph of microcracks in secondary electron images of 700 times of the wire-cut surface after the three samples used in the present example were actually wire-cut processed;

FIG. 10 is a graph showing a comparison of microcracks of corrosion deterioration of electron microscopic images (cross sections) of a wire cut surface at 700 times magnification after the wire cut surface was actually cut with three samples used in the present example;

fig. 11 shows the results of the dynamic potential polarization scan test for samples A, B and C in this example.

Detailed Description

In order that those skilled in the art will better understand the present application, a technical solution in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present application without making any inventive effort, shall fall within the scope of the present application.

It should be noted that the terms "first," "second," and the like in the description and the claims of the present application and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the application described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Example 1

As shown in table 1, this comparative experiment includes sample A, B, C, which is a cemented carbide material composed of the formulation shown in table 1, including a powder forming a hard constituent and a powder forming a binder.

These powders were pulverized in a wet ball mill together with paraffin wax as a lubricant, folic acid as an anti-agglutinant and ethanol as a solvent, and a uniform mixture having a 50% peak pattern of 0.50 to 0.600miron was obtained by measurement with a particle size distribution instrument, and then spray-granulated into a sphere by a spray dryer.

The dried powder is subjected to a hydraulic forming machine at a speed of about 0.8 to 1.2ton/cm ² After pressing into a green body, wet CIP treatment was performed under conditions of a pressure of 150MPa for 5 minutes and a pressure of 90MPa for 2.5 minutes and a pressure of 30MPa for 1 minute, followed by sintering.

The sintering temperature is carried out at two stages of 370 ℃ and 450 ℃, vacuum sintering is carried out until 1350 ℃ after dewaxing is carried out by using 7-10L/min Ar gas, wherein the temperature is kept for about 1 hour from 1350 ℃ to 1420-1460 ℃, high-pressure treatment of argon gas of 3.0-5.0MPa is carried out after the end, the structure is densified, the structure is naturally cooled to 800-600 ℃, and a forced cooling fan is started for cooling after 800-600 ℃ to obtain the corresponding hard alloy material.

Reference symbol	A (comparison product)	B (comparison product)	C (application)
				WC	83.8	85.0	84.8
WC crystal grain size	0.8	0.8	0.6
				Ni (mass%)	5.0	4.5	4.0
Co (mass%)	10.0	9.5	10.0
				Cr ₃ C ₂ (mass%)	1.2	1.0	1.2

TABLE 1

The wettability of Co and Ni with respect to WC is θ=0° with no gap therebetween. However, at high temperatures, the solid solubility of WC in the metallic binder phase varies greatly, for example, at 1280 ℃ the WC content in the Co phase is about 3.94%, the WC content in the Ni phase is about 2.97%, and the solubility of WC in Co > the solubility of WC in Ni. But reverses to a WC content of about 1.22% in the Co phase, a WC content of about 1.43% in the Ni phase at 1100 c, the solubility of WC in Ni > the solubility of WC in Co.

As shown in the simulated binary state diagram of FIG. 1, the liquid phase appearance temperature of the WC-Co system is 1280-1330 ℃, the liquid phase appearance temperature of the WC-Ni system is 1350-1420 ℃, and the liquid phase appearance temperature of the WC-Ni system is about 70-90 ℃ higher than the liquid phase appearance temperature of the WC-Co system, so that the electrochemical corrosion resistance during high-temperature discharge processing is improved.

The greatest innovation of WC-Co-Ni-Cr cemented carbide in the application is that submicron tungsten carbide powder smaller than 0.7 μm is used, co and Ni are used as binding phase, certain solid solution amount of W in Co and Ni is kept, corrosion resistance is improved, and Cr or Cr is added ₃ C ₂ The dispersion is uniform in the liquid phase, the corrosion resistance is further improved, the distribution state of Co and Ni in the hard alloy is inclined by adopting the sintering method, and the super corrosion resistance and super crack resistance hard alloy is put into practical use.

By adding a small amount of Ni into the WC-Co alloy, the bonding stage is rapidly moved to the low carbon side; meanwhile, the C percent set during batching is 5% -10% lower than the theoretical carbon quantity, so that the solid solution quantity of W in a binding phase is obviously increased, and the corrosion resistance and the crack resistance are improved. However, if the Ni addition amount is too large in the experiment, the overall hardness is lowered. This is because increasing the amount of Ni causes the growth of high carbon alloy particles such as WC to cause coarse granulation, so the present application controls the Ni increase to 3.2 to 4.3wt%.

As shown in fig. 2, fig. 2 shows the elemental plane distribution of Co, cr, ni, W of various samples, but it can be seen that the sample C has the best uniformity of Co, ni, cr dispersion. In sample C, it can be seen that WC is solid-dissolved in Co and Ni as binder phases.

As shown in fig. 3 and 4, a WC-Co-Ni-Cr-based cemented carbide is required to have high strength and wear resistance, which are required to be corrosion-resistant and crack-resistant. Therefore, cr or Cr needs to be added ₃ C ₂ In the initial stage of oxidationAt the same time, the corrosion inhibitor can inhibit partial oxidation, and if the corrosion inhibitor has good corrosion resistance, the defects such as dry corrosion, wet corrosion and the like can not be generated on the surface. That is, the occurrence frequency of surface cracks due to stress concentration is reduced, and thus the life of the alloy is prolonged, that is, the crack resistance is improved. The experimental results revealed that the addition ratio of Co and Ni to the cemented carbide of the present application, i.e., co/ni=70/30 to 80/20, increased Co in order to maintain wear resistance.

To ensure that the experiments were accurate in these examples, powder unification was purchased from the following suppliers: co is from Nanjing Cold Sharp, ni is from Yingke, canada, cr3C2 is from Changsha Wei Hui, WC is from Xiamen's Egret, china, and W for C% adjustment is from Jiujiang Egret, china.

The physical properties of table 2 are specifications used in the cemented carbide field, i.e. density according to ISO3369:1975, hardness according to IS03878: measured in 1983. As shown in fig. 5, the grain size of the sintered tungsten carbide is an average value obtained by photographing and measuring each of A, B, C fields of view with a reflected electron image 7500 magnification of an electron microscope.

Reference symbol	A (comparison product)	B (comparison product)	C (application)
				Density (g/cm 3)	13.8-14.0	13.8-14.0	14.0-14.2
Hardness (Hv 30)	1300-1350	1340-1390	1370-1420
				Toughness (K1 c)	17.0-18.0	16.5-17.5	16.0-17.0

TABLE 2

The powder prepared by the method described in the beginning of the example and the mold for the test piece having a bending strength of 21.9×7.4×5.8mm after sintering and 21.0×6.5×5.25mm after grinding were used, and the samples for corrosion test were prepared by the molding method, CIP (cold isostatic pressing) method and sintering method described in the beginning of the example, 3 pieces were immersed in the acid solution for 72 hours, and the corrosion rate was measured. The results are shown in Table 3. Table 4 shows the results of the reproduction test.

The addition ratio of the acidic solution is as follows:

hydrochloric acid 15ml, nitric acid 5ml, water 30ml. When the increment is required, the additional production is performed at the same rate.

Corrosion Rate calculation method = { (weight before Corrosion-weight after Corrosion)/(weight before Corrosion } ×100)

TABLE 3 Table 3

To confirm reproducibility, the same test table 4 was again implemented

TABLE 4 Table 4

As shown in fig. 6, it is clear that the state of the strong acid solution was observed only in the test. In addition, fig. 7 shows that the samples subjected to the corrosion test were ground, and the cross-section was photographed, and it was confirmed that the C of the present application hardly corroded. The surface etch depths were sample a=12 μm, sample b=15 μm, sample c=0 μm.

As shown in FIG. 3, no corrosion of any of the superhard materials in the alkaline solution occurs. However, in a verification sense, the alkaline corrosion rate was confirmed by using a sodium hydroxide adjustment solution of pH 10.

The results are shown in Table 5.

TABLE 5

There is no difference in any of the materials a.b.c.

As shown in fig. 8, the results shown in table 5 are reflected in fig. 3.

As shown in fig. 9, the three samples a.b.c were actually subjected to wire-cut processing, and the secondary electron images of 700 times were amplified on the wire-cut processed surface, and microcracks caused by the wire-cut processing were observed in the samples a and B, and the lengths and widths of microcracks were greatly improved in the sample C.

As shown in fig. 10, the wire-cut surface was subjected to electron microscopic imaging (cross section) at 700 x magnification, and in the cross section observation, the wire-cut surface of sample A, B was subjected to microcracking of corrosion degradation, while the surface layer crystal structure and the internal crystal structure of sample C were kept in the same form without corrosion degradation.

Samples A, B and C were simultaneously prepared as square 6.5mm side and 2mm thick samples embedded in resin, and mirror finished using #2000 to prepare smooth surfaced samples. The dynamic potential polarization test was carried out using AMETEK VERSA SATA4 produced in the united states. ASTM G61 test was performed at room temperature by samples A, B and C,

the following changes were made. ASTM G61 specifies the procedure for dynamic potential polarization measurement. A medium with aerated HCl having an acidity of pH 2.5 was used instead of standard 3.5% NaCl solution, which is a modification point. The acidity of the medium is typical of the acidity of a cemented carbide machining line tool operation. These test bodies were washed, degreased with acetone in ultrasonic waves, dried in air, and then the samples were immersed in the solution. The test solution was stirred with a magnetic stirrer to 600rpm. The corrosion potential (Ecorr) was observed for 1 hour, and then dynamic potential scanning was performed in the positive direction. Results of dynamic potential polarization scan test for samples A, B and C shown in FIG. 11

Table 6 shows the electrochemical parameters derived from dynamic potential testing. Dynamic potential positive polarization testing methods are commonly used to locally corrode materials at their resistance levels in a defined environment. The principle of this test method is that when a positive potential is applied to a test body, decomposition of a non-dynamic film is promoted, whereby localized corrosion starts. The susceptibility to localized corrosion of a material can be assessed from the potential at which the positive current rises rapidly due to non-dynamic film corrosion of the surface, known as the break potential (Ep), by sweeping the potential in the positive direction at a constant rate. The more positive the corrosion potential, the more corrosion resistant the material. For very corrosion resistant materials, it is difficult to measure the break-down potential. In this case, the entire surface of the non-dynamic film may enter the stable passivation region. The break-out potential is defined as the first current density exceeding 0.1mA/cm during potential scanning ² Is set in the above-described range (a).

Sample of	Corrosion potential Ecorr (mV SCE)
		A	-0.0887
B	-0.0577
		C (application)	-0.0356

TABLE 6

Sample a shown in fig. 11 and table 6 lacks corrosion resistance and shows no evidence of non-dynamic and dynamic corrosion at the beginning of the potential sweep. In addition, it can be seen that the degree of corrosion of sample B was greatly improved, and a corrosion potential of 347mV (SCE) was observed. Fig. 11 and table 6 show even more that the corrosion resistance of sample C is significantly improved, and the stable passivation zone of the entire surface before the break-down potential occurs appears at a very high potential.

Those of ordinary skill in the art will recognize that the embodiments described herein are for the purpose of aiding the reader in understanding the principles of the present application and should be understood that the scope of the application is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific modifications and combinations from the teachings of the present disclosure without departing from the spirit thereof, and such modifications and combinations remain within the scope of the present disclosure.

Claims

1. A cemented carbide, characterized by:

the preparation method comprises the following steps:

3.2 to 4.3 weight percent of Ni, 9.2 to 10.5 weight percent of Co and 1.2 weight percent of Cr ₃ C ₂ And the remainder being a powder of WC composition;

crushing the mixture and lubricant, anticoagulant and solvent in a wet ball mill to obtain a uniform mixture with 50% peak diagram reaching 0.50-0.600miron, wherein the total carbon distribution ratio of WC is 4.80-5.40wt% and the average grain diameter of WC is less than 0.7 mu m;

granulating the mixture into spheres by spraying through a spray dryer;

the spherical powder is dried by using an oil press at a speed of 0.8-1.2ton/cm ² Is pressed into a green body;

the sintering temperature is set at 370 ℃ for 180 minutes and 450 ℃ for 90 minutes, 7-10L/min Ar gas is used for dewaxing, then vacuum sintering is carried out until 1350 ℃ for 60 minutes, and then the temperature is kept for 1 hour from 1350 ℃ to 1420-1460 ℃ to finish;

finally, carrying out high-pressure treatment of Ar3.0-5.0MPa, and naturally cooling to 800-600 ℃ after the structure is compact;

and (3) after 800-600 ℃, a forced cooling fan is started for cooling.

2. Cemented carbide according to claim 1, characterized in that: the WC content is 83.2-87.1 wt%.

3. Cemented carbide according to claim 2, characterized in that: the WC content was 84.8wt%.

4. Cemented carbide according to claim 1, characterized in that: the average particle size of the cemented tungsten carbide was 0.6 μm.

5. Cemented carbide according to claim 1, characterized in that: the Ni content was 4.0wt%.

6. Cemented carbide according to claim 1, characterized in that: the Co content was 10.0wt%.

7. A method of manufacturing a cemented carbide according to any one of claims 1-6, characterized by;

placing the powder, a lubricant, an anticoagulant and a solvent into a wet ball mill for crushing to obtain a uniform mixture with 50% peak diagram reaching 0.50-0.600 miron;

granulating the mixture into spheres by spraying through a spray dryer;

and (3) after 800-600 ℃, a forced cooling fan is started for cooling.

8. The method of producing cemented carbide according to claim 7, wherein: the lubricant is paraffin wax.

9. The method of producing cemented carbide according to claim 7 or 8, characterized in that: the anticoagulant is folic acid.

10. The method of producing cemented carbide according to claim 7 or 8, characterized in that: the solvent is ethanol.