CN103741000B - A kind of cobalt-rich superfine grain gradient cemented carbide and its preparation method - Google Patents

Abstract

The invention belongs to Wimet and manufacture field, be specifically related to Ultra-fine Grained gradient hard alloy of a kind of rich surface cobalt and preparation method thereof.The Ultra-fine Grained gradient hard alloy metallographic structure of rich surface cobalt of the present invention is for core hard phase with WC and Emission in Cubic carbonitride, take cobalt as the gradient layer that Binder Phase forms 10 ~ 40 μm of thick rich surface cobalts, wherein in hard phase and gradient layer, the mean sizes of WC grain is 0.2-0.4 μm, cobalt contents in the gradient layer of rich surface cobalt is 1.2-2 times of Wimet nominal cobalt contents, not containing Emission in Cubic carbonitride in the gradient layer of rich surface cobalt; First preparation method prepares burden, and wet-milling is also pressed into material base, the rare gas element of charged pressure 5 ~ 10MPa before reaching liquid phase sintering conditions, and liquid phase sintering conditions is 1350 ~ 1500 DEG C.The present invention, by being filled with the gas of certain pressure in the liquid phase sintering stage, prepares the Ultra-fine Grained gradient hard alloy of rich surface cobalt, and refinement WC grain, obtains certain thickness rich surface cobalt layers, shorten the sintering period, reduce production cost.

Description

A kind of cobalt-rich superfine grain gradient cemented carbide and its preparation method

technical field

The invention belongs to the field of cemented carbide manufacturing, and in particular relates to a cobalt-rich ultrafine-grain gradient cemented carbide and a preparation method thereof.

Background technique

Due to its high strength, hardness and good wear resistance, cemented carbide is mainly used to make cutting tools and is widely used in the field of cutting processing. In recent years, with the development of material science, more and more difficult-to-machine materials have begun to be used in many applications, so the performance of cemented carbide tools used in processing materials has been put forward higher and higher requirements, and with the modern manufacturing industry The development of the development requires that the cemented carbide tool is suitable for high-speed continuous cutting, etc., which requires the cemented carbide tool not only to have good wear resistance, but also to have good toughness and impact resistance. It is difficult to meet the requirements in terms of performance, strength and toughness. According to Hallpech's formula, the smaller the grain size, the greater the strength of the material. Therefore, it is the main development direction in the future to improve the strength of cemented carbide by refining the grain and preparing cemented carbide with ultrafine grains. For applications that require high toughness and wear resistance, cemented carbide with nano- or micro-sized grains has higher strength and can better meet actual requirements.

In order to further improve the wear resistance of cemented carbide tools, the currently used cemented carbide tools usually need to be coated with one or more layers of wear-resistant coatings on their surfaces by chemical vapor deposition (CVD) or physical vapor deposition (PVD). , such as TiN, Al ₂ O ₃ and so on. Since the temperature of this coating technology is generally above 800°C, due to the difference in thermal expansion coefficient between the coating and the substrate, a certain thermal stress will be generated between the coating and the substrate during the cooling process, and some micro Cracks, during the cutting and use of the tool, these micro-cracks will expand into the matrix, resulting in reduced tool wear resistance and chipping failure, which requires the matrix to have higher toughness. In addition, in order to improve the bonding strength between the coating and the substrate, it is also required to have better wettability between the coating and the substrate. In order to solve this problem, a cemented carbide substrate with high toughness that is rich in cobalt on the surface can be used, which is usually called a gradient cemented carbide with cobalt-rich surface. Due to the high surface toughness of the cobalt-rich gradient coating cemented carbide substrate, it can absorb the energy of crack propagation, slow down the crack propagation into the substrate, and the good wettability between the surface cobalt-rich layer and the coating, thereby improving And prolong the performance and service life of cemented carbide.

The current technology for making this gradient cemented carbide is called gradient sintering, such as US patents 4277283 and 4610931, which use nitrogen-containing additives to sinter in vacuum, while US patent 4548786 adds nitrogen to the gas phase, both of which are A surface binder-phase-rich region substantially free of cubic phases is obtained. US Patent No. 4830930 obtains a surface rich in binder phase region by decarburization after sintering. These sintering processes all adopt a two-step sintering method (pre-sintering and gradient sintering are completed in two steps), and the sintering atmosphere is nitrogen-free vacuum. The grain size of WC in gradient cemented carbide prepared by two-step sintering method is larger, the performance is lower, and the production cost is increased, which is not conducive to large-scale production.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a cobalt-rich ultrafine-grained gradient cemented carbide and a preparation method thereof. By adopting a one-step sintering method, the production process is shortened, and the production cost is reduced. The inert gas with a certain pressure is filled to suppress the growth of WC grains. On the basis of refining the WC grains of cemented carbide, an ultra-fine-grained gradient cemented carbide substrate with a cobalt-rich gradient layer on the surface is prepared.

The cobalt-rich superfine-grain gradient cemented carbide of the present invention has the following components by mass percentage: 2-6%Ti(C,N), 6-15%Co, 0-0.5%VC, 0.2-0.8%Cr ₃ C ₂ and 0-0.5% carbon black, the balance is WC, its metallographic structure is based on WC and cubic phase carbonitride as the core hard phase, and cobalt as the binder phase to form a 10-40 μm thick surface rich Gradient layer of cobalt, in which the average size of WC grains in the hard phase and gradient layer is 0.2-0.4μm, the cobalt content in the gradient layer rich in cobalt on the surface is 1.2-2 times the nominal cobalt content of the cemented carbide, the surface The cobalt-rich gradient layer does not contain cubic carbonitrides.

The preparation method of the superfine-grained gradient cemented carbide with cobalt-rich surface of the present invention is carried out according to the following steps:

(1) Cemented carbide raw materials added with carbonitrides are used for batching, and its composition is: 2-6%Ti(C,N), 6-15%Co, 0-0.5%VC, 0.2-0.8% by mass percentage Cr ₃ C ₂ and 0-0.5% carbon black, the balance is WC;

(2) After mixing the above raw materials, put them into a wet ball mill for wet grinding, let the wet-milled mixed slurry stand for 8~12 hours, then put it in a vacuum drying oven at 60~90°C for 1~2 hours, dry it with 40 Sieve through a mesh screen, press the sifted powder into a billet with a press and a mold, the pressure is 5-20 tons, and the holding time is 5-30s;

(3) Put the billet in the vacuum furnace, evacuate the vacuum furnace to below 10Pa and start to heat up, raise the temperature to 400~600°C and keep it warm for 1~6h, at the same time, pass in hydrogen for dewaxing and deoxidation, and then empty the furnace The hydrogen in the cavity continues to heat up, and it is filled with an inert gas with a pressure of 5-10 MPa before reaching the liquid-phase sintering temperature. The liquid-phase sintering temperature is 1350-1500°C, and it is kept for 0.1-2 hours under the pressure of the inert gas. After the heat preservation is completed, it is cooled with the furnace to room temperature, the cobalt-rich superfine-grain gradient cemented carbide is obtained.

Among them, the average particle size of WC powder added is 0.4 μm, the average particle size of Ti(C,N) powder is 0.2~1.5 μm, the atomic ratio of C to N is 0.5:0.5, the average particle size of Co powder is 1 μm, VC and The average particle size of the Cr ₃ C ₂ powder is less than 1 μm.

When performing wet grinding in step (2), the ball-to-material ratio is (10-15):1, the wet-grinding medium is alcohol, the rotational speed is 40-100 r/min, and the wet-milling time is 48-72 hours.

The inert gas is argon.

Compared with prior art, feature and beneficial effect of the present invention are:

The cobalt-rich ultrafine-grained cemented carbide matrix of the present invention mainly uses WC as the hard phase, its average grain size is about 0.2 μm-0.4 μm, and cobalt is used as the metal binder phase, and one or more A carbonitride solid solution, and a carbide containing V and Cr is added as a grain inhibitor. Under the one-step sintering process, the obtained surface cobalt-rich layer has a thickness of about 10 μm-40 μm, does not contain cubic carbides, and the cobalt content of the binder phase of the surface cobalt-rich layer is about 1.2-2 times the nominal binder phase content. The average grain size of the WC grains in the cobalt-rich layer on the surface and the core is about 0.3 μm. In applications that require high toughness and wear resistance, cemented carbide with nano-micron grains has higher strength, and coated tools have higher wear resistance, and gradient coatings with ultra-fine grains are prepared. Layered carbide cutting tools are of great significance for improving the performance of cemented carbide and expanding the application of cemented carbide.

Firstly, the method of the present invention includes four steps of raw material configuration, ball milling, molding and sintering. The sintering steps are followed by three stages of dewaxing and deoxidation, heating and sintering, heat preservation sintering and cooling. That is, in the one-step sintering process, the The phase sintering stage is filled with a certain pressure of gas to prepare a cobalt-rich ultra-fine-grained gradient cemented carbide, which refines the WC grains and obtains a certain thickness of the surface cobalt-rich layer, which shortens the sintering cycle and reduces production costs. ;

Since the gas with a certain pressure is filled in the liquid phase stage, the flow of the liquid phase is promoted, so that the liquid phase can fully fill the gaps between the WC powder particles in a short time, reducing the porosity of the cemented carbide and improving the hardness of the cemented carbide. The density of the alloy, thereby improving the performance of the cemented carbide; reducing the sintering temperature, can inhibit the growth of WC grains, and obtain an ultra-fine-grained cemented carbide matrix; Existence reduces the dissolution and decomposition temperature of titanium carbonitride, increases the diffusion channel of titanium carbonitride, and promotes the diffusion speed of N atoms outward and Ti atoms inward in the surface hard alloy, and liquid cobalt can quickly fill N The vacancies left after the diffusion of Ti atoms and Ti atoms are conducive to the formation of the surface cobalt-rich layer, and a thicker surface cobalt-rich gradient layer is obtained;

Secondly, the cobalt-rich surface cobalt-rich gradient cemented carbide prepared by the present invention has a high cobalt content and does not contain cubic phase, so that the cemented carbide has good surface toughness and impact resistance, which can effectively prevent extension of cracks;

Thirdly, in the cobalt-rich superfine-grain gradient cemented carbide prepared by the present invention, the grain size of the hard phase WC is small, and has high strength and wear resistance.

Description of drawings

Fig. 1 is the metallographic structure diagram of the superfine-grain gradient cemented carbide with cobalt-rich surface prepared in Example 1 of the present invention;

Fig. 2 is the crystal grain size analysis diagram of the superfine-grain gradient cemented carbide with cobalt-rich surface prepared in Example 1 of the present invention;

Fig. 3 is the metallographic structure diagram of the superfine-grain gradient cemented carbide with cobalt-rich surface prepared in Example 2 of the present invention;

Fig. 4 is the crystal grain size analysis diagram of the superfine-grain gradient cemented carbide with cobalt-rich surface prepared in Example 2 of the present invention;

Fig. 5 is the metallographic structure diagram of the superfine-grained gradient cemented carbide with cobalt-rich surface prepared in Example 3 of the present invention;

Fig. 6 is an analysis diagram of the grain size of the cobalt-rich superfine-grained gradient cemented carbide prepared in Example 3 of the present invention.

Detailed ways

Example 1

The cobalt-rich ultrafine-grained gradient cemented carbide of the present invention has the following components by mass percentage: 80%WC, 5%Ti(C,N), 14%Co, 0.3%VC, 0.7%Cr ₃ C ₂ , Its metallographic structure is based on WC and cubic phase carbonitride as the core hard phase, and cobalt is used as the binder phase to form a 15 μm thick surface cobalt-rich gradient layer, in which the average of WC grains in the hard phase and gradient layer The size is 0.32 μm, the cobalt content in the cobalt-rich gradient layer on the surface is 1.4 times the nominal cobalt content of the cemented carbide, and the cobalt-rich gradient layer on the surface does not contain cubic carbonitride.

The preparation method of the superfine-grained gradient cemented carbide with cobalt-rich surface of the present invention is carried out according to the following steps:

(1) Cemented carbide raw materials added with carbonitrides are used for batching. The composition range is: 80%WC, 5%Ti(C,N), 14%Co, 0.3%VC, 0.7%Cr ₃ C ₂ , where the average particle size of WC powder added is 0.4 μm, the average particle size of Ti(C,N) powder is 1.5 μm, the average particle size of bonding metal Co powder is ₁ μm, grain inhibitor VC and _Cr3C2 powder The average particle size is less than 1 μm;

(2) Mix the above raw materials and put them into a wet ball mill for wet grinding. The ball-to-material ratio is 12:1. The wet-milling medium is alcohol, the speed is 60r/min, and the wet-milling time is 60h. Put it in place for 10 hours, then put it in a vacuum drying oven at 60°C for 2 hours, sieve it with a 40-mesh sieve after drying, press the sieved powder into a blank with a press and a mold, the pressure is 20 tons, and keep the pressure The time is 5s;

(3) Put the billet in the vacuum furnace, evacuate the vacuum furnace to below 10Pa and start to heat up, raise the temperature to 400°C and keep it warm for 6 hours, and at the same time, inject hydrogen for dewaxing and deoxidation, and then empty the hydrogen in the furnace cavity Continue to heat up, fill in argon with a pressure of 9 MPa before reaching the liquid phase sintering temperature of 1400 ° C, and keep it warm for 1 hour. After the heat preservation is completed, it is cooled to room temperature with the furnace to obtain an ultra-fine-grained gradient cemented carbide with a cobalt-rich surface thickness of about 15 μm. The average grain size of WC grains is about 0.33 μm, the hardness of cemented carbide is about HV ₃₀ 1780, and the bending strength is about 2400 MPa. The metallographic structure diagram is shown in Figure 1, and the grain size analysis diagram is shown in Figure 2 shown.

Example 2

The cobalt-rich ultrafine-grained gradient cemented carbide of the present invention has the following components by mass percentage: 77.2%WC, 6%Ti(C,N), 15%Co, 0.5%VC, 0.8%Cr ₃ C ₂ , 0.5% carbon black, the metallographic structure is based on WC and cubic phase carbonitride as the core hard phase, and cobalt is used as the binder phase to form a 20 μm thick cobalt-rich gradient layer on the surface, in which the hard phase and the gradient layer The average size of WC grains is 0.33 μm, and the cobalt content in the cobalt-rich gradient layer on the surface is 1.3 times the nominal cobalt content of the cemented carbide, and the cobalt-rich gradient layer on the surface does not contain cubic carbonitride.

The preparation method of the superfine-grained gradient cemented carbide with cobalt-rich surface of the present invention is carried out according to the following steps:

(1) Cemented carbide raw materials added with carbonitrides are used for batching, and the composition range is: 77.2%WC, 6%Ti(C,N), 15%Co, 0.5%VC, 0.8%Cr ₃ C _2. 0.5% carbon black, wherein the average particle size of WC powder added is 0.4 μm, the average particle size of Ti(C,N) powder is 0.2 μm, the average particle size of bonding metal Co powder is 1 μm, grain inhibitor VC and The average particle size of Cr ₃ C ₂ powder is less than 1 μm;

(2) Mix the above raw materials and put them into a wet ball mill for wet grinding. The ball-to-material ratio is 10:1. The wet-milling medium is alcohol, the speed is 70r/min, and the wet-milling time is 48h. Set it for 8 hours, then put it in a vacuum drying oven at 90°C for 1 hour, sieve it with a 40-mesh sieve after drying, and press the sieved powder into a blank with a press and a mold at a pressure of 5 tons. The time is 30s;

(3) Put the billet in a vacuum furnace, evacuate the vacuum furnace to below 10Pa and start heating up, raise the temperature to 500°C and keep it warm for 4 hours, and at the same time pass in hydrogen for dewaxing and deoxidation, and then empty the hydrogen in the furnace cavity Continue to heat up, fill with argon gas at a pressure of 5 MPa before reaching the liquid phase sintering temperature of 1350°C, and keep it warm for 2 hours. After the heat preservation is completed, it is cooled to room temperature with the furnace to obtain an ultrafine-grained gradient cemented carbide with a cobalt-rich surface thickness of about 20 μm. The average grain size of WC grains is about 0.33μm, the hardness of cemented carbide is about HV ₃₀ 1800, and the bending strength is about 2600MPa. The corresponding metallographic structure diagram is shown in Figure 3, and the grain size analysis diagram is shown in Figure 3. 4.

Example 3

The cobalt-rich ultrafine-grained gradient cemented carbide of the present invention has the following components by mass percentage: 91.5% WC, 2% Ti(C, N), 6% Co, 0.2% Cr ₃ C ₂ , 0.3% carbon black , its metallographic structure is based on WC and cubic phase carbonitride as the core hard phase, and cobalt as the binder phase to form a 40 μm thick cobalt-rich gradient layer on the surface, in which the hard phase and WC grains in the gradient layer The average size is 0.28 μm, the cobalt content in the cobalt-rich gradient layer on the surface is 1.5 times the nominal cobalt content of the cemented carbide, and the cobalt-rich gradient layer on the surface does not contain cubic carbonitride.

The preparation method of the superfine-grained gradient cemented carbide with cobalt-rich surface of the present invention is carried out according to the following steps:

(1) Cemented carbide raw materials with added carbonitrides are used for batching. The composition range is: 91.5%WC, 2%Ti(C,N), 6%Co, 0.2%Cr ₃ C ₂ , 0.3% Carbon black, wherein the average particle size of WC powder added is 0.4 μm, the average particle size of Ti(C,N) powder is 0.2 μm, the average particle size of binder metal Co powder is 1 μm, the grain inhibitor Cr ₃ C ₂ powder is The average particle size is less than 1 μm;

(2) After mixing the above raw materials, put them into a wet ball mill for wet grinding, the ball-to-material ratio is 15:1, the wet grinding medium is alcohol, the speed is 80r/min, the wet grinding time is 72h, and the wet-milled mixed slurry is statically Set it for 12 hours, then put it in a vacuum drying oven at 80°C for 1.5 hours, and sieve it with a 40-mesh sieve after drying, press the sieved powder into a blank with a press and a mold, the pressure is 10 tons, and keep Pressing time is 15s;

(3) Place the billet in a vacuum furnace, evacuate the vacuum furnace to below 10Pa and start heating up, raise the temperature to 600°C and keep it warm for 1 hour, and at the same time, pass in hydrogen for dewaxing and deoxidation, and then evacuate the hydrogen in the furnace cavity Continue to heat up, fill in argon with a pressure of 10MPa before reaching the liquid phase sintering temperature of 1500°C, and keep it warm for 0.1h. After the heat preservation is completed, cool down to room temperature with the furnace to obtain an ultra-fine-grained gradient cemented carbide with a cobalt-rich surface thickness of about 40μm , the average grain size of WC grains is about 0.28μm, the hardness of cemented carbide is about HV ₃₀ 1830, and the bending strength is about 2800MPa. The corresponding metallographic structure diagram is shown in Figure 5, and the grain size analysis diagram is shown in Figure 5. 6.

Claims (3)

1. a preparation method of an ultrafine-grained gradient hard alloy rich in cobalt on the surface, characterized in that it is carried out according to the following steps: (1) Cemented carbide raw materials added with carbonitrides are used for batching, and its composition is: 2-6%Ti(C,N), 6-15%Co, 0-0.5%VC, 0.2-0.8% by mass percentage Cr ₃ C ₂ and 0-0.5% carbon black, the balance is WC; the average particle size of the WC powder is 0.4 μm, the average particle size of the Ti(C,N) powder is 0.2-1.5 μm, and the atoms of C and N The ratio is 0.5:0.5, the average particle size of Co powder is 1 μm, and the average particle size of VC and Cr ₃ C ₂ powder is less than 1 μm; (2) After mixing the above raw materials, put them into a wet ball mill for wet grinding, let the wet-milled mixed slurry stand for 8~12 hours, then put it in a vacuum drying oven at 60~90°C for 1~2 hours, dry it with 40 Sieve through a mesh screen, press the sifted powder into a billet with a press and a mold, the pressure is 5-20 tons, and the holding time is 5-30s; (3) Put the billet in the vacuum furnace, evacuate the vacuum furnace to below 10Pa and start to heat up, raise the temperature to 400~600°C and keep it warm for 1~6h, at the same time, pass in hydrogen for dewaxing and deoxidation, and then empty the furnace The hydrogen in the cavity continues to heat up, and it is filled with an inert gas with a pressure of 5-10 MPa before reaching the liquid-phase sintering temperature. The liquid-phase sintering temperature is 1350-1500°C, and it is kept for 0.1-2 hours under the pressure of the inert gas. After the heat preservation is completed, it is cooled with the furnace to room temperature, the ultra-fine-grained gradient cemented carbide with rich cobalt on the surface is obtained, and its metallographic structure is based on WC and cubic phase carbonitride as the core hard phase, and cobalt is used as the binder phase to form a 10-40 μm thick surface rich Gradient layer of cobalt, wherein the average size of WC grains in the hard phase and gradient layer is 0.2-0.4μm, and the cobalt content in the gradient layer rich in cobalt on the surface is 1.2-2 times the nominal cobalt content of the cemented carbide. 2. According to claim 1, a method for preparing cobalt-rich ultra-fine-grained gradient cemented carbide, characterized in that when step (2) is wet grinding, the ball-to-material ratio is (10~15):1, and the wet The grinding medium is alcohol, the rotation speed is (40~100)r/min, and the wet grinding time is 48~72h. 3. The method for preparing a cobalt-rich ultrafine-grained gradient cemented carbide according to claim 1, wherein the inert gas is argon.