A method for brazing cemented carbide / alloy steel joints with a fully solid solution interlayer

Abstract

The application discloses a cemented carbide / alloy steel brazing connection method of full solid solution joint, comprising the following steps: respectively electroplating a cobalt layer on the surface of WC-Co cemented carbide and alloy steel, and then welding the WC-Co cemented carbide and the alloy steel after being plated with cobalt by using a filler; the brazing joint is in a full solid solution structure; wherein the cobalt layer of the WC-Co cemented carbide is in a cellular plated layer, and the cellular plated layer is composed of cellular grains with a particle size of 50-200 nm; the cobalt layer of the alloy steel is in a cellular plated layer, and the cellular plated layer is composed of cellular grains with a particle size of 700-900 nm. The method can effectively avoid the formation of intermetallic compounds in the weld structure, obtain the weld structure of full solid solution, improve the plasticity of the joint, relieve the residual stress of the connection part, and improve the impact toughness and connection strength of the weld.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide brazing technology, and more particularly to a method for brazing cemented carbide / alloy steel joints with a fully solid solution structure. Background Technology

[0002] The main component of WC-Co cemented carbide is WC, which is commonly used to make cutting tools. In the engineering field, to improve the stability of cutting tools, WC-Co cemented carbide is often brazed together with conventional alloy steel.

[0003] However, traditional inert brazing filler metals have poor affinity and wettability with WC-Co cemented carbide and alloy tool steel. Current technologies generally use active brazing filler metals such as AgCuTi to improve wettability; however, the active elements in the filler metal inevitably introduce brittle intermetallic compounds into the joint, negatively impacting its toughness and plasticity.

[0004] To improve the wetting behavior of the brazing interface while avoiding the formation of brittle compounds at the joint, other metal coatings can be added to the base metal interface. For example, adding a Co coating to the surface of cemented carbide and alloy steel can improve the spreading and wetting of the brazing filler metal on the coating surface while avoiding the introduction of other elements into the joint system. However, current Co coatings on WC-Co cemented carbide surfaces still suffer from problems such as easy coating peeling, inconsistent thickness, low deposition efficiency, and less than ideal interfacial wetting. These problems limit the interfacial bond strength between cemented carbide and alloy steel, and the stability of the cutting tools still needs improvement. Summary of the Invention

[0005] Based on the technical problems existing in the background art, the present invention proposes a brazing connection method for cemented carbide / alloy steel joints with a full solid solution structure. The method of the present invention can effectively avoid the formation of intermetallic compounds in the weld structure, obtain a weld structure with a full solid solution structure, improve the joint plasticity, relieve residual stress in the connection part, and improve the impact toughness and connection strength of the weld.

[0006] This invention proposes a brazing method for a cemented carbide / alloy steel joint with a full solid solution structure, comprising the following steps: electroplating a cobalt layer on the surface of WC-Co cemented carbide and alloy steel respectively, and then welding the cobalt-plated WC-Co cemented carbide and the cobalt-plated alloy steel with brazing filler metal; the brazed joint has a full solid solution structure. Among them, the cobalt layer of WC-Co cemented carbide is a cellular coating, which is composed of tightly packed cellular grains with a particle size of 50-200nm. The cobalt layer of alloy steel is a cellular coating, which is composed of tightly packed cellular grains with a particle size of 700-900 nm.

[0007] The structure of the above-mentioned brazed joint is a symmetrical structure of FeCo solid solution reaction layer / intermediate solid solution / FeCo solid solution reaction layer, and the entire brazed joint has a full solid solution structure.

[0008] Preferably, the thickness of the WC-Co cemented carbide cobalt layer is 2.7-3.7 μm.

[0009] Preferably, the thickness of the cobalt layer in the alloy steel is 6-9 μm.

[0010] Preferably, the roughness of the WC-Co cemented carbide cobalt layer is 0.26-0.8 μm.

[0011] Preferably, the roughness of the cobalt layer in the alloy steel is 0.1-0.3 μm.

[0012] Preferably, the current density of the electroplated cobalt layer is 0.9-1.1 A / dm³. 2 The electroplating temperature is 45-55℃ and the electroplating time is 5-10 minutes.

[0013] The current density of the aforementioned electroplated cobalt layer can be 0.9, 0.95, 1, 1.05, or 1.1 A / dm³. 2 The electroplating temperature can be 45, 46, 47, 48, 49, 50, 51, 52, 53, 54 or 55℃, and the electroplating time can be 5, 6, 7, 8, 9 or 10 minutes.

[0014] Preferably, when electroplating a cobalt layer, the raw materials of the electroplating solution include: 15-30 g / L cobalt salt, 10-20 g / L acidic corrosion inhibitor, 1-2 g / L complexing agent, and 8-15 g / L reaction accelerator.

[0015] Preferably, the pH of the electroplating solution is 4.0-5.0.

[0016] Preferably, the solvent of the electroplating solution is water, more preferably distilled water.

[0017] Preferably, the cobalt salt is cobalt sulfate.

[0018] Preferably, the acidic corrosion inhibitor is boric acid.

[0019] Preferably, the complexing agent is cyclohexanone oxime.

[0020] Preferably, the reaction accelerator is sodium chloride.

[0021] By selecting appropriate electroplating parameters, this invention can obtain a cobalt coating composed of tightly packed fine cellular grains. This structure reduces voids and internal defects, reduces internal stress concentration points, allows for more complete stress release, and ensures a more complete metallurgical bond between the coating and the substrate, thus avoiding stress concentration that could lead to coating peeling. Secondly, during the subsequent connection process, the coatings on both sides of the base material play a better transition role, so that the brazed joint forms a symmetrical structure with FeCo solid solution reaction layer / intermediate solid solution layer / FeCo solid solution reaction layer, which is conducive to balancing the stress amplitude of the interface on both sides and to relieving the residual stress of the joint. Furthermore, the Co layer of the microstructure described in this invention can be combined with inert silver-based brazing filler metal to effectively prevent the formation of intermetallic compounds in the weld structure, resulting in a fully solid solution weld structure. This method can significantly improve joint plasticity, alleviate residual stress at the connection site, and enhance the impact toughness and connection strength of the weld. In addition, the fine grain size of the coating, the smooth surface of the coating, and the absence of oxide inclusions can improve the hardness of the coating, promote the spread of molten brazing filler metal, reduce the wetting angle, reduce interfacial voids, and thus further improve the welding strength.

[0022] Before electroplating the cobalt layer, both WC-Co cemented carbide and alloy steel undergo cleaning and activation treatment; the preferred activation solution contains: 4wt% hydrofluoric acid, 3wt% nitric acid, and 3mg / mL ammonium fluoride, with distilled water as the solvent.

[0023] Preferably, the Co content in the WC-Co cemented carbide is 7.5-8.5 wt%.

[0024] Preferably, the Cr content in the alloy steel is 0.8-1.1 wt%.

[0025] Preferably, the raw materials of the alloy steel include, by weight percentage: Cr 0.8-1.1%, Mn 0.5-0.8%, Si 0.17-0.37%, C 0.37-0.44wt%, with the balance being Fe.

[0026] Preferably, the solder is an inert silver-based solder.

[0027] Preferably, the Cu content in the inert silver-based solder is 26-30 wt%.

[0028] The raw materials in the above-mentioned inert silver-based solder include, by weight percentage: Cu 26-30wt%, with the balance being Ag.

[0029] Preferably, a pressure of 4-6 kPa is applied during the welding process.

[0030] Preferably, the vacuum degree during welding is ≤10. -2 Pa.

[0031] Preferably, the welding temperature procedure is as follows: hold at 750-760℃ for 8-12 minutes, raise the temperature to 780-900℃ and hold for 5-20 minutes, and then cool down to room temperature.

[0032] Preferably, the cooling rate is 8-12℃ / min.

[0033] Beneficial effects: This invention employs appropriate electroplating parameters to obtain a cobalt layer with a specific microstructure on the surface of WC-Co cemented carbide and alloy steel. This reduces porosity and internal defects, minimizes internal stress concentration points, and facilitates metallurgical bonding between the plating layer and the substrate, preventing cobalt layer detachment. It also promotes the spread of molten brazing filler metal, reduces the wetting angle, minimizes interfacial voids, and improves weld strength. Furthermore, the specific morphology of the two cobalt layers complements the brazing filler metal, effectively preventing the formation of intermetallic compounds in the weld structure and resulting in a fully solid solution brazed joint, thus enhancing joint plasticity. The symmetrical structure of the brazed joint—FeCo solid solution reaction layer / intermediate solid solution layer / FeCo solid solution reaction layer—effectively alleviates residual stress at the joint, improves the impact toughness and connection strength of the weld, and enables excellent welding between WC-Co cemented carbide and alloy steel. Attached Figure Description

[0034] Figure 1 SEM images of the cross-section of the cobalt-plated layer on WC-Co cemented carbide under different electroplating conditions.

[0035] Figure 2 SEM images of the cobalt-plated surface of WC-Co cemented carbide under different electroplating conditions.

[0036] Figure 3 The roughness test results are for cobalt-plated WC-Co cemented carbide layers and cobalt-plated 40Cr alloy steel layers under different electroplating conditions.

[0037] Figure 4 SEM images of the cross-section of the cobalt-plated layer on 40Cr alloy steel under different electroplating conditions.

[0038] Figure 5 SEM images of the cobalt-plated surface of 40Cr alloy steel under different electroplating conditions.

[0039] Figure 6 The results show the wettability of cobalt-plated 40Cr alloy steel to silver-copper brazing filler metal under different electroplating conditions. 40Cr Without Co represents 40Cr alloy steel without cobalt plating.

[0040] Figure 7 The results show the wettability test results of the cobalt-plated YG8 cemented carbide layer on silver-copper brazing filler metal under different electroplating conditions. YG8 Without Co represents YG8 cemented carbide without cobalt plating.

[0041] Figure 8 The test results show the shear strength of the joints of cobalt-plated WC-Co cemented carbide and cobalt-plated 40Cr alloy steel after being welded with silver-copper brazing filler metal under different electroplating conditions.

[0042] Figure 9 Current density 1 A / dm 2 SEM microstructure of the joint obtained by welding cobalt-plated WC-Co cemented carbide and cobalt-plated 40Cr alloy steel with silver-copper brazing filler metal at a temperature of 50℃.

[0043] Figure 10 Metallographic images of the weld microstructure of cobalt-plated WC-Co cemented carbide and cobalt-plated 40Cr alloy steel after welding under different electroplating conditions. Detailed Implementation

[0044] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0045] Example 1

[0046] A method for brazing a cemented carbide / alloy steel joint with a fully solid solution microstructure includes the following steps: Take YG8 cemented carbide (Co content is 8.0wt%) and 40Cr alloy steel (the raw materials of the alloy steel include by weight percentage: Cr 1wt%, Mn 0.6wt%, Si 0.25wt%, C 0.4wt%, and the balance is Fe); YG8 cemented carbide and 40Cr alloy steel were ground sequentially with 200#, 400#, 800#, 1000# and 2000# diamond discs to remove the oxide surface. Then, YG8 cemented carbide and 40Cr alloy steel were cleaned in an alcohol bath with an ultrasonic cleaner for 5 minutes. Next, YG8 cemented carbide and 40Cr alloy steel were placed in an activation solution (the activation solution contained 4wt% hydrofluoric acid, 3wt% nitric acid, and 3mg / mL ammonium fluoride, and the solvent was distilled water) and activated at 50°C for 3 minutes. Then, copper wire is evenly wound onto YG8 cemented carbide and connected to the negative electrode. The electrode is then immersed in an electrolyte solution (the electrolyte solution consists of: 20 g / L cobalt sulfate, 15 g / L boric acid (acidic corrosion inhibitor), 1.5 g / L cyclohexanone oxime (complexing agent), 10 g / L sodium chloride (reaction accelerator), pH 4.5, and distilled water as solvent). Two cobalt plates are symmetrically placed on either side of the negative electrode as anodes. The current density is adjusted to 0.5, 1, and 2 A / dm³, respectively. 2 Electroplating of cobalt layer was performed for 10 minutes at electrolyte temperatures of 30, 50, and 70℃ to obtain cobalt-plated WC-Co cemented carbide. Copper wire was evenly wound around 40Cr alloy steel and connected to the negative electrode. The steel was then placed in the electrolyte. Two cobalt plates were symmetrically placed on either side of the negative electrode as the anode. The current density was adjusted to 0.5, 1, and 2 A / dm³, respectively. 2Electroplating of cobalt layer was performed for 10 minutes at electrolyte temperatures of 30, 50, and 70℃ to obtain cobalt-plated 40Cr alloy steel. The cobalt-plated WC-Co cemented carbide and cobalt-plated alloy steel are welded using an inert silver-based brazing filler metal (the raw materials of the inert silver-based brazing filler metal include, by weight percentage: Cu 28wt%, balance Ag). During the welding process, a pressure of 5 kPa is applied, and the vacuum degree is ≤10. -2 The welding temperature procedure is as follows: hold at 760℃ for 10 min, raise the temperature to 790℃ and hold for 10 min, then cool down to room temperature at a rate of 10℃ / min.

[0047] SEM images of cobalt-plated WC-Co cemented carbide layers under different electroplating conditions are shown below. Figure 1-2 As shown.

[0048] SEM images of cobalt-plated layers on 40Cr alloy steel under different electroplating conditions are shown below. Figure 4-5 As shown.

[0049] The roughness test results of the cobalt plating layer under different electroplating conditions are as follows: Figure 3 As shown.

[0050] Figure 1 SEM images of the cross-section of the cobalt-plated layer on WC-Co cemented carbide under different electroplating conditions.

[0051] Figure 2 SEM images of the cobalt-plated surface of WC-Co cemented carbide under different electroplating conditions.

[0052] Figure 3 The roughness test results are for cobalt-plated WC-Co cemented carbide layers and cobalt-plated 40Cr alloy steel layers under different electroplating conditions.

[0053] Figure 4 SEM images of the cross-section of the cobalt-plated layer on 40Cr alloy steel under different electroplating conditions.

[0054] Figure 5 SEM images of the cobalt-plated surface of 40Cr alloy steel under different electroplating conditions.

[0055] Depend on Figure 1-5 It can be seen that at lower current densities, such as 0.5 A / dm², 2 The cobalt-plated layer exhibits a thin, elongated morphology. Gaps between these strips and defects in the substrate result in weak adhesion between the plating and the substrate, making the cobalt-plated layer prone to detachment. Furthermore, the gaps between the strips lead to internal stress concentration. When the current density reaches 1 A / dm³... 2 The cobalt plating layer exhibits a compact and refined cellular structure. This dense structure reduces internal defects, resulting in a more thorough metallurgical bond between the plating layer and the substrate, and good ductility. At high current densities, such as 2A / dm³, [the coating can achieve high current density]. 2There are a few cracks at the junction of the cellular protrusions. This is because the hydrogen evolution is aggravated by the excessive current density. The inclusion of coating impurities and the dispersion ability of electrolyte decrease with the increase of current density, affecting the uniformity and integrity of the coating. Different temperatures and current densities affect the surface morphology of the cobalt plating layer. When the current is low or the temperature is low, the deposition rate of the plating layer is low, which can easily lead to problems such as weak coating adhesion and easy peeling. When the electroplating temperature is too high, it can also lead to an aggravation of hydrogen evolution reaction, which affects the uniformity of the plating layer. Current density is 1 A / dm 2 At a temperature of 50℃, the coating roughness is 0.277μm, which means that the cobalt coating has fine and smooth crystals; the current density is 1A / dm³. 2 At a temperature of 30℃, although the coating roughness is lower, the elongated coating grains are not sufficiently aggregated and have more voids.

[0056] Figure 6 The results show the wettability of cobalt-plated 40Cr alloy steel to silver-copper brazing filler metal under different electroplating conditions. 40Cr Without Co represents 40Cr alloy steel without cobalt plating.

[0057] Figure 7 The results show the wettability test results of the cobalt-plated YG8 cemented carbide layer on silver-copper brazing filler metal under different electroplating conditions. YG8 Without Co represents YG8 cemented carbide without cobalt plating.

[0058] Depend on Figure 6-7 It can be seen that under the condition of holding at 860℃ for 20 minutes, both 40Cr alloy steel and YG8 cemented carbide can be greatly improved in wettability and promote the spread of brazing filler metal after cobalt plating.

[0059] Figure 8 The results show the shear strength of the weld seams of cobalt-plated WC-Co cemented carbide and cobalt-plated 40Cr alloy steel after welding with silver-copper brazing filler metal under different electroplating conditions.

[0060] Depend on Figure 8 It can be seen that the current density is 1 A / dm. 2 At a temperature of 50℃, the weld shear strength of cobalt-plated WC-Co cemented carbide and cobalt-plated 40Cr alloy steel is the highest, with a joint strength of 287.1MPa and a shear strain of 12.4%.

[0061] Figure 9 Current density 1 A / dm 2 SEM microstructure of the joint obtained by welding cobalt-plated WC-Co cemented carbide and cobalt-plated 40Cr alloy steel with silver-copper brazing filler metal at a temperature of 50℃.

[0062] Depend on Figure 9 It can be seen that the joint structure is compact, and no defects were found. The joint can be divided into three distinct regions: region I at the 40Cr interface, the intermediate layer of region II, and region III near the YG8 side. Regions I and III consist of FeCo solid solutions, while region II exhibits a typical silver-copper eutectic structure, containing both Ag-based and Cu-based solid solutions. Therefore, the joint is composed entirely of a solid solution structure.

[0063] Figure 10 Metallographic images of the weld microstructure of cobalt-plated WC-Co cemented carbide and cobalt-plated 40Cr alloy steel after welding under different electroplating conditions.

[0064] Depend on Figure 10 It can be seen that under different electroplating process parameters, there are significant differences in the non-welding defects in the joint; when the current density is 1A / dm 2 When the electroplating temperature was 30℃, continuous non-welding defects appeared in the joint. As the electroplating temperature increased to 50℃, the wettability of the brazing filler metal to the base material surface improved, and the welding defects in the joint disappeared. However, when the electroplating temperature increased to 70℃, with the change in the state of the Co layer on the base material surface, the wettability of the brazing filler metal to the base material deteriorated, and a small number of welding defects appeared in the joint. When the electroplating temperature was 50℃, with the increase of electroplating current density (1, 1.5, 2 A / dm³), 2 The welding defects in the joints also showed a trend of first decreasing and then increasing; in addition, it is worth noting that when the electroplating current density is 1A / dm 2 When the electroplating temperature is 50℃, the reaction layer at the base material interface of the obtained brazed joint has the most uniform and continuous thickness.

[0065] This phenomenon indicates that, under optimized electroplating process parameters, a cobalt layer with a specific morphology can be obtained. This layer can work in conjunction with the brazing filler metal to achieve a good wetting reaction between the filler metal and the base material surface. It also effectively prevents the formation of intermetallic compounds in the weld structure, resulting in a complete, continuous, and fully solid-solid brazed joint (the brazed joint has a symmetrical structure of FeCo solid solution reaction layer / intermediate solid solution layer / FeCo solid solution reaction layer). This improves the joint plasticity, alleviates residual stress in the connection area, and enhances the impact toughness and connection strength of the weld, enabling good welding between WC-Co cemented carbide and alloy steel.

[0066] In summary, the current density is 1 A / dm. 2At a temperature of 50℃, the plating rate is approximately 3-5 min / μm. The resulting cobalt plating consists of tightly packed fine cellular Co particles. This structure reduces voids and internal defects, minimizes internal stress concentration points, and facilitates metallurgical bonding between the plating layer and the substrate, preventing cobalt layer detachment. It also promotes the spread of molten brazing filler metal, reduces the wetting angle, decreases interfacial voids, and improves weld strength. Furthermore, the specific morphology of the two cobalt layers can complement the brazing filler metal, effectively preventing the formation of intermetallic compounds in the weld structure. This results in a complete, continuous, and fully solid solution brazed joint (the brazed joint has a symmetrical structure of FeCo solid solution reaction layer / intermediate solid solution layer / FeCo solid solution reaction layer), enabling excellent welding between WC-Co cemented carbide and alloy steel.

[0067] Optimizing and controlling the microstructure of the Co-plated layer on the surface of cemented carbide and alloy steel is a key step in improving the wetting of the base metal interface by inert silver-based brazing filler metal and obtaining a full solid solution weld microstructure.

[0068] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for brazing a cemented carbide / alloy steel joint with a fully solid solution microstructure, characterized in that, The process includes the following steps: electroplating a cobalt layer onto the surfaces of WC-Co cemented carbide and alloy steel, respectively; then welding the cobalt-plated WC-Co cemented carbide and the cobalt-plated alloy steel together with brazing filler metal; the brazed joint has a solid solution structure. Among them, the cobalt layer of WC-Co cemented carbide is a cellular coating, which is composed of tightly packed cellular grains with a particle size of 50-200nm. The cobalt layer of alloy steel is a cellular coating, which is composed of tightly packed cellular grains with a particle size of 700-900 nm.

2. The method for brazing a cemented carbide / alloy steel joint with a fully solid solution microstructure according to claim 1, characterized in that, The thickness of the WC-Co cemented carbide cobalt layer is 2.7-3.7 μm; preferably, the thickness of the alloy steel cobalt layer is 6-9 μm.

3. The method for brazing a cemented carbide / alloy steel joint with a fully solid solution microstructure according to claim 1 or 2, characterized in that, The roughness of the WC-Co cemented carbide cobalt layer is 0.26-0.8 μm; preferably, the roughness of the alloy steel cobalt layer is 0.1-0.3 μm.

4. The method for brazing a cemented carbide / alloy steel joint with a fully solid solution microstructure according to any one of claims 1-3, characterized in that, The current density of the electroplated cobalt layer is 0.9-1.1 A / dm³. 2 The electroplating temperature is 45-55℃ and the electroplating time is 5-10 minutes.

5. The method for brazing a cemented carbide / alloy steel joint with a fully solid solution microstructure according to any one of claims 1-4, characterized in that, When electroplating a cobalt layer, the raw materials of the electroplating solution include: 15-30 g / L cobalt salt, 10-20 g / L acidic corrosion inhibitor, 1-2 g / L complexing agent, and 8-15 g / L reaction accelerator; preferably, the pH of the electroplating solution is 4.0-5.0; preferably, the solvent of the electroplating solution is water; preferably, the cobalt salt is cobalt sulfate; preferably, the acidic corrosion inhibitor is boric acid; preferably, the complexing agent is cyclohexanone oxime; preferably, the reaction accelerator is sodium chloride.

6. The method for brazing a cemented carbide / alloy steel joint with a fully solid solution microstructure according to any one of claims 1-5, characterized in that, The Co content in WC-Co cemented carbide is 7.5-8.5 wt%.

7. The method for brazing a cemented carbide / alloy steel joint with a fully solid solution microstructure according to any one of claims 1-6, characterized in that, The Cr content in the alloy steel is 0.8-1.1 wt%; preferably, the raw materials of the alloy steel include, by weight percentage: Cr 0.8-1.1%, Mn 0.5-0.8%, Si 0.17-0.37%, C 0.37-0.44 wt%, with the balance being Fe.

8. The method for brazing a cemented carbide / alloy steel joint with a fully solid solution microstructure according to any one of claims 1-7, characterized in that, The solder is an inert silver-based solder.

9. The method for brazing a cemented carbide / alloy steel joint with a fully solid solution microstructure according to claim 8, characterized in that, In inert silver-based solders, the Cu content is 26-30 wt%.

10. The method for brazing a cemented carbide / alloy steel joint with a fully solid solution microstructure according to any one of claims 1-9, characterized in that, A pressure of 4-6 kPa is applied during welding; preferably, the vacuum degree during welding is ≤10. -2 Pa; preferably, the welding temperature program is as follows: hold at 750-760℃ for 8-12 min, raise the temperature to 780-900℃ and hold for 5-20 min, and then cool down to room temperature; preferably, the cooling rate is 8-12℃ / min.

Images