High-strength hard alloy drill bit and welding method thereof

Abstract

The invention discloses a high-strength hard alloy drill bit and a welding method thereof, and relates to the technical field of machining cutters, and the welding method comprises the following steps that a hard alloy drill bit and a quenched and tempered steel drill handle which are designed in a cobalt content gradient mode are adopted, and a multi-layer composite middle layer composed of nickel base and copper base alloy is introduced; in the welding process, a multi-layer composite middle layer composed of nickel-based and copper-based alloy foils is used as brazing filler metal; preheating in a vacuum environment; brazing is carried out in two temperature stages, so that the brazing filler metal with different melting points is sequentially melted, wetted and filled into a welding interface; after welding, a segmented cooling process is adopted, and heat preservation is conducted at a key temperature point; carrying out low-temperature stress relief annealing treatment; and the welded workpiece is subjected to accurate grinding. By introducing the multi-layer composite middle layer and the controllable stepped cooling process, thermal stress is effectively relieved, the microstructure of a welding interface is optimized, and therefore high welding strength and long service life are achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of machining tools, in particular relates to a high-strength hard alloy drill bit and a welding method thereof. BACKGROUND

[0002] In the prior art, hard alloy drill bits are usually connected with steel drill shanks by welding to achieve high strength and wear resistance. However, the traditional welding methods (such as high-frequency brazing or laser welding) have the following problems: due to the large difference in the thermal expansion coefficients of hard alloy (such as WC-Co alloy) and steel shank (such as 45# steel) (the thermal expansion coefficient of hard alloy is about 5.5x10 -6 / ℃, while the thermal expansion coefficient of steel is about 12x10 -6 / ℃), during the welding process, rapid heating and cooling will cause thermal stress concentration, and then microcracks will be generated at the welding interface. These microcracks will expand into macrocracks during the use of the drill bit, especially in high-load and high-impact drilling operations, which will lead to a decrease in welding strength, drill bit shedding or early failure. Therefore, in view of the above problems, the following solutions are proposed. SUMMARY

[0003] The present application aims to provide a high-strength hard alloy drill bit and a welding method thereof, which effectively relieves thermal stress and optimizes the microstructure of the welding interface by introducing a multi-layer composite intermediate layer and a controllable stepwise cooling process, thereby achieving high welding strength and long service life, and solving the problem of interface microcracks caused by the mismatch of material thermal expansion coefficients in the existing hard alloy drill bit welding technology, which leads to insufficient welding strength and shortened service life.

[0004] To solve the above technical problems, the present application is realized by the following technical solutions:

[0005] The present application is a high-strength hard alloy drill bit, the hard alloy head is connected with the steel drill shank through a welding layer; the welding layer is a multi-layer composite structure, including a first filler layer adjacent to the hard alloy head and a second filler layer adjacent to the steel drill shank; the hard alloy head is a WC-Co gradient hard alloy, the Co content of the surface layer is 5-7wt%, and the Co content of the core is 9-11wt%.

[0006] Further, the first filler layer is a nickel-based alloy layer, which contains, in terms of weight percentage, Ni-6.0~8.0Cr-2.5~3.5B-4.0~5.0Si-2.5~3.5Fe, and the thickness is 0.08~0.12mm;

[0007] The second filler layer is a copper-based alloy layer, which contains, in terms of weight percentage, Cu-1.5~2.5Ni-0.4~0.6P, and the thickness is 0.04~0.06mm.

[0008] Further, the material of the steel drill shank is 42CrMo steel, and the interface connected with the cemented carbide head is a tapered interface with a taper range of 1:8 to 1:12.

[0009] A method for welding the high-strength cemented carbide drill head as claimed in any one of the preceding claims, comprising the following steps:

[0010] Step S1, pretreatment: precisely grinding the welding interface of the cemented carbide head and the steel drill shank, controlling the surface roughness Ra≤0.8μm, ultrasonic cleaning and drying;

[0011] Step S2, assembly: placing a multi-layer composite intermediate layer between the welding interface of the cemented carbide head and the steel drill shank, and fixing the assembly using a clamp;

[0012] Step S3, vacuum brazing: placing the fixed assembly into a vacuum brazing furnace, and performing stepwise heating brazing and stepwise cooling;

[0013] The stepwise heating brazing comprises: heating at a rate of 8-12℃ / min to 280-320℃, holding for 8-12 minutes; then heating at a rate of 4-6℃ / min to 580-620℃, holding for 13-17 minutes; then heating at a rate of 2-4℃ / min to 970-990℃, holding for 4-6 minutes; finally heating to 1040-1060℃, holding for 7-9 minutes, and applying a pressure of 0.5-1.0MPa to the welding interface through the clamp during the holding stage;

[0014] The stepwise cooling comprises: cooling at a rate of 4-6℃ / min to 780-820℃, holding for 8-12 minutes; then cooling at a rate of 8-12℃ / min to 480-520℃, holding for 13-17 minutes; finally cooling at a rate of 13-17℃ / min to room temperature;

[0015] Step S4, post-treatment: stress relief annealing treatment is performed on the completed drill head, and then finishing and non-destructive testing are performed.

[0016] Further, the vacuum degree of the vacuum brazing process in step S3 is always better than 5×10 -3 Pa.

[0017] Further, the stress relief annealing treatment in step S4 is specifically: under the protection of inert gas, heating at a rate of 4-6℃ / min to 380-420℃, holding for 1.5-2.5 hours, and then furnace cooling to room temperature.

[0018] Further, the non-destructive inspection in step S4 includes penetration detection and X-ray detection, and the mechanical property test after the finishing is required to have the tensile strength of the welded joint not less than 80% of the strength of the hard alloy body, and the Charpy impact energy not less than 14J.

[0019] The present application has the following advantages:

[0020] The present application alleviates the thermal stress concentration caused by the difference in the thermal expansion coefficient of the materials in the welding process by adopting the combination of the multi-layer composite intermediate layer and the step thermal cycle process, thereby reducing the tendency of micro-cracks at the welding interface and improving the integrity of the welded joint; the interface microstructure formed in the welding process is improved, the filler metal and the base material are metallurgically combined, and the interface diffusion layer is more uniform and dense, which helps to improve the bonding strength and toughness; the mechanical properties of the welded joint are more stable, so that the drill bit shows good impact resistance and fatigue resistance when subjected to complex loads. The present method helps to improve the quality and reliability of the welding interface of the hard alloy drill bit, and thus plays a positive role in prolonging the overall service life of the drill bit.

[0021] Of course, implementing any product of the present application does not necessarily require all the advantages described above. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0023] Figure 1 The flowchart of the preparation method of the high-strength hard alloy drill bit of the present application is shown in the figure.

[0024] Figure 2 The flowchart of the welding method of the high-strength hard alloy drill bit of the present application is shown in the figure. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0026] Please refer to Figure 1 The preparation steps of the high-strength hard alloy drill bit of the present application include:

[0027] Step S1, selecting cemented carbide material and designing bit head geometry

[0028] The cemented carbide material adopts WC-Co alloy, but its composition is gradient designed: the Co content of the surface layer is 6wt%, and the Co content of the core is 10wt%, and the gradient design is realized through a powder metallurgy process, specifically:

[0029] After the WC powder with a particle size of 1.0-2.0 μm and the Co powder are mixed in proportion and formed through cold isostatic pressing, they are sintered in a vacuum sintering furnace at 1450°C for 2 hours;

[0030] Gradient heat treatment is carried out under argon protection, and the Co element is diffused to form a gradient distribution at 1200°C for 1 hour, which can improve the wear resistance of the bit surface layer and the toughness of the core;

[0031] The bit head geometry includes: a top angle of 135°±2°, a helix angle of 30°±1°, and double chip flutes, the depth of the chip flutes is 15% of the bit diameter, and the width is 20% of the bit diameter, the design is completed through computer-aided design (CAD) software and is optimized for stress distribution based on finite element analysis (FEA) to reduce stress concentration in use;

[0032] Step S2, preparing a steel drill shank

[0033] The drill shank material is selected to be 42CrMo steel, and its composition is: C 0.38-0.45%, Cr 0.90-1.20%, Mo 0.15-0.25%, and the balance is Fe, the drill shank is subjected to quenching and tempering treatment: first oil quenching at 850°C and then tempering at 560°C for 2 hours, the hardness reaches HRC 30-35, and the connecting end of the drill shank to the bit is designed as a tapered interface (taper 1:10) to increase the welding area and the mechanical locking effect,

[0034] Step S3, processing the welding interface

[0035] The welding interface of the cemented carbide head and the steel drill shank is precisely ground, and the surface roughness is controlled to be below Ra 0.8 μm;

[0036] The interface is subjected to ultrasonic cleaning: first soaked in acetone solution for 10 minutes, and then cleaned in an ultrasonic cleaning machine at a frequency of 40 kHz for 5 minutes to remove oil stains and oxides, and dried under nitrogen protection after cleaning to prevent secondary oxidation,

[0037] Please refer to Figure 2 The present application is a welding method for a high-strength cemented carbide bit, which comprises the following steps:

[0038] Step S1, preparing a multi-layer composite intermediate layer

[0039] The multi-layered interlayer is composed of two layers: the first layer is a nickel-based filler metal (BNi-2 type, composition: Ni-7.0Cr-3.0B-4.5Si-3.0Fe, thickness 0.1mm), the second layer is a copper-based filler metal (BCu-1 type, composition: Cu-2.0Ni-0.5P, thickness 0.05mm), the two layers are pre-stacked in the form of foils with the nickel-based layer facing the cemented carbide interface and the copper-based layer facing the steel shank interface, the nickel-based layer can effectively wet the cemented carbide and the copper-based layer can buffer thermal stress and the interdiffusion between the two layers can form a ductile interfacial phase;

[0040] The multi-layered interlayer is cut into the same shape as the welding interface and fixed between the cemented carbide head and the steel shank using a clamp to ensure close contact;

[0041] Step S2, preheating before welding

[0042] The assembled drill bit and shank are placed in a vacuum brazing furnace for stepwise preheating:

[0043] Step S21: heated to 300℃ at a rate of 10℃ / min, and held for 10 minutes;

[0044] Step S22: heated to 600℃ at a rate of 5℃ / min, and held for 15 minutes, the preheating process is carried out at a vacuum degree better than 5×10 -3 Pa to prevent oxidation, this preheating step can reduce thermal shock, and by slow stepwise heating, the interlayer can be preliminarily activated and thermal stress can be reduced;

[0045] Step S3, brazing process

[0046] After preheating, continue to heat at a rate of 3℃ / min to the brazing temperature, which is divided into two stages:

[0047] Step S31: heated to 980℃ and held for 5 minutes to melt the nickel-based filler metal and wet the cemented carbide interface;

[0048] Step S32: heated to 1050℃ and held for 8 minutes to melt the copper-based filler metal and react with the steel shank interface, the entire brazing process is carried out under vacuum conditions, and the vacuum degree is maintained at 1×10 -3 Pa;

[0049] During the holding stage, a slight pressure (0.5-1.0MPa) is applied to the welding interface through the clamp to promote filler metal flow and interface bonding, and the pressure is achieved through a spring-loaded mechanism to ensure uniform distribution;

[0050] Step S4, stepwise cooling process

[0051] After brazing is completed, a controllable stepwise cooling process is carried out:

[0052] cooling at a rate of 5°C / min to 800°C for 10 minutes;

[0053] cooling at a rate of 10°C / min to 500°C for 15 minutes;

[0054] cooling at a rate of 15°C / min to room temperature. The cooling process is completed in a vacuum furnace, which allows the stress to be fully released through the holding stage and avoids cracks caused by rapid cooling. After cooling, the welded joint forms a uniform diffusion layer with a thickness of about 10-15 μm;

[0055] Step S5, post-weld heat treatment

[0056] The welded drill bit is subjected to stress relief annealing: heating to 400°C at a rate of 5°C / min under argon protection, holding for 2 hours, and then furnace cooling to room temperature. This step further eliminates residual stress and optimizes the interface microstructure.

[0057] Step S6, final processing and inspection

[0058] The welded joint is finely ground to remove excess brazing material and ensure the overall dimensional accuracy of the drill bit, and then non-destructive testing is performed:

[0059] Step S61: surface cracks are checked using penetration testing (PT), followed by X-ray testing for internal defects;

[0060] Step S62: mechanical property testing: including tensile testing (to ensure that the welding strength is not less than 80% of the hard alloy body) and impact testing (Charpy impact energy not less than 15 J). Only drill bits that pass the inspection are considered qualified.

[0061] In the description of the present specification, the description referring to the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0062] The preferred embodiments of the application disclosed above are only used to help explain the application. The preferred embodiments do not describe all the details and limit the application to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of the present specification. The present specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the application, so that those skilled in the art can well understand and utilize the application. The application is limited only by the claims and their full scope and equivalents.

Claims

1. A high-strength cemented carbide drill bit, characterized in that, The cemented carbide head is connected to the steel drill shank by a weld layer; the weld layer is a multi-layer composite structure, including a first brazing filler metal layer adjacent to the cemented carbide head and a second brazing filler metal layer adjacent to the steel drill shank; the cemented carbide head is a WC-Co graded cemented carbide, with a Co content of 5-7wt% on the surface and a Co content of 9-11wt% in the core.

2. The high-strength cemented carbide drill bit according to claim 1, characterized in that, The first solder layer is a nickel-based alloy layer, whose composition by weight percentage includes: Ni-6.0~8.0, Cr-2.5~3.5, B-4.0~5.0, Si-2.5~3.5, and Fe, with a thickness of 0.08~0.12 mm; The second solder layer is a copper-based alloy layer, whose composition by weight percentage includes: Cu-1.5~2.5Ni-0.4~0.6P, and its thickness is 0.04~0.06mm.

3. A high-strength cemented carbide drill bit according to claim 1, characterized in that, The steel drill shank is made of 42CrMo steel, and its interface with the carbide head is a tapered interface with a taper range of 1:8 to 1:

12.

4. A method for welding high-strength cemented carbide drill bits as described in any one of claims 1-3, characterized in that, Includes the following steps: Step S1, Pre-treatment: Precision grinding is performed on the welding interface between the carbide head and the steel drill shank to control the surface roughness Ra≤0.8μm, followed by ultrasonic cleaning and drying. Step S2, Assembly: A multi-layer composite intermediate layer is placed between the welding interface of the carbide head and the steel drill shank, and the assembly is fixed with a clamp. Step S3, Vacuum Brazing: Place the fixed assembly into a vacuum brazing furnace for stepped heating brazing and stepped cooling. The stepped heating brazing process includes: heating to 280-320℃ at a rate of 8-12℃ / min and holding for 8-12 minutes; then heating to 580-620℃ at a rate of 4-6℃ / min and holding for 13-17 minutes; then heating to 970-990℃ at a rate of 2-4℃ / min and holding for 4-6 minutes; and finally heating to 1040-1060℃ and holding for 7-9 minutes, with a pressure of 0.5-1.0 MPa applied to the welding interface using a fixture during the holding stage. The stepped cooling process includes: cooling to 780-820℃ at a rate of 4-6℃ / min and holding for 8-12 minutes; then cooling to 480-520℃ at a rate of 8-12℃ / min and holding for 13-17 minutes; and finally cooling to room temperature at a rate of 13-17℃ / min. Step S4, Post-processing: The welded drill bit is subjected to stress-relieving annealing, followed by finishing and non-destructive testing.

5. The welding method for a high-strength cemented carbide drill bit according to claim 4, characterized in that, The vacuum degree in the vacuum brazing process described in step S3 is always better than 5 × 10⁻⁶. -3 Pa.

6. The welding method for a high-strength cemented carbide drill bit according to claim 4, characterized in that, The stress-relief annealing process described in step S4 is as follows: under inert gas protection, the temperature is raised to 380-420℃ at a heating rate of 4-6℃ / min, held for 1.5-2.5 hours, and then cooled to room temperature in the furnace.

7. The welding method for a high-strength cemented carbide drill bit according to claim 4, characterized in that, The non-destructive testing in step S4 includes penetrant testing and X-ray testing. After finishing, mechanical property testing is required, and the tensile strength of the welded joint is not less than 80% of the strength of the cemented carbide body, and the Charpy impact energy is not less than 14J.

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