Medium wind pressure down-the-hole drill and preparation method thereof

Abstract

The invention discloses a medium-wind-pressure down-the-hole drill and a preparation method thereof. The preparation method comprises the following steps that (A) round steel is subjected to hot forging treatment, and then a down-the-hole drill bit steel billet is obtained; (B) machining the down-the-hole drill billet obtained in the step (A) to obtain a down-the-hole drill matrix with a spline; (C) the down-the-hole drill matrix obtained in the step (B) is heated to 850-870 DEG C for vacuum quenching; (D) heating the down-the-hole drill matrix obtained in the step (C) to 460-480 DEG C, and carrying out vacuum tempering; (E) carrying out surface quenching on the spline part of the basal body of the down-the-hole drill obtained in the step (D), wherein the hardening depth is 1.5-2.5 mm; and (F) the down-the-hole drill base body obtained in the step (E) is subjected to low-temperature tempering at the temperature of 130-220 DEG C. The preparation method has good economical efficiency, the prepared down-the-hole drill has excellent wear resistance and good impact fatigue resistance, and the service life of the product is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of down-the-hole drills, in particular to a medium-pressure down-the-hole drill and a preparation method thereof. Background Art

[0002] The drill bits of medium and low air pressure DTH drilling tools are mostly used in earthwork engineering, mining of non-metallic minerals such as coal mines, pile foundation construction, etc. The production process is closely related to the performance of the drill bit.

[0003] With the advancement of host equipment technology, the compressed air pressure of low-pressure drilling tools has entered the medium-pressure range. The main material of low-pressure down-the-hole drills is 42CrMo. Traditionally, a quenching and tempering heat treatment process is used, and the performance indicators are limited. After being used in medium-pressure occasions, the impact work on the drill bit increases, and abnormal conditions such as matrix fracture and severe deformation are prone to occur, which directly leads to an increase in mining costs. High-pressure down-the-hole drills generally use good low-carbon alloy steel and adopt carburizing heat treatment technology. While obtaining excellent performance on the surface and core, the manufacturing cost is high, which is not suitable for the use of medium and low-pressure drilling tools that pursue economic performance.

[0004] Therefore, we propose a medium-pressure down-the-hole drill bit and a preparation method thereof. Summary of the invention

[0005] The purpose of the present invention is to provide a medium-pressure down-the-hole drill and a preparation method thereof. The preparation method has good economy. At the same time, the prepared down-the-hole drill has excellent wear resistance and good impact fatigue resistance, thereby extending the service life of the product.

[0006] The technical solution adopted by the present invention is: a method for preparing a medium-pressure down-the-hole drill, comprising the following steps: (A): The round steel is hot forged to obtain the down-the-hole drill bit steel billet; (B): The down-the-hole drill bit steel blank obtained in (A) is machined to obtain a down-the-hole drill bit base body with splines; (C): heating the down-the-hole drill matrix obtained in (B) to 850-870°C for vacuum quenching; (D): heating the down-the-hole drill matrix obtained in (C) to 460-480°C for vacuum tempering; (E): The spline part of the DTH drill base obtained in (D) is surface quenched to a hardening depth of 1.5 to 2.5 mm; (F): The down-the-hole drill base obtained in (E) is subjected to low-temperature tempering at 130-220°C; (G): Drill holes on the down-the-hole drill base obtained in (F) and embed carbide column teeth to obtain a medium-pressure down-the-hole drill.

[0007] As a preferred solution, in step (A), the round steel is made of 30CrNiMoV; The hot forging process includes the following steps: (1) The round steel is heated to 980-1010°C, and before the temperature reaches 800°C, roughening, diameter reduction, and die forging are completed in sequence to obtain a down-the-hole drill bit blank, and then the blank is cooled to room temperature using sand cooling; (2) normalizing the down-the-hole drill bit blank cooled to room temperature in (1) at 850-865°C, and air-cooling it to room temperature after it is taken out of the furnace; Subsequently, stress relief annealing is performed at 640-660°C, the steel is cooled to 600°C in a furnace, and then air-cooled to room temperature to obtain a down-the-hole drill bit steel billet.

[0008] As a preferred solution, in the step (B), the machining includes drilling a central deep hole, and rounding and finishing the bottom of the central deep hole so that the overall roughness is not greater than Ra3.2.

[0009] As a preferred solution, the vacuum quenching method in step (C) is to first heat the DTH drill base to 580-600°C and keep it for 1-3 hours under vacuum environment; then heat it to 850-870°C and keep it for 2-4 hours, and then quench it.

[0010] As a preferred solution, in step (C), the vacuum degree of vacuum quenching is less than 50 Pa; the quenching time of vacuum quenching is 20 to 40 minutes, and the quenching oil temperature is 40 to 55°C.

[0011] As a preferred solution, in step (D), the vacuum degree of vacuum tempering is less than 50Pa; During the vacuum tempering process, the temperature is kept at 460-480°C for 2-4.5 hours, and 2 atmospheres of nitrogen is used for rapid air cooling during cooling; after vacuum tempering, a down-the-hole drill matrix with a hardness of 36-42HRC is obtained.

[0012] As a preferred solution, in step (E), the surface quenching adopts medium frequency induction heating, the heating time is 3 to 8 seconds, and the quenching depth is 1.5 to 2.5 mm.

[0013] As a preferred embodiment, in step (F), the low temperature tempering time is 1 to 2.5 hours; after the low temperature tempering, the product is air-cooled to room temperature.

[0014] As a preferred embodiment, in step (A) (1), the round steel is heated using medium frequency induction heating for 10 to 20 minutes.

[0015] A medium-pressure down-the-hole drill is prepared according to a method for preparing a medium-pressure down-the-hole drill.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention adopts forging process, vacuum quenching process, surface heat treatment and local machining process, and finally obtains a medium-pressure down-the-hole drill bit with small heat treatment deformation and no decarburization and oxidation, high surface hardness, strong wear resistance and fatigue resistance, excellent core impact resistance and long service life.

[0017] 2. The preparation method of the medium-pressure down-the-hole drill bit provided by the present invention is simple in process, and the obtained medium-pressure down-the-hole drill bit has a greatly improved service life compared with ordinary low-pressure down-the-hole drills. It is cheaper than high-pressure down-the-hole drill bits, and meets the use requirements of mine terminals for medium-pressure down-the-hole drills.

[0018] 3. The round steel material is 30CrNiMoV, which is added with a variety of alloy elements. Compared with the traditional 42CrMo steel, under the same strength, 30CrNiMoV has higher toughness and stronger quenching and hardenability. Combined with the preparation method of the medium-pressure down-the-hole drill bit of the present invention, a new performance down-the-hole drill bit that meets the use requirements can be produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is a metallographic image of the core of the down-the-hole drill after low-temperature tempering in Example 1 of the present invention; Figure 2 This is a metallographic diagram of the surface hardened layer of the down-the-hole drill after low-temperature tempering in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The present invention is described in detail below by way of exemplary embodiments. However, it should be understood that, without further description, elements, structures and features in one embodiment may also be beneficially combined in other embodiments.

[0022] It should be noted that: unless otherwise defined, the technical terms or scientific terms used in this document shall have the usual meanings understood by people with ordinary skills in the field to which the invention belongs. The words "one", "an" or "the" and the like used in the patent application specification and claims of the present invention do not express quantity restrictions, but indicate the existence of at least one; the words "first", "second" and "third" used in this document shall not be regarded as restrictions on the order of components, but are only used to distinguish different components; words such as "include" or "comprise" and the like indicate that the elements or objects appearing before "include" or "comprise" include the elements or objects listed after "include" or "comprise" and their equivalents, but do not exclude other elements or objects with the same function.

[0023] The present invention provides the following technical solutions: A method for preparing a medium-pressure down-the-hole drill comprises the following steps: (A): A down-the-hole drill bit steel blank is obtained by hot forging a round steel made of 30CrNiMoV. The hot forging process includes the following steps: (1): The steel round bar is heated to 980-1010℃, and then roughened by free forging. After roughening, the bar is further forged to reduce the diameter and extend it into a longer bar. Finally, it is forged by forming die to form a down-the-hole drill bit blank with one end larger than the other. The workpiece temperature after forging is greater than 800℃, and it is immediately placed in a sandbox and cooled to room temperature with sand. The round steel is heated by medium frequency induction heating for 10-20 minutes to ensure that the core and the surface are heated thoroughly. (2): The down-the-hole drill blank cooled to room temperature in (1) is normalized at 850-865℃, air-cooled to room temperature after being taken out of the furnace; then stress relief annealing is performed at 640-660℃, cooled to 600℃ in the furnace, and air-cooled to room temperature after being taken out of the furnace to obtain a down-the-hole drill blank. The application of normalizing and staged slow cooling refines the workpiece structure and avoids incomplete structural transformation when the workpiece is cooled, which affects the subsequent heat treatment quality and product performance.

[0024] The performance requirements of the medium-pressure down-the-hole drill bit of the present invention are higher than those of the original low-pressure drill bit, and the economic efficiency of production needs to be met by the user. Experiments have shown that 30CrNiMoV meets the requirements for manufacturing drill bits. This material is based on carbon steel and has a variety of alloy elements added. Compared with traditional 42CrMo steel, 30CrNiMoV has higher toughness and stronger quenching hardenability at the same strength. Through the application of the new process, a new performance down-the-hole drill bit that meets the use requirements can be produced.

[0025] By roughening and reducing the diameter, the impurities in the round steel can be evenly dispersed to avoid the formation of bands. The use of die forging ensures uniform deformation and dimensional retention of the product during forging, and reduces oxidation. Sand cooling after forging ensures smooth organizational transformation and stress release.

[0026] (B): machining the down-the-hole drill bit steel billet obtained in (A), wherein the machining of the steel billet includes rough turning, fine turning, drilling a center deep hole, milling splines, milling grooves, deburring and finishing, etc., to obtain a down-the-hole drill bit base body with splines; except for drilling the center deep hole, other machining processes are not particularly limited, and the machining methods and parameters familiar to those skilled in the art can be used; The center deep hole is drilled with an arc gun drill. After clamping the workpiece, it is processed and formed in one step, and the bottom of the center deep hole is rounded and polished at the same time to make the overall roughness no greater than Ra3.2. The arc gun drill is homemade, and is obtained by grinding the arc head of a conventional gun drill using a special grinder.

[0027] (C): In a vacuum environment with a vacuum degree of less than 50Pa, first heat to 580-600℃ and keep warm for 1-3 hours; then heat to 850-870℃ and keep warm for 2-4 hours, followed by vacuum quenching. The quenching time of vacuum quenching is 20-40 minutes, and the quenching oil temperature is 40-55℃; then perform ultrasonic cleaning.

[0028] The first stage of vacuum quenching heating ensures that the temperature of the workpiece is uniform during the heating process. Properly extending the quenching and holding time is conducive to the uniformization of alloy elements. Vacuum oil quenching can prevent the surface of the workpiece from oxidation in a high temperature environment, avoid the formation of a decarburized layer, and reduce stress vulnerable points on the surface of the workpiece.

[0029] (D): Under a vacuum environment with a vacuum degree of less than 50 Pa, the DTH drill matrix obtained in (C) is vacuum tempered, first at 460-480°C for 2-4.5 hours, and then rapidly cooled with 2 atmospheres of nitrogen; after vacuum tempering, a workpiece with a hardness of 36-42 HRC is obtained.

[0030] Rapid cooling after tempering helps reduce the second type of temper brittleness. After vacuum tempering, the impact toughness of the workpiece is >70J / cm2.

[0031] (E): The spline part of the DTH drill base obtained in (D) is surface hardened by medium frequency induction heating for 3 to 8 seconds to achieve a hardening depth of 1.5 to 2.5 mm.

[0032] Surface quenching heat treatment improves the hardness of the spline surface, which is about 6 to 10 hardness values ​​higher than the core, thereby enhancing the surface wear resistance. At the same time, the core maintains good toughness and maintains good comprehensive mechanical properties.

[0033] (F): The DTH drill base obtained in (E) is subjected to low temperature tempering at 130-220°C for 1-2.5 hours, and air-cooled to room temperature after being taken out of the furnace; (G): Drill holes on the down-the-hole drill base obtained in (F) and embed carbide column teeth to obtain a medium-pressure down-the-hole drill.

[0034] There is no special limitation on inlaying alloy teeth, and the process methods and parameters well known to those skilled in the art can be used.

[0035] The present invention also provides a medium-pressure down-the-hole drill produced by the method for producing the medium-pressure down-the-hole drill.

[0036] The following is explained in conjunction with specific embodiments. In the embodiments, the Rockwell hardness test is based on the standard "GB / T230.1-2018"; the impact toughness test is based on the standard "GB / T 229-2020".

[0037] Embodiment 1: A method for preparing a medium-pressure down-the-hole drill comprises the following steps: (A): A down-the-hole drill bit steel blank is obtained by hot forging a round steel made of 30CrNiMoV. The hot forging process includes the following steps: (1) The round steel bar is heated to 1010°C for 20 minutes, and then roughened by free forging. After roughening, the bar is further forged to reduce the diameter and extend it into a longer bar. Finally, a forming die is used for forging to form a down-the-hole drill bit blank with one end larger than the other. The temperature of the workpiece after forging is greater than 800°C, and it is immediately placed in a sandbox and cooled to room temperature using sand. (2) The down-the-hole drill bit blank cooled to room temperature in (1) is normalized at 865°C for 5 hours, and then air-cooled to room temperature after being taken out of the furnace; subsequently, stress relief annealing is performed at 660°C, and the blank is cooled to 600°C in a furnace and air-cooled to room temperature after being taken out of the furnace to obtain a down-the-hole drill bit steel billet.

[0038] (B): The down-the-hole drill bit steel blank obtained in (A) is machined, and the machining of the steel blank includes rough turning, fine turning, drilling a center deep hole, milling splines, milling grooves, deburring and finishing, etc., to obtain a down-the-hole drill bit base with splines; After machining, the center deep hole is drilled with an arc gun drill, and the bottom of the center deep hole is rounded and polished at the same time to make the overall roughness Ra2.3; (C): In a vacuum environment with a vacuum degree of 10Pa, first heat to 600℃ and keep warm for 2 hours; then heat to 870℃ and keep warm for 3 hours, followed by vacuum quenching, the quenching time of vacuum quenching is 35 minutes, and the quenching oil temperature is 50℃; then ultrasonic cleaning is performed.

[0039] (D): Under a vacuum environment with a vacuum degree of 8 Pa, the DTH drill matrix obtained in (C) was vacuum tempered, first at 480°C for 4 hours, and then rapidly cooled with 2 atmospheres of nitrogen; after vacuum tempering, a workpiece with a hardness of 42HRC was obtained; (E): The spline part of the DTH drill base obtained in (D) was surface hardened by medium frequency induction heating at a speed of 6 mm / s for 5 seconds, with a hardening depth of 1.7 mm. (F): The DTH drill matrix obtained in (E) is subjected to low temperature tempering at 220°C for 2 hours, and then air-cooled to room temperature after being taken out of the furnace; (G): Drill holes on the down-the-hole drill base obtained in (F) and embed carbide column teeth to obtain a medium-pressure down-the-hole drill.

[0040] See also Figure 1 and Figure 2 After a specific heat treatment process, the core is a sorbite structure with high toughness; the surface hardened layer is martensite with high wear resistance and strong fatigue resistance; the combination of the core and the surface gives the product excellent comprehensive mechanical properties.

[0041] Embodiment 2: A method for preparing a medium-pressure down-the-hole drill comprises the following steps: (A): A down-the-hole drill bit steel blank is obtained by hot forging a round steel made of 30CrNiMoV. The hot forging process includes the following steps: (1) The round steel bar is heated to 1000°C for 25 minutes, and then roughened by free forging. After roughening, the bar is further reduced by forging to be extended into a longer bar. Finally, a forming die is used for forging to form a down-the-hole drill bit blank with one end larger than the other. The temperature of the workpiece after forging is greater than 800°C, and it is immediately placed in a sandbox and cooled to room temperature using sand. (2) The down-the-hole drill bit blank cooled to room temperature in (1) is normalized at 855°C for 5 hours, and then air-cooled to room temperature; subsequently, stress relief annealing is performed at 660°C for 6.5 hours, and then cooled to 600°C in a furnace and air-cooled to room temperature to obtain a down-the-hole drill bit steel billet.

[0042] (B): The down-the-hole drill bit steel blank obtained in (A) is machined, and the machining of the steel blank includes rough turning, fine turning, center deep hole drilling, spline milling, groove milling, burr removal and finishing, etc., to obtain a down-the-hole drill bit base with splines; After machining, a circular arc gun drill is used to drill holes synchronously, and the bottom of the central deep hole is rounded and polished to make the overall roughness Ra3.0.

[0043] (C): In a vacuum environment with a vacuum degree of 5Pa, first heat to 600℃ and keep warm for 2 hours; then heat to 865℃ and keep warm for 4 hours, followed by vacuum quenching, the quenching time of vacuum quenching is 40 minutes, and the quenching oil temperature is 55℃; then ultrasonic cleaning is performed.

[0044] (D): In a vacuum environment with a vacuum degree of 10Pa, the DTH drill substrate obtained in (C) was vacuum tempered, first at 460°C for 4.5 hours, and then rapidly cooled with 2 atmospheres of nitrogen; after vacuum tempering, a workpiece with a hardness of 41HRC was obtained; the average impact toughness of the workpiece was about 90J / cm2.

[0045] (E): The spline part of the DTH drill base obtained in (D) was surface hardened by medium frequency induction heating at a speed of 6 mm / s for 5 seconds, with a hardening depth of 1.5 mm. (F): The DTH drill matrix obtained in (E) is subjected to low temperature tempering at 180°C for 2.5 hours, and then air-cooled to room temperature after being taken out of the furnace; (G): Drill holes on the down-the-hole drill base obtained in (F) and embed carbide column teeth to obtain a medium-pressure down-the-hole drill.

[0046] The parts not described in detail in this embodiment are prior art.

[0047] It should be noted that although the present invention is described by the above embodiments, the present invention may also have other various embodiments. Without departing from the spirit and scope of the present invention, it is obvious that those skilled in the art may make various corresponding changes and deformations to the present invention, but these changes and deformations should all fall within the scope of protection of the appended claims of the present invention and their equivalents.

Claims

1. A method for preparing a medium-pressure down-the-hole drill, characterized in that: The following steps are involved: (A): The round steel is hot forged to obtain the down-the-hole drill bit steel billet; (B): The down-the-hole drill bit steel blank obtained in (A) is machined to obtain a down-the-hole drill bit base body with splines; (C): heating the down-the-hole drill matrix obtained in (B) to 850-870°C for vacuum quenching; (D): heating the down-the-hole drill matrix obtained in (C) to 460-480°C for vacuum tempering; (E): The spline part of the DTH drill base obtained in (D) is surface quenched to a hardening depth of 1.5 to 2.5 mm; (F): The down-the-hole drill base obtained in (E) is subjected to low-temperature tempering at 130-220°C; (G): Drill holes on the down-the-hole drill base obtained in (F) and embed carbide column teeth to obtain a medium-pressure down-the-hole drill.

2. The method for preparing a medium-pressure down-the-hole drill according to claim 1, characterized in that: In step (A), the round steel is made of 30CrNiMoV; The hot forging process includes the following steps: (1) The round steel is heated to 980-1010°C, and before the temperature reaches 800°C, roughening, diameter reduction, and die forging are completed in sequence to obtain a down-the-hole drill bit blank, and then the blank is cooled to room temperature using sand cooling; (2) normalizing the down-the-hole drill bit blank cooled to room temperature in (1) at 850-865°C, and air-cooling it to room temperature after it is taken out of the furnace; Subsequently, stress relief annealing is performed at 640-660°C, the steel is cooled to 600°C in a furnace, and then air-cooled to room temperature to obtain a down-the-hole drill bit steel billet.

3. The method for preparing a medium-pressure down-the-hole drill according to claim 1, characterized in that: In the step (B), the machining includes drilling a central deep hole, and rounding and finishing the bottom of the central deep hole so that the overall roughness is not greater than Ra3.

2.

4. The method for preparing a medium-pressure down-the-hole drill according to claim 1, characterized in that: In step (C), the vacuum quenching method is to first heat the DTH drill base to 580-600° C. and keep it for 1-3 hours under vacuum environment; then heat it to 850-870° C. and keep it for 2-4 hours, and then quench it.

5. The method for preparing a medium-pressure down-the-hole drill according to claim 1, characterized in that: In step (C), the vacuum degree of vacuum quenching is less than 50 Pa; the quenching time of vacuum quenching is 20 to 40 minutes, and the quenching oil temperature is 40 to 55°C.

6. The method for preparing a medium-pressure down-the-hole drill according to claim 1, characterized in that: In step (D), the vacuum degree of vacuum tempering is less than 50 Pa; During the vacuum tempering process, the temperature is kept at 460-480°C for 2-4.5 hours, and 2 atmospheres of nitrogen is used for rapid air cooling during cooling; after vacuum tempering, a down-the-hole drill matrix with a hardness of 36-42HRC is obtained.

7. The method for preparing a medium-pressure down-the-hole drill according to claim 1, characterized in that: In step (E), the surface quenching adopts medium frequency induction heating, the heating time is 3 to 8 seconds, and the quenching depth is 1.5 to 2.5 mm.

8. The method for preparing a medium-pressure down-the-hole drill according to claim 1, characterized in that: In step (F), the low temperature tempering time is 1 to 2.5 hours; after the low temperature tempering, the product is air-cooled to room temperature.

9. The method for preparing a medium-pressure down-the-hole drill according to claim 2, characterized in that: In step (A) (1), the round steel is heated using medium frequency induction heating for 10 to 20 minutes.

10. A medium-pressure down-the-hole drill made according to the method for making a medium-pressure down-the-hole drill according to any one of claims 1 to 9.

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