Production method for controlling banded structure of CrNiMo carburizing drill rod

Abstract

The invention discloses a production method for controlling a banded structure of a CrNiMo carburizing drill rod, which adopts a continuous casting billet rolled material as a raw material, and adopts the production process route of square billet continuous casting, rolling cogging, drilling and core loading, cored rolling, core pulling, drill rod manufacturing and carburizing quenching and tempering, the continuous casting billet is adopted as the raw material, and rolling processing with the pressure ratio reaching 8 is carried out, so that the banded structure of the CrNiMo carburizing drill rod is controlled. The production of the hollow steel for the drill rod is realized by drilling a hole and adding a core rod, coating the surface of the core rod with a lime aqueous solution, controlling the heating temperature and time and rolling with a core, the strip grade in the steel is reduced to be within 1.5 grade, and the surface carburization is carried out to control the surface carburization layer to be 0.9-1.1 mm after the later drill rod manufacturing processing; the carbon concentration is controlled to be 0.5-0.7%, after temperature equalization is conducted for 30 min at the temperature of 860 DEG C, quenching cooling is conducted in a cooling tower, rapid cooling is conducted at the temperature of 500-860 DEG C at the speed larger than 20 DEG C / min, and the cooling speed is controlled to be 5.5 DEG C / min at the low-temperature section. The banding level of the matrix structure of the drill rod produced through the method is controlled within 1.0, the structure performance is good, the homogenization degree is high, and the rock drilling service life is greatly prolonged.

Description

Technical Field

[0001] The invention relates to a method for producing a rock drilling drill rod, in particular to a method for producing a CrNiMo carburized drill rod with controlled banded structure, belonging to the technical field of steel production. Background Art

[0002] The drill rod is an important part of rock drilling tools. When working, it transfers impact energy to the drill bit for rock drilling. The core hole is passed through high-pressure water or compressed air to cool the drill bit and remove slag. The drill rod is a slender rod, which mainly bears bending fatigue stress, high-frequency tensile and compressive fatigue impact and torsional stress. The core hole is also subjected to stress corrosion. The working environment is extremely harsh. The uniformity of the drill rod structure has a great influence on its fatigue performance and corrosion resistance.

[0003] At present, CrNiMo alloy structural steel is used for carburizing treatment at home and abroad, and 22CrNi3Mo is mainly used. The material manufacturers are mainly Sandvik and OVAKO, and domestically they are generally provided by Shanghai Baosteel or Daye Steel Plant. However, due to different manufacturing processes, the matrix structure of the drill rod has a higher banding level, which not only has a greater impact on the life of the drill rod, but also the high banding level makes the domestic drill rod less stable and has a short rock drilling life, which is far behind imported products. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a production method for controlling the banded structure of a CrNiMo carburized drill rod, thereby reducing the banded structure level of the drill rod matrix and improving the stability and rock drilling life of the drill rod.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for producing a CrNiMo carburizing drill rod with controlled banded structure uses continuous casting billet rolled material as raw material, and the production process route is: continuous casting billet rolled material - drilling - coring - core hot rolling with core - core pulling - drill making - carburizing quenching and tempering.

[0007] The method uses continuous casting billet rolled material as raw material, and produces drill rods through processes such as drilling, coring, cored hot rolling, core pulling, brazing, and carburizing heat treatment. The continuous casting billet rolled material used as raw material has the characteristics of high composition uniformity, ensuring the density of the brazing rod to improve the bending fatigue performance of the material, and low production cost. The purpose of coring and hot rolling after drilling is to realize the production of hollow steel raw materials for brazing, and at the same time control the banding level of the brazing rod base material. Water-penetrating controlled cooling after rolling improves the uniformity of the material grain size and reduces the banding level. During carburizing quenching and tempering, graded quenching is used to increase the quenching speed in the range of 500 to 860°C, so as to remove the banding level of the finished brazing rod.

[0008] The present invention mainly aims at low-carbon carburized drill steel, and its representative steel grade is 22CrNi3Mo. Other similar low-carbon carburized drill rods are also applicable.

[0009] A production method for controlling the banded structure of CrNiMo carburized drill rods according to the present invention includes the following specific steps:

[0010] (1) Continuously cast billet rolling is used as the raw material, and the reduction ratio of the continuously cast billet rolled material is required to be greater than 8. The size of the rolled material is φ160 - 180, and the length is 1.5 - 3 meters.

[0011] (2) Mechanically drill the continuously cast billet rolled material to remove the core loose material. The drilling size is φ43 - 67. A mandrel is installed in the drilled inner hole. The gap between the mandrel and the core hole is 1 - 1.5 mm, and lime water is smeared on the surface of the mandrel with a thickness of 0.2 - 0.4 mm.

[0012] (3) The raw material with the mandrel installed is heated in a heating furnace. The temperature of the preheating section is lower than 550°C, the temperature of the first heating section is controlled at 940 - 1100°C, the second heating section is controlled at 1120 - 1200°C, the soaking section temperature is controlled at 1140 - 1200°C, the heating time is controlled at 2.8 - 3.5 h, and the furnace outlet temperature is controlled at 1060 - 1140°C.

[0013] (4) Semi-continuous rolling is used for rolling. The starting rolling temperature is controlled at 1050 - 1100°C, and the temperature entering the continuous rolling is controlled at 940°C - 980°C. The final rolling temperature is 890 - 950°C, and the rolling specifications are hollow steel of H35, R38, R46, and R52.

[0014] (5) After rolling, the bars are rapidly cooled by passing through water. The surface temperature of the bars leaving the water-passing device is controlled at 680 - 740°C, and the temperature entering the cooling bed is controlled below 740°C. The materials entering the cooling bed are rapidly collected, and the collection temperature is controlled above 300°C. The rolled materials are rapidly collected and put into the pit for slow cooling, and the heat preservation time is 24 hours. After heat preservation, the core material of the hollow steel is extracted after sizing sawing.

[0015] (6) The hollow steel after sizing sawing is induction heated to 1050 - 1150°C at the parts that need to be upset and then forged into shape. Immediately after forging, soft annealing is carried out at 300 mm from both ends of the end faces, the annealing temperature is 680°C ± 10°C, and the annealing time is 2.5 hours. After annealing, connection threads are processed.

[0016] (7) After the cold working is completed, the drill rod is carburized at a temperature of 910 °C ± 10 °C. The carburizing is carried out by a strong carburizing + diffusion process. The carbon potential during the strong carburizing period is 1.0 - 1.1, and the carbon potential during the diffusion period is 0.7. After diffusion, the drill rod is cooled to 860 °C for soaking. After reaching the temperature, it is held for 30 minutes. The material after soaking is taken out of the furnace and enters the air-cooling tower for quenching. During the period of 500 °C - 860 °C, the cooling rate is controlled above 20 °C / min. During the period of 300 - 500 °C, the cooling rate is controlled at 5.5 °C / min. Below 300 °C, rapid cooling is adopted, and the cooling intensity is greater than 5.4 °C / min to room temperature. The quenched material enters the furnace for tempering treatment at 160 - 200 °C.

[0017] Furthermore, the production method uses continuous casting billet rolled material as raw material, and the rolling reduction ratio should be greater than 8. Then, it is processed by drilling the core, hot rolling with the core, and removing the core before making the drill rod.

[0018] Furthermore, the production method requires hot rolling with the core. The gap between the mandrel and the base material is 1 - 1.5 mm. A coating with a thickness of 0.2 - 0.4 mm must be added to the surface of the mandrel to prevent the drill rod and the base material from being welded together during the subsequent rolling process.

[0019] Furthermore, during quenching after carburizing, the production method adopts step quenching. During the period of 500 °C - 860 °C, the cooling rate is controlled above 20 °C / min. During the period of 300 - 500 °C, the cooling rate is controlled at 5.5 °C / min. Below 300 °C, rapid cooling is adopted, and the cooling intensity is greater than 5.4 °C / min to room temperature.

[0020] Optionally, the coating applied on the surface of the mandrel in the production method uses lime aqueous solution with a concentration of 50 - 70%. The thickness of the applied lime water coating is 0.2 - 0.4 mm.

[0021] Beneficial effects: Compared with the prior art, the present invention has developed a new production process for drill rods. The matrix structure of the drill rod produced by this method is uniform, the banding level is controlled within 0.5 level, the tissue uniformity is significantly improved, the longitudinal and transverse properties of the material are greatly improved, and the bending fatigue performance of the threaded part and the stress corrosion resistance of the inner hole are improved.

[0022] The banding level of the drill rod using this production method is controlled at 0.5 level, the grain size is controlled above 8.5 level, and the martensite-austenite level of the carburized layer is controlled within 2.0. The rock drilling life of the drill rod can reach the advanced level at home and abroad. Through rapid cooling by water injection after rolling, the banding level in the steel is reduced to within 1.5 levels. After subsequent drill rod processing and surface carburizing, the surface carburized layer is controlled at 0.9 - 1.1 mm, and the carbon concentration is controlled at 0.5 - 0.7%, resulting in a significant improvement in the rock drilling life. Specific embodiments

[0023] The present invention will be specifically described below in conjunction with specific embodiments and examples, and the advantages and various effects of the present invention will be presented more clearly therefrom. Those skilled in the art should understand that these specific embodiments and examples are used to illustrate the present invention, rather than limiting the present invention.

[0024] The technical solution of the embodiment of the present application is to solve the above technical problems, and the general idea is as follows:

[0025] According to a typical embodiment provided by the present invention, a production method for controlling the banded structure of a CrNiMo carburized drill rod is provided, including the following steps:

[0026] (1) Using continuous casting billet rolled material as raw material, the size of the continuous casting billet rolled material is controlled at φ160 - 180, and the reduction ratio is greater than 8.

[0027] (2) After drilling, core - inserted hot rolling is carried out, and water - through controlled cooling is carried out after hot rolling.

[0028] (3) The hot - rolled finished product is cut to length and core - removed.

[0029] (4) Drill rod production.

[0030] (5) Carburizing quenching and tempering.

[0031] The production method uses continuous casting billet rolled material as raw material, and the reduction ratio is required to be greater than 8 to ensure the density of the raw material and at the same time control the banded grade of the base metal. Then, the production process of drill rod is carried out through drilling, core - inserting, core - inserted hot rolling, and core - removing.

[0032] In the production method, it is required to apply 0.2 - 0.4 mm coating on the surface of the mandrel, and control the gap between the mandrel and the base metal at 1 - 1.5 mm, to ensure the roundness of the core hole and prevent the base metal from welding with the mandrel during the rolling process.

[0033] In the method, the temperature of the second heating stage during rolling is controlled at 1120 - 1200 °C, the soaking temperature is controlled at 1140 - 1200 °C, and the heating time is controlled at 2.8 - 3.5 h.

[0034] The reason for controlling the rolling heating temperature and heating time is to ensure the high - temperature diffusion of the billet, reduce the composition segregation brought by the continuous casting billet, and ensure the uniform temperature of the billet core and surface. If the temperature is greater than 1200 °C, long - time high - temperature heating may produce overheated structure and aggravated decarburization, affecting the surface quality of the rolled material. If the heating time is less than 2.8 hours, the temperature inside and outside the billet is uneven, and if the heating time is longer than 3.5 h, serious decarburization and oxidation will also occur.

[0035] In the production method, after rolling, the bar is rapidly cooled by water - through, and the surface temperature when leaving the water - through device is controlled at 680 - 740 °C, and the temperature when entering the cooling bed is controlled below 740 °C.

[0036] After rolling, the material is passed through water quickly to avoid the growth of grains and the precipitation of the second phase, achieving the purpose of controlling banding.

[0037] During quenching after carburizing in the production method, step quenching is adopted, and the cooling rate is controlled at 20 - 25 °C / min during the period of 500 °C to 860 °C.

[0038] During the period of 500 - 860 °C, the cooling rate is controlled to quickly pass through the two-phase region to achieve the control of tissue uniformity. If the cooling rate is higher than 25 °C / min, the thermal stress of the drill rod will increase, resulting in uneven temperatures at different parts of the drill rod in the furnace and increasing the bending degree of the drill rod.

[0039] As an optional rolling process, the semi-continuous rolling process is adopted. The starting rolling temperature is controlled at 1050 - 1100 °C, the temperature for entering continuous rolling is controlled at 940 °C to 980 °C, and the finishing rolling temperature is 890 - 950 °C. The rolling specifications are hollow steel with H35, R38, R46, and R52.

[0040] Controlling the starting rolling temperature at 1050 - 1100 °C is to ensure the temperature for entering continuous rolling and the finishing rolling temperature, and to control the grain size of the material. The finishing rolling temperature needs to be controlled within the temperature range of 850 °C - 950 °C because when rolling below 850 °C or above 950 °C, the low-carbon high-nickel steel is prone to appear with coarse grains, mixed grains and other structures.

[0041] As an option, the surface of the mandrel adopts a lime aqueous solution, and lime water is smeared on the surface of the mandrel with a thickness of 0.2 - 0.4 mm.

[0042] Controlling the thickness of the lime water smeared on the surface of the mandrel to be 0.2 - 0.4 mm is to ensure that the mandrel and the base material will not be welded and adhered during the subsequent high-temperature rolling. A thickness greater than 0.4 mm will increase the difficulty of loading the mandrel.

[0043] The production method of the steel for the drill tail of a rock drill according to the present application will be specifically described below with reference to specific embodiments.

[0044] Example 1:

[0045] This embodiment provides a production method for controlling the banded structure of a CrNiMo carburized drill rod, including the following steps:

[0046] (1) Using a φ180 continuous casting billet rolled material as the raw material, and the rolling reduction ratio of the rolled material is greater than 8.

[0047] (2) Drilling the 2.75-meter φ180 rolled material, and the drilling size is

[0048] (3) Using φ47 0 -0.5The bar stock is coated with lime water on the surface and then loaded into the base material and they enter the heating furnace together for heating. The temperature in the preheating section is 530 °C, the temperature in the first heating section is controlled at 965 °C, the second heating section is controlled at 1160 °C, the soaking section temperature is controlled at 1180 °C, the heating time is controlled at 2.8 h, and the furnace outlet temperature is 1080 °C.

[0049] (4) The starting rolling temperature is 1050, the temperature entering the continuous rolling is 960 °C, and the finishing rolling temperature is 910 °C

[0050] (5) After rolling, it passes through water, the temperature out of the water tank is 690 °C, and the temperature entering the cooling bed is 725 °C. After sizing and sawing, it is put into the heat preservation pit for 24 hours.

[0051] (6) After sizing the rolled material, core extraction is carried out. The core-extracted material is processed for making brazing rods and carburized. After carburizing, it is directly soaked at 860 °C for half an hour and then enters the fractional cooling tower for quenching and tempering. The cooling rate in the first stage is 21 °C / min. When the temperature drops to 520 °C, the cooling rate is reduced to 5 °C / min. After the temperature drops to 300 °C, rapid cooling is carried out to increase the cooling rate to 5.5 °C / min.

[0052] Example 2:

[0053] This example provides a production method for controlling the banded structure of CrNiMo carburized brazing rods, including the following steps:

[0054] (1) Use the φ165 continuous casting billet rolled material as the raw material, and the rolling reduction ratio of the rolled material is greater than 8.

[0055] (2) Drill holes in the 2.75-meter φ165 rolled material, and the drilling size is

[0056] (3) Use The bar stock is coated with lime water on the surface and then loaded into the base material and they enter the heating furnace together for heating. The temperature in the preheating section is 550 °C, the temperature in the first heating section is controlled at 980 °C, the second heating section is controlled at 1140 °C, the soaking section temperature is controlled at 1160 °C, the heating time is controlled at 2.9 h, and the furnace outlet temperature is 1080 °C.

[0057] (4) The starting rolling temperature is 1080, the temperature entering the continuous rolling is 970 °C, and the finishing rolling temperature is 915 °C

[0058] (5) After rolling, it passes through water, the temperature out of the water tank is 700 °C, and the temperature entering the cooling bed is 730 °C. After sizing and sawing, it is put into the heat preservation pit for 24 hours.

[0059] (6) After sizing the rolled material, core extraction is carried out. The core-extracted material is processed into drill rods and carburized. After carburization, it is directly soaked at 860 °C for half an hour and then enters the fractionated cooling tower for quenching and tempering. The cooling rate in the first stage is 22 °C / min. When the temperature drops to 520 °C, the cooling rate is reduced to 4.5 °C / min. After the temperature drops to 300 °C, rapid cooling is carried out to increase the cooling rate to 5.8 °C / min.

[0060] Comparative Example 1:

[0061] The production of ordinary drill rods includes the following production steps:

[0062] (1) Use a continuous casting billet rolled material with a diameter of φ180 as the raw material, and the rolling reduction ratio of the rolled material is greater than 8.

[0063] (2) Drill a hole in the φ165 rolled material with a length of 2.75 meters, and the drilling size is

[0064] (3) Use bar stock, load it into the base material and then enter the heating furnace together for heating. The temperature in the preheating section is 550 °C, the temperature in the first heating section is controlled at 980 °C, the second heating section is controlled at 1060 °C, the soaking section temperature is controlled at 1070 °C, the heating time is controlled at 2.3 h, and the furnace outlet temperature is 1000 °C.

[0065] (4) The rolling start temperature is 980, the temperature entering the continuous rolling is 930 °C, and the final rolling temperature is 890 °C

[0066] (5) After sizing and sawing, it is put into the heat preservation pit for 24 hours.

[0067] (6) After sizing the rolled material, core extraction is carried out. The core-extracted material is processed into drill rods and carburized. After carburization, it is directly soaked at 860 °C for half an hour and then enters the fractionated cooling tower for quenching and tempering. In the first stage, a constant wind speed is adopted, and the cooling rate of the drill rod is 4.5 - 18 °C / min. After the temperature drops to 300 °C, rapid cooling is carried out to increase the cooling rate to 5.8 °C / min.

[0068] The CrNiMo series alloy steel provided in Examples 1 - 2 and Comparative Example 1 is prepared into the same steel for the shank of the drill rod, and physical detection and comparison are carried out. The specific results are shown in the following table.

[0069]

[0070]

[0071] As can be seen from the above table, compared with Comparative Example 1, the steel materials for the shank of the drill rod provided in Examples 1 - 2 of the present application are in a better level in terms of indicators of grain size, carburized layer structure, banding level and other tissue homogenization. The rock drilling life of the shank products produced has also been greatly improved.

[0072] Throughout the specification, unless otherwise specifically stated, the terms used herein shall be understood to have the meanings as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention pertains. In case of any contradiction, this specification shall prevail. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in the present invention can be obtained through market purchase or can be prepared by existing methods.

Claims

1. A method for producing a CrNiMo carburized drill rod with controlled banded structure, characterized in that: The following steps are involved: (1) Continuous casting billet rolling is used as the raw material, and the continuous casting billet rolling ratio is required to be greater than 8; (2) Mechanical drilling is used to remove loose materials in the core of the continuous casting billet, and a core rod is inserted into the inner hole after drilling, with a gap between the core rod and the core hole of 1 to 1.5 mm; before inserting the core rod, a coating with a thickness of 0.2 to 0.4 mm is applied on the surface of the core rod; (3) The raw material with the core rod is put into the heating furnace for heating. The temperature of the preheating section is lower than 550°C, the temperature of the first heating section is controlled at 940-1100°C, the temperature of the second heating section is controlled at 1120-1200°C, the temperature of the soaking section is controlled at 1140-1200°C, the heating time is controlled at 2.8-3.5h, and the temperature out of the heating furnace is controlled at 1050-1150°C; (4) The rolling adopts semi-continuous rolling, the starting rolling temperature is controlled at 1050-1100°C, the entering continuous rolling temperature is controlled at 940°C-980°C, the final rolling temperature is 850-950°C, and the rolling specifications are hollow steel of H35, R38, R46 and R52; (5) After rolling, the bar is cooled quickly by water penetration, the surface temperature of the water piercer is controlled at 680-740°C, the temperature entering the bed is controlled below 740°C, the material entering the bed is quickly collected, and the collection temperature is controlled above 300°C. The rolled material is quickly collected and slowly cooled in the pit, and the insulation time is 24 hours. After the insulation, the hollow steel is cut to a fixed length and the core material is extracted; (6) After the hollow steel is cut to size, the parts that need to be upset are heated to 1050-1150℃ by induction heating and then forged. After forging, the two ends are immediately softened and annealed at 300mm from the end face. The annealing temperature is 680℃±10℃ and the annealing time is 2.5 hours. After annealing, the connecting threads are processed; (7) After cold processing, the drill rod is carburized at a temperature of 910°C ± 10°C. The carburizing process is strong carburizing + diffusion. The carbon potential during the strong carburizing period is 1.0-1.1, and the carbon potential during the diffusion period is 0.

7. The drill rod after diffusion is cooled to 860°C for uniform heating. After reaching the temperature, it is kept warm for 30 minutes. The material after uniform heating is taken out of the furnace and enters the air cooling tower for quenching. The cooling rate is controlled at 20-25°C / min during the period of 500°C to 860°C, and the cooling rate is controlled at 5.5°C / min during the period of 300-500°C. Rapid cooling is used below 300°C, and the cooling intensity is greater than 5.4°C / min to room temperature. The quenched material enters the furnace for tempering at 160-200°C.

2. The method for producing a CrNiMo carburizing drill rod with controlled banded structure according to claim 1, characterized in that: In the step (1), the size of the rolled material is φ160-180 and the length is 1.5-3 meters.

3. The method for producing a CrNiMo carburizing drill rod with controlled banded structure according to claim 1, characterized in that: In the step (2), the drilling hole size is φ43-67; the coating is lime water solution with a concentration of 50-70%.

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