Abrasion-resistant, corrosion-resistant and long-fatigue-life square steel for light hollow drill rod and production method of square steel

Abstract

The invention relates to wear-resistant, corrosion-resistant and long-fatigue-life square steel for a light drill rod and a production method of the square steel. The production method comprises the following steps of converter smelting, external refining, RH vacuum degassing, round billet continuous casting, slow cooling, stepping furnace heating, 1100 rolling mill cogging, continuous rolling mill rolling, slow cooling, peeling, shot blasting and chamfering and inspection and inspection. The square steel for the drill rod produced through the method is uniform in chemical component and compact in macrostructure, zero decarburized layer delivery is achieved, the use requirement of the light hollow drill rod is completely met, the manufactured drill rod is good in corrosion resistance and abrasion resistance, the rock drilling fatigue life of the hollow drill rod can be prolonged under the complex working condition environment, and the construction cost is reduced.

Description

Technical Field

[0001] The invention relates to a square steel for a light hollow drill rod which is wear-resistant, corrosion-resistant and has a long fatigue life and a production method thereof, and belongs to the technical field of alloy steel materials. Background Art

[0002] Rock drilling tools are tools used to drill rocks and soil. They are widely used in mining, urban subways, highways and other engineering construction projects. They are essential consumable tools for engineering construction. As a key component of rock drilling tools, hollow drill rods are subjected to longitudinal stress, bending stress, torsional stress and mine water corrosion during service. They are subjected to complex forces and work in harsh environments. After a certain period of use, they fail in the form of wear and fracture and cannot be used any more. It is necessary to develop higher-grade drill rod products to further improve product fatigue life and enhance market competitiveness.

[0003] In view of the above problems, the present invention provides a square steel for a light hollow drill rod which is wear-resistant, corrosion-resistant and has a long fatigue life, and a production method thereof. Summary of the invention

[0004] In order to solve the above problems, the present invention discloses a square steel for a light hollow drill rod with wear resistance, corrosion resistance and high fatigue life and a production method thereof. The specific technical scheme is as follows: The invention discloses a square steel for a light hollow drill rod with wear resistance, corrosion resistance and high fatigue life. The square steel belongs to a new type of alloy structural steel of medium C-high Si-MoV series designed according to the microalloying principle, and comprises components and the mass percentage of each component is as follows: C 0.50-0.60%, Si 1.10-1.40%, Mn 0.50-0.90%, P 0.018%, S 0.005-0.020%, Cr 0.10%, Ni 0.10%, Mo 0.40-0.60%, V 0.01-0.06%, Cu 0.10%, Al 0.010-0.040%, O 0.0015%, N 0.0050-0.010%, H 0.00015%, and the rest is Fe and unavoidable impurities.

[0005] A production method for the above-mentioned wear-resistant, corrosion-resistant, and long fatigue life light square steel for hollow drill rods, comprising the steps of smelting → continuous casting of round billets → slow cooling → heating in a walking furnace → billeting with a 1100 rolling mill → rolling with a continuous rolling mill → slow cooling → peeling → shot blasting, chamfering → inspection and examination, and the specific steps are as follows: Step 1, smelting: adopt converter smelting + LF refining + RH vacuum degassing, converter tapping temperature is 1610-1650℃, alloy is added with tapping, LF arrival temperature is greater than 1500℃, temperature is 1600℃~1650℃, enters RH station for vacuum degassing treatment, RH vacuum holding time is greater than 25 minutes, maximum vacuum degree is 100Pa, after breaking vacuum, hydrogen content of molten steel is less than 1.2ppm, weak argon stirring soft blowing is carried out according to molten steel temperature, soft blowing time is 25-35 minutes; Step 2, continuous casting of round billets: after vacuum degassing, the temperature of the molten steel is controlled at 1545-1565°C, the ladle is placed in the LF furnace station to adjust the temperature, the ladle is placed in the five-machine five-stream large round billet continuous casting machine for continuous casting, and the crystallizer, the end, and the secondary cooling section are electromagnetically stirred; Step 3, slow cooling: the continuous casting round billet is put into the pit for slow cooling in time, the slow cooling pit is covered, and the slow cooling time is more than 72h; Step 4, heating in a walking beam furnace: the continuous casting round billet is cold loaded into the furnace, and an empty step is added. The preheating section temperature is 550-850°C, the heating section temperature is 860-1030°C, the heating section temperature is 1200-1240°C, the soaking section temperature is 1220-1260°C, and the total heating time is 6-9h; Step 5, 1100 rolling mill: the 1100 rolling mill has a temperature of 1100-1150°C, and reciprocating rolling is performed for 15 passes to produce a semi-finished product with a size of 170 mm×180 mm; Step 6, rolling by continuous rolling mill: the rolling temperature of continuous rolling mill is greater than 900°C, the fourth rolling mill produces finished products, the finished product size is 150mm×150mm, the total rolling ratio of square steel is greater than 7.0, the length is 5.6 meters and the fixed length is collected, the Brinell hardness is controlled to be less than 298HBW, the cooling bed uses a heat preservation cover, the square steel enters the pit and cools slowly, the pit entry temperature is 450~700°C, and the pit exit temperature is ≤150°C; Step 7, peeling: Use a square billet peeling machine to grind the square steel surface and four edges, the grinding wheel diameter is 550-600mm, the grinding wheel speed is 1900-1950rpm, the trolley speed is 55m / min, the feed amount is 14mm, the grinding depth is 0.8mm~1.0mm, the size deviation after grinding and peeling is ±1.5mm, the diagonal difference is <3.0mm, and the fillet radius is >18mm; Step 8, shot blasting and chamfering: Use a shot blasting machine to mill the surface of the square steel and remove the burrs on the end of the square steel; Step 9, inspection and examination: the curvature of the produced square steel is ≤2.5mm / m, the dimensional deviation is ±1.5mm, the diagonal difference is <3.0mm, the fillet radius is >18mm, and the flaw detection is carried out according to the A-level quality requirements specified in the GB / T 4162 standard.

[0006] Furthermore, the smelting ingredients are: 90% molten iron + 10% scrap steel by mass, the ferroalloy is baked, and the loading amount is controlled at 80-100 tons.

[0007] Furthermore, the converter adopts a top and bottom blowing converter, and the top and bottom blowing converter smelting is specifically as follows: 350-400kg of lime and 200-400kg of dolomite are added to the converter slag, the total slag consumption is 80-100kg / t, the steel tapping P: ≤0.012%, and the steel tapping amount is 85±5 tons; the slag in the ladle during the steel tapping process: 550±100 kg of lime, 100±5 kg of composite deoxidizer, 200±10 kg of pre-melted slag, and the amount of aluminum added per ton of steel: 1.0 kg / t~1.5kg / t; the order of adding the deoxidizer and alloy in the ladle during the converter tapping process: aluminum cake→ordinary carburizer→alloy→low titanium refined slag→lime, which are added in the early stage of converter tapping.

[0008] Further, the LF refining is specifically as follows: when the temperature is ≥1500°C, the LF refining station is entered, and after electric heating for ≥20 minutes, the temperature is appropriate and the slag turns white, a sample is taken to analyze the chemical composition, and according to the composition analysis results, ferromanganese, ferrosilicon, ferromolybdenum, and ferrovanadium are added in batches to adjust the composition according to the internal control chemical composition regulations; argon control during the refining process: 100-400NL / min; Al control during the refining process: the target Al mass content is 0.030-0.050% when entering the refining, such as Al mass If the content is not within the target, feed Al once at the target of 0.050% in the early stage of refining; slag adjustment during the process: add high-purity silicon carbide, aluminum particles and lime for slag adjustment, the target composition of the refined slag is CaO: 40-45%, SiO2: 10-15%, Al2O3: 28-35%, MgO≤10%, basicity R: 3-4.5; after the slag turns white, add Si-C powder and C powder in batches for diffusion deoxidation, add 1.5-2.5kg / time, and the white slag refining time is ≥25 minutes.

[0009] Furthermore, in step 2, a φ500 mm round billet is continuously casted using five machines and five streams, the liquidus temperature of the steel is 1475° C., the continuous casting overheat is controlled at 15 to 35° C., and the pulling speed is 0.31 m / min.

[0010] Furthermore, an optical microscope was used to inspect the depth of the decarburization layer of the hot-rolled square steel. The maximum depth of the decarburization layer at the four sides and corners of the square steel was 0.70 mm, and there was no complete decarburization layer. The decarburization layer included ferrite and a transition layer. After the square steel was peeled, the depth of the decarburization layer was 0, achieving zero decarburization delivery.

[0011] The square steel for light hollow drill rod with wear resistance, corrosion resistance and long fatigue life is obtained by the production method of the square steel for light hollow drill rod with wear resistance, corrosion resistance and long fatigue life.

[0012] Furthermore, the macrostructures of general porosity, central porosity, ingot-shaped segregation, general point segregation, and edge point segregation of the square steel are 0.5-1.0, 1.0-1.5, 0, 0, and 0, respectively; Brinell hardness is 270-275HBW; The austenite grain size is 8.0; The metallographic structure is bainite + a small amount of ferrite.

[0013] Furthermore, segregation detection was performed at the center, 1 / 4 side length and edge of the square steel test block, and the segregation amounts of C, Mn and Mo were obtained as 0.036%, 0.026% and 0.015% respectively.

[0014] The beneficial effects of the present invention are: The square steel involved in the present invention is produced by continuous casting and rolling of large round billets, has uniform chemical composition, dense low-multiple structure, and is delivered with zero decarburization. It is the first time in China that square steel for hollow drill rods is produced by continuous casting and rolling of large round billets.

[0015] The square steel produced by the present invention has uniform chemical composition, dense macrostructure, and zero decarburization layer, and can fully meet the use requirements of light hollow drill rods.

[0016] The hollow drill rod made of the square steel involved in the present invention is wear-resistant, corrosion-resistant and fatigue-resistant during rock drilling under complex working conditions, which can significantly improve the fatigue life of the drill rod and reduce the manufacturing cost. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0018] The square steel of the present invention belongs to a new type of alloy structural steel of medium C-high Si-MoV series designed according to the microalloying principle, including components and the mass percentage of each component is: C 0.50-0.60%, Si 1.10-1.40%, Mn 0.50-0.90%, P0.018%, S 0.005-0.020%, Cr 0.10%, Ni 0.10%, Mo 0.40-0.60%, V 0.01-0.06%, Cu 0.10%, Al 0.010-0.040%, O 0.0015%, N 0.0050-0.010%, H 0.00015%, and the rest is Fe and unavoidable impurities. The specific analysis of each chemical composition is as follows: C is the main strengthening element after iron, which directly affects the strength, plasticity, toughness and other indicators of steel. With the increase of carbon content, the strength and hardness of steel increase, while the plasticity and toughness decrease. In order to ensure the strength and impact toughness of the drill rod, the C content is controlled at 0.50%~0.60%.

[0019] The Si element can form a solid solution with the iron element to improve the strength and hardness of the steel, improve the wear resistance, and form a silicon oxide film on the surface of the steel to improve the corrosion resistance. At the same time, it is an important deoxidizer and reducing agent in the steelmaking process. The Si content is controlled at 1.10%-1.40%.

[0020] The Mn element can form an infinite solid solution with Fe, which can improve the strength of steel and has little effect on the plasticity index. The Mn content is controlled at 0.50%-0.90%.

[0021] P and S are harmful elements in steel. If the content of P and S is high, the impact toughness and corrosion resistance of steel can be significantly reduced. To ensure the cutting performance of the product, a certain content of S should be controlled, P < 0.018%, S: 0.005%-0.020%.

[0022] Cr and Ni elements are used to improve hardenability, impact toughness and strength of steel. According to product performance requirements and new steel grade design ideas, Cr and Ni elements are controlled to be less than 0.10%.

[0023] The Mo element can improve the hardenability of steel, inhibit the segregation of harmful elements and improve the temper brittleness of steel. It can form dense oxides to improve the corrosion resistance of steel. The Mo content is controlled at 0.40%-0.60%.

[0024] V element is the main element for refining steel structure and grains, mainly existing in the form of carbides and nitrides, improving strength and toughness and wear resistance. The V content is controlled at 0.01%-0.06%.

[0025] The Al element can improve the hardenability of steel, and cooperate with nitrogen to improve the surface hardness and wear resistance of steel. At the same time, as the main deoxidizer, it can also play a role in refining grains. The Al content is controlled at 0.010% to 0.040%.

[0026] The interaction between N element and V and Al can improve the strength and corrosion resistance of steel. It can also affect the plasticity and toughness of steel and increase the failure tendency. Reasonable control is very important. The N content is controlled at 0.0050-0.010%.

[0027] O and H are harmful elements in steel and affect the fatigue life of the product. Oxygen exists in steel in the form of inclusions such as oxides. The smelting process requires deep deoxidation to ensure the vacuum degassing effect, reduce the oxygen and hydrogen content, improve the purity, and control O < 0.0015% and H < 0.00015%.

[0028] Combined with the above analysis of elements, the chemical elements in the square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life of the present invention have synergistic effects and are indispensable.

[0029] The chemical composition design of the square steel for the light hollow drill rod with wear resistance, corrosion resistance and high fatigue life involved in the present invention is shown in Table 1.

[0030] Table 1 Unit: %

[0031] The present invention also relates to a method for preparing the above-mentioned square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life, the process comprising: Smelting → continuous casting of round billets → slow cooling → heating in a walking furnace → billeting in 1100 rolling mill → rolling in a continuous rolling mill → slow cooling → peeling → shot blasting, chamfering → inspection and examination. The specific description of each process is as follows: The specific smelting method is: converter smelting + LF refining + RH vacuum degassing, the converter tapping temperature is 1610-1650°C, alloys are added during tapping, LF arrival temperature is >1500°C, RH vacuum holding time is greater than 25 minutes, the maximum vacuum degree is 100Pa, and the soft blowing time is 25-35 minutes.

[0032] The method of continuous casting round billets is specifically as follows: five-machine five-strand large round billets φ500mm are continuously cast, the liquidus temperature of the steel is 1475°C, the continuous casting superheat is controlled at 15-35°C, the pulling speed is controlled at 0.31m / min, and the crystallizer, end, and second cooling section are electromagnetically stirred.

[0033] The specific method of slow cooling is: the continuous casting round billet is put into the pit for slow cooling in time, the slow cooling pit is covered, and the slow cooling time is greater than 72h.

[0034] The specific method of heating in a walking beam furnace is as follows: the continuous casting billet is charged into the furnace in a cold state, an empty step is added, the preheating section temperature is 550-850°C, the heating section temperature is 860-1030°C, the heating section temperature is 1200-1240°C, the soaking section temperature is 1220-1260°C, and the total heating time is 6-9h.

[0035] The specific method of 1100 rolling mill is as follows: the 1100 rolling mill has a temperature of 1100-1150°C, and reciprocating rolling is performed for 15 passes to produce a semi-finished product with a size of 170mm×180mm.

[0036] The specific rolling method of the continuous rolling mill is as follows: the rolling temperature of the continuous rolling mill is greater than 900°C, the fourth rolling mill produces finished products, the finished product size is 150mm×150mm, the total rolling ratio of square steel is greater than 7.0, the length is 5.6 meters and the fixed length is collected, the Brinell hardness is controlled to be less than 298HBW, the cooling bed uses a heat preservation cover, the square steel enters the pit and cools slowly, the pit entry temperature is 450~700°C, and the pit exit temperature is ≤150°C; The specific method of peeling is: use a square billet peeling machine to grind the square steel surface and four edges, the grinding wheel diameter is 550-600mm, the grinding wheel speed is 1900-1950rpm, the trolley speed is 55m / min, the feed amount is 14mm, and the grinding depth is 0.8mm~1.0mm. After grinding and peeling, the size deviation is ±1.5mm, the diagonal difference is <3.0mm, and the fillet radius is >18mm.

[0037] The inspection and examination results are: the curvature of the produced square steel is ≤2.5mm / m, the dimensional deviation is ±1.5mm, the diagonal difference is <3.0mm, the fillet radius is >18mm, and the flaw detection is carried out according to the A-level quality requirements specified in the GB / T 4162 standard.

[0038] The performance indicators of the square steel for hollow drill rod prepared by the method of the present invention are as follows: (1) Low-magnification tissue (Table 2): / level Table 2

[0039] (2) Brinell hardness: square steel Brinell hardness 270-275 HBW; (3) Non-metallic inclusions (Table 3): / Grade Table 3

[0040] (4) The austenite grain size is 8.0.

[0041] (5) Metallographic structure and decarburization layer: The metallographic structure is bainite + a small amount of ferrite. The maximum depth of the decarburization layer (ferrite + transition layer) at the four sides and corners of the hot-rolled square steel is 0.70 mm, and there is no complete decarburization layer. The depth of the decarburization layer of the square steel after peeling is 0.

[0042] (6) Composition segregation (Table 4): / % Table 4 Example

[0043] The production method of the square steel for light hollow drill steel with wear resistance, corrosion resistance and high fatigue life involved in this embodiment comprises: Smelting → continuous casting of round billets → slow cooling → heating in walking beam furnace → billet opening by 1100 rolling mill → rolling by continuous rolling mill → slow cooling → peeling → shot blasting, chamfering → inspection and examination.

[0044] (1) Round billet smelting The smelting adopts top and bottom blowing converter + LF refining + RH vacuum degassing + five-machine five-stream continuous casting of large round billets.

[0045] Ingredients: 90% molten iron + 10% scrap steel. The ferroalloy must be baked and the loading amount is controlled at 80-100 tons.

[0046] The top and bottom blowing converter smelting is as follows: 350-400kg lime and 200-400kg dolomite are added to the converter slag, the total slag consumption is 80-100kg / t, and the steel tapping P is ≤0.012%. The tapping temperature is 1610℃~1660℃, and the tapping volume is 85±5 tons. The slag in the tapping process is: 550±100 kg lime, 100±5 kg composite deoxidizer, 200±10 kg pre-melted slag, and the amount of aluminum added per ton of steel is 1.0 kg / t~1.5kg / t. The order of adding deoxidizers and alloys in the tapping process of the converter is: aluminum cake → ordinary carburizer → alloy → low titanium refined slag → lime, which is added in the early stage of converter tapping.

[0047] LF refining is as follows: when the temperature is ≥1500℃, enter the LF refining station, and after electric heating for ≥20 minutes, when the temperature is appropriate and the slag turns white, take samples to analyze the chemical composition. According to the composition analysis results, add ferromanganese, ferrosilicon, ferromolybdenum, and ferrovanadium in batches to adjust the composition according to the internal control chemical composition regulations; argon control during refining: 100-400NL / min. Al control during refining: the target Al (0.030-0.050%) is set when entering the refining. If it is not within the target, feed Al once at the target of 0.050% in the early stage of refining. Slag adjustment during the process: high-purity silicon carbide, aluminum particles, lime, etc. can be appropriately added for slag adjustment. The target composition of the refined slag is CaO: 40-45%, SiO2: 10-15%, Al2O3: 28-35%, MgO≤10%, and basicity R: 3-4.5. After the slag turns white, Si-C powder and C powder can be added in small amounts and multiple batches for diffusion deoxidation, at a rate of 1.5-2.5 kg / time, and the white slag refining time is ≥25 minutes.

[0048] RH vacuum degassing is specifically as follows: the temperature is 1600℃~1650℃, and the steel is put into the RH station for vacuum degassing. The vacuum degree is maintained at 100pa for ≥25 minutes. After breaking the vacuum, the hydrogen content of the molten steel is less than 1.2ppm. According to the temperature of the molten steel, soft blowing (weak argon stirring) operation is performed for 20~35 minutes.

[0049] Continuous casting of large round billets: After vacuum degassing, the temperature of the molten steel is controlled at 1545~1565℃, the ladle is put into the LF furnace station to adjust the temperature, and the ladle is put into the five-machine five-stream large round billet continuous casting machine for continuous casting of the continuous casting billet. The electromagnetic stirring, cooling parameters, and straightening machine parameters are appropriate to produce high-quality continuous casting large round billets with high purity and high uniformity.

[0050] Slow cooling of continuous casting billets: The continuous casting billets are put into the pit for slow cooling in time and covered with insulation covers. The slow cooling time is greater than 72 hours.

[0051] (2) Rolled square steel Walking beam furnace heating: φ500mm continuous casting billet is heated by walking beam heating furnace. The continuous casting billet is loaded into the furnace in cold state, and the loading method is to add an empty step. The preheating section temperature is 550~850℃, the heating section temperature is 860~1030℃, the heating section temperature is 1200~1240℃, the soaking section temperature is 1220~1260℃, and the total heating time is 6~9h.

[0052] The specific method of 1100 rolling mill is as follows: the 1100 rolling mill has a temperature of 1100-1150°C, and reciprocating rolling is performed for 15 passes to produce a semi-finished product with a size of 170mm×180mm.

[0053] The specific rolling method of the continuous rolling mill is: the starting temperature of the continuous rolling mill is greater than 900°C, the fourth rolling mill produces finished products, the finished product size is 150mm×150mm, the total rolling ratio of square steel is greater than 7.0, the length is 5.6 meters and the fixed length is collected, the Brinell hardness is controlled to be less than 298HBW, the cooling bed uses a heat preservation cover, the square steel enters the pit for slow cooling, the pit entry temperature is 450~700°C, and the pit exit temperature is ≤150°C.

[0054] (3) Peeling The specific method of peeling is: use a square billet peeling machine to grind the square steel surface and four edges, the grinding wheel diameter is 550-600mm, the grinding wheel speed is 1900-1950rpm, the trolley speed is 55m / min, the feed amount is 14mm, and the grinding depth is 0.8mm~1.0mm. After grinding and peeling, the size deviation is ±1.5mm, the diagonal difference is <3.0mm, and the fillet radius is >18mm.

[0055] Shot blasting and chamfering is to use a shot blasting machine to mill the surface of the square steel and remove the burrs on the end of the square steel.

[0056] The inspection and examination results are: the curvature of the produced square steel is ≤2.5mm / m, the dimensional deviation is ±1.5mm, the diagonal difference is <3.0mm, the fillet radius is >18mm, and the flaw detection is carried out according to the A-level quality requirements specified in the GB / T 4162 standard.

[0057] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0058] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life, characterized in that: The square steel belongs to a new type of alloy structural steel of medium C-high Si-MoV series designed according to the microalloying principle, including components and the mass percentage of each component is as follows: C 0.50-0.60%, Si 1.10-1.40%, Mn 0.50-0.90%, P 0.018%, S 0.005-0.020%, Cr0.10%, Ni 0.10%, Mo 0.40-0.60%, V 0.01-0.06%, Cu 0.10%, Al 0.010-0.040%, O 0.0015%, N 0.0050-0.010%, H 0.00015%, and the rest are Fe and unavoidable impurities.

2. A method for producing square steel for light hollow drill rods with wear resistance, corrosion resistance and high fatigue life as claimed in claim 1, characterized in that: It includes the following processes: smelting → continuous casting of round billets → slow cooling → heating in a walking furnace → billeting in 1100 rolling mill → rolling in a continuous rolling mill → slow cooling → peeling → shot blasting, chamfering → inspection and examination. The specific processes are as follows: Step 1, smelting: adopt converter smelting + LF refining + RH vacuum degassing, converter tapping temperature is 1610-1650℃, alloy is added with tapping, LF arrival temperature is greater than 1500℃, temperature is 1600℃~1650℃, enters RH station for vacuum degassing treatment, RH vacuum holding time is greater than 25 minutes, maximum vacuum degree is 100Pa, after breaking vacuum, hydrogen content of molten steel is less than 1.2ppm, weak argon stirring soft blowing is carried out according to molten steel temperature, soft blowing time is 25-35 minutes; Step 2, continuous casting of round billets: after vacuum degassing, the temperature of the molten steel is controlled at 1545-1565°C, the ladle is placed in the LF furnace station to adjust the temperature, the ladle is placed in the five-machine five-stream large round billet continuous casting machine for continuous casting, and the crystallizer, the end, and the secondary cooling section are electromagnetically stirred; Step 3, slow cooling: the continuous casting round billet is put into the pit for slow cooling in time, the slow cooling pit is covered, and the slow cooling time is more than 72h; Step 4, heating in a walking beam furnace: the continuous casting round billet is cold loaded into the furnace, and an empty step is added. The preheating section temperature is 550-850°C, the heating section temperature is 860-1030°C, the heating section temperature is 1200-1240°C, the soaking section temperature is 1220-1260°C, and the total heating time is 6-9h; Step 5, 1100 rolling mill: the 1100 rolling mill has a temperature of 1100-1150°C, and reciprocating rolling is performed for 15 passes to produce a semi-finished product with a size of 170 mm×180 mm; Step 6, rolling by continuous rolling mill: the rolling temperature of continuous rolling mill is greater than 900°C, the fourth rolling mill produces finished products, the finished product size is 150mm×150mm, the total rolling ratio of square steel is greater than 7.0, the length is 5.6 meters and the fixed length is collected, the Brinell hardness is controlled to be less than 298HBW, the cooling bed uses a heat preservation cover, the square steel enters the pit and cools slowly, the pit entry temperature is 450~700°C, and the pit exit temperature is ≤150°C; Step 7, peeling: Use a square billet peeling machine to grind the square steel surface and four edges, the grinding wheel diameter is 550-600mm, the grinding wheel speed is 1900-1950rpm, the trolley speed is 55m / min, the feed amount is 14mm, the grinding depth is 0.8mm~1.0mm, the size deviation after grinding and peeling is ±1.5mm, the diagonal difference is <3.0mm, and the fillet radius is >18mm; Step 8, shot blasting and chamfering: Use a shot blasting machine to mill the surface of the square steel and remove the burrs on the end of the square steel; Step 9, inspection and examination: the curvature of the produced square steel is ≤2.5mm / m, the dimensional deviation is ±1.5mm, the diagonal difference is <3.0mm, the fillet radius is >18mm, and the flaw detection is carried out according to the A-level quality requirements specified in the GB / T 4162 standard.

3. The method for producing square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life according to claim 2, characterized in that: The smelting ingredients are: 90% molten iron + 10% scrap steel in percentage by weight, baked ferroalloy, and the loading amount is controlled at 80-100 tons.

4. The method for producing square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life according to claim 3, characterized in that: The converter adopts a top and bottom blowing converter, and the top and bottom blowing converter smelting is specifically as follows: 350-400kg of lime and 200-400kg of dolomite are added to the converter slag, the total slag consumption is 80-100kg / t, the steel tapping P is ≤0.012%, and the steel tapping amount is 85±5 tons; the slag in the ladle during the steel tapping process includes: 550±100kg of lime, 100±5kg of composite deoxidizer, 200±10kg of pre-melted slag, and the amount of aluminum added per ton of steel is 1.0kg / t-1.5kg / t; the order of adding the ladle deoxidizer and alloy in the converter tapping process is: aluminum cake→ordinary carburizer→alloy→low titanium refined slag→lime, and they are added in the early stage of converter tapping.

5. The method for producing square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life according to claim 2, characterized in that: The LF refining is specifically as follows: when the temperature is ≥1500°C, the LF refining station is entered, and electric heating is applied for ≥20 minutes. After the temperature is appropriate and the slag turns white, a sample is taken to analyze the chemical composition. According to the composition analysis results, ferromanganese, ferrosilicon, ferromolybdenum and ferrovanadium are added in batches according to the internal control chemical composition regulations to adjust the composition; argon control during the refining process: 100-400NL / min; Al control during the refining process: the target Al mass content is 0.030-0.050% when entering the refining, if the Al mass content is not Within the target, feed Al once at the target of 0.050% in the early stage of refining; slag adjustment during the process: add high-purity silicon carbide, aluminum particles and lime for slag adjustment, the target composition of the refined slag is CaO: 40-45%, SiO2: 10-15%, Al2O3: 28-35%, MgO≤10%, basicity R: 3-4.5; after the slag turns white, add Si-C powder and C powder in batches for diffusion deoxidation, adding 1.5-2.5kg / time, and the white slag refining time is ≥25 minutes.

6. The method for producing square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life according to claim 2, characterized in that: In the step 2, a φ500 mm round billet is continuously casted in five machines and five streams, the liquidus temperature of the steel is 1475° C., the continuous casting overheat is controlled at 15-35° C., and the pulling speed is 0.31 m / min.

7. The method for producing square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life according to claim 2, characterized in that: The depth of decarburization layer of hot-rolled square steel was inspected with an optical microscope. The maximum depth of decarburization layer at the four sides and corners of the square steel was 0.70mm. There was no complete decarburization layer. The decarburization layer included ferrite and transition layer. The depth of decarburization layer of the square steel after peeling was 0, achieving zero decarburization delivery.

8. A square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life obtained by the production method of square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life as described in any one of claims 2 to 7.

9. The square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life according to claim 8, characterized in that: The macrostructures of the square steel of general porosity, central porosity, ingot-shaped segregation, general point segregation, and edge point segregation are 0.5-1.0, 1.0-1.5, 0, 0, and 0, respectively; Brinell hardness is 270-275HBW; The austenite grain size is 8.0; The metallographic structure is bainite + a small amount of ferrite.

10. The square steel for light hollow drill rod with wear resistance, corrosion resistance and high fatigue life according to claim 8, characterized in that: The center, 1 / 4 side length and edge positions of the square steel test block were taken for segregation detection, and the segregation amounts of C, Mn and Mo were obtained as 0.036%, 0.026% and 0.015% respectively.

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