A long-life low-cost large-size round steel for a drill rod of a breaking hammer and a manufacturing method thereof

Abstract

This invention discloses a high-life, low-cost, large-size round steel bar for hydraulic breaker chisels and its manufacturing method. The chemical composition of the round steel bar, by mass percentage, is: C: 0.32~0.42%, Si: 0.5~1.4%, Mn: 0.80~1.50%, P: ≤0.025%, S: ≤0.015%, Cr: 1.00~1.40%, Cu: ≤0.25%, Mo: 0.05~0.10%, Nb: 0.02~0.04%, Al: 0.015~0.035%, H: ≤0.0002%, with the balance being Fe and unavoidable impurities. The diameter of the round steel bar ranges from 150 to 250 mm. The manufacturing method includes converter / electric furnace smelting, LF refining, RH / VD degassing, continuous casting, billet surface treatment, round steel rolling, and cooling processes, each with precise process parameter control. The round steel prepared by this invention has good hardenability and excellent strength-toughness matching. The service life of the drill rod made from it is 2-3 times longer than that of 42CrMo, and the amount of Mo added is significantly reduced, effectively controlling production costs. At the same time, it improves the atmospheric corrosion resistance of the drill rod, making it suitable for large-scale hydraulic breakers in mining, building demolition and other fields.

Description

Technical Field

[0001] This invention belongs to the field of high-grade chisel steel manufacturing for hydraulic breakers in the metallurgical industry. Specifically, it relates to a round steel bar for large-size hydraulic breaker chisels with high service life and low cost, and its manufacturing method. It is applicable to the preparation of large-size hydraulic breaker chisels in fields such as mining and building demolition. Background Technology

[0002] As a non-explosive demolition auxiliary machine, hydraulic breakers have become the mainstream breaking method due to their safety and high efficiency, and their application in mining, construction and other fields continues to increase. The chisel is the core component of the hydraulic breaker, which comes into direct contact with hard media such as ore and concrete, and its quality directly determines the working efficiency and working time of the hydraulic breaker.

[0003] The primary failure mode of drill rods during operation is wear, with a small number of abnormal fractures also occurring. The current standard manufacturing process for drill rods is: round steel → sawing → forging → machining → heat treatment (quenching + low-temperature tempering) → salt bath tempering of the drill bit shank → finishing → finished product. To address wear failure, drill rod manufacturers typically increase the hardness after heat treatment by lowering the tempering temperature. However, this method increases the drill rod's brittleness, making it highly susceptible to abnormal fractures during use, resulting in equipment downtime and cost losses.

[0004] Currently, 42CrMo steel is the mainstream material used by drill rod manufacturers. To improve the strength-toughness balance of 42CrMo drill rods, some companies have partnered with steel mills to develop special modified materials, increasing the Mo content to 0.30%-0.40 wt.% and the Mn content to 1.1 wt.% based on 42CrMo. While Mo can increase the tempering temperature and alleviate low-temperature tempering brittleness while maintaining tempering hardness, Mo alloys are expensive. Significantly increasing the Mo content will lead to a significant increase in drill rod manufacturing costs and reduce the product's cost-effectiveness.

[0005] In summary, existing drill rod steels suffer from problems such as short service life, high cost, difficulty in balancing strength and toughness, and insufficient corrosion resistance. How to improve the service life, strength, toughness, and corrosion resistance of drill rods without increasing or even decreasing the Mo content, while controlling production costs, has become a pressing technical challenge in this field. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a high-life, low-cost, large-size hydraulic breaker drill rod round steel and its manufacturing method, addressing the aforementioned shortcomings of existing technologies. By rationally designing the alloy chemical composition and combining it with precise smelting, continuous casting, rolling, and slow cooling processes, the hardenability, toughness, and corrosion resistance of the round steel are synergistically improved, while significantly reducing the amount of Mo added, thus controlling production costs. The drill rods made from the prepared round steel have a service life 2-3 times longer than those made from traditional 42CrMo, and are suitable for large-size hydraulic breakers of 150-250mm, meeting the industry's demand for large-size, high-performance, and low-cost drill rods.

[0007] The technical solution adopted by this invention to solve the above problems is as follows: a round steel bar for high-life, low-cost, large-specification hydraulic breaker chisel rods, wherein the chemical composition of the round steel bar, by mass percentage, is: C: 0.32~0.42%, Si: 0.50~1.40%, Mn: 0.80~1.50%, P: ≤0.025%, S: ≤0.015%, Cr: 1.00~1.40%, Cu: 0.15~0.25%, Mo: 0.05~0.10%, Nb: 0.02~0.04%, Al: 0.015~0.035%, H: ≤0.0002%, with the balance being Fe and unavoidable impurity elements; the diameter of the round steel bar is 150-250mm.

[0008] The design principles and content control criteria for each alloying element are as follows: C: Carbon is a core strengthening element in steel. Too low a content will result in insufficient strength and hardness, failing to meet the wear resistance requirements of the drill rod; too high a content will significantly reduce the plasticity of the steel, easily leading to drill rod breakage. This invention controls the C content at 0.32~0.42%, balancing the strength, hardness, and plasticity of the steel.

[0009] Si: Silicon is a ferrite solid solution strengthening and deoxidizing element, which can effectively strengthen ferrite, improve the yield strength and yield strength ratio of steel, and at the same time have excellent resistance to temper softening. It can replace part of the role of Mo and alleviate low-temperature temper brittleness. This invention increases the Si content to 0.50~1.40% to give full play to its solid solution strengthening and temper softening resistance effects.

[0010] Mn: Manganese is a solid solution strengthening element and an austenite stabilizing element. It can improve the austenitizing stability of steel and enhance the ability to obtain martensite structure during quenching, thereby improving the hardenability of steel and ensuring the uniformity of microstructure of large-size round steel. This invention controls the Mn content at 0.80~1.50%, which is suitable for the hardenability requirements of large-size round steel.

[0011] Cr: Chromium is a hardenability-enhancing element. Adding an appropriate amount can effectively improve the hardenability and strength of steel, and its cost is far lower than that of Mo. However, excessive chromium content will increase steel production costs and easily lead to carbide segregation. This invention controls the Cr content at 1.00~1.40%, improving hardenability while controlling costs.

[0012] Niobium (Nb) is a highly efficient microalloying element that refines austenite grains. It can increase the recrystallization temperature of austenite and, when combined with the rolling process, can significantly refine the austenite grains during rolling, resulting in a uniform fine-grained structure and achieving a synergistic improvement in the strength and toughness of steel. This invention controls the Nb content at 0.02~0.04% to achieve the optimal fine-grain strengthening effect.

[0013] Cu: Copper is an austenite stabilizing element that significantly improves the atmospheric corrosion resistance of steel, solving the problem of rust and spalling of drill rods under open-air storage or complex working conditions, and extending the storage and service life of the drill rods. This invention controls the Cu content at 0.15~0.25%, balancing corrosion resistance and steel processing performance.

[0014] Mo: Molybdenum is a strong carbide-forming element that can improve the steel's resistance to temper softening and reduce and avoid temper brittleness, but it is expensive. This invention reduces the Mo content to 0.05~0.10%, retaining its core role while compensating for performance by increasing the content of Si, Mn, and Cr, thus significantly reducing costs.

[0015] P and S: Phosphorus and sulfur are harmful impurity elements in steel, which can reduce the grain boundary strength of steel, cause grain boundary brittleness, and increase the risk of drill rod breakage; however, excessively low P and S contents will significantly increase smelting costs. This invention controls P to ≤0.025% and S to ≤0.015% within the allowable quality range, balancing grain boundary purity and smelting costs.

[0016] Al: Aluminum is a deoxidizing element for steel, effectively removing oxygen impurities. However, excessive Al content can cause nozzle clogging during continuous casting, affecting production continuity. This invention controls the Al content to 0.015~0.035%, achieving efficient deoxidation while avoiding nozzle clogging.

[0017] H: Hydrogen is a harmful element in high-strength steel, easily causing hydrogen-induced delayed fracture and significantly reducing the safety of the drill rod. This invention strictly controls the hydrogen content in the steel to ≤0.0002% (2ppm), significantly reducing the hydrogen embrittlement sensitivity of high-strength steel and improving the safety of the drill rod.

[0018] The above-mentioned method for manufacturing round steel The process includes the following steps, each controlled with precise process parameters to ensure that the microstructure and properties of the round steel meet design requirements: S1 Steel Smelting The raw materials are sequentially smelted in a converter or electric furnace, refined in an LF furnace, and degassed in an RH or VD furnace to obtain qualified molten steel; wherein: Converter / electric furnace process: control the phosphorus content of tapped steel to ≤0.020% to reduce phosphorus impurities from the source; add slag and alloys along the steel flow during tapping to ensure that the alloys are fully mixed with the molten steel and that the composition is uniform.

[0019] LF refining process: After the reducing slag is formed in the furnace, Nb-containing alloy is added to prevent the Nb element from being oxidized, ensure the yield of the Nb element, and give full play to its grain-refining and strengthening effect.

[0020] RH / VD vacuum degassing: control the vacuum degree <150Pa, vacuum treatment time 15min~20min, effectively remove hydrogen, nitrogen and other gaseous impurities in molten steel, reduce the risk of hydrogen embrittlement; after refining, let the molten steel stand for 20min and perform soft blowing argon treatment to allow the inclusions in the molten steel to float to the surface and be removed, ensuring the purity of the molten steel, and then wait for casting.

[0021] S2 Continuous Casting Large round billets with a diameter of 600-700mm are used for continuous casting, which is suitable for rolling large round bars with a diameter of 150-250mm. The superheat of the molten steel with qualified chemical composition is controlled at 25-45℃ to avoid excessive superheat, which would lead to coarse grains and compositional segregation in the billet. Insufficient superheat would prevent the nozzle from freezing during continuous casting. Argon gas is used for protection during the entire continuous casting process in the tundish to prevent secondary oxidation of the molten steel from contacting air and to ensure the purity of the billet.

[0022] After being flame-cut, the continuously cast billet is immediately sent to a slow cooling pit for cooling. The slow cooling time is >48 hours, and the billet temperature after exiting the pit is <200℃. Through slow cooling, the thermal stress and structural stress inside the billet are effectively released, preventing cracks from forming in the billet. At the same time, the billet structure is ensured to be uniform, avoiding component segregation.

[0023] S3 billet preparation After slow cooling, the continuously cast billet should be subjected to a comprehensive visual inspection. If defects such as cracks, slag inclusions, or scale are found on the surface, they should be removed in a timely manner by mechanical or flame methods to ensure that the billet surface is free of defects and to avoid the expansion of defects during the rolling process, which would affect the quality of the finished round steel.

[0024] S4 round steel rolling The surface-treated billets are cold-charged into a walking beam furnace to avoid uneven billet temperature caused by hot charging. Specific heating parameters are as follows: Preheating section: Temperature ≤700℃, billet heating time 240min~360min, to achieve uniform preheating of billet and prevent thermal stress cracks caused by excessively rapid heating of billet; Heating section + homogenization section: temperature 1140~1220℃, total heating and homogenization time 240-360min, ensuring uniform internal temperature of billet, full austenite formation and uniform grain size, laying the foundation for fine grain strengthening in subsequent rolling.

[0025] After the billet is heated, it is immediately subjected to high-pressure water descaling with a descaling pressure of ≥180 bar to thoroughly remove the iron oxide scale from the surface of the billet and prevent the iron oxide scale from being pressed into the steel body, which would affect the surface quality and mechanical properties of the finished round steel.

[0026] After descaling, the billet enters the rolling mill for rolling. The rolling process is divided into roughing and finishing rolling, and a combination of temperature-controlled rolling and high-reduction rolling is used to achieve grain refinement and uniform microstructure. Rough rolling: A reciprocating rolling mill is used, with a rough rolling temperature of 1050-1150℃. At least 5 passes are rolled with large reduction, and the reduction per pass is ≥20%. Through large reduction rolling, the coarse austenite grains of the billet are broken, and preliminary grain refinement is achieved.

[0027] Finishing rolling: Temperature-controlled rolling is adopted, with a finishing rolling temperature of 900-1000℃ and a total deformation of 30-50%. Rolling within this temperature range can fully utilize the dynamic recrystallization effect of rolling deformation, further refine the austenite grains, obtain a uniform fine-grained structure, and improve the strength and toughness of the steel.

[0028] The rolled bars are immediately hot-saved at a temperature >650℃ to avoid cold cracking caused by low-temperature sawing. The sawn bars are then quickly fed into a slow cooling pit under the cooling bed for slow cooling at a temperature >550℃ to ensure slow cooling during the critical stage of austenite to ferrite / pearlite transformation. The slow cooling time is ≥48h, and the temperature exiting the slow cooling pit is ≤150℃. This effectively releases the internal stress generated during rolling, prevents bar deformation and cracking, and ensures the uniformity of the microstructure of the round steel.

[0029] After the above processes, a high-life, low-cost, large-size round steel bar for hydraulic breaker chisels is obtained.

[0030] Applications of the above-mentioned round steel The round steel of this invention is processed into a hydraulic breaker drill rod according to conventional drill rod manufacturing processes. The specific process is as follows: round steel → sawing → forging rough forming → machining → heat treatment → salt bath tempering of the drill bit tail → finishing → finished drill rod; wherein two heat treatment processes are used, which can be selected according to the working conditions of the drill rod: Low-temperature tempering process: quenching at 870~910℃ + tempering at 200~250℃. After treatment, the tensile strength of the round steel is ≥1650MPa, the hardness is ≥50HRC, and the room temperature impact KV2 is ≥31J. It is suitable for harsh working conditions with high requirements for hardness and wear resistance. Medium-temperature tempering process: quenching at 870~910℃ + tempering at 380~450℃. After treatment, the tensile strength of the round steel is ≥1350MPa, the hardness is ≥40HRC, and the room temperature impact KV2 is ≥31J. It is suitable for working conditions that require a balance between toughness and strength.

[0031] Both heat treatment processes can ensure an excellent balance of strength and toughness in the drill rod, avoiding the problem of traditional drill rods being "hard and brittle, tough but not wear-resistant".

[0032] Compared with the prior art, the present invention has the following beneficial effects: 1. Through alloy composition optimization and precise process control, the round steel prepared by this invention has good hardenability, refined austenite grains, and excellent strength and toughness matching. The service life of the drill rod made from it is 2-3 times longer than that of the traditional 42CrMo, which greatly reduces the replacement frequency and usage cost of the drill rod.

[0033] 2. This invention reduces the Mo content from 0.30%-0.40% in traditional 42CrMo modified materials to 0.05-0.10%. By increasing the Si, Mn, and Cr content, the performance effect of Mo is compensated, which significantly reduces the cost of using precious metal alloys. At the same time, the smelting and rolling processes do not require additional equipment, resulting in low overall production costs.

[0034] 3. The round steel prepared by this invention can reach a diameter of 150-250mm. Through high-reduction rolling, temperature-controlled rolling and precise slow cooling processes, the uniformity of the internal structure and properties of the large-size round steel is ensured, solving the technical problem that traditional drill rod steel is difficult to adapt to large-size hydraulic breakers.

[0035] 4. The manufacturing process of this invention uses conventional metallurgical equipment, and the process parameters of each process are precise and easy to control, avoiding production problems such as nozzle nodules and billet / rolled material cracks caused by excessive Al content. The production has good continuity and stability, and is suitable for large-scale industrial production. Attached Figure Description

[0036] Figure 1 The image shows the metallographic structure of the round steel after heat treatment according to an embodiment of the present invention (observation magnification ×1000). The metallographic structure is uniform tempered martensite. Detailed Implementation

[0037] The technical solution of the present invention will be described in more detail below with reference to preferred embodiments. However, these embodiments are merely descriptions of preferred implementations of the present invention and should not be construed as limiting the scope of the present invention. Example 1

[0038] A high-life, low-cost, large-size hydraulic breaker chisel rod with a diameter of 210mm has the following chemical composition by mass percentage: C: 0.38%, Si: 1.10%, Mn: 1.12%, P: 0.015%, S: 0.002%, Cr: 1.29%, Cu: 0.15%, Mo: 0.06%, Nb: 0.028%, Al: 0.025%, H: 0.0001%, with the balance being Fe and unavoidable impurity elements.

[0039] The manufacturing method of the above-mentioned round steel includes the following steps: Steelmaking: Converter smelting is adopted, and the P content of the tapped steel is controlled to be ≤0.020%. Slag, silicon manganese alloy and ferrochrome alloy are added along the steel stream during tapping. In LF refining, ferroniobium and copper alloy are added after the formation of reducing slag. RH vacuum degassing is adopted with a vacuum degree of 120Pa and a vacuum treatment time of 15min. After refining, the molten steel is allowed to stand for 20min, and then sent to the continuous casting machine after soft blowing of argon gas.

[0040] Continuous casting: 700mm large round billets are used for continuous casting. The molten steel is superheated to 30℃. Argon gas is used for argon protection during the entire casting process in the tundish. After the billets are cut by fire, they are sent to a slow cooling pit for 54 hours. The temperature at the bottom of the pit is 180℃.

[0041] Billet preparation: Visually inspect the billet after slow cooling to remove minor surface defects such as scabs.

[0042] Round steel rolling: The billet is cold-charged into a walking beam furnace, with a preheating section temperature of 650℃ and a heating time of 300 min; the heating section + homogenization section temperature is 1160℃, and the total heating and homogenization time is 600 min; after exiting the furnace, high-pressure water descaling is performed, with a descaling pressure of 200 bar; roughing is carried out using a reciprocating mill, with a roughing temperature of 1120℃, and 6 passes using large reduction rolling, with a single pass reduction of 22-25%; finishing rolling temperature is 950℃, and the total deformation of finishing rolling is 40%; after rolling, it is hot-sawing at a sawing temperature of 680℃; after sawing, it is quickly sent into a slow cooling pit, with an inlet temperature of 580℃, a slow cooling time of 50 h, and an outlet temperature of 120℃ to obtain the finished round steel.

[0043] After the above round steel is quenched at 870~910℃ and tempered at 200~250℃, its mechanical properties are tested: yield strength 1480MPa, tensile strength 1760MPa, room temperature impact KV2 45J, hardness 52HRC; the drill rod made from it has a service life three times that of traditional 42CrMo drill rods when used in mining operations. Example 2

[0044] A high-life, low-cost, large-size hydraulic breaker chisel rod with a diameter of 250mm has the following chemical composition by mass percentage: C: 0.41%, Si: 0.87%, Mn: 1.22%, P: 0.013%, S: 0.001%, Cr: 1.27%, Cu: 0.18%, Mo: 0.08%, Nb: 0.032%, Al: 0.020%, H: 0.0001%, with the balance being Fe and unavoidable impurity elements.

[0045] The manufacturing method of the above-mentioned round steel includes the following steps: Steelmaking: Electric furnace smelting is adopted, and the P content of the tapped steel is controlled to be ≤0.020%. Slag, silicon manganese alloy and ferrochrome alloy are added along the steel flow during tapping. In LF refining, ferroniobium and copper alloy are added after the formation of reducing slag. RH vacuum degassing is adopted with a vacuum degree of 100Pa and a vacuum treatment time of 18min. After refining, the molten steel is allowed to stand for 20min, and then sent to the continuous casting machine after soft blowing of argon gas.

[0046] Continuous casting: 700mm large round billets are used for continuous casting. The molten steel is superheated to 35℃. Argon gas is used for argon protection throughout the casting process in the tundish. After the billets are cut by fire, they are sent to a slow cooling pit for 60 hours. The temperature at the bottom of the pit is 160℃.

[0047] Billet preparation: Visually inspect the slowly cooled billet to remove minor surface cracks and defects.

[0048] Round steel rolling: The billet is cold-charged into a walking beam furnace, with a preheating section temperature of 680℃ and a heating time of 320 min; the heating section + homogenization section temperature is 1180℃, and the total heating and homogenization time is 600 min; after exiting the furnace, high-pressure water descaling is performed, with a descaling pressure of 200 bar; roughing is carried out using a reciprocating mill, with a roughing temperature of 1130℃, and 7 passes using large reduction rolling, with a single pass reduction of 20-24%; finishing rolling temperature is 960℃, and the total deformation of finishing rolling is 45%; after rolling, it is hot-sawing at a sawing temperature of 700℃; after sawing, it is quickly sent into a slow cooling pit, with an inlet temperature of 600℃, a slow cooling time of 55 h, and an outlet temperature of 110℃ to obtain the finished round steel.

[0049] After the above-mentioned round steel was quenched at 870~910℃ and tempered at a low temperature of 200~250℃, its mechanical properties were tested: yield strength 1520MPa, tensile strength 1780MPa, room temperature impact KV2 41J, hardness 53HRC; the drill rod made from it has a service life 2.8 times that of traditional 42CrMo drill rods when used in building demolition conditions.

[0050] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A round steel for a high-life low-cost large-diameter breaking hammer drill rod, characterized by, The chemical composition of the round steel, by mass percentage, is as follows: C: 0.32~0.42%, Si: 0.50~1.40%, Mn: 0.80~1.50%, P: ≤0.025%, S: ≤0.015%, Cr: 1.00~1.40%, Cu: 0.15~0.25%, Mo: 0.05~0.10%, Nb: 0.02~0.04%, Al: 0.015~0.035%, H: ≤0.0002%, with the balance being Fe and unavoidable impurity elements; the diameter of the round steel is 150-250mm.

2. The method of manufacturing a long-life, low-cost, large-diameter round steel for a drill rod of a breaking hammer according to claim 1, characterized in that, The process includes the following steps: S1 steelmaking: The raw materials are successively smelted in a converter or electric furnace, refined in LF, and degassed in RH or VD to obtain qualified molten steel; S2 Continuous casting: The qualified molten steel from step S1 is continuously cast into large round billets. After being flame-cut, the billets are cooled in a slow cooling pit. S3 Billet Preparation: Inspect and treat the surface defects of the continuously cast billet after slow cooling; S4 Round steel rolling: The billet from step S3 is heated, descaled by high-pressure water, rough rolled, and fine rolled, then sawn and slowly cooled to obtain finished round steel. The process parameters for each step meet the requirements for precise control.

3. The method of manufacturing a long-life, low-cost, large-diameter round steel for a drill rod of a breaking hammer according to claim 2, characterized in that, In step S1, the tapping P of the converter or electric furnace process is controlled to be ≤0.020%, and slag and alloy are added along the steel flow during tapping; in the LF refining process, Nb-containing alloy is added after the formation of reducing slag; the vacuum degree of RH or VD vacuum treatment is <150Pa, and the vacuum treatment time is 15min~20min; after refining, the molten steel is allowed to stand for 20min, and then subjected to soft blowing argon gas treatment before casting.

4. The method of manufacturing a long-life, low-cost, large-diameter round steel for a drill rod of a breaking hammer according to claim 2, characterized in that, In step S2, large round billets with a specification of 600~700mm are used for continuous casting, and the superheat of the molten steel is controlled at 25-45℃; argon gas is used for protection during the entire continuous casting process in the tundish; the slow cooling time of the continuously cast billet is >48h, and the billet temperature after exiting the pit is <200℃.

5. The method of manufacturing a long-life, low-cost, large-diameter round steel for a drill rod of a breaking hammer according to claim 2, characterized in that, In step S4, the billet is heated by a walking beam furnace with a preheating temperature of ≤700℃ and a heating time of 240min~360min in the preheating section; the heating and homogenization temperatures are 1140~1220℃ and the total heating and homogenization time is 240-360min.

6. The method of manufacturing a long-life, low-cost, large-diameter round steel for a drill rod of a breaking hammer according to claim 2, characterized in that, In step S4, the descaling pressure of the high-pressure water descaling is ≥180 bar; the roughing is carried out using a reciprocating mill with a roughing temperature of 1050-1150℃, and at least 5 passes of roughing are rolled with large reduction, with a single pass reduction of ≥20%; the finishing is carried out using temperature-controlled rolling with a finishing temperature of 900-1000℃ and a total finishing deformation of 30-50%.

7. The method of manufacturing a long-life, low-cost, large-diameter round steel for a drill rod of a breaking hammer according to claim 2, characterized in that, In step S4, the sawing temperature is >650℃, and the sawn bar is quickly fed into the slow cooling pit under the cooling bed for slow cooling. The temperature entering the slow cooling pit is >550℃; the slow cooling time is ≥48h, and the temperature exiting the slow cooling pit is ≤150℃.

8. Use of a high life low cost large size round steel for a shank of a breaking hammer according to claim 1, characterized in that, The round steel is sawn into blanks, forged into rough shape, machined, heat treated, tempered in a salt bath at the shank, and then trimmed to make a breaker rod; the heat treatment is quenching at 870~910℃ + low-temperature tempering at 200~250℃, or quenching at 870~910℃ + medium-temperature tempering at 380~450℃.

9. Use of a high life low cost large size round steel for a shank of a breaking hammer according to claim 8, characterized in that, The round steel, after being quenched at 870~910℃ and tempered at 200~250℃, has a tensile strength ≥1650MPa, a hardness ≥50HRC, and a room temperature impact KV2 ≥31J; after being quenched at 870~910℃ and tempered at 380~450℃, it has a tensile strength ≥1350MPa, a hardness ≥40HRC, and a room temperature impact KV2 ≥31J.

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