Deformed steel bar with yield strength larger than or equal to 930 MPa and production method

Abstract

The invention discloses engineering machinery steel with excellent plate shape and yield strength larger than or equal to 930 MPa. The engineering machinery steel comprises, by weight, 0.35%-0.50% of C, 0.60%-1.20% of Si, 0.80%-1.40% of Mn, smaller than or equal to 0.035% of P, smaller than or equal to 0.035% of S, 0.050%-0.120% of Al, 0.0008%-0.0035% of B, 0.02%-0.08% of V, 0.0045%-0.0100% of N and 0.50%-0.75% of Zr. Pretreating molten iron; smelting in a converter; refining in an LF furnace; casting into a square billet; heating the casting blank; performing rough rolling and intermediate rolling; finish rolling is conducted according to two sections; cooling is performed; groove profile cold shearing is carried out; and pit cooling to room temperature. On the premise that the hot rolling yield strength Rel is larger than or equal to 930 MPa, the tensile strength Rm is larger than or equal to 1080 MPa, the elongation A is larger than or equal to 6%, and the total elongation Agt under the maximum force is larger than or equal to 3.5%, the product performance is stable, on the premise that the cost is greatly reduced by increasing the heating temperature, the rolling mill load is reduced, the production efficiency is improved, the process adaptability is high, in addition, the process window is wide, and the production cost is reduced. And on-site operation and smooth production are facilitated.

Description

Technical Field

[0001] The present invention relates to a threaded steel and a production method, in particular to a threaded steel with a yield strength of ≥930MPa and a production method, which is particularly suitable for producing a fine-rolled threaded steel with a yield strength of ≥930MPa and a method with a diameter of 25-36mm. Background Art

[0002] Finely rolled threaded steel bar, also known as prestressed concrete threaded steel bar, is a straight steel bar with discontinuous external threads and no longitudinal ribs on the entire surface of the steel bar. This steel bar is directly connected with nuts and spiral sleeves, without welding and machining screw buckles. It has the advantages of simple connection and anchoring, strong adhesion, safe and reliable tensioning and anchoring, convenient construction, fast speed, and material saving. Finely rolled threaded steel bar is widely used in large-scale water conservancy and hydropower projects, continuous beams and large frame structures in industrial and civil buildings, highways, high-speed railways, large bridge baskets, nuclear power plants, ground anchors, slope anchors, and other super-large buildings, frame structures, bridges and culverts and other projects.

[0003] Finished rolled steel bar products are high-tech steel products in China, and have extremely strict requirements on the grade and quality of the products. Since there is no need to consider the impact of welding performance, a variety of micro-alloying or heat treatment processes can be used to produce this steel. According to the characteristics of finished rolled threaded steel bars, the connection device and finished product pass of the finished rolling mill need to be redesigned, and high control accuracy is required during the rolling process.

[0004] Compared with the traditional general bar rolling production line, the high-speed bar production line uses roller ring rolling mill to produce finished products with higher precision. The single-bar torsion-free low-temperature controlled rolling technology is used in the finishing area to achieve alloy reduction production. Placing a single bar for cooling and aligning a single tooth groove on the cooling bed can obtain a higher yield rate. Based on these advantages, high-speed bar production technology has developed rapidly in recent years.

[0005] There are currently two main types of high-speed bar production lines: one is a single-line high-speed bar production line, also referred to as a single-high bar production line, that is, the rough rolling, intermediate rolling, pre-finishing rolling, and finishing rolling units are all single-bar rolling, and after finishing rolling, they are sent to a cooling bed by a set of high-speed steel-loading system; the other is a double-line high-speed bar production line, also referred to as a double-high bar production line, that is, rough rolling and intermediate rolling are single-bar rolling, pre-finishing rolling is two-slice rolling, and after pre-finishing rolling, double lines enter two groups of finishing rolling units at the same time, each line rolls a single bar in each group of finishing rolling, and after finishing rolling, they are merged and sent to the cooling bed by a set of double high-speed steel-loading system that can meet the needs of double lines on the cooling bed at the same time.

[0006] In the national standard GB / T 20065-2016, the chemical composition (melting composition) of finished rolled threaded steel bars is not clearly specified except that the mass fraction of S and P is controlled to be ≤0.035%. The chemical composition and alloy elements are selected by the manufacturer to ensure that the finished steel bars processed by different methods meet the mechanical property requirements specified in the standard. Finished rolled threaded steel bars have added relaxation, fatigue, and non-metallic inclusion inspection items, and the quality requirements are significantly higher than those of ordinary threaded steel bars.

[0007] Finished rolled threaded steel bars are classified according to the yield strength level, including five grades: PSB785, PSB830, PSB930, PSBl080, and PSB1200, among which PSB785 and PSB830 are used in large quantities. PSB930 is difficult to produce, and the commonly used processes are microalloying + controlled rolling and controlled cooling, or conventional hot rolling + post-rolling quenching and tempering heat treatment. Since the yield strength of the steel grade is as high as 930MPa and the tensile strength reaches 1080MPa, especially under rapid cooling, the temperature of the steel parts is very low, and the requirements for the multiple-length flying shear capacity and the mechanical strength of the shear body and shear arm are very high. At the same time, cold shearing is prone to collapse and injury. At the same time, when the alloy content is high and the ambient temperature is below 28°C, it is necessary to quickly shear, collect and bundle, and slow cool in a suitable position.

[0008] After searching:

[0009] The document with Chinese patent application number CN201910978574.9 discloses "A method for online controlled rolling and controlled cooling of PSB930 finely rolled threaded steel bars". It mainly uses a steel billet with a size of 160mm×160mm as raw material, designs the compression ratio of the rolled piece in different units, and controls the compression ratio of the rough rolling unit to be ≥6.0, the compression ratio of the intermediate rolling unit to be ≥1.4, and the compression ratio of the finishing rolling unit to be ≥3.8 during the rolling process. The final rolling speed is 7m / s; during the cooling process, the temperature of the rolled piece after passing through the first group of controlled cooling devices of the finishing rolling unit is 600-640℃, and the temperature of the rolled piece after passing through the second group of controlled cooling devices of the finishing rolling unit is 530-550℃, and the rest of the processing is carried out according to the conventional process. The surface cooling rate in the first group of controlled cooling devices of the finishing rolling unit is 157-178℃ / s, and the surface cooling rate of the rolled piece in the second group of controlled cooling devices of the finishing rolling unit is 70-80℃ / s. This document uses online controlled cooling and quenching + self-tempering to control the cooling water tank. The cooling speed is fast, which can easily lead to uneven core and surface structure of the rolled piece. The surface is prone to produce martensitic brittle structure due to excessive concentrated cooling. During the cut-to-length shearing, the end of the finished product is prone to collapse and pop out, causing injury.

[0010] The document of Chinese patent application number CN201510863527.1 (publication number CN 105296853B) discloses "A 930MPa high-strength fine-rolled threaded steel and its preparation process", the composition of which is: C: 0.40-0.50%, Mn: 0.80-1.20%, Si: 1.45-1.85%, V: 0.120-0.220%, S≤0.030%, P≤0.030%, the balance is Fe, and the preparation process adopts the rolling production process route of "cold charging of steel billets into heating furnaces for heating + full-process low-temperature controlled rolling + multiple intermittent controlled cooling + pinch rollers for pinching tail steel + multiple-length flying shear segmentation + cooling bed cooling + indoor stacking cooling". Three-stage water-penetrating cooling is adopted, and the final cooling bed tempering temperature is 650-670℃. Since this document adopts low-temperature rolling throughout the entire process, the mill load current is large, the roll steel passing rate is low, the roll consumption is high, and the frequency of roll changing is increased, thereby reducing the rolling production efficiency.

[0011] The document of Chinese patent application number CN201110347552.6 (publication number CN 102363832A) discloses "A production process for fine-rolled threaded steel bars", whose process route is heating of steel billets → rolling → online controlled cooling → natural cooling on a cooling bed → sizing → stack cooling; the square billets are made of medium carbon steel with a size of 150mm×150mm; a three-stage heating method of preheating, heating and soaking is adopted in the heating process; in the rolling process, the starting temperature is controlled at 1000℃-1100℃; in the online controlled cooling process, the water inlet temperature is controlled at 920-1000℃, and one-time cooling is adopted, and the PSB930 self-tempering temperature is controlled at 430-480℃; natural cooling on a cooling bed, and the cooling rate is controlled at 1-5℃ / s; in the stack cooling process, offline stack cooling is performed at 150-350℃, and the stack cooling time is not less than 48 hours; it has the disadvantages of high cost, long stack cooling time and poor cooling effect.

[0012] The document of Chinese patent application number CN201910646827.2 (publication number CN 110218952A) introduces "A kind of fine-rolled threaded steel bar and its production method", which includes the following steel components: carbon: 0.28-0.33%, silicon: 0.55-0.80%, manganese: 1.20-1.60%, chromium: 0.30%-0.45%, vanadium: 0.10%-0.12%, phosphorus: <0.025%, sulfur: <0.025%, boron ≤0.0035%, N: 0.017-0.023%; the remainder is iron and unavoidable impurities. The continuous casting billet is slowly cooled for more than 24 hours before rolling; the temperature of the soaking section of the heating furnace is controlled at 1050℃~1070℃, the heating time is 125min~140min, the billet starting rolling temperature is 950℃~980℃, and the final rolling temperature is controlled at 840℃~890℃. It has the disadvantages of long heating time, high energy consumption, poor cooling effect, and low production efficiency.

[0013] The document of Chinese patent application number CN202210329814.4 (publication number CN 114686764A) discloses "A low-relaxation ultra-high-strength threaded steel bar and its preparation method". The invented low-relaxation ultra-high-strength fine-rolled threaded steel bar has the following chemical composition by mass percentage: C 0.24%-0.50%, Si 1.3-2.0%, Mn 0.5%-1.4%, V 0.07%-0.14%, Nb0.10-0.21%, B 0.01-0.04%, Ni 0.1%-0.2%, Mo 0.10%-0.15%, Hf 0.1%-0.2%, Zr0.02%-0.05%, P≤0.035%, S≤0.035%, the remainder is iron and unavoidable impurities, and the relationship is satisfied: 0.23%≤0.55[Ni]+[Mo]+0.27[Hf]+0.1[Zr]≤0.25%. The fine-rolled threaded steel bar provided in the document can achieve the mechanical properties of steel bar such as strength and toughness while effectively improving the corrosion resistance of steel bar; the yield strength of threaded steel bar is ≥785MPa, the tensile strength is ≥980MPa, the elongation after fracture is ≥12%, and the total elongation at maximum force is ≥4.5%. After continuous rolling, it is not directly water-cooled, but first air-cooled to a specific temperature of 820-850℃, then water-cooled to 450-460℃, and finally air-cooled to room temperature. The steel bar is maintained in a certain austenite state by air cooling, and then the surface is quenched into martensite by water cooling. During the cooling process, the residual heat is transmitted from the core to temper the surface and form tempered martensite. In addition to conventional C, Si, and Mn, the steel in this document also adds V, Nb, B, Ni, Mo, Hf, Zr and other alloying elements with specific amounts. The chemical composition design is very complex, the composition hit rate of the smelting process is not high, the production efficiency of the enterprise is low, and the production cost is high. Summary of the invention

[0014] The present invention aims at the shortcomings of the prior art such as high alloy content of steel bars, high energy consumption, poor cooling effect, low production efficiency and many shearing process failures. The present invention provides a threaded steel bar with a yield strength of ≥930MPa and a production method with a diameter of 25-36mm and a yield strength of ≥930MPa, which is suitable for use in high-rise buildings and other fields while ensuring hot-rolled yield strength Rel≥930MPa, tensile strength Rm≥1080MPa, elongation A≥6%, and total elongation Agt≥3.5% under maximum force. The present invention not only ensures stable product performance and high production efficiency, but also has a simple process.

[0015] Measures to achieve the above objectives:

[0016] A threaded steel bar with a yield strength of 930 MPa or more, wherein the components and weight percentage contents thereof are: C: 0.35-0.50%, Si: 0.60-1.20%, Mn: 0.80-1.40%, P≦0.035%, S≦0.035%, Al: 0.050-0.120%, B: 0.0008-0.0035%, V: 0.02-0.08%, N: 0.0045-0.0100%, Zr: 0.50-0.75%, and the remainder is Fe and unavoidable impurities.

[0017] Preferably, the weight percentage of C is 0.38-0.45%.

[0018] Preferably, the weight percentage of Si is 0.63-1.00%.

[0019] Preferably, the weight percentage of Mn is 0.90-1.28%.

[0020] Preferably, the weight percentage of Al is between 0.060% and 0.110%.

[0021] Preferably, the weight percentage of B is 0.0009-0.0029%.

[0022] Preferably, the weight percentage of V is 0.03-0.07%.

[0023] Preferably, the weight percentage of N is between 0.0055% and 0.0900%.

[0024] Preferably, the weight percentage of Zr is 0.55-0.70%.

[0025] A method for producing a threaded steel bar with a yield strength of ≥930 MPa, comprising the following steps:

[0026] 1) Pre-treat the molten iron. After desulfurization, the molten iron has P < 0.020%, S < 0.020%;

[0027] 2) Converter smelting, control the converter endpoint C at 0.06-0.30%; when the molten steel is 2 / 3 out, add the alloy and carburizer all at once;

[0028] 3) Carry out LF furnace refining, the refining time is not less than 25min, and argon is blown throughout the refining process; after the composition is adjusted, the molten steel is prohibited from being exposed;

[0029] 4) Casting into billets, during which a large tank long nozzle and a crystallizer immersion nozzle are used to protect the pouring, and the superheat of the molten steel in the middle package is controlled at 20-35°C; the cross-sectional size of the continuous casting billet is 155-170mm;

[0030] 5) Heat the ingot, control the temperature of the soaking section at 1080-1200°C, and the total heating time at 60-90 minutes;

[0031] 6) performing rough rolling and intermediate rolling, and controlling the starting rolling temperature to be between 980°C and 1050°C, and controlling the cumulative deformation rate of rough rolling and intermediate rolling to be between 20% and 60%;

[0032] 7) Finish rolling is performed in two stages, during which: the temperature of the finishing rolling stage I is controlled at 810-850°C, the temperature of the finishing rolling stage II is controlled at 790-830°C, and the rolling speed of the final stand is controlled at 20-45 m / s;

[0033] 8) Cooling, controlling the temperature of the cooling bed to 590-630° C., and cooling to room temperature at a cooling rate of 6.5-11.0° C. / s;

[0034] 9) Perform cold shearing of grooves;

[0035] 10) Cool to room temperature, but when the ambient temperature is below 28℃, the cooling time shall not be less than 24h.

[0036] Functions and mechanisms of each component and main process in the present invention

[0037] C: C is the cheapest and most effective strengthening element in steel materials. It can play a role of solid solution strengthening when dissolved in the matrix. If the C content is lower than 0.35%, it is difficult to ensure the yield strength and tensile strength of the steel bar. If the C content is higher than 0.50%, the toughness of the steel will deteriorate. Therefore, the C content is controlled at 0.35-0.50%.

[0038] Si: Si exists in steel in a solid solution state to increase strength and is also a deoxidizing element for steelmaking. Under the premise of ensuring the toughness and strength of the steel bars, as much cheap Si as possible should be used, but the content should not be too high to avoid reducing the toughness and plasticity of the steel, so it is controlled at 0.60-1.20%.

[0039] Mn: Mn dissolves in ferrite to improve the strength of steel, reduce the supercooled austenite transformation temperature, refine ferrite grains, and is beneficial to improving the strength and toughness of steel bars. However, Mn is also an element that is prone to segregation. The higher the content, the more likely it is to segregate. Composition segregation will lead to the formation of bainite structure during continuous cooling of the steel bar, which is not conducive to ensuring the toughness of the steel bar. Therefore, it is controlled at 0.80-1.40%.

[0040] Al: Al is the most efficient deoxidizer and can effectively improve the purity of molten steel. At the same time, AlN particles can refine grains and strengthen precipitation, but too high Al will deteriorate the mechanical properties of steel, so it is controlled at 0.050-0.120%.

[0041] B: B in alloy steel mainly improves the hardenability of steel, but the performance of steel bars themselves does not involve hardenability. In the present invention, B is a strong nitride-forming element, and the formation of fine dispersed BN can produce precipitation strengthening effect, improve the strength of steel, and has a strong affinity with O element, which can reduce free oxygen and nitrogen elements in steel, which is conducive to eliminating the aging phenomenon of steel bars. At the same time, adding trace hardenability elements can make up for the lack of online controlled cooling ability and accelerate the transformation of organization, but when the B content is too high, the strength and toughness of steel will deteriorate, so the content is controlled at 0.0008-0.0035%.

[0042] V: One of the most common microalloying elements, V is a strong nitride and carbide forming element. During heating or rolling, when fine dispersed second phase particles are generated, strong solid solution and precipitation strengthening effects can be produced, and grains can be refined to improve the strength and toughness of steel. When the V content is too high, the size of the precipitates will increase, which may worsen the above effects, so the content is controlled at 0.02-0.08%.

[0043] N: N is a gas element that combines with V microalloying elements in steel to form second phase particles such as VN, which enhances precipitation strengthening and fine grain strengthening, significantly improves the strength of steel and improves toughness. Adding too little is difficult to ensure the above-mentioned strengthening effect, while adding too much will reduce the toughness of the steel bar and increase the difficulty of smelting operation, so the content is controlled at 0.0045~0.0100%.

[0044] Zr: Zr can degas and refine grains, but too high a zirconium content will increase smelting difficulty and production costs, and cause local segregation, deteriorating steel properties, so the content is controlled at 0.50-0.75%.

[0045] The reason why the temperature of the soaking section is controlled at 1080-1200° C. in the present invention is that it is beneficial to the uniform diffusion and full solid solution of each component in the steel, which is beneficial to the uniform microstructure and stable performance.

[0046] The reason why the present invention controls the start rolling temperature at 980-1050°C during rough and medium rolling, and controls the cumulative deformation rate of rough and medium rolling at 20-60% is that the use of this start rolling temperature can ensure that the steel billet is fully austenitized in the heating furnace and undergoes austenite rolling deformation in the subsequent rolling, which is beneficial to the uniformity of composition and structure. Controlling the cumulative deformation rate can ensure uniform and refined microstructure.

[0047] The reason why the temperature of entering the finishing rolling stage I is controlled at 810-850°C, the temperature of entering the finishing rolling stage II is controlled at 790-830°C, and the rolling speed of the final stand is controlled at 20-45m / s is that the finishing rolling still adopts rolling deformation in the austenite zone, which is beneficial to ensure the appropriate strength and plasticity of the finished steel product; the speed of the final stand is controlled at 20-45m / s because different rolling speeds are adopted for different specifications, which, on the one hand, exerts the deformation-induced strengthening effect, and on the other hand, ensures smooth production and increases hourly output.

[0048] The reason why the present invention controls the temperature entering the cooling bed at 590-630°C is to obtain appropriate strength and plasticity. If the temperature entering the cooling bed is too low, the strength of the steel will be too high and the plasticity will be insufficient. Otherwise, the strength of the steel will be insufficient and the plasticity will be too high.

[0049] The reason why the pit cooling time is not less than 24 hours when the ambient temperature is lower than 28°C is that the steel is prone to air quenching when the ambient temperature is lower than 28°C, thereby causing cracks on the steel surface.

[0050] Compared with the prior art, the present invention not only ensures that the hot-rolled yield strength Rel≥930MPa, the tensile strength Rm≥1080MPa, the elongation A≥6%, and the total elongation under maximum force Agt≥3.5%, but also reduces the load of the rolling mill by increasing the heating temperature while greatly reducing the cost, which is beneficial to improving production efficiency and having strong process adaptability. In addition, the process window is wide, which is beneficial to on-site operation and smooth production. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a picture showing that the surface metallographic structure of the thread of the present invention is martensite;

[0052] Figure 2 This is a picture of the metallographic structure of the thread core of the present invention being bainite + pearlite + ferrite. DETAILED DESCRIPTION

[0053] The present invention is described in detail below:

[0054] Table 1 is a list of chemical composition values ​​of various embodiments and comparative examples of the present invention;

[0055] Table 2 is a list of process parameters of the smelting process of various embodiments and comparative examples of the present invention;

[0056] Table 3 is a list of rolling process parameters of various embodiments of the present invention and comparative examples;

[0057] Table 4 shows the test results of various embodiments of the present invention and comparative examples.

[0058] Each embodiment of the present invention is produced according to the following steps

[0059] 1) Pre-treat the molten iron. After desulfurization, the molten iron has P < 0.020%, S < 0.020%;

[0060] 2) Converter smelting, control the converter endpoint C at 0.06-0.30%; when the molten steel is 2 / 3 out, add the alloy and carburizer all at once;

[0061] 3) Carry out LF furnace refining, the refining time is not less than 25min, and argon is blown throughout the refining process; after the composition is adjusted, the molten steel is prohibited from being exposed;

[0062] 4) Casting into billets, during which a large tank long nozzle and a crystallizer immersion nozzle are used to protect the pouring, and the superheat of the molten steel in the middle package is controlled at 20-35°C; the cross-sectional size of the continuous casting billet is 155-170mm;

[0063] 5) Heat the ingot, control the temperature of the soaking section at 1080-1200°C, and the total heating time at 60-90 minutes;

[0064] 6) performing rough rolling and intermediate rolling, and controlling the starting rolling temperature to be between 980°C and 1050°C, and controlling the cumulative deformation rate of rough rolling and intermediate rolling to be between 20% and 60%;

[0065] 7) Finish rolling is performed in two stages, during which: the temperature of the finishing rolling stage I is controlled at 810-850°C, the temperature of the finishing rolling stage II is controlled at 790-830°C, and the rolling speed of the final stand is controlled at 20-45 m / s;

[0066] 8) Cooling, controlling the temperature of the cooling bed to 590-630° C., and cooling to room temperature at a cooling rate of 6.5-11.0° C. / s;

[0067] 9) Perform cold shearing of grooves;

[0068] 10) Cool to room temperature, but when the ambient temperature is below 28℃, the cooling time shall not be less than 24h.

[0069] Table 1 List of chemical components of various embodiments of the present invention (wt%)

[0070]

[0071] Table 2 List of process parameters of the smelting process of each embodiment of the present invention and the comparative example

[0072]

[0073]

[0074] Table 3 List of rolling process parameters of various embodiments of the present invention and comparative examples

[0075]

[0076] Table 4 Experimental results of various embodiments of the present invention and comparative examples

[0077]

[0078]

[0079] Note: The thread diameters of the above embodiments are all within the range of 25-36 mm.

[0080] It can be seen from Table 4 that compared with the comparative example, the steel of the embodiment of the present invention has higher yield strength, tensile strength and more suitable plastic properties such as elongation, and no cracking occurs on the steel surface.

[0081] This specific implementation is only the best example and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. A threaded steel with a yield strength of ≥930 MPa, wherein the components and weight percentages thereof are: C: 0.35-0.50%, Si: 0.60-1.20%, Mn: 0.80-1.40%, P≦0.035%, S≦0.035%, Al: 0.050-0.120%, B: 0.0008-0.0035%, V: 0.02-0.08%, N: 0.0045-0.0100%, Zr: 0.50-0.75%, and the remainder is Fe and unavoidable impurities.

2. A threaded steel bar with a yield strength of ≥930 MPa as claimed in claim 1, characterized in that: The weight percentage of C is 0.38-0.45%.

3. A threaded steel bar with a yield strength of ≥930 MPa as claimed in claim 1, characterized in that: The weight percentage of Si is 0.63-1.00%.

4. The threaded steel bar with a yield strength of ≥930 MPa according to claim 1, characterized in that: The weight percentage of Mn is 0.90-1.28%.

5. The threaded steel bar with a yield strength of ≥930 MPa according to claim 1, characterized in that: The weight percentage of Al is between 0.06 and 0.11%.

6. The threaded steel bar with a yield strength of ≥930 MPa according to claim 1, characterized in that: The weight percentage of B is 0.0009-0.0029%.

7. The threaded steel bar with a yield strength of ≥930 MPa according to claim 1, characterized in that: The weight percentage of V is 0.03-0.07%.

8. The threaded steel bar with a yield strength of ≥930 MPa according to claim 1, characterized in that: The weight percentage of N is between 0.0055% and 0.0900%.

9. The threaded steel bar with a yield strength of ≥930 MPa according to claim 1, characterized in that: The weight percentage of Zr is 0.55-0.70%.

10. A method for producing a threaded steel bar with a yield strength of ≥930 MPa as claimed in claim 1, comprising the steps of: 1) Pre-treat the molten iron. After desulfurization, the molten iron has P < 0.020%, S < 0.020%; 2) Converter smelting, control the converter endpoint C at 0.06-0.30%; when the molten steel is 2 / 3 out, add the alloy and carburizer all at once; 3) Carry out LF furnace refining, the refining time is not less than 25min, and argon is blown throughout the refining process; after the composition is adjusted, it is forbidden to store molten steel In the phenomenon of nudity; 4) Casting into billets, during which a large tank long nozzle and a crystallizer immersion nozzle are used to protect the pouring, and the superheat of the molten steel in the middle package is controlled at 20-35°C; the cross-sectional size of the continuous casting billet is 155-170mm; 5) Heat the ingot, control the temperature of the soaking section at 1080-1200°C, and the total heating time at 60-90 minutes; 6) performing rough rolling and intermediate rolling, and controlling the starting rolling temperature to be between 980°C and 1050°C, and controlling the cumulative deformation rate of rough rolling and intermediate rolling to be between 20% and 60%; 7) Finish rolling is performed in two stages, during which: the temperature of the finishing rolling stage I is controlled at 810-850°C, the temperature of the finishing rolling stage II is controlled at 790-830°C, and the rolling speed of the final stand is controlled at 20-45 m / s; 8) Cooling, controlling the temperature of the cooling bed to 590-630° C., and cooling to room temperature at a cooling rate of 6.5-11.0° C. / s; 9) Perform cold shearing of grooves; 10) Cool to room temperature, but when the ambient temperature is below 28℃, the cooling time shall not be less than 24h.

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