On-line quenched steel production method for high-hardness 40Cr bar round steel

Abstract

The invention discloses an online quenched steel production method for high-hardness 40Cr bar round steel, and relates to the technical field of steel rolling. According to the production method of the on-line quenched steel of the high-hardness 40Cr bar round steel, the high-hardness 40Cr bar round steel comprises the following components in percentage by weight: 0.40-0.43% of C, 0.2-0.3% of Si, 0.68-0.72% of Mn, 0.86-0.95% of Cr, less than or equal to 0.015% of P, less than or equal to 0.015% of S, less than or equal to 0.030% of Ni and the balance of Fe and inevitable impurities. High-hardness 40Cr is obtained in an on-line quenching mode, Rel of the high-hardness 40Cr is larger than or equal to 860 MPa, Rm of the high-hardness 40Cr is larger than or equal to 960 MPa, A of the high-hardness 40Cr is larger than or equal to 12%, Z of the high-hardness 40Cr is larger than or equal to 28%, Aku of the high-hardness 40Cr is larger than or equal to 39 J, the surface hardness of the high-hardness 40Cr is larger than or equal to 360 HBW, and the metallographic structure of the high-hardness 40Cr sequentially comprises tempered sorbite, tempered sorbite, tempered sorbite, tempered bainite and bainite from the surface to the interior. Comprising the following steps of S1, steel billet heating, S2, rolling, S3, online quenching, S4, online tempering and S5, slow cooling.

Description

Technical Field

[0001] The invention relates to the technical field of steel rolling, and in particular to a method for producing high-hardness 40Cr bar and round steel online quenching steel. Background Art

[0002] 40Cr bar round steel, also known as 40Cr alloy round steel, is an important alloy structural steel in my country's GB standard steel grade. Its main components include carbon, silicon, manganese, sulfur, phosphorus, chromium and other elements. Through specific heat treatment processes, such as quenching and high-temperature tempering, it can obtain excellent mechanical properties. This steel has been widely used in many industrial fields due to its high strength, good toughness, wear resistance and processing performance. However, most domestic production lines currently require customers to use subsequent heat treatment processes to achieve excellent mechanical properties when producing 40Cr.

[0003] Chinese invention patent CN112251678A discloses a high-toughness 40Cr hot-rolled round steel and its production method. By controlling the starting rolling temperature and cooling rate entering the rough rolling, the temperature is lowered, and normalizing treatment is not required, thereby reducing the bending of the rolled material and the burning loss in the furnace after normalizing. This invention patent can effectively improve the yield rate of the product by optimizing the steelmaking process. Chinese invention patent CN114990307A discloses a method for producing a 40Cr steel for direct cutting using a controlled rolling and controlled cooling process, which controls the continuous rolling temperature to ≤860°C, and the product has good plasticity and toughness. Both of the above two invention methods cannot obtain 40Cr with high surface hardness. Summary of the invention

[0004] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a method for producing high-hardness 40Cr bar and round steel online quenching steel, which can solve the above-mentioned problem.

[0005] To achieve the above object, the present invention provides the following technical solution: a high-hardness 40Cr bar round steel, comprising the following components in weight percentage: C: 0.40-0.43%, Si: 0.2-0.3%, Mn: 0.68-0.72%, Cr: 0.86-0.95%, P≤0.015%, S≤0.015%, Ni≤0.030%, and the balance is Fe and unavoidable impurities;

[0006] High hardness 40Cr is obtained by online quenching, with Rel≥860MPa, Rm≥960MPa, A≥12%, Z≥28%, Aku≥39J, surface hardness≥360HBW, and the metallographic structures from surface to inside are tempered troostite, tempered troostite, tempered troostite, tempered bainite, and bainite.

[0007] Preferably, a method for producing high-hardness 40Cr bar and round steel online quenching steel comprises the following steps: S1 billet heating, S2 rolling, S3 online quenching, S4 online tempering and S5 slow cooling.

[0008] Preferably, the S1 steel billet heating: the steel billet is heated and kept at 1160-1200°C for 2.5-4h to make the billet heated evenly, and the furnace exit temperature is 1050-1100°C.

[0009] Preferably, the S2 rolling is: firstly rolling the intermediate rectangular billet by a two-roller reversible rolling mill through 7-11 passes, then entering the continuous rolling unit at a temperature of >890°C, and rolling the billet through 4-8 rolling mills.

[0010] Preferably, the S3 online quenching: the round steel after rolling enters the online quenching pool through a step-by-step method, the temperature entering the online quenching pool is greater than 820°C, the quenching time is 40-80s, and the outlet water temperature is 70-150°C.

[0011] Preferably, the S4 online tempering: after the red tempering, the steel enters the heat preservation cover for online quenching, the red tempering temperature is 500-650°C, and the temperature out of the heat preservation cover is 300-350°C.

[0012] Preferably, the S5 slow cooling: after exiting the heat preservation cover, entering a pit for cooling, and the exit pit temperature is less than 200°C.

[0013] Preferably, the cross-sectional dimensions of the steel billet are 350*430 and 280*280.

[0014] Preferably, the clean circulating water used in the online quenching water pool has a pH value of 7-9, a total hardness (measured in CaCO3) of 150 mg / l, a chloride ion (Cl-) ≤ 150 mg / l, an oil content ≤ 5 mg / l, a conductivity ≤ 1000 μS / cm, and a temperature ≤ 35°C.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The high-hardness 40Cr bar and round steel online quenching steel production method realizes the automatic online quenching + automatic online tempering process on the bar and round steel process line, improves production efficiency, reduces manual operation, avoids safety accidents caused by human factors in the traditional quenching process, and ensures the personal safety of operators. At the same time, it reduces manpower input, energy and water consumption, thereby reducing production costs and improving the competitiveness of enterprises.

[0017] 2. The online quenching steel production method of the high-hardness 40Cr bar round steel. The online quenching of this scheme enables the material to obtain high hardness and good wear resistance, and the subsequent tempering treatment further improves the toughness and ductility of the material. The combination of the two enables the material to maintain high strength while also having good impact resistance and machinability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0019] Figure 1 It is a metallographic schematic diagram of the present invention;

[0020] Figure 2 It is a metallographic schematic diagram of the present invention;

[0021] Figure 3 It is a metallographic schematic diagram of the present invention;

[0022] Figure 4 It is a metallographic schematic diagram of the present invention;

[0023] Figure 5 It is a metallographic schematic diagram of the present invention. DETAILED DESCRIPTION

[0024] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the scope of protection of the present invention.

[0025] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0026] In the description of the present invention, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0027] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0028] See also Figure 1-5 , the present invention provides a technical solution:

[0029] A high-hardness 40Cr bar round steel comprises the following components in weight percentage: C: 0.40-0.43%, Si: 0.2-0.3%, Mn: 0.68-0.72%, Cr: 0.86-0.95%, P≤0.015%, S≤0.015%, Ni≤0.030%, and the balance is Fe and unavoidable impurities.

[0030] The present invention adopts an online quenching method to obtain high-hardness 40Cr, wherein Rel≥860MPa, Rm≥960MPa, A≥12%, Z≥28%, Aku≥39J, surface hardness≥360HBW, and the metallographic structures from the surface to the inside are: tempered troostite, tempered troostite, tempered troostite, tempered bainite, and bainite.

[0031] A method for producing high-hardness 40Cr bar and round steel online quenching steel mainly comprises the following steps: S1 steel billet heating, S2 rolling, S3 online quenching, S4 online tempering and S5 slow cooling.

[0032] The specific operations are as follows:

[0033] S1 Billet heating: The billet is heated and kept at 1160-1200℃ for 2.5-4h to make the billet heated evenly, and the furnace temperature is 1050-1100℃;

[0034] S2 rolling: first use a two-roll reversible rolling mill) to roll into an intermediate rectangular billet through 7-11 passes, then enter the continuous rolling unit at >890℃ and roll into finished products through 4-8 rolling mills.

[0035] S3 online quenching: The round steel after rolling enters the online quenching pool through a step-by-step method. The temperature entering the online quenching pool is greater than 820°C, the quenching time is 40-80s, and the outlet water temperature is 70-150°C.

[0036] S4 online tempering: After the steel is tempered, it enters the heat preservation cover for online quenching. The tempering temperature is 500-650℃, and the temperature out of the heat preservation cover is 300-350℃.

[0037] S5 slow cooling: After leaving the insulation cover, it goes into the pit for cooling, and the exit temperature is less than 200℃.

[0038] Furthermore, the cross-sectional dimensions of the steel billet are 350*430 and 280*280.

[0039] Furthermore, the clean circulating water used in the online quenching water pool has a pH value of 7-9, a total hardness (measured in CaCO3) of 150 mg / l, a chloride ion (Cl-) ≤150 mg / l, an oil content ≤5 mg / l, a conductivity ≤1000 μS / cm, and a temperature ≤35°C.

[0040] Embodiment 1:

[0041] When rolling 40Cr of 115 specification, an online modulation test was carried out, with water temperature of 21℃, water inlet temperature of 844℃, quenching time of 41s, water outlet temperature of 74℃, red-returning temperature of 650℃. It was hoisted by steel rope and slowly cooled in the insulation pit along with other round steels of the batch. The steel billet was heated and kept at 1180℃ for 2.5h and the outlet temperature was 1050℃. Rolling: first a two-roll reversible rolling mill was used) to roll the intermediate rectangular billet through 9 passes, which entered the continuous rolling unit at 920℃ and was rolled into finished products through 6 rolling mills.

[0042] Specific control parameters

[0043]

[0044] Test conditions: mechanics, hardness

[0045]

[0046] Furthermore, the metallographic structures from the surface to the inside are: tempered troostite, tempered bainite, and the surface hardened layer is greater than 3 cm.

[0047] Furthermore, the solution realizes the automated online quenching + automatic online tempering process on the bar and round steel process line, improves production efficiency, reduces manual operations, avoids safety accidents caused by human factors in the traditional quenching process, and ensures the personal safety of operators. At the same time, it reduces manpower input, energy and water consumption, thereby reducing production costs and improving the competitiveness of enterprises.

[0048] Furthermore, the online quenching of this scheme enables the material to obtain high hardness and good wear resistance, while the subsequent tempering treatment further improves the toughness and ductility of the material. The combination of the two enables the material to maintain high strength while also having good impact resistance and machinability.

[0049] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present invention.

Claims

1. A high hardness 40Cr round steel bar, characterized by: The following weight percentages are included: Composition: C: 0.40-0.43%, Si: 0.2-0.3%, Mn: 0.68-0.72%, Cr: 0.86-0.95%, P≤0.015%, S≤0.015%, Ni≤0.030%, the balance is Fe and unavoidable impurities; High hardness 40Cr is obtained by online quenching, with Rel≥860MPa, Rm≥960MPa, A≥12%, Z≥28%, Aku≥39J, surface hardness≥360HBW, and the metallographic structures from surface to inside are tempered troostite, tempered troostite, tempered troostite, tempered bainite, and bainite.

2. A method for producing high-hardness 40Cr bar round steel online quenching steel, characterized in that: The following steps are involved: S1 billet heating, S2 rolling, S3 online quenching, S4 online tempering and S5 slow cooling.

3. The method for producing high-hardness 40Cr bar and round steel online quenching steel according to claim 2, characterized in that: The S1 billet heating: the billet is heated and kept at 1160-1200°C for 2.5-4h to make the billet heated evenly, and the out-of-furnace temperature is 1050-1100°C.

4. The method for producing high-hardness 40Cr bar and round steel online quenching steel according to claim 2, characterized in that: The S2 rolling process is as follows: firstly, a two-roller reversible rolling mill is used to roll the intermediate rectangular billet through 7-11 passes, and then the billet enters the continuous rolling unit at a temperature of more than 890° C. and is rolled into a product through 4-8 rolling mills.

5. The method for producing high-hardness 40Cr bar and round steel online quenching steel according to claim 2, characterized in that: The S3 online quenching: the round steel after rolling enters the online quenching pool through a step-by-step method, the temperature entering the online quenching pool is greater than 820°C, the quenching time is 40-80s, and the outlet water temperature is 70-150°C.

6. The method for producing high-hardness 40Cr bar and round steel online quenching steel according to claim 2, characterized in that: The S4 online tempering: after the red tempering, it enters the heat preservation cover for online quenching, the red tempering temperature is 500-650℃, and the temperature out of the heat preservation cover is 300-350℃.

7. The method for producing high-hardness 40Cr bar and round steel online quenching steel according to claim 2, characterized in that: The S5 slow cooling: after leaving the heat preservation cover, it is put into the pit for cooling, and the exit temperature of the pit is less than 200°C.

8. The method for producing high-hardness 40Cr bar and round steel online quenching steel according to claim 2, characterized in that: The cross-sectional dimensions of the steel billet are 350*430 and 280*280.

9. The method for producing high-hardness 40Cr bar and round steel online quenching steel according to claim 2, characterized in that: The clean circulating water used in the online quenching water pool has a pH value of 7-9, a total hardness (calculated as CaCO3) of 150 mg / l, a chloride ion (Cl-) ≤150 mg / l, an oil content ≤5 mg / l, a conductivity ≤1000 μS / cm, and a temperature ≤35°C.

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