600MPa-grade reinforcing steel bar used in frozen soil environment (-50 DEG C) and preparation method of 600MPa-grade reinforcing steel bar

Abstract

The invention discloses a 600MPa-grade reinforcing steel bar used in a frozen soil environment (-50 DEG C) and a preparation method thereof, and relates to the technical field of reinforcing steel bars. The 600MPa-grade reinforcing steel bar for the frozen soil environment (-50 DEG C) and the preparation method thereof comprise the following component systems (in percentage by mass): 0.05-0.15% of C; 0.25 to 0.40 percent of Si; mn: 1.30 to 1.50%; less than or equal to 0.015% of P; less than or equal to 0.015% of S; 1.0-2.0% of Ni (the low-temperature-resistant toughness is improved, and the brittle failure risk is reduced); the preparation method comprises the following method steps and parameters: S1, converter smelting, S2, LF furnace refining, S3VD process, S4, calcium treatment, S5, square billet continuous casting and S6, heating and rolling, the low-temperature toughness is obviously improved by introducing 1.0-2.0% of nickel (Ni) element, refining grains (the grain size is greater than or equal to 7 grades) through solid solution strengthening, reducing the ductile-brittle transition temperature to below-60 DEG C, and reducing the temperature of the low-temperature toughness to below-60 DEG C; the impact absorbing energy at-50 DEG C is greater than or equal to 27J, which is improved by 35% compared with the traditional steel bar; phosphorus (P is less than or equal to 0.015%) and sulfur (S is less than or equal to 0.015%) impurities are strictly controlled, the grain boundary embrittlement factor is eliminated, the low-temperature ductility (A) is kept above 20%, and the deformation resistance is improved by 40%.

Description

Technical Field

[0001] The present invention relates to the technical field of steel bars, and in particular to a 600MPa grade steel bar for use in a frozen soil environment (-50°C) and a preparation method thereof. Background Art

[0002] In infrastructure construction in permafrost regions around the world (such as Siberia and Alaska), ultra-low temperatures of -50°C pose severe challenges to the mechanical properties of steel. Permafrost projects are characterized by frequent freeze-thaw cycles, complex geothermal gradients, and long service lives (design life ≥ 50 years). Traditional HRB400 / 500 grade steel bars are no longer able to meet these requirements. The main technical bottlenecks are as follows:

[0003] 1. Insufficient low-temperature mechanical properties

[0004] Significant ductile-brittle transition: Traditional steel bars (such as HRB500) undergo obvious ductile-brittle transition below -30℃. At -50℃, the impact absorption energy (KV2) is only 15-18J, which is far below the cold resistance design requirements in permafrost areas (≥27J). As a result, the structure is prone to brittle fracture under the action of frost heave force.

[0005] Imbalance between strength and toughness: Conventional microalloying processes (such as adding only V elements) cannot achieve both high strength and low-temperature toughness. When the yield strength (RP0.2) reaches 600 MPa, the elongation (A) at -50°C is often less than 18%, which cannot meet the ductility requirements of seismic design.

[0006] 2. Limitations of Chemical Composition Regulation

[0007] Influence of impurity elements: Traditional smelting processes have insufficient control over phosphorus (P) and sulfur (S) (P≤0.025%, S≤0.020%). Phosphorus segregation layers and sulfide inclusions are easily formed at low temperatures, exacerbating grain boundary embrittlement and increasing the risk of hot cracking during welding by more than 50%.

[0008] Lack of low-temperature resistant alloys: Lack of introduction of effective low-temperature resistant alloying elements (such as Ni), insufficient solid solution strengthening effect, the ductile-brittle transition temperature (DBTT) of steel is generally higher than -40°C, and it cannot adapt to the extreme environment of -50°C. Summary of the Invention

[0009] 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 600MPa grade steel bar for use in a frozen soil environment (-50°C) and a preparation method thereof, which can solve the problem of insufficient low-temperature mechanical properties.

[0010] To achieve the above object, the present invention provides the following technical solution: a 600MPa grade steel bar for use in a frozen soil environment (-50°C), comprising the following component system (mass percentage):

[0011] C: 0.05-0.15%;

[0012] Si: 0.25-0.40%;

[0013] Mn: 1.30-1.50%;

[0014] P:≤0.015%;

[0015] S:≤0.015%;

[0016] Ni: 1.0-2.0% (improves low-temperature toughness and reduces the risk of brittle fracture);

[0017] V: 0.08-0.10% (refines grains and precipitation strengthens), the Ni element: refines grains through solid solution strengthening, reduces the ductile-brittle transition temperature of the steel, and maintains good impact resistance (impact absorption energy ≥ 27J) at -50°C.

[0018] Preferably, the P element is strictly controlled to be ≤0.015% to avoid increase of low-temperature brittleness and reduce the risk of welding cracks.

[0019] Preferably, a method for preparing 600MPa grade steel bars for a frozen soil environment (-50°C) includes the following method steps and parameters: S1 converter smelting, S2 LF furnace refining, S3 VD process, S4 calcium treatment, S5 billet continuous casting and S6 heating and rolling.

[0020] Preferably, the S1 converter smelting:

[0021] End point control: C≤0.05%, P≤0.009%;

[0022] Key points of the process: Use low-phosphorus smelting technology and improve dephosphorization efficiency by optimizing the slag-making system.

[0023] Preferably, the S2LF furnace refining:

[0024] Basicity: R = 3-6 (CaO / SiO2 ratio);

[0025] White slag time: ≥15 minutes (to ensure that inclusions are fully adsorbed).

[0026] Preferably, the S3VD process:

[0027] Vacuum degree: ≤67Pa;

[0028] Vacuum holding time: ≥10 minutes.

[0029] Preferably, the S4 calcium treatment:

[0030] Start-up furnace: 60-110 meters solid core pure calcium wire;

[0031] Continuous casting furnace: 30-80 meters solid pure calcium wire;

[0032] Soft blowing time: ≥15 minutes (to promote the floating of inclusions).

[0033] Preferably, the S5 billet continuous casting:

[0034] Primary cooling water flow: 105~120m 3 / h;

[0035] Secondary cooling water specific water volume: 0.5~0.7L / kg;

[0036] Casting speed control: Match the superheat of molten steel to ensure the surface quality of the ingot.

[0037] Preferably, the S6 heating and rolling

[0038] Heating temperature: 1150-1200°C (holding time > 120 minutes to ensure full solid solution of V element);

[0039] Rolling temperature: 1100-1150℃ (rolling in the austenite recrystallization zone);

[0040] Finish rolling temperature: 1020~1060℃ (to ensure grain refinement);

[0041] Cooling rate after rolling: ≥200℃ / s (strong cooling process improves microstructure uniformity).

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. 600MPa grade steel bars for frozen soil environments (-50°C) and their preparation method achieve significant improvement in low-temperature toughness:

[0044] The introduction of 1.0-2.0% nickel (Ni) element refines the grains through solid solution strengthening (grain size ≥ 7 levels), reduces the ductile-brittle transition temperature to below -60°C, and the impact absorption energy at -50°C is ≥ 27J, which is 35% higher than that of traditional steel bars.

[0045] Phosphorus (P≤0.015%) and sulfur (S≤0.015%) impurities are strictly controlled to eliminate grain boundary embrittlement factors, maintain low-temperature elongation (A) above 20%, and improve deformation resistance by 40%.

[0046] 2. 600MPa grade steel bars for frozen soil environments (-50°C) and their preparation method, which achieve high strength and uniformity of structure:

[0047] The microalloying element vanadium (V = 0.08-0.10%) is combined with controlled rolling and controlled cooling processes to generate nano-scale carbonitrides (size ≤ 100nm), achieving precipitation strengthening, with a yield strength (RP0.2) ≥ 600MPa and a tensile strength (Rm) of 710-735MPa;

[0048] The cooling rate after rolling is ≥200℃ / s, which promotes the formation of fine-grained ferrite + pearlite + a small amount of bainite structure, improves the uniformity of the core and edge structure, and avoids performance differences caused by composition segregation.

[0049] 3. 600MPa grade steel bars for frozen soil environments (-50°C) and their preparation method, which achieve process adaptability and cost advantages:

[0050] VD vacuum treatment (vacuum degree ≤ 67Pa) reduces gas content (H ≤ 2ppm), reduces white spot defects, and improves steel purity;

[0051] By utilizing the existing converter-continuous casting-rolling production line and optimizing the rolling temperature (final rolling 1020-1060°C) and cooling parameters, no new equipment is required and the production cost only increases by 8-12%, which is a significant cost-effectiveness.

[0052] 4. 600MPa grade steel bars for frozen soil environments (-50°C) and their preparation method, which optimize engineering service performance:

[0053] The impact toughness of the heat-affected zone of welding is increased by 25% compared with traditional processes, and the reliability of the joint is enhanced, which is suitable for the welding needs of complex structures in frozen soil areas;

[0054] The corrosion resistance is improved (the tendency to intergranular corrosion is reduced), and the service life is expected to be extended to more than 50 years, reducing the subsequent maintenance costs by more than 30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0056] Figure 1 Schematic diagram of the chemical composition and mechanical properties of the present invention;

[0057] Figure 2 This is a schematic diagram of the metallographic structure of the edge (tempered troostite) of the present invention;

[0058] Figure 3 This is a metallographic diagram of 1 / 2 radius-(F+P+a small amount of B) of the present invention;

[0059] Figure 4 This is a schematic diagram of the low-temperature mechanical properties of the present invention;

[0060] Figure 5 This is a schematic diagram of the metallographic structure of the core part (F+P+B) of the present invention. DETAILED DESCRIPTION

[0061] 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 should not be understood as a limitation on the scope of protection of the present invention.

[0062] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They 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. Therefore, they cannot be understood as limitations on the present invention.

[0063] In the description of this invention, terms such as "greater than," "less than," and "exceed" are understood to exclude the number itself, while terms such as "above," "below," and "within" are understood to include the number itself. The use of terms such as "first" and "second" is solely for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly specifying the number of the indicated technical features, or implicitly specifying the order of the indicated technical features.

[0064] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, and connecting 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.

[0065] See also Figure 1-5 The present invention provides a technical solution: a 600MPa grade steel bar for use in a frozen soil environment (-50°C), comprising the following component system (mass percentage):

[0066] C: 0.05-0.15%;

[0067] Si: 0.25-0.40%;

[0068] Mn: 1.30-1.50%;

[0069] P:≤0.015%;

[0070] S:≤0.015%;

[0071] Ni: 1.0-2.0% (improves low-temperature toughness and reduces the risk of brittle fracture);

[0072] V: 0.08-0.10% (grain refinement, precipitation strengthening);

[0073] Element functions and control points:

[0074] Among them, Ni element: refines grains through solid solution strengthening, reduces the ductile-brittle transition temperature of steel, and maintains good impact resistance (impact absorption energy ≥ 27J) at -50°C.

[0075] Among them, P element: strictly controlled ≤ 0.015% to avoid increased low-temperature brittleness and reduce the risk of welding cracks;

[0076] A method for preparing 600MPa grade steel bars for use in a frozen soil environment (-50°C) comprises the following steps and parameters:

[0077] S1 converter smelting:

[0078] End point control: C≤0.05%, P≤0.009%;

[0079] Key points of the process: Adopt low-phosphorus smelting process and improve dephosphorization efficiency by optimizing the slag making system;

[0080] S2LF furnace refining:

[0081] Basicity: R = 3-6 (CaO / SiO2 ratio);

[0082] White slag time: ≥15 minutes (to ensure that inclusions are fully adsorbed);

[0083] S3VD process:

[0084] Vacuum degree: ≤67Pa;

[0085] Vacuum holding time: ≥10 minutes;

[0086] S4 calcium treatment:

[0087] Start-up furnace: 60-110 meters solid core pure calcium wire;

[0088] Continuous casting furnace: 30-80 meters solid pure calcium wire;

[0089] Soft blowing time: ≥15 minutes (to promote the floating of inclusions);

[0090] S5 billet continuous casting:

[0091] Primary cooling water flow: 105~120m 3 / h;

[0092] Secondary cooling water specific water volume: 0.5~0.7L / kg;

[0093] Casting speed control: matching the superheat of molten steel to ensure the surface quality of the ingot;

[0094] S6 heating and rolling heating temperature: 1150 ~ 1200 ℃ (holding time > 120 minutes to ensure sufficient solid solution of V element); rolling temperature: 1100 ~ 1150 ℃ (rolling in the austenite recrystallization zone);

[0095] Finish rolling temperature: 1020~1060℃ (to ensure grain refinement);

[0096] Cooling rate after rolling: ≥200℃ / s (strong cooling process improves microstructure uniformity);

[0097] Implementation Cases:

[0098] 1. For chemical composition and mechanical properties, please refer to Figure 1 ;

[0099] 2. Low temperature mechanical properties, please refer to Figure 4 ;

[0100] 3. Metallographic structure, please refer to Figure 2 、 Figure 3 、 Figure 5 ;

[0101] Edge: tempered troostite (uniform grains, enhanced toughness);

[0102] 1 / 2 radius: ferrite (F) + pearlite (P) + a small amount of bainite (B);

[0103] Core: ferrite (F) + pearlite (P) + bainite (B);

[0104] Furthermore, this preparation method achieves a significant improvement in low-temperature toughness:

[0105] The introduction of 1.0-2.0% nickel (Ni) element refines the grains through solid solution strengthening (grain size ≥ 7 levels), reduces the ductile-brittle transition temperature to below -60°C, and the impact absorption energy at -50°C is ≥ 27J, which is 35% higher than that of traditional steel bars.

[0106] Phosphorus (P≤0.015%) and sulfur (S≤0.015%) impurities are strictly controlled to eliminate grain boundary embrittlement factors, maintain low-temperature elongation (A) above 20%, and improve deformation resistance by 40%;

[0107] Furthermore, the preparation method achieves high strength and tissue uniformity:

[0108] The microalloying element vanadium (V = 0.08-0.10%) is combined with controlled rolling and controlled cooling processes to generate nano-scale carbonitrides (size ≤ 100nm), achieving precipitation strengthening, with a yield strength (RP0.2) ≥ 600MPa and a tensile strength (Rm) of 710-735MPa;

[0109] The cooling rate after rolling is ≥200℃ / s, which promotes the formation of fine-grained ferrite + pearlite + a small amount of bainite structure, improves the uniformity of the core and edge structure, and avoids performance differences caused by component segregation;

[0110] Furthermore, the preparation method achieves process adaptability and cost advantages:

[0111] VD vacuum treatment (vacuum degree ≤ 67Pa) reduces gas content (H ≤ 2ppm), reduces white spot defects, and improves steel purity;

[0112] By utilizing the existing converter-continuous casting-rolling production line and optimizing the rolling temperature (final rolling 1020-1060°C) and cooling parameters, no new equipment is required and the production cost only increases by 8-12%, offering a significant cost-effectiveness.

[0113] Furthermore, this preparation method achieves optimization of engineering service performance:

[0114] The impact toughness of the heat-affected zone of welding is increased by 25% compared with traditional processes, and the reliability of the joint is enhanced, which is suitable for the welding needs of complex structures in frozen soil areas;

[0115] The corrosion resistance is improved (the tendency to intergranular corrosion is reduced), and the service life is expected to be extended to more than 50 years, reducing the subsequent maintenance costs by more than 30%.

[0116] 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 scope of knowledge possessed by ordinary technicians in the technical field without departing from the scope of the present invention.

Claims

1. A 600 MPa grade steel bar for use in a frozen soil environment (-50°C), comprising the following composition system (in percentage by mass): C:0.05-0.15％； Si: 0.25-0.40%; Mn: 1.30-1.50%; P:≤0.015％； S:≤0.015％； Ni: 1.0-2.0% (improves low-temperature toughness and reduces the risk of brittle fracture); V: 0.08-0.10% (grain refinement, precipitation strengthening), characterized by: The Ni element strengthens and refines the grains through solid solution, reduces the ductile-brittle transition temperature of the steel, and maintains good impact resistance (impact absorption energy ≥ 27J) at -50°C.

2. The 600MPa grade steel bar for frozen soil environment (-50°C) according to claim 1, characterized in that: The P element is strictly controlled to be ≤0.015% to avoid increased low-temperature brittleness and reduce the risk of welding cracks.

3. A method for preparing 600MPa grade steel bars for use in frozen soil environments (-50°C), characterized by: The method includes the following steps and parameters: S1 converter smelting, S2 LF furnace refining, S3 VD process, S4 calcium treatment, S5 billet continuous casting and S6 heating and rolling.

4. The method for preparing 600 MPa grade steel bars for use in a frozen soil environment (-50°C) according to claim 3, characterized in that: The S1 converter smelting: End point control: C≤0.05%, P≤0.009%; Key points of the process: Use low-phosphorus smelting technology and improve dephosphorization efficiency by optimizing the slag-making system.

5. The method for preparing 600 MPa grade steel bars for use in a frozen soil environment (-50°C) according to claim 3, characterized in that: The S2LF furnace refining: Basicity: R = 3-6 (CaO / SiO2 ratio); White slag time: ≥15 minutes (to ensure that inclusions are fully adsorbed).

6. The method for preparing 600MPa grade steel bars for use in a frozen soil environment (-50°C) according to claim 3, characterized in that: The S3VD process: Vacuum degree: ≤67Pa; Vacuum holding time: ≥10 minutes.

7. The method for preparing 600 MPa grade steel bars for use in a frozen soil environment (-50°C) according to claim 3, characterized in that: The S4 calcium treatment: Start-up furnace: 60-110 meters solid core pure calcium wire; Continuous casting furnace: 30-80 meters solid pure calcium wire; Soft blowing time: ≥15 minutes (to promote the floating of inclusions).

8. The method for preparing 600MPa grade steel bars for use in a frozen soil environment (-50°C) according to claim 3, characterized in that: The S5 billet continuous casting: Primary cooling water flow: 105~120m 3 / h; Secondary cooling water specific water volume: 0.5~0.7L / kg; Casting speed control: Match the superheat of molten steel to ensure the surface quality of the ingot.

9. The method for preparing 600MPa grade steel bars for use in a frozen soil environment (-50°C) according to claim 3, characterized in that: The S6 heating and rolling: Heating temperature: 1150-1200°C (holding time > 120 minutes to ensure full solid solution of V element); Rolling temperature: 1100-1150℃ (rolling in the austenite recrystallization zone); Finish rolling temperature: 1020~1060℃ (to ensure grain refinement); Cooling rate after rolling: ≥200℃ / s (strong cooling process improves microstructure uniformity).

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