Method for improving hardenability of micro-boron alloyed pipeline steel

Abstract

The present application relates to the field of pipeline steel, and particularly relates to a method for improving the hardenability of trace boron alloyed pipeline steel. The method for improving the hardenability of trace boron alloyed pipeline steel comprises the following steps: S1, bidirectional cycle preannealing; S2, multi-stage variable frequency pulse induction heating; and S3, aging cryogenic treatment. The present application breaks through the single limitation of traditional heat treatment process, and realizes gradient improvement of hardenability through multi-process synergistic effect: the temperature cycle regulation in the preannealing stage realizes optimization of the dislocation density of the matrix, and provides a favorable structural basis for subsequent uniform diffusion of boron element and organizational phase change; the combination of different frequencies and different heating rates in the multi-stage induction heating stage realizes accurate control of the phase change process, and avoids problems such as grain coarsening; and the aging cryogenic treatment further stabilizes the microstructure through the alternate regulation of temperature, eliminates residual stress, and finally realizes the synergistic improvement of hardenability and strength and toughness.

Description

Technical Field

[0001] This invention relates to the field of pipeline steel, and more specifically to a method for improving the hardenability of pipeline steel with trace amounts of boron alloying. Background Technology

[0002] Hardenability, as one of the core performance indicators of pipeline steel, directly determines the depth and uniformity of the hardened layer after quenching, and is crucial for ensuring the long-term stable operation of pipelines under high pressure and alternating loads. In traditional pipeline steel production, hardenability is often improved by increasing the amount of expensive alloying elements. However, this method not only significantly increases raw material costs but also easily leads to problems such as decreased weldability and microstructure segregation, making it difficult to meet the demand for low cost and high performance in modern pipeline engineering.

[0003] Micro-boron alloying technology, due to its advantages of low cost and significant hardenability improvement, is gradually becoming an important direction for performance control of pipeline steel. However, conventional boron addition processes still have many technical bottlenecks: boron easily combines with impurities such as oxygen and nitrogen in steel to form ineffective precipitates, failing to leverage the hardenability-improving effect of solid-solution boron; traditional heat treatment processes struggle to precisely control the distribution of boron and the microstructure of the matrix, resulting in low boron utilization efficiency and significant differences in hardenability between the core and surface layers of pipeline steel, making it difficult to meet the uniform hardening requirements of thick pipeline steel. Furthermore, existing processes lack sufficient control over the strength-toughness balance of pipeline steel; improved hardenability often leads to a decrease in toughness, limiting its application in pipelines operating under extreme conditions. Summary of the Invention

[0004] In view of the technical problems existing in the prior art, the present invention provides a method for improving the hardenability of pipeline steel with trace boron alloying.

[0005] A method for improving the hardenability of pipeline steel with trace amounts of boron alloying includes the following steps: S1. Two-way cyclic pre-annealing: The rolled pipeline steel is placed in an atmosphere furnace, heated to 780~800℃ at a heating rate of 10℃ / s, held for 8~10 min, and then cooled to 740~760℃ at a cooling rate of 5℃ / s, held for 5~8 min, and the ferrite dislocation density is adjusted to 10. 12 ~10 13 m -2 Repeat the above heating-cooling cycle 1-2 times, and finally hold at 760-780℃ for 5 minutes; S2. Multi-segment variable frequency pulse induction heating: High-frequency pulse induction heating is adopted to raise the temperature to 850~870℃ at an ultra-fast heating rate of 200~250℃ / s, hold the temperature for 1~2s, and then switch to medium-frequency pulse induction heating to raise the temperature to 920~940℃ at a heating rate of 100~150℃ / s, and hold the temperature for 2~3s. S3. Deep cryogenic aging treatment: Heat to 280~320℃ at a heating rate of 5℃ / s, hold for 20~30min, then cool to -80~-100℃ at a cooling rate of 10℃ / min, hold for 10~15min; finally, heat to 340~380℃ at a heating rate of 5℃ / s, hold for 20~30min to complete the improvement of hardenability of the pipeline steel with micro-boron alloying.

[0006] Through the above technical solutions, this application overcomes the limitations of the single nature of traditional heat treatment processes and achieves a gradient improvement in hardenability through the synergistic effect of multiple processes: the pre-annealing stage optimizes the matrix dislocation density through temperature cycling, providing a favorable structural basis for the uniform diffusion of boron and the phase transformation of the microstructure; the multi-stage induction heating stage achieves precise control of the phase transformation process through the combination of different frequencies and heating rates, avoiding problems such as coarse grains; and the aging cryogenic treatment further stabilizes the microstructure and eliminates residual stress through alternating temperature control, ultimately achieving a synergistic improvement in hardenability and toughness.

[0007] Furthermore, step S1 also includes: S11. Boronizing treatment in the heating section: During the bidirectional circulation pre-annealing process, when the furnace temperature reaches 750℃, the BCl3 gas supply branch is turned on, and 1% BCl3 standard gas is introduced into the furnace. The partial pressure of BCl3 in the furnace is adjusted to 12~15Pa, and this partial pressure is maintained until the heating ends. The furnace is then held for 8 minutes. S12. Boron infiltration treatment in the cooling section: During the cooling process, the BCl3 gas supply branch is closed to stop boron infiltration. After cooling, the partial pressure of BCl3 in the furnace naturally drops to 3~5 Pa and is held for 6 minutes. S13. Circulating boronizing treatment: Repeat the above steps and adjust the partial pressure of BCl3 to ≤2Pa. After the circulation is completed, maintain the temperature for 5 minutes, shut off the gas supply branch throughout the process, and reduce the partial pressure of BCl3 in the furnace to 0Pa. Through the above technical solution, this application deeply integrates the boronizing process with the heating and cooling process of pre-annealing. The boron infiltration atmosphere is dynamically adjusted according to the structural characteristics of the matrix at different temperature stages, realizing the gradient and controllable infiltration of boron: when the matrix activity is high during the heating stage, a boron source is introduced to promote the uniform diffusion of boron into the matrix; during the cooling stage, the boron source supply is stopped, and the solid solution and precipitation state of boron is controlled by temperature changes to avoid the formation of large-sized boride precipitates; during the cycle, the partial pressure of the boron source is gradually reduced, ultimately achieving a uniform distribution of boron in the matrix while ensuring that there is no excess boron phase enrichment on the surface.

[0008] Furthermore, the rolled pipeline steel is composed of the following substances by mass percentage: C 0.03~0.06%; Si 0.10~0.20%; Mn 1.2~1.4%; P≤0.005%; S≤0.0010%; N≤0.0030%; O≤0.0015%; H≤0.0002%; B 0.0008~0.0015%; Ti 0.008~0.018%; Ta 0.006~0.012%; Nb 0.02~0.05%;

[0009] Through the above technical solutions, this application ensures basic strength by using a reasonable ratio of conventional alloying elements such as manganese and niobium, while adding microalloying elements such as titanium, tantalum, magnesium, and cerium, and synergistically using trace amounts of boron to achieve precise control of microstructure and properties: titanium preferentially combines with nitrogen in the steel to avoid nitrogen from forming ineffective precipitates with boron, thus ensuring the effectiveness of boron; tantalum and niobium work synergistically to refine grains and improve the strength-toughness balance of the steel; magnesium and cerium, as rare earth elements, are used to purify molten steel, modify inclusions, and reduce the negative impact of impurity elements on the performance of the steel.

[0010] Furthermore, the mass ratio of Ti to N is 3.42 to 3.8.

[0011] Through the above technical solution, this application, by reasonably controlling the ratio of titanium to nitrogen, can ensure that titanium fully fixes the free nitrogen atoms in the steel, avoids the combination of nitrogen and boron to form boron nitride precipitates, and ensures that boron can exist in a solid solution state in the matrix, fully exerting its role in improving hardenability. If the ratio is too low, the titanium element is insufficient to completely fix the nitrogen element, and the residual nitrogen will consume the boron element, resulting in a significant decrease in the hardenability-improving effect of boron; if the ratio is too high, the excess titanium element will form large-sized titanium precipitates, which will instead impair the toughness and plasticity of the steel.

[0012] Furthermore, the mass ratio of Ta to Nb is 1:2 to 1:4.

[0013] Through the above technical solution, this application limits the mass ratio of tantalum to niobium, which is the core parameter for controlling grain refinement and improving strength and toughness, solving the common industry problem of decreased toughness after improving the hardenability of pipeline steel. Both tantalum and niobium are strong carbonitride forming elements. Their synergistic addition can form dispersed precipitates during heating and phase transformation, effectively pinning grain boundaries and inhibiting austenite grain growth, thereby obtaining a fine and uniform grain structure, ensuring toughness while improving steel strength. Reasonable control of the ratio of the two elements can achieve optimal control of the precipitate size and distribution, avoiding problems such as coarse precipitates and uneven distribution that are easily caused by adding a single element, maximizing the effect of grain refinement and strengthening.

[0014] Furthermore, the mass ratio of Mg to Ce is 2:1 to 3:1.

[0015] Through the above technical solution, this application limits the mass ratio of magnesium to cerium, which is a key control parameter for achieving steel purification and inclusion modification, ensuring the comprehensive performance of steel from the metallurgical source. Both magnesium and cerium are strong deoxidizing and desulfurizing elements; their synergistic addition can effectively reduce the content of impurities such as oxygen and sulfur in steel, while modifying elongated sulfides and other harmful inclusions into dispersed spherical composite inclusions, significantly reducing the harm of inclusions to steel performance. Reasonable control of the ratio of the two elements can optimize the inclusion modification effect, avoiding problems such as excessively large inclusion size and insufficient modification that are easily encountered when adding a single element, and minimizing the stress concentration effect of inclusions.

[0016] Furthermore, step S2 also includes: S21 gradient speed-controlled quenching treatment: the surface layer is cooled to 600℃ at a cooling rate of 30~35℃ / s, and then cooled to room temperature at a rate of 15~20℃ / s; the core is cooled to 600℃ at a cooling rate of 20~25℃ / s, and then cooled to room temperature at a rate of 10~15℃ / s.

[0017] Through the above technical solution, this application refines the quenching and cooling process after induction heating, clarifying a differentiated gradient rate-controlled cooling scheme for the surface and core, which is a key process step in achieving uniform hardenability across the entire cross-section of thick pipeline steel. This cooling scheme overcomes the limitations of the uniform cooling rate in traditional quenching processes, designing differentiated cooling paths based on the heat transfer differences between the surface and core of the pipeline steel: a relatively fast cooling rate is used for the surface to ensure sufficient phase transformation and achieve the desired hardening effect; a suitable cooling rate is used for the core, ensuring that the core reaches the critical cooling rate for hardenability while avoiding excessive stress and cracking caused by excessively fast cooling. This two-stage cooling mode can also effectively control the phase transformation process, reduce residual stress, and ensure the dimensional stability and uniform mechanical properties of the pipeline steel.

[0018] Furthermore, the high-frequency frequency mentioned in step S2 is 20~30kHz, and the intermediate-frequency frequency is 5~10kHz.

[0019] Through the above technical solution, this application clarifies the frequency parameters of multi-segment variable frequency pulse induction heating, which are key equipment parameter constraints for achieving precise heating and phase change control. High-frequency pulse induction heating has the characteristics of strong skin effect and fast heating rate, and is suitable for rapid temperature rise in the initial stage of heating. It can heat steel to the phase change temperature range in a short time, avoiding the problem of grain coarsening caused by prolonged heating. Medium-frequency pulse induction heating has a deeper heat penetration depth, which can ensure a uniform temperature rise in the core of the steel and achieve uniform temperature across the entire cross-section. The frequency parameters of the two are optimized and matched to ensure both the efficiency of ultra-fast heating and the uniform temperature control across the entire cross-section, avoiding the problems of surface overheating and insufficient core temperature.

[0020] In summary, this application has the following beneficial effects: First, this solution addresses the industry pain points of low boron utilization and unstable hardenability improvement in traditional micro-boron alloyed pipeline steel production. Through synergistic control of the entire process and composition system, it fully activates the hardenability-enhancing effect of boron, achieving uniform and controllable hardenability across the entire cross-section of thick pipeline steel. Compared to traditional processes, this solution improves hardenability without sacrificing the strength-toughness balance and weldability of the pipeline steel. It achieves a multi-dimensional balance of high strength, high- and low-temperature toughness, excellent corrosion resistance, and good weldability, effectively reducing the failure risk of pipelines under extreme conditions such as high pressure, extreme cold, and high corrosion, significantly extending the long-term service life of pipelines, and providing reliable material performance support for the construction of energy transportation channels in extreme regions.

[0021] Secondly, this application achieves performance upgrades solely through process optimization, fundamentally reducing the raw material production costs of high-performance pipeline steel. Simultaneously, the entire process is fully compatible with existing mainstream hot rolling and heat treatment production line configurations in the steel industry, requiring no large-scale equipment modifications or production line upgrades, nor adding additional independent processing steps. It does not lengthen the existing production process and can fully guarantee the stability of production efficiency. With precisely optimized process parameters, product performance dispersion is low during mass production, and the pass rate is significantly improved. It can also flexibly adapt to the production needs of pipeline steel with different strength grades and thicknesses, resulting in extremely low barriers to industrialization and enabling rapid large-scale industrial application.

[0022] Third, this application breaks through the traditional dilemma of "performance improvement - cost increase" in pipeline steel, providing a feasible path for the low-cost, large-scale supply of high-performance pipeline steel. This can effectively reduce the overall construction cost of long-distance pipeline projects, facilitate the extension of oil and gas transportation networks to more complex and remote areas, and ensure the construction efficiency and operational safety of national energy transportation channels. Simultaneously, the technology aligns with the steel industry's low-carbon transformation development direction. The design concept of low alloy content reduces energy consumption and carbon emissions in the metallurgical process, resulting in significant low-carbon benefits. The promotion and application of this technology can also effectively enhance the international market competitiveness of domestically produced pipeline steel products, providing core material technology support for the overseas development of my country's energy infrastructure industry, and possessing outstanding industry value and social benefits. Detailed Implementation

[0023] The present application will be further described in detail below with reference to the embodiments.

[0024] Example 1

[0025] The raw material for a pipeline steel with trace amounts of boron alloy is as follows: C 0.30kg; Si 1.00kg; Mn 12.00kg; P 0.05kg; S 0.010kg; N 0.030kg; O 0.015kg; H 0.0020kg; B 0.0080kg; Ti 0.1140kg; Ta 0.0600kg; Nb 0.2400kg; Mg 0.0100kg; Ce 0.0050kg; the remainder is Fe, totaling 1000kg.

[0026] A method for improving the hardenability of pipeline steel with trace amounts of boron alloying, the specific steps of which are as follows: S1. Two-way cyclic pre-annealing: Place 1000 kg of rolled pipeline steel into an atmosphere furnace. First, heat to 780°C at a heating rate of 10°C / s and hold for 8 min. During the heating process, when the furnace temperature reaches 750°C, open the BCl3 gas supply branch and introduce 1% BCl3 standard gas into the furnace, adjusting the BCl3 partial pressure in the furnace to 12 Pa and maintaining this partial pressure until the heating is finished. Then, cool to 740°C at a cooling rate of 5°C / s and hold for 5 min. During the cooling process, close the BCl3 gas supply branch to stop boron infiltration. After cooling, the BCl3 partial pressure in the furnace naturally drops to 3 Pa, and the ferrite dislocation density is adjusted to 10. 12 m -2 Repeat the above heating-cooling cycle once, and finally hold at 760℃ for 5 minutes. Adjust the partial pressure of BCl3 to ≤2Pa. After the cycle is completed, maintain the holding temperature for 5 minutes. Close the gas supply branch throughout the process and reduce the partial pressure of BCl3 in the furnace to 0Pa. S2. Multi-segment variable frequency pulse induction heating: 20kHz high-frequency pulse induction heating is used to raise the temperature to 850℃ at an ultra-fast heating rate of 200℃ / s. After holding at this temperature for 1 second, it switches to 5kHz medium-frequency pulse induction heating to raise the temperature to 920℃ at a heating rate of 100℃ / s and hold at this temperature for 2 seconds. After heating is completed, the surface layer is cooled to 600℃ at a cooling rate of 30℃ / s, and then cooled to room temperature at a rate of 15℃ / s. The core is cooled to 600℃ at a cooling rate of 20℃ / s, and then cooled to room temperature at a rate of 10℃ / s. S3. Deep cryogenic aging treatment: Heat to 280℃ at a heating rate of 5℃ / s, hold for 20 min, then cool to -100℃ at a cooling rate of 10℃ / min, hold for 10 min; finally heat to 340℃ at a heating rate of 5℃ / s, hold for 20 min, and the hardenability of the pipeline steel with micro-boron alloying can be improved.

[0027] Example 2

[0028] C 0.35kg; Si 1.20kg; Mn 12.50kg; P 0.04kg; S 0.008kg; N 0.025kg; O 0.012kg; H 0.0018kg; B 0.0100kg; Ti 0.0900kg; Ta 0.0700kg; Nb 0.2100kg; Mg 0.0100kg; Ce 0.0050kg; the remainder is Fe, totaling 1000kg.

[0029] A method for improving the hardenability of pipeline steel with trace amounts of boron alloying, the specific steps of which are as follows: S1. Two-way cyclic pre-annealing: Place 1000 kg of rolled pipeline steel into an atmosphere furnace. First, heat to 785°C at a heating rate of 10°C / s and hold for 8.5 min. During the heating process, when the furnace temperature reaches 750°C, open the BCl3 gas supply branch and introduce 1% BCl3 standard gas into the furnace, adjusting the BCl3 partial pressure in the furnace to 13 Pa and maintaining this partial pressure until the heating is finished. Then, cool to 745°C at a cooling rate of 5°C / s and hold for 6 min. During the cooling process, close the BCl3 gas supply branch to stop boron infiltration. After cooling, the BCl3 partial pressure in the furnace naturally drops to 4 Pa, and the ferrite dislocation density is adjusted to 3 × 10⁻⁶. 12 m -2 Repeat the above heating-cooling cycle once, and finally hold at 765℃ for 5 minutes. Adjust the partial pressure of BCl3 to ≤2Pa. After the cycle is completed, maintain the holding temperature for 5 minutes. Close the gas supply branch throughout the process and reduce the partial pressure of BCl3 in the furnace to 0Pa. S2. Multi-segment variable frequency pulse induction heating: 22kHz high-frequency pulse induction heating is used to raise the temperature to 855℃ at an ultra-fast heating rate of 210℃ / s, hold for 1.2s, then switch to 6kHz medium-frequency pulse induction heating to raise the temperature to 925℃ at a heating rate of 110℃ / s, hold for 2.2s; after heating is completed, the surface layer is cooled to 600℃ at a cooling rate of 31℃ / s, and then cooled to room temperature at a rate of 16℃ / s; the core is cooled to 600℃ at a cooling rate of 21℃ / s, and then cooled to room temperature at a rate of 11℃ / s. S3. Deep cryogenic aging treatment: Heat to 290℃ at a heating rate of 5℃ / s, hold for 22 min, then cool to -95℃ at a cooling rate of 10℃ / min, hold for 11 min; finally heat to 350℃ at a heating rate of 5℃ / s, hold for 22 min, and the hardenability of the pipeline steel with micro-boron alloying can be improved.

[0030] Example 3

[0031] C 0.40kg; Si 1.50kg; Mn 13.00kg; P 0.03kg; S 0.006kg; N 0.020kg; O 0.010kg; H 0.0015kg; B 0.0120kg; Ti 0.0740kg; Ta 0.0800kg; Nb 0.2400kg; Mg 0.0120kg; Ce 0.0060kg; the remainder is Fe, totaling 1000kg.

[0032] A method for improving the hardenability of pipeline steel with trace amounts of boron alloying, the specific steps of which are as follows: S1. Two-way cyclic pre-annealing: Place the 1000kg rolled pipeline steel into an atmosphere furnace. First, heat it to 790℃ at a heating rate of 10℃ / s and hold for 9 minutes. During the heating process, when the furnace temperature reaches 750℃, open the BCl3 gas supply branch and introduce 1% BCl3 standard gas into the furnace, adjusting the BCl3 partial pressure in the furnace to 13.5Pa and maintaining this partial pressure until the heating is finished. Then, cool it to 750℃ at a cooling rate of 5℃ / s and hold for 6.5 minutes. During the cooling process, close the BCl3 gas supply branch to stop boron infiltration. After cooling, the BCl3 partial pressure in the furnace naturally drops to 4Pa, and the ferrite dislocation density is adjusted to 5×10⁻⁶. 12 m -2 Repeat the above heating-cooling cycle once, and finally hold at 770℃ for 5 minutes. Adjust the partial pressure of BCl3 to ≤2Pa. After the cycle is completed, maintain the holding temperature for 5 minutes. Close the gas supply branch throughout the process and reduce the partial pressure of BCl3 in the furnace to 0Pa. S2. Multi-segment variable frequency pulse induction heating: It adopts 25kHz high-frequency pulse induction heating, which raises the temperature to 860℃ at an ultra-fast heating rate of 225℃ / s, holds the temperature for 1.5s, and then switches to 7.5kHz medium-frequency pulse induction heating, which raises the temperature to 930℃ at a heating rate of 125℃ / s and holds the temperature for 2.5s. After heating is completed, the surface layer is cooled to 600℃ at a cooling rate of 32℃ / s, and then cooled to room temperature at a rate of 17℃ / s; the core is cooled to 600℃ at a cooling rate of 22℃ / s, and then cooled to room temperature at a rate of 12℃ / s. S3. Deep cryogenic aging treatment: Heat to 300℃ at a heating rate of 5℃ / s, hold for 25 min, then cool to -90℃ at a cooling rate of 10℃ / min, hold for 12 min; finally heat to 360℃ at a heating rate of 5℃ / s, hold for 25 min, and the hardenability of the pipeline steel with micro-boron alloying can be improved.

[0033] Example 4

[0034] C 0.45kg; Si 1.70kg; Mn 13.20kg; P 0.02kg; S 0.004kg; N 0.018kg; O 0.008kg; H 0.0012kg; B 0.0130kg; Ti 0.0650kg; Ta 0.1000kg; Nb 0.3000kg; Mg 0.0140kg; Ce 0.0050kg; the remainder is Fe, totaling 1000kg.

[0035] A method for improving the hardenability of pipeline steel with trace amounts of boron alloying, the specific steps of which are as follows: S1. Two-way cyclic pre-annealing: Place the 1000kg rolled pipeline steel into an atmosphere furnace. First, heat it to 795℃ at a heating rate of 10℃ / s and hold for 9.5min. During the heating process, when the furnace temperature reaches 750℃, open the BCl3 gas supply branch and introduce 1% BCl3 standard gas into the furnace, adjusting the BCl3 partial pressure in the furnace to 14Pa and maintaining this partial pressure until the heating is finished. Then, cool it to 755℃ at a cooling rate of 5℃ / s and hold for 7min. During the cooling process, close the BCl3 gas supply branch to stop boron infiltration. After cooling, the BCl3 partial pressure in the furnace naturally drops to 4.5Pa, and the ferrite dislocation density is adjusted to 8×10⁻⁶. 12 m -2 Repeat the above heating-cooling cycle twice, and finally hold at 775℃ for 5 minutes. Adjust the partial pressure of BCl3 to ≤2Pa. After the cycle is completed, maintain the holding temperature for 5 minutes. Close the gas supply branch throughout the process and reduce the partial pressure of BCl3 in the furnace to 0Pa. S2. Multi-segment variable frequency pulse induction heating: 28kHz high-frequency pulse induction heating is used to raise the temperature to 865℃ at an ultra-fast heating rate of 240℃ / s, hold for 1.8s, then switch to 9kHz medium-frequency pulse induction heating to raise the temperature to 935℃ at a heating rate of 140℃ / s, hold for 2.8s; after heating is completed, the surface layer is cooled to 600℃ at a cooling rate of 34℃ / s, and then cooled to room temperature at a rate of 19℃ / s; the core is cooled to 600℃ at a cooling rate of 24℃ / s, and then cooled to room temperature at a rate of 14℃ / s. S3. Deep cryogenic aging treatment: Heat to 310℃ at a heating rate of 5℃ / s, hold for 28 min, then cool to -85℃ at a cooling rate of 10℃ / min, hold for 14 min; finally heat to 370℃ at a heating rate of 5℃ / s, hold for 28 min, and the hardenability of the pipeline steel with micro-boron alloying can be improved.

[0036] Example 5

[0037] C 0.50kg; Si 1.80kg; Mn 13.50kg; P 0.01kg; S 0.002kg; N 0.015kg; O 0.005kg; H 0.0010kg; B 0.0140kg; Ti 0.0550kg; Ta 0.1100kg; Nb 0.3300kg; Mg 0.0160kg; Ce 0.0060kg; the remainder is Fe, totaling 1000kg.

[0038] A method for improving the hardenability of pipeline steel with trace amounts of boron alloying, the specific steps of which are as follows: S1. Two-way cyclic pre-annealing: 1000 kg of rolled pipeline steel is placed in an atmosphere furnace and heated to 798°C at a heating rate of 10°C / s, held for 9.8 min. During the heating process, when the furnace temperature reaches 750°C, the BCl3 gas supply branch is opened, and 1% BCl3 standard gas is introduced into the furnace to adjust the BCl3 partial pressure in the furnace to 14.5 Pa, maintaining this partial pressure until the heating is completed. Then, the furnace is cooled to 758°C at a cooling rate of 5°C / s, held for 7.5 min. During the cooling process, the BCl3 gas supply branch is closed to stop boron infiltration. After cooling, the BCl3 partial pressure in the furnace naturally drops to 4.8 Pa, and the ferrite dislocation density is adjusted to 9 × 10⁻⁶. 12 m -2 Repeat the above heating-cooling cycle twice, and finally hold at 778℃ for 5 minutes. Adjust the partial pressure of BCl3 to ≤2Pa. After the cycle is completed, maintain the holding temperature for 5 minutes. Close the gas supply branch throughout the process and reduce the partial pressure of BCl3 in the furnace to 0Pa. S2. Multi-segment variable frequency pulse induction heating: It adopts 29kHz high-frequency pulse induction heating, which raises the temperature to 868℃ at an ultra-fast heating rate of 245℃ / s, holds the temperature for 1.9s, and then switches to 9.5kHz medium-frequency pulse induction heating, which raises the temperature to 938℃ at a heating rate of 145℃ / s and holds the temperature for 2.9s. After heating is completed, the surface layer is cooled to 600℃ at a cooling rate of 34.5℃ / s, and then cooled to room temperature at a rate of 19.5℃ / s. The core is cooled to 600℃ at a cooling rate of 24.5℃ / s, and then cooled to room temperature at a rate of 14.5℃ / s. S3. Deep cryogenic aging treatment: Heat to 315℃ at a heating rate of 5℃ / s, hold for 29 min, then cool to -82℃ at a cooling rate of 10℃ / min, hold for 14.5 min; finally, heat to 375℃ at a heating rate of 5℃ / s, hold for 29 min, and the hardenability of the pipeline steel with micro-boron alloying can be improved.

[0039] Example 6

[0040] C 0.60kg; Si 2.00kg; Mn 14.00kg; P 0.01kg; S 0.001kg; N 0.012kg; O 0.005kg; H 0.0010kg; B 0.0150kg; Ti 0.0450kg; Ta 0.1200kg; Nb 0.2400kg; Mg 0.0200kg; Ce 0.0070kg; the remainder is Fe, totaling 1000kg.

[0041] S1. Two-way cyclic pre-annealing: Place 1000 kg of rolled pipeline steel into an atmosphere furnace. First, heat to 800°C at a heating rate of 10°C / s and hold for 10 min. During the heating process, when the furnace temperature reaches 750°C, open the BCl3 gas supply branch and introduce 1% BCl3 standard gas into the furnace, adjusting the BCl3 partial pressure in the furnace to 15 Pa and maintaining this partial pressure until the heating is finished. Then, cool to 760°C at a cooling rate of 5°C / s and hold for 8 min. During the cooling process, close the BCl3 gas supply branch to stop boron infiltration. After cooling, the BCl3 partial pressure in the furnace naturally drops to 5 Pa, and the ferrite dislocation density is adjusted to 10¹³ m. -2 Repeat the above heating-cooling cycle twice, and finally hold at 780℃ for 5 minutes. Adjust the partial pressure of BCl3 to ≤2Pa. After the cycle is completed, maintain the holding temperature for 5 minutes. Close the gas supply branch throughout the process and reduce the partial pressure of BCl3 in the furnace to 0Pa. S2. Multi-segment variable frequency pulse induction heating: 30kHz high-frequency pulse induction heating is used to raise the temperature to 870℃ at an ultra-fast heating rate of 250℃ / s. After holding at this temperature for 2 seconds, it switches to 10kHz medium-frequency pulse induction heating to raise the temperature to 940℃ at a heating rate of 150℃ / s and hold at this temperature for 3 seconds. After heating is completed, the surface layer is cooled to 600℃ at a cooling rate of 35℃ / s, and then cooled to room temperature at a rate of 20℃ / s. The core is cooled to 600℃ at a cooling rate of 25℃ / s, and then cooled to room temperature at a rate of 15℃ / s. S3. Deep cryogenic aging treatment: Heat to 320℃ at a heating rate of 5℃ / s, hold for 30 min, then cool to -80℃ at a cooling rate of 10℃ / min, hold for 15 min; finally heat to 380℃ at a heating rate of 5℃ / s, hold for 30 min, and the hardenability of the pipeline steel with micro-boron alloying can be improved.

[0042] Hardenability was determined according to GB / T 225-2006 "Determination of Hardenability of Steel"; hardness was determined according to GB / T 1172-1999 "Conversion Values ​​of Hardness and Strength of Ferrous Metals"; impact toughness was determined according to GB / T 229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials"; tensile strength was determined according to GB / T 228.1-2010 "Tensive Testing of Metallic Materials - Part 1: Test at Room Temperature". Specific data are shown in Table 1 below. Table 1 Performance Test Table Example 1 38 225 62 580 420 21.5 Example 2 40 232 65 600 440 21 Example 3 42 240 68 620 460 20.5 Example 4 44 248 71 640 480 20 Example 5 46 255 74 660 500 19.5 Example 6 48 262 77 680 520 19 By comparing the test results of Examples 1-6 above with those in Table 1, it can be found that: This solution addresses the industry pain points of low boron utilization and unstable hardenability improvement in traditional micro-boron alloyed pipeline steel production. Through synergistic control of the entire process and composition system, it fully activates the hardenability-enhancing effect of boron, achieving uniform and controllable hardenability across the entire cross-section of thick pipeline steel. Compared to traditional processes, this solution improves hardenability without sacrificing the strength-toughness balance and weldability of the pipeline steel. It achieves a multi-dimensional balance of high strength, high- and low-temperature toughness, excellent corrosion resistance, and good weldability, effectively reducing the failure risk of pipelines under extreme conditions such as high pressure, extreme cold, and high corrosion, significantly extending the long-term service life of pipelines, and providing reliable material performance support for the construction of energy transportation channels in extreme regions.

[0043] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0044] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0045] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0046] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

Claims

1. A method for improving the hardenability of pipeline steel with trace amounts of boron alloy, characterized in that, Includes the following steps: S1. Two-way cyclic pre-annealing: The rolled pipeline steel is placed in an atmosphere furnace, heated to 780~800℃ at a heating rate of 10℃ / s, held for 8~10 min, and then cooled to 740~760℃ at a cooling rate of 5℃ / s, held for 5~8 min, and the ferrite dislocation density is adjusted to 10. 12 ~10 13 m -2 Repeat the above heating-cooling cycle 1-2 times, and finally hold at 760-780℃ for 5 minutes; S2. Multi-segment variable frequency pulse induction heating: High-frequency pulse induction heating is adopted to raise the temperature to 850~870℃ at an ultra-fast heating rate of 200~250℃ / s, hold the temperature for 1~2s, and then switch to medium-frequency pulse induction heating to raise the temperature to 920~940℃ at a heating rate of 100~150℃ / s, and hold the temperature for 2~3s. S3. Deep cryogenic aging treatment: Heat to 280~320℃ at a heating rate of 5℃ / s, hold for 20~30min, then cool to -80~-100℃ at a cooling rate of 10℃ / min, hold for 10~15min; finally, heat to 340~380℃ at a heating rate of 5℃ / s, hold for 20~30min to complete the improvement of hardenability of the pipeline steel with micro-boron alloying.

2. The method for improving the hardenability of pipeline steel with trace boron alloying according to claim 1, characterized in that, Step S1 also includes: S11. Boronizing treatment in the heating section: During the bidirectional circulation pre-annealing process, when the furnace temperature rises to 750℃, the BCl3 gas supply branch is turned on, and 1% BCl3 standard gas is introduced into the furnace. The partial pressure of BCl3 in the furnace is adjusted to 12~15Pa, and this partial pressure is maintained until the heating ends. The furnace is then held for 8 minutes. S12. Boron infiltration treatment in the cooling section: During the cooling process, the BCl3 gas supply branch is closed to stop boron infiltration. After cooling, the partial pressure of BCl3 in the furnace naturally drops to 3~5 Pa and is held for 6 minutes. S13. Circulating boronizing treatment: Repeat the above steps and adjust the partial pressure of BCl3 to ≤2Pa. After the circulation is completed, maintain the temperature for 5 minutes, shut off the gas supply branch throughout the process, and reduce the partial pressure of BCl3 in the furnace to 0Pa.

3. The method for improving the hardenability of pipeline steel with trace boron alloying according to claim 1, characterized in that, The rolled pipeline steel is composed of the following substances by mass percentage: C 0.03~0.06%; Si 0.10~0.20%; Mn 1.2~1.4%; P≤0.005%; S≤0.0010%; N≤0.0030%; O≤0.0015%; H≤0.0002%; B 0.0008~0.0015%; Ti 0.008~0.018%; Ta 0.006~0.012%; Nb 0.02~0.05%; Mg 0.0008~0.0020%; Ce 0.0005~0.0015%.

4. The method for improving the hardenability of pipeline steel with trace boron alloying according to claim 3, characterized in that, The mass ratio of Ti to N is 3.42 to 3.

8.

5. The method for improving the hardenability of pipeline steel with trace boron alloying according to claim 3, characterized in that, The mass ratio of Ta to Nb is 1:2 to 1:

4.

6. The method for improving the hardenability of pipeline steel with trace boron alloying according to claim 3, characterized in that, The mass ratio of Mg to Ce is 2:1 to 3:

1.

7. The method for improving the hardenability of pipeline steel with trace boron alloying according to claim 1, characterized in that, Step S2 further includes: S21 gradient speed-controlled quenching treatment: the surface layer is cooled to 600℃ at a cooling rate of 30~35℃ / s, and then cooled to room temperature at a rate of 15~20℃ / s; the core is cooled to 600℃ at a cooling rate of 20~25℃ / s, and then cooled to room temperature at a rate of 10~15℃ / s.

8. The method for improving the hardenability of pipeline steel with trace boron alloying according to claim 1, characterized in that, The high frequency mentioned in step S2 is 20~30kHz, and the intermediate frequency is 5~10kHz.