A dual high-speed bar temperature-controlled rolling method

Abstract

The embodiment of the present invention provides a temperature-controlled rolling method for double-high-speed bars, comprising: sequentially performing a rough rolling process, an intermediate rolling process, a pre-finishing rolling process, a finishing rolling process, a diameter reduction process, and a cut-to-length shearing process; wherein, between the pre-finishing rolling process and the finishing rolling process, a first controlled cooling process is provided; between the finishing rolling process and the diameter reduction process, a second controlled cooling process is provided. The technical solution of the present invention adopts a multi-stage controlled cold rolling technology, and during the controlled cooling process, the temperature of the rolled piece is always controlled within the two-phase region of austenite and ferrite, thereby effectively avoiding the formation of a closed-loop tempering structure on the surface of the finished threaded steel, and greatly improving the yield rate.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to a temperature-controlled rolling method for double-high-speed bars. Background Art

[0002] The traditional ordinary bar rolling line adopts the post-rolling controlled cooling process. There are 18 rolling mills in the whole line, and multi-line cutting technology with more than three cuttings is adopted. The rolled products are not cooled during the rolling process. They are only strongly cooled after the rolling process is completed and the steel is thrown to the cooling bed. Therefore, only a post-rolling temperature control water tank is arranged.

[0003] In the process of implementing the present invention, the inventors found that there are at least the following problems in the prior art:

[0004] The existing technology does not cool during the rolling process, and only adopts post-rolling controlled cooling technology. The temperature of the rolled piece is high after rolling (>950℃), so it is very easy to form a closed-loop tempered structure on the surface of the steel bar. According to the provisions of "GB / T 1499.2-2018 Steel for Reinforced Concrete Part 2: Hot-rolled Ribbed Steel Bars", there must be no tempered structure on the surface of the rebar, otherwise it will be difficult to ensure the mechanical properties of the finished product, which makes it difficult for the yield of the existing technology to meet the expected requirements. Therefore, how to avoid the formation of surface tempered structure of rebar during rolling and improve the yield is a problem that needs to be solved. Summary of the invention

[0005] The embodiment of the present invention provides a dual high-speed bar temperature-controlled rolling method, that is, a dual-line high-speed bar production method, to solve the problem in the prior art that the surface of threaded steel is prone to form a tempered structure during the rolling process, thereby improving the yield rate.

[0006] To achieve the above-mentioned purpose, an embodiment of the present invention provides a dual high-speed bar temperature-controlled rolling method, comprising: sequentially performing a rough rolling process, an intermediate rolling process, a pre-finishing rolling process, a finishing rolling process, a diameter reducing process and a fixed-length shearing process; wherein, between the pre-finishing rolling process and the finishing rolling process, a first controlled cooling process is arranged; between the finishing rolling process and the diameter reducing process, a second controlled cooling process is arranged.

[0007] Furthermore, a post-rolling controlled cooling process is arranged between the diameter reducing process and the cut-to-length shearing process.

[0008] Furthermore, the first controlled cooling process includes a first cooling process and a first recovery process; the second controlled cooling process includes a second cooling process and a second recovery process; and the post-rolling controlled cooling process includes a post-rolling cooling process and a post-rolling recovery process.

[0009] Furthermore, the post-rolling controlled cooling process adopts a multi-stage graded controlled cooling method.

[0010] Furthermore, the cooling methods of the first cooling process, the second cooling process and the post-rolling cooling process are all water cooling.

[0011] Furthermore, in the first controlled cooling process, the temperature of the rolled piece is controlled within the two-phase region of austenite and ferrite; in the second controlled cooling process, the temperature of the rolled piece is controlled within the two-phase region of austenite and ferrite; in the post-rolling controlled cooling process, the temperature of the rolled piece is controlled within the two-phase region of austenite and ferrite.

[0012] Furthermore, the rough rolling process adopts a single set of rough rolling equipment; the intermediate rolling process adopts a single set of intermediate rolling equipment; the pre-finishing rolling process adopts a single set of pre-finishing rolling equipment; the finishing rolling process adopts two sets of finishing rolling equipment, and the two sets of finishing rolling equipment are arranged in parallel; the diameter reducing process adopts two sets of diameter reducing equipment, and the two sets of diameter reducing equipment are arranged in parallel; the cut-to-length shearing process adopts a single set of cut-to-length shearing equipment.

[0013] Furthermore, the composition of the rod is: C: 0.201-0.24Wt%, Si: 0.30-0.71Wt%, Mn: 1.30-1.56Wt%, P: ≤0.043Wt%, S: ≤0.035Wt%, Nb: 0.012-0.015Wt%.

[0014] Furthermore, the rolled raw material is a bar; the specification of the bar is Φ12mm~Φ16mm.

[0015] Furthermore, the specification of the rod is Φ12mm; in the first controlled cooling process, the temperature of the rolled piece is controlled at 950±20℃; in the second controlled cooling process, the temperature of the rolled piece is controlled at 900±20℃; in the post-rolling controlled cooling process, the temperature of the rolled piece is controlled at 850±20℃.

[0016] The above technical solution has the following beneficial effects:

[0017] In the technical solution of the present invention, a water cooling device and a recovery section guide groove are added between the pre-finishing rolling unit and the finishing rolling unit, and between the finishing rolling unit and the reducing unit. The rolled piece undergoes two-stage graded cooling control during the rolling process, and the temperature of the rolled piece is controlled in the two-phase region for rolling to achieve the effect of increasing the internal dislocation density of the ferrite grains not in the crystallization zone and refining the size of the recrystallized ferrite grains. After rolling, a multi-stage weak graded cooling control device is added to further refine the grains, so that the steel performance meets the national standard requirements, and ensures that the surface metallographic structure of the finished threaded steel has no tempered structure, thereby effectively improving the yield rate.

[0018] In addition, this technical solution also has the following characteristics:

[0019] 1. In the traditional rolling process, since there is no cooling during the rolling process, only one strong cooling is performed. After the rolling is completed, the temperature of the rolled piece is high, the grains are coarse, and the ferrite grain size rating after rolling is about 9.5. In order to ensure that the mechanical properties of the steel meet the national standards, it is necessary to add more alloy strengthening elements such as Nb and V (the content is 0.024%) to the steel billet, thereby increasing the billet alloy cost. In this application, the dual high-speed bar rolling process increases the pre-water cooling section and the finishing water cooling section, adopts the graded controlled cold rolling technology, controls the temperature of the rolled piece in the two-phase region, and then passes through the finishing rolling unit and the diameter reducing unit to fully refine the ferrite grains. When cooled to room temperature, the steel has a high degree of grain refinement (grain size rating of 11), improves the mechanical properties of the steel, and effectively reduces the content of the Nb element in the steel billet, thereby greatly reducing the cost.

[0020] 2. Traditional ordinary bars are rolled The multi-line cutting technology of more than three cuts is used for screw rolling, which has a high process failure rate, and the finished product (18V pass) uses high-speed steel rollers, the hole type is not wear-resistant, and the replacement is frequent, and the rolling line output is low. In this application, the production line is designed as a two-cut rolling technology. After the rolled piece leaves the pre-finishing rolling mill, it enters the A / B two-line rolling mill for rolling; at the same time, in order to match the rolling line capacity and reduce the replacement frequency of the finished product roller ring, a special tungsten carbide roller ring with a grade of YGA60 is configured for the finished product. This roller ring is developed for low-temperature rolling process. By improving the alloy composition, forming and heat treatment process of the roller ring, the hole type rolling volume is greatly improved, the roller consumption and replacement time are reduced, the effective operation rate of the rolling line is improved, and the economic benefits are greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 It is a flow chart of a dual high-speed bar temperature-controlled rolling method according to an embodiment of the present invention;

[0023] Figure 2 It is a phase change diagram of the rolling process of the prior art;

[0024] Figure 3 It is a process layout diagram of a bar rolling line in the prior art;

[0025] Figure 4 is a phase change diagram of the rolling process in an embodiment of the present invention;

[0026] Figure 5is a process layout diagram of a bar rolling line in a specific example of the present invention;

[0027] Figure 6 It is a surface metallographic structure diagram of a finished product in a specific example of the present invention;

[0028] Figure 7 It is a metallographic structure diagram of a quarter of the finished product in a specific example of the present invention;

[0029] Figure 8 It is a metallographic structure diagram of the central part of the finished product in a specific example of the present invention;

[0030] Figure numbers: 1. Roughing mill; 2. Intermediate rolling mill; 3. Pre-finishing mill; 4. First temperature-controlled water tank; 5. First recovery guide trough; 6. Finishing mill; 7. Second temperature-controlled water tank; 8. Second recovery guide trough; 9. Reducing mill; 10. Post-rolling temperature-controlled water tank; 11. Post-rolling recovery section; 12. Segmented shear and upper steel guide trough. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] like Figure 1 As shown, an embodiment of the present invention provides a dual high-speed bar temperature-controlled rolling method, comprising:

[0033] The rough rolling process, intermediate rolling process, pre-finishing rolling process, finishing rolling process, diameter reducing process and cut-to-length process are carried out in sequence;

[0034] Wherein, a first controlled cooling process is arranged between the pre-finishing rolling process and the finishing rolling process;

[0035] A second controlled cooling step is provided between the finishing step and the diameter reducing step.

[0036] In order to reduce the deformation resistance of the steel billet and increase its plasticity and ductility, the steel billet needs to be heated to the austenite region in a heating furnace before rolling. Figure 2 As shown, it passes through the following three phase regions in sequence: austenite region - including austenite recrystallization region and austenite non-recrystallization region → two-phase region (austenite + ferrite) → ferrite + pearlite region. Usually the opening temperature of the steel billet is 1020±30℃. Since the rolling process is a speed-up rolling, the traditional bar rolling line and rolling process are as follows Figure 3As shown, cooling is only carried out after rolling, and there is no intermediate temperature control condition. The temperature of the rolled piece after final rolling is about 30°C different from the starting rolling temperature. Therefore, the temperature of the rolled piece after final rolling is high, and the austenite grains are coarse, which is not conducive to improving the performance of the steel. At the same time, it is easy to form a tempered structure on the surface of the finished product.

[0037] To solve this problem, the present application sets up controlled cooling processes between the pre-finishing rolling process and the finishing rolling process, and between the finishing rolling process and the diameter reduction process during the rolling process, and adopts the advanced temperature-controlled rolling technology of graded controlled cooling, and adopts a low-temperature rolling process to improve the performance of steel, thereby avoiding the appearance of tempered structure on the surface of the finished product, and under the premise of ensuring that the mechanical properties of the steel meet the requirements of the national standard, it can realize the industrial production of low-alloy billets and achieve the purpose of reducing costs and increasing efficiency. After adopting the method of the present application, the rolling process phase change diagram is as follows Figure 4 As shown in the figure, Tnr represents the non-recrystallization temperature of austenite; Ar3 is the critical phase transformation temperature of austenite to ferrite; Ar1 ​​is the critical phase transformation temperature of austenite to pearlite.

[0038] Furthermore, a post-rolling controlled cooling process is provided between the diameter reducing process and the cut-to-length shearing process, and the post-rolling cooling process adopts a multi-stage graded controlled cooling method, that is, it is composed of multiple post-rolling temperature control water tanks and multiple post-rolling recovery sections.

[0039] By setting a controlled cooling step during the rolling process, the dislocation density inside the ferrite grains that are not in the crystallization zone can be increased and the size of the recrystallized ferrite grains can be refined. At the same time, by adding a multi-stage weak-grade controlled cooling device after rolling, the grains can be further refined.

[0040] Further, the first controlled cooling process includes a first cooling process and a first recovery process;

[0041] The second controlled cooling process includes a second cooling process and a second recovery process;

[0042] The post-rolling controlled cooling process includes the post-rolling cooling process and the post-rolling recovery process.

[0043] In order to achieve better results, the first recovery process is set after the first cooling process (i.e., the first recovery guide groove is set after the first temperature control water tank), so that the rolled piece has sufficient time to recover the surface temperature after the first cooling process and to even out the core and surface temperatures. Correspondingly, the second recovery guide groove can be set after the second temperature control water tank, and the post-rolling recovery guide groove can be set after the post-rolling temperature control water tank. Each recovery guide groove should have a certain length, which is determined according to actual needs.

[0044] Furthermore, the cooling methods of the first cooling process, the second cooling process and the post-rolling cooling process are all water cooling.

[0045] In this application, each hole cooling process adopts water cooling, and a temperature-controlled water tank is set in the relevant processes.

[0046] Furthermore, in the first controlled cooling process, the temperature of the rolled piece is controlled within the austenite and ferrite two-phase region;

[0047] In the second controlled cooling process, the temperature of the rolled piece is controlled within the austenite and ferrite two-phase region;

[0048] In the post-rolling controlled cooling process, the temperature of the rolled piece is controlled within the two-phase region of austenite and ferrite.

[0049] like Figure 4 As shown, in order to refine the recrystallized ferrite grain size, eliminate the tempered structure on the surface of the finished product, and ensure the mechanical properties of the steel, measures such as controlling the water flow rate should be taken in each controlled cooling process to strictly ensure that the temperature of the rolled piece is within the two-phase region.

[0050] Furthermore, the rough rolling process uses a single set of rough rolling equipment; the intermediate rolling process uses a single set of intermediate rolling equipment; the pre-finishing rolling process uses a single set of pre-finishing rolling equipment; the finishing rolling process uses two sets of finishing rolling equipment, which are arranged in parallel; the diameter reducing process uses two sets of diameter reducing equipment, which are arranged in parallel; the cut-to-length shearing process uses a single set of cut-to-length shearing equipment. The rough rolling equipment, intermediate rolling equipment, pre-finishing rolling equipment, finishing rolling equipment, and diameter reducing equipment are all composed of multiple rolling mills. The rough rolling mill group, intermediate rolling mill group, and pre-finishing mill group are all single-line, and the finishing mill group and the diameter reducing mill group are all double-line.

[0051] In the application, the multi-line slitting technology of more than three slittings commonly used in the prior art was abandoned, and the entire production line was designed as a two-slitting rolling technology, that is, after the pre-finishing mill, the finishing mill and the reducing mill were designed as two groups arranged in parallel, and then merged together during the cut-to-length shearing. After the cut-to-length shearing is completed, the rolled piece is transported to the cooling bed through the upper steel guide trough.

[0052] Furthermore, the rolled raw material is a bar; the specification of the bar is Φ12mm~Φ16mm; the composition of the bar is: C: 0.201~0.24Wt%, Si: 0.30~0.71Wt%, Mn: 1.30~1.56Wt%, P: ≤0.043Wt%, S: ≤0.035Wt%, Nb: 0.012~0.015Wt%.

[0053] The dual high-speed bar production line of the present application is mainly used for rolling small-size rebars of Φ12 to Φ16, and the daily output can reach 4,200 to 4,700 tons, greatly improving the rolling line capacity.

[0054] Furthermore, in one embodiment, the specification of the raw material bar is Φ12mm; in the first controlled cooling process, the temperature of the rolled piece is controlled at 950±20℃; in the second controlled cooling process, the temperature of the rolled piece is controlled at 900±20℃; in the post-rolling controlled cooling process, the temperature of the rolled piece is controlled at 850±20℃.

[0055] The following is a specific example to illustrate the dual high-speed bar temperature controlled rolling method of the present application:

[0056] This specific example is used for rolling Φ12mm HRB400E-0NbS rebar, double-wire rolling, and the finishing speed is 35-40 m / s, for example, 38 m / s.

[0057] The production line layout of this specific example is as follows Figure 5 As shown, the production line consists of a roughing mill group 1, an intermediate rolling mill group 2, a pre-finishing mill group 3, a first temperature-controlled water tank 4, a first recovery guide trough 5, a finishing mill group 6, a second temperature-controlled water tank 7, a second recovery guide trough 8, a diameter reducing mill group 9, a post-rolling temperature-controlled water tank 10, a post-rolling recovery section 11, and a segmented shear and an upper steel guide trough 12. There are 30 rolling mills in total on the whole line, of which 1#~6# are rough rolling mills, 7#~12# are medium rolling mills, 13#~18# are pre-finishing mills, 19#~22# and 25#~28# are finishing mills, 23#~24# and 29#~30# are reducing mills, a first temperature-controlled water tank and a first recovery guide groove are arranged between the pre-finishing mill and the finishing mill, a second temperature-controlled water tank and a second recovery guide groove are arranged between the finishing process and the reducing process, and a plurality of post-rolling temperature-controlled water tanks 10 and a plurality of post-rolling recovery sections 11 are arranged after the reducing mill 9. In this specific example, three groups of post-rolling temperature-controlled water tanks 10 and post-rolling recovery sections 11 are arranged in each package, and each group of post-rolling temperature-controlled water tanks 10 and post-rolling recovery sections 11 are arranged alternately.

[0058] In each controlled cooling process, the controlled temperature of the rolled piece is shown in Table 1.

[0059]

[0060] Table 1. Temperature control values ​​for each cooling process

[0061] At the same time, the finished product batch is equipped with a 24V special tungsten carbide roller ring with the brand name YGA60 (its relevant parameters are shown in Table 2). The roller ring is developed for the low-temperature rolling process. By improving the alloy composition, forming and heat treatment process of the roller ring, the hole rolling volume is greatly improved, with obvious economic benefits.

[0062]

[0063] Table 2. Relevant performance parameters of special tungsten carbide roller ring

[0064] The mechanical properties of the finished rebar are shown in Table 3. It can be seen that all mechanical properties meet the national standards and have a large margin. And after adopting this method, the Nb element in the billet can be effectively reduced (see Table 4, the content is 0.013%). According to the market price of Nb between 300,000 and 400,000 yuan per ton, the cost of low-alloy billets is 30-40 yuan / ton lower than that of traditional process billets. The dual high-speed bar rolling line of this specific example can produce 4,200 to 4,700 tons of rebar per day, saving 140,000 to 190,000 yuan per day, with good economic benefits.

[0065]

[0066] Table 3. Mechanical properties of finished steel

[0067]

[0068] Table 4. Chemical finished product table of the blank In addition, the metallographic structure analysis of the finished product is shown in the following table, and the metallographic structure diagram of the finished product is shown in Figure 6 to Figure 8 As shown:

[0069] Macroscopic Metallography Surface tissue One quarter Central Organization Grain size / grade No tempering structure F+P F+P F+P 11

[0070] Table 5. Metallographic structure analysis of finished products

[0071] Through Table 2 and Figure 6 to Figure 8 It can be seen that after rolling with the new process, the surface metallographic structure of the Φ12mm rebar has no tempered structure; the structures of the surface, one quarter and center are all F+P (ferrite + pearlite), which meets the metallographic requirements of rebar in the new national standard for rebar (GB-T 1499.2-2018 Steel for reinforced concrete Part 2: Hot-rolled ribbed steel bars).

[0072] In the above detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiments of the claimed subject matter require more features than are clearly stated in each claim. On the contrary, as reflected in the appended claims, the invention is in a state of having less than all the features of the disclosed individual embodiments. Therefore, the appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0073] The disclosed embodiments are described above to enable any person skilled in the art to implement or use the present invention. Various modifications of these embodiments are obvious to those skilled in the art, and the general principles defined herein may also be applied to other embodiments without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure is not limited to the embodiments given herein, but is consistent with the broadest scope of the principles and novel features disclosed in this application.

[0074] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A dual high-speed bar temperature-controlled rolling method, It is characterized in that include: The rough rolling process, intermediate rolling process, pre-finishing rolling process, finishing rolling process, diameter reducing process and cut-to-length shearing process are carried out in sequence; Wherein, a first controlled cooling process is arranged between the pre-finishing rolling process and the finishing rolling process; A second controlled cooling process is provided between the finishing process and the diameter reducing process; A post-rolling controlled cooling process is also provided between the diameter reducing process and the cut-to-length shearing process; The first controlled cooling process includes a first cooling process and a first recovery process; The second controlled cooling process includes a second cooling process and a second recovery process; The post-rolling controlled cooling process includes a post-rolling cooling process and a post-rolling recovery process; The post-rolling controlled cooling process adopts a multi-stage graded controlled cooling method; In the first controlled cooling step, the temperature of the rolled piece is controlled within the two-phase region of austenite and ferrite; In the second controlled cooling step, the temperature of the rolled piece is controlled within the austenite and ferrite two-phase region; In the post-rolling controlled cooling process, the temperature of the rolled piece is controlled within the austenite and ferrite two-phase region; The composition of the rod is: C: 0.201~0.24Wt%, Si: 0.30~0.71Wt%, Mn: 1.30~1.56Wt%, P: ≤0.043Wt%, S: ≤0.035Wt%, Nb: 0.012~0.015Wt%; The specification of the bar is Φ12mm; in the first controlled cooling process, the temperature of the rolled piece is controlled at 950±20°C; in the second controlled cooling process, the temperature of the rolled piece is controlled at 900±20°C; in the post-rolling controlled cooling process, the temperature of the rolled piece is controlled at 850±20°C; The surface metallographic structure of Φ12mm threaded steel has no tempered structure; the structure of the surface, one quarter and center is ferrite + pearlite, and the grain size is 11; The strength-to-yield ratio reaches 1.32, and the maximum force extension Agt is 16%.

2. The dual high-speed bar temperature-controlled rolling method according to claim 1, It is characterized in that The post-rolling controlled cooling process adopts a multi-stage graded controlled cooling method.

3. The dual high-speed bar temperature-controlled rolling method according to claim 2, It is characterized in that The cooling methods of the first cooling step, the second cooling step and the post-rolling cooling step are all water cooling.

4. The dual high-speed bar temperature-controlled rolling method according to claim 1, It is characterized in that The rough rolling process adopts a single set of rough rolling equipment; The intermediate rolling process adopts a single set of intermediate rolling equipment; The pre-finishing rolling process adopts a single set of pre-finishing rolling equipment; The finishing rolling process uses two sets of finishing rolling equipment, and the two sets of finishing rolling equipment are arranged in parallel; The diameter reduction process uses two sets of diameter reduction equipment, and the two sets of diameter reduction equipment are arranged in parallel; The cut-to-length process uses a single set of cut-to-length equipment.

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