A straight HRB635E high-strength threaded steel bar and its rolling method

Abstract

The present invention discloses a straight HRB635E high-strength threaded steel bar and a rolling method thereof, belonging to the technical field of steel section rolling. The rolling method comprises the following steps: a steel billet heated in a heating furnace is rolled through ten passes; wherein, during the rolling process, a box-shaped hole is used in the first and second passes, wherein the bite angle of the first pass is not greater than 26° and the reduction is 45-50 mm; the holes from the third to the tenth passes are all elliptical or circular, wherein the reduction of the third to the eighth passes is 30-40 mm; the reduction of the ninth and tenth passes is 20-25 mm; the inner diameter of the circular hole in the tenth pass is 48.5±0.8 mm, the roll gap is 3-4 mm, the cross rib height is 3.2±1.2 mm, and the cross rib top width is 2.3-2.5 mm. The steel bar rolling method of the present invention can obtain straight HRB635E high-strength steel bars with a yield strength ReL≥675MPa, a tensile strength Rm≥850MPa, and a specification of Φ50mm.

Description

Technical Field

[0001] The present invention relates to the technical field of section steel rolling, and in particular to a straight HRB635E high-strength threaded steel bar and a rolling method thereof. Background Art

[0002] High-strength rebar refers to hot-rolled ribbed steel bars with a yield strength of 500 MPa or higher. Compared to ordinary rebar, it offers higher strength and better overall performance, can withstand greater loads, and improves the seismic resistance and safety of concrete structures. Currently, the primary production of straight rebar is HRB400E (Ø12-40mm), with smaller quantities of HRB500E and HRB600E (Ø12-32mm). For large high-rise buildings and long-span public structures, high-strength rebar of 500 MPa or higher is preferred, and some key bridges and other structures require large-scale high-strength rebar.

[0003] However, the strength of Φ50mm steel bars produced using current small-size technology is difficult to meet the requirements, and the size that can meet the strength requirements cannot reach Φ50mm. Moreover, as the steel bar market environment continues to deteriorate, the pressure to reduce costs and increase efficiency is gradually increasing. While producing qualified high-strength steel bars with specifications reaching Φ50mm, cost issues must also be considered. Therefore, it is urgent to reasonably design the rolling method of Φ50mmHRB635E so that the products produced can meet the quality and performance requirements while minimizing costs. Summary of the Invention

[0004] To address the shortcomings of the prior art, the present invention provides a straight HRB635E high-strength threaded steel bar and a rolling method thereof. This rolling method produces high-strength steel bars with a yield strength ReL ≥ 675 MPa and a tensile strength Rm ≥ 850 MPa. It can also produce large-format straight high-strength steel bars up to 50 mm in diameter, while significantly reducing costs. This is achieved through the following techniques.

[0005] A method for rolling straight HRB635E high-strength threaded steel bars comprises the following steps:

[0006] The steel billet heated in the heating furnace is rolled through ten passes to obtain the steel billet;

[0007] Among them, during the rolling process, the hole profiles of the first and second passes are both box-shaped holes, wherein the bite angle of the first pass is not greater than 26° and the reduction is 45-50mm;

[0008] The hole shapes of the third to tenth passes are respectively elliptical holes or circular holes;

[0009] The third to eighth passes have a reduction of 30-40 mm; the ninth and tenth passes have a reduction of 20-25 mm.

[0010] The inner diameter d of the hole in the tenth pass is 48.5±0.8 mm, the roller gap s is 3-4 mm, the transverse rib height h is 3.2±1.2 mm, and the transverse rib top width b is 2.3-2.5 mm.

[0011] The choice of hole type in hole design is very important, especially for finished hole. Improper size design will result in size not meeting the requirements and negative difference cannot be rolled out, that is, the actual weight is greater than the theoretical weight, resulting in increased costs.

[0012] Furthermore, the heating temperature and time of the heating furnace are: preheating section temperature ≤ 950°C, heating section temperature 1215-1240°C, soaking section temperature 1205-1240°C, and heating time ≥ 100 min.

[0013] Furthermore, the rolling mills from the first pass to the tenth pass are horizontal rolling mills and vertical rolling mills alternatingly.

[0014] Furthermore, in the tenth pass, the milling groove depth is 3.0-3.4 mm.

[0015] Furthermore, in the tenth pass, the transverse rib spacing is 16±1.0 mm.

[0016] Furthermore, in the tenth pass, the included angle between the transverse rib and the axis is 63°-67°, and the transverse rib oblique angle is 47°-48°.

[0017] Furthermore, the hole shapes from the third pass to the tenth pass are alternately set to be elliptical holes and circular holes.

[0018] Furthermore, the steel billet includes the following elements in weight percentage: C 0.26-0.28%, Si 0.65-0.80%, Mn 1.50-1.60%, V 0.165-0.175%, P≤0.035%, S≤0.035%, Nb 0.013-0.020%, and carbon equivalent Ceq 0.56-0.58%.

[0019] Under the same billet specifications, as the rolling specifications increase, the compression ratio of the rolled piece decreases and the steel bar strength becomes lower. Therefore, for billets with the same composition, performance issues are more likely to occur when rolling larger specifications.

[0020] During the heating stage in the furnace, prolonged heating or too high a temperature will result in coarse original austenite grains. Too low a temperature or too short a heating time will affect the phase transformation and the uniformity of alloy element diffusion, thus affecting the performance of the steel bar. Therefore, it is very important to design a reasonable heating process.

[0021] In addition, to address the problem of large temperature differences (about 60°C) between the head, middle and tail of the steel billet, which leads to large differences in the performance of the same steel bar, the present invention has made the following improvements: the heating load of the preheating section is reduced, and the temperature of the preheating section is optimized from the original ≤1050°C to ≤950°C, thereby increasing the heating load of the heating section and the soaking section, increasing the gas volume, and lengthening the combustion flame, so that the temperature difference between the head, middle and tail of the steel billet is controlled within 30°C.

[0022] A straight HRB635E high-strength threaded steel bar is prepared by the above rolling method.

[0023] Straight high-strength threaded steel bars usually adopt the microalloying process, which uses the addition of niobium, vanadium, etc. to form niobium and vanadium carbides and nitrides that precipitate in the steel, achieving the purpose of grain refinement and precipitation strengthening, thereby improving the performance of the steel bars.

[0024] Niobium (Nb) is a strong carbonitride-forming element. By dissolving in the matrix, it refines grains and promotes precipitation strengthening. However, the precipitation temperature of Nb carbonitrides is higher than that of V, and the precipitation strengthening effect during steel bar rolling is often not significant. Furthermore, excessive Nb content increases the risk of cracking in rolled products.

[0025] V is the most important alloying element in 600MPa grade high-strength steel bars. It can effectively improve the strength of steel bars through precipitation strengthening, solid solution strengthening and fine grain strengthening, and can make full use of cheap N elements, which is a more economical microalloying method.

[0026] Carbon dissolves in the matrix, significantly increasing the strength of the steel through solid solution strengthening. It also combines with strong carbide-forming elements to form carbides, contributing to grain refinement and precipitation strengthening. However, while carbon significantly improves the hardenability of steel, excessive carbon content can lead to the formation of bainite or martensite in the structure, reducing the steel's plasticity and worsening its weldability. To ensure optimal overall performance, the carbon content of 600MPa-grade high-strength steel bars can be designed within a range of 0.22%-0.28%.

[0027] Si can increase strength through solid solution strengthening, which helps improve the elastic limit and yield strength of steel bars. It is also an important deoxidizer. Si also promotes the precipitation of vanadium carbide (VC) and enhances the precipitation of vanadium (V). The Si content of 600MPa grade high-strength steel bars can be designed within the range of 0.40%-0.80%.

[0028] Mn significantly increases the tensile strength of steel, but also improves hardenability. When the Mn content exceeds 1.5%, it can easily cause abnormal structure in the steel, which is detrimental to both ductility and weldability. The Mn content also affects the precipitation of vanadium nitride (VN). The higher the Mn content, the less VN is precipitated. Therefore, the appropriate Mn content control range is 1.30%-1.60%. In the rolling method of the present invention, the Mn content in the steel billet can be controlled to 1.50-1.60%.

[0029] P and S are both harmful elements. When the P and S content is high, the plasticity and toughness of the steel bars will be reduced, cracks will easily occur during the rolling process, and it will also be harmful to the welding and cold bending properties. When designing the composition, the upper limit values ​​of P and S should be reduced as much as possible according to the actual production conditions.

[0030] Furthermore, the specification of the steel bar is Φ50mm.

[0031] Furthermore, the yield strength of the steel bar ReL ≥ 675 MPa, the tensile strength Rm ≥ 850 MPa, the total elongation at maximum force Agt ≥ 9.5%, R°m / R°eL ≥ 1.26, and R°eL / ReL ≤ 1.08.

[0032] Compared with the prior art, the present invention is beneficial in that:

[0033] 1. The composition control combined with the rolling method of the present invention can produce large-size threaded steel bars of Φ50mm, and the yield strength ReL of the steel bars is ≥675MPa, the tensile strength Rm is ≥850MPa, the maximum force total elongation Agt is ≥9.5%, R°m / R°eL is ≥1.26, and R°eL / ReL is ≤1.08;

[0034] 2. The rolling method of the present invention controls the heating temperature and time so that the temperature difference between the head, middle and tail of the steel billet is within 30°C, thus maintaining the stability of the performance of the same steel bar;

[0035] 3. The hole shape of the tenth pass finished hole of the present invention is reasonably designed. The size of the rolled finished product not only meets the requirements, but also the actual weight is less than the theoretical weight, thus achieving the goal of cost reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the cross-sectional view of the finished hole after the tenth pass;

[0037] Figure 2 This is the cross-sectional view of the tenth milling pass of the transverse rib;

[0038] Figure 3 This is the longitudinal cross-section of the tenth finished hole. DETAILED DESCRIPTION

[0039] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0040] The present invention provides an exemplary method for rolling straight HRB635E high-strength threaded steel bars, comprising the following steps:

[0041] The steel billet is heated in a heating furnace and then rolled ten times to obtain the straight HRB635E high-strength threaded steel bar of the present invention;

[0042] Among them, during the rolling process, the hole profiles of the first and second passes are both box-shaped holes, wherein the bite angle of the first pass is not greater than 26° and the reduction is 45-50mm;

[0043] The hole shapes of the third to tenth passes are oval or circular holes, respectively. The reduction of the third to eighth passes is 30-40mm; the reduction of the ninth and tenth passes is 20-25mm.

[0044] The inner diameter d of the hole in the tenth pass is 48.5±0.8 mm, the roller gap s is 3-4 mm, the transverse rib height h is 3.2±1.2 mm, and the transverse rib top width b is 2.3-2.5 mm.

[0045] In some examples of the present invention, the heating temperature and time of the heating furnace can be: preheating section temperature ≤ 950°C, heating section temperature 1215-1240°C, soaking section temperature 1205-1240°C, and heating time ≥ 100 min.

[0046] In some examples of the present invention, the rolling mills from the first pass to the tenth pass may be alternating between flat rolling mills and vertical rolling mills.

[0047] In order to facilitate grooving during rolling and reduce the failure of the guard plate wrapping around the roller at the exit, in some examples of the present invention, in the tenth pass, the milling groove depth can be 3.0-3.4 mm.

[0048] In order to extend the service life of the roller, in some examples of the present invention, in the tenth pass, the transverse rib spacing L may be 16±1.0 mm.

[0049] In order to facilitate the groove removal of the rolled piece, in some examples of the present invention, in the tenth pass, the angle β between the transverse rib and the axis can be 63°-67°, and the transverse rib oblique angle α can be 47°-48°.

[0050] In some examples of the present invention, the hole shapes from the third pass to the tenth pass may be alternately arranged as elliptical holes and circular holes.

[0051] In some examples of the present invention, the steel billet may include the following elements in weight percentage: C 0.26-0.28%, Si 0.65-0.80%, Mn 1.50-1.60%, V 0.165-0.175%, P≤0.035%, S≤0.035%, Nb 0.013-0.020%, and carbon equivalent Ceq 0.56-0.58%.

[0052] The technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0053] In some examples of the present invention, the ten rolling mills are numbered 1#, 2#, 3#, 4#, 5#, 6#, 7#, 8#, 9#, and 10# respectively.

[0054] In some examples of the present invention, according to the finished product size requirements, the reduction amount of each pass is allocated according to the total deformation amount:.

[0055] The pass profiles of 1# and 2# are box-shaped, and rolling deformation is achieved through large reduction. 1# is the first pass, and smooth bite is required. The bite angle should not exceed 26°, and the reduction of 1# and 2# is set to 45-50mm.

[0056] The hole types from 3# to 10# alternate between elliptical holes and circular holes, and a small reduction is used to control the width expansion to ensure stable rolling and that the rolled piece size meets the requirements. Among them, the reduction of 3#, 4#, 5#, 6#, 7#, and 8# are all 30-40mm; the reduction of 9# and 10# are both 20-25mm.

[0057] The maximum reduction can be calculated using the formula Δh = D(1-cosα) (D is the working roll diameter, i.e., the diameter of the roll working surface). In this invention, the width expansion coefficient (Δb / Δh, Δb is the width deformation) is approximately 0.25-0.55. The width expansion coefficient for the 1# box hole is 0.27, which can be used to calculate the width of the 1# rolled piece. For 3#-10#, the width expansion coefficient for elliptical holes is 0.4-0.5, and the width expansion coefficient for round holes is 0.3-0.4. Combining the width expansion coefficients for each pass can be used to calculate the size of the rolled piece for each pass.

[0058] Example 1

[0059] The method for rolling straight HRB635E high-strength threaded steel bars provided in this embodiment includes the following steps:

[0060] S1. Acceptance of steel billet composition: 162mm×162mm HRB635E steel billet contains the following elements by weight: C 0.27%, Si 0.67%, Mn 1.55%, V 0.169%, P 0.022%, S 0.027%, Nb 0.016, carbon equivalent Ceq 0.57%. Each billet is visually inspected to confirm that the cross section, shape, dimensions, surface quality, etc. meet the specified requirements.

[0061] S2. The steel billet from step S1 is placed in a heating furnace for heating. The heating furnace temperatures are: 925°C in the preheating section, 1225°C in the heating section, and 1220°C in the soaking section. The heating furnace is automatically temperature controlled. The furnace time is strictly controlled to 103 minutes to allow the alloy elements to fully dissolve and diffuse. While ensuring the furnace temperature, the heating section and the soaking section adopt a high heat load mode and increase the flame length.

[0062] S3, rolling the steel billet obtained in step S2 through ten passes to obtain the straight HRB635E high-strength threaded steel bar of the present invention;

[0063] In this embodiment, if Figure 1-3 As shown in Figure 1, the circular hole of the tenth pass is the finished hole, with an inner diameter d of 48.3 mm, a transverse rib height h of 3 mm, a transverse rib top width b of 2.3 mm, a transverse rib spacing L of 16.3 mm, an angle β between the transverse rib and the axis of the cross-rib of 65°, and a transverse rib bevel angle α of 47.5°. The rolling parameter settings of each pass are shown in Table 1.

[0064] Table 1 Rolling parameter settings for each pass

[0065]

[0066] The applicant conducted extensive testing within the present invention's steel slab composition, heating furnace parameters, and rolling parameters, and found that the present invention's straight HRB635E high-strength threaded steel bars could be produced. Furthermore, the steel slab in step S2 was controlled at a temperature of approximately 1120-1150°C at the inlet of the 9# rolling mill, with a temperature difference of 30°C between the beginning, middle, and end of the slab.

[0067] Example 2

[0068] This embodiment is substantially the same as embodiment 1, except that the steel billet in this embodiment includes the following elements in weight percentages: C 0.27%, Si 0.69%, Mn 1.56%, V 0.168%, P 0.031%, S 0.033%, Nb 0.015, and a carbon equivalent Ceq of 0.57%.

[0069] Comparative Example 1

[0070] This comparative example is basically the same as Example 1, except that the steel billet in this comparative example includes the following elements in weight percentage: C 0.27%, Si 0.67%, Mn 1.55%, V 0.149%, P 0.022%, S 0.027%, Nb 0.016, and carbon equivalent Ceq 0.57%.

[0071] That is, in the steel billet of this comparative example, the weight percentage of V is lower than the range of the present invention.

[0072] Comparative Example 2

[0073] This comparative example is basically the same as Example 1, except that the inner diameter d of the finished hole of the tenth pass of the rolling mill in this comparative example is 49.5 mm.

[0074] That is, the inner diameter d of the finished hole of the tenth pass of the rolling mill in this comparative example exceeds the scope of the present invention.

[0075] Comparative Example 3

[0076] This comparative example is basically the same as Example 1, except that the height h of the transverse rib of the finished hole of the tenth pass of the rolling mill in this comparative example is 4.5 mm.

[0077] That is, the transverse rib height h of the finished hole of the tenth pass of the rolling mill in this comparative example exceeds the scope of the present invention.

[0078] Application Examples

[0079] The steel bars of Examples 1-2 and Comparative Examples 1-3 were dimensionally measured and performance tested according to the method described in "Steel for Reinforced Concrete Part 2: Hot-rolled Ribbed Bars" (GB / T 1499.2-2018). The dimensional measurement results and performance test results are shown in Table 2 below.

[0080] Table 2 Steel bar (HRB635E) dimension measurement and performance test results

[0081]

[0082] In Table 2, ReL represents the standard requirement value, which is 635 MPa. R°m is the measured tensile strength of the steel bar; and R°eL is the measured lower yield strength of the steel bar.

[0083] In the present invention, the quality inspection standards are: yield strength ReL≥635MPa, tensile strength Rm≥795MPa, total elongation at maximum force Agt≥9.0%, R°m / R°eL≥1.25, R°eL / ReL≤1.30.

[0084] As can be seen from Table 2, Examples 1-2 can stably prepare HRB635E threaded steel bars with a large size of 50 mm, and the steel bar yield strength ReL ≥ 675 MPa, tensile strength Rm ≥ 850 MPa, maximum force total elongation Agt ≥ 9.5%, R°m / R°eL ≥ 1.26, and R°eL / ReL ≤ 1.08.

[0085] Compared with Example 1, the performance, finished product dimensions, and negative difference of Comparative Examples 1-3 did not meet the requirements. The yield strength of the steel bars in Comparative Example 1 did not meet the requirements. The negative difference of the steel bars in Comparative Example 2 did not meet the requirements. The inner diameter of the steel bars in Comparative Example 3 was too small, not meeting the requirements. In addition, the transverse ribs in Comparative Example 3 were too high, making it difficult to remove the transverse ribs from the grooves, resulting in steel blockage.

[0086] The above specific embodiments describe the implementation of the present invention in detail, but the present invention is not limited to the specific details of the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

Claims

1. A method for rolling straight HRB635E high-strength threaded steel bars, characterized in that: The following steps are involved: The steel billet heated in the heating furnace is rolled through ten passes to obtain the steel billet; Among them, during the rolling process, the hole profiles of the first and second passes are both box-shaped holes, wherein the bite angle of the first pass is not greater than 26° and the reduction is 45-50mm; The hole shapes of the third to ninth passes are respectively elliptical holes or circular holes; The third to eighth passes have a reduction of 30-40 mm; the ninth and tenth passes have a reduction of 20-25 mm. The inner diameter of the circular hole in the tenth pass is 48.5±0.8mm, the roller gap is 3-4mm, the transverse rib height is 3.2±1.2mm, and the width of the transverse rib top is 2.3-2.5mm.

2. The rolling method according to claim 1, characterized in that The steel billet includes the following elements in weight percentage: C 0.26-0.28%, Si 0.65-0.80%, Mn 1.50-1.60%, V 0.165-0.175%, P≤0.035%, S≤0.035%, Nb 0.013-0.020%, and carbon equivalent Ceq 0.56-0.58%.

3. The rolling method according to claim 1, characterized in that The heating temperature and time of the heating furnace are: preheating section temperature ≤ 950°C, heating section temperature 1215-1240°C, soaking section temperature 1205-1240°C, and heating time ≥ 100min.

4. The rolling method according to claim 1, characterized in that The rolling mills from the first pass to the tenth pass are alternately flat rolling mills and vertical rolling mills.

5. The rolling method according to claim 1, characterized in that In the tenth pass, the milling groove depth is 3.0-3.4 mm.

6. The rolling method according to claim 1, characterized in that In the tenth pass, the transverse rib spacing is 16±1.0 mm.

7. The rolling method according to claim 1, characterized in that In the tenth pass, the included angle between the transverse rib and the axis is 63°-67°, and the oblique angle of the transverse rib is 47°-48°.

8. The rolling method according to claim 1, characterized in that The hole shapes of the third to tenth passes are alternately arranged as elliptical holes and circular holes.

9. A straight HRB635E high-strength threaded steel bar, characterized in that: The steel sheet is prepared by the rolling method according to any one of claims 1 to 8.

10. The straight HRB635E high-strength threaded steel bar according to claim 9, characterized in that: The specification of the steel bar is Φ50mm.

Images