Hot rolled ribbed steel bars produced by double high bar

Abstract

The application provides a hot-rolled ribbed steel bar produced by double high rods, and ingredients of the hot-rolled ribbed steel bar are as follows in percentage by weight: C: 0.21% to 0.25%, Si: 0.40% to 0.70%, Mn: 1.10% to 1.30%, P: less than or equal to 0.045%, S: less than or equal to 0.045%, and the rest is Fe; the specification of the hot-rolled ribbed steel bar is φ10 to φ20 mm, and two cutting and rolling are adopted; the hot-rolled ribbed steel bar has the following properties: yield strength is greater than or equal to 440 MPa, tensile strength is greater than or equal to 600 MPa, elongation after fracture A is greater than or equal to 25%, total elongation at maximum force Agt is greater than or equal to 13%, and the ratio of strength to yield is greater than or equal to 1.33.

Description

[0001] The application is a divisional application of the parent application with the application number 2022105947479 and the invention name "Method for producing hot-rolled ribbed steel bar by double high bar", and the filing date is May 27, 2022. TECHNICAL FIELD

[0002] The application relates to the field of steel rolling, in particular to a hot-rolled ribbed steel bar produced by double high bar. BACKGROUND

[0003] The hot-rolled ribbed steel bar is the most widely used steel in the world, which is widely used in highways, bridges and various buildings. With the implementation of GB / T 1499.2-2018 "Steel for reinforced concrete Part 2: Hot-rolled ribbed steel bar", it is clearly stated in the standard that the metallographic structure of the steel bar should mainly be ferrite plus pearlite, and no tempered martensite structure should appear on the base circle. This marks that the process path of using water cooling and then self-tempering to obtain tempered sorbite to improve the strength of the steel bar is no longer available. At present, most steel plants improve the strength of the steel bar by adding Nb, V, Ti and other micro-alloys to the steel to utilize solid solution strengthening, fine-grain strengthening and precipitation strengthening. However, the addition of Nb, V, Ti and other micro-alloys will significantly increase the alloy cost and reduce the profit of the enterprise.

[0004] In summary, the existing technology has the following problems: how to produce hot-rolled ribbed steel bars that meet the standard without adding Nb, V, Ti and other micro-alloys and without having tempered martensite and sorbite structures. SUMMARY

[0005] The application provides a method for producing hot-rolled ribbed steel bars by double high bar (i.e. a method for producing hot-rolled ribbed steel bars by double high-speed bar), to solve the problem of producing hot-rolled ribbed steel bars with no tempered martensite and sorbite structures and qualified performance without adding Nb, V, Ti and other micro-alloys.

[0006] To this end, the application provides a method for producing hot-rolled ribbed steel bars by double high bar, which comprises:

[0007] The composition of the hot-rolled ribbed steel bar is as follows in terms of weight percentage: C: 0.21% to 0.25%, Si: 0.40% to 0.70%, Mn: 1.10% to 1.30%, P≤0.045%, S≤0.045%, and the rest is Fe;

[0008] The specification of the hot-rolled ribbed steel bar is φ10 to φ20 mm;

[0009] The production method adopts two-slit rolling, and the production method comprises the following steps: hot metal smelting by a blast furnace, hot metal desulfurization pretreatment, molten steel smelting by a converter, bloom continuous casting, heating furnace heating, rough rolling, medium rolling, water tank (2) before finishing rolling and recovery section, finishing rolling, water tank (2) before reducing diameter and recovery section, reducing diameter, cutting length, cooling bed, cutting length, collecting, and bundling.

[0010] The open rolling temperature is 950-1000 DEG C, the entering finishing rolling temperature is 900-930 DEG C, the entering reducing diameter temperature is controlled to be 830-870 DEG C, and the post-rolling natural cooling is performed.

[0011] Further, the hot metal is discharged by using a slide plate after BOF blowing, then alloy and deoxidizer are added, so that the C content is 0.21%-0.25%, the Si content is 0.40%-0.70%, the Mn content is 1.10%-1.30%, and the P and S contents are less than or equal to 0.045%, then the hot metal is sent to an argon station to blow argon, and full-process protection casting process is used for pouring.

[0012] Further, the heating furnace is divided into four areas, which are a preheating area, a first heating area, a second heating area, and a soaking area, the first heating area temperature is controlled to be 1000-1060 DEG C, the second heating area temperature is controlled to be 1060-1120 DEG C, the soaking area temperature is controlled to be 1040-1100 DEG C, the open rolling temperature is controlled to be 950-1000 DEG C, the entering finishing rolling temperature is controlled to be 900-930 DEG C, the entering reducing diameter temperature is controlled to be 830-870 DEG C, and the post-rolling natural cooling is performed.

[0013] Further, the two water tanks before the finishing rolling machine are opened by 40%-80% water, and the two water tanks before the reducing diameter machine are opened by 20%-50% water, the water amount is only used for controlling the temperature in the rolling process, preventing the temperature from being too high and the grain from growing, and the water amount is less than the water amount for water cooling, so that the post-rolling weak cooling is realized, the entering reducing diameter temperature is controlled to be 830-870 DEG C, and the steel surface will not have tempered sorbite and martensite.

[0014] Further, the rolling speed is 14 m / s-42 m / s.

[0015] Further, the finished product specification is φ10 mm, the rolling speed is 40 m / s, the finished product specification is φ12 mm, the rolling speed is 36 m / s, the finished product specification is φ14 mm, the rolling speed is 27 m / s, the finished product specification is φ16 mm, the rolling speed is 23 m / s, the finished product specification is φ18 mm, the rolling speed is 16 m / s, or the finished product specification is φ20 mm, and the rolling speed is 15 m / s.

[0016] Further, the hot-rolled ribbed steel bar has the following components: C: 0.22%, Si: 0.48%, Mn: 1.18%, P: 0.027%, S: 0.031%, and the rest is Fe.

[0017] Further, the hot-rolled ribbed steel bar has the following components: C: 0.23%, Si: 0.45%, Mn: 1.18%, P: 0.041%, S: 0.026%, and the rest is Fe.

[0018] Further, the open rolling temperature is controlled at 990℃, the K2 temperature of the finish rolling is 916℃, the temperature of the reducing diameter is 846℃, and the natural cooling on the cooling bed is performed.

[0019] Further, the open rolling temperature is controlled at 984℃, the K2 temperature of the finish rolling is 919℃, the temperature of the reducing diameter is 857℃, and the natural cooling on the cooling bed is performed.

[0020] Further, the first heating section temperature is controlled at 1012℃, the second heating section temperature is controlled at 1097℃, the soaking section temperature is controlled at 1059℃, and the heating time is 82 minutes.

[0021] The application further provides a hot-rolled ribbed steel bar produced by the double-high-bar method, and the hot-rolled ribbed steel bar has the following components in percentage by weight: C: 0.21%-0.25%, Si: 0.40%-0.70%, Mn: 1.10%-1.30%, P≤0.045%, S≤0.045%, and the rest is Fe.

[0022] The hot-rolled ribbed steel bar has a specification of φ10-φ20mm, and is rolled by two cutting methods.

[0023] Further, the rolling speed is 40m / s when the finished product specification is φ10mm, the rolling speed is 36m / s when the finished product specification is φ12mm, the rolling speed is 27m / s when the finished product specification is φ14mm, the rolling speed is 23m / s when the finished product specification is φ16mm, the rolling speed is 16m / s when the finished product specification is φ18mm, or the rolling speed is 15m / s when the finished product specification is φ20mm.

[0024] Further, the production method of the hot-rolled ribbed steel bar produced by the double-high-bar method comprises the following steps: blast furnace molten iron smelting, molten iron desulfurization pretreatment, converter molten steel smelting, bloom continuous casting, heating furnace heating, rough rolling, medium rolling, finish rolling, water tank (2) before finish rolling and recovery section, finish rolling, water tank (2) before reducing diameter and recovery section, reducing diameter, cutting length, cooling bed, cutting length, collecting, and bundling.

[0025] Further, the hot-rolled ribbed steel bar of the present application has the following metallographic structure: macrostructure: no ring; surface layer structure: P+F (pearlite + ferrite); 1 / 4 structure: P+F (pearlite + ferrite); 1 / 4 grain size: 11.0-12 grade; 1 / 4 P (pearlite) content: 34%-41%; center structure: P+F.

[0026] Further, the hot-rolled ribbed steel bar of the present application has the following properties: yield strength: ≥440Mpa, tensile strength: ≥600Mpa, elongation A: ≥25%, total elongation Agt: ≥13%, and strength-yield ratio: ≥1.33.

[0027] Further, the hot-rolled ribbed steel bar of the present application has the following properties: yield strength: 445M-470pa, tensile strength: 610-630Mpa, elongation A: 27%-31%, total elongation Agt: 13.9%-18%, and strength-yield ratio: 1.34-1.36.

[0028] By using the present application, the fine-grain strengthening effect of controlled rolling and controlled cooling can be fully utilized, the use amount of Nb, V, Ti and other micro-alloys can be reduced, the hot-rolled ribbed steel bar with no tempered martensite and sorbite structure that meets the standard of hot-rolled ribbed steel bar can be obtained, the yield strength is ≥440Mpa, the tensile strength is ≥600Mpa, the elongation A is ≥25%, the total elongation Agt is ≥13%, and the strength-yield ratio is ≥1.33. The alloy cost per ton of steel is 65 yuan, and the labor intensity can be reduced. DETAILED DESCRIPTION

[0029] In order to have a clearer understanding of the technical features, objects and effects of the present application, the present application will now be described.

[0030] The principle of the present application is that Nb, V, Ti and other micro-alloys can improve the strength performance of steel bars through solid solution strengthening, fine-grain strengthening and precipitation strengthening, etc., so that reducing the use amount of Nb, V, Ti and other micro-alloys can significantly reduce the strength of the steel bars. In order to ensure that the strength of the steel bars still meets the requirements of GB / T 1499.2-2018 "Steel for Reinforced Concrete Part 2: Hot Rolled Ribbed Steel Bar", other ways are needed to improve the strength of the steel bars. Among them, the controlled rolling and controlled cooling technology can significantly refine the grains and greatly improve the strength of the steel bars.

[0031] Component design: the chemical components of the general speed bar (hereinafter referred to as general bar) are as follows in terms of weight percentage: C: 0.21%-0.25%, Si: 0.40%-0.70%, Mn: 1.10%-1.30%, P≤0.045%, S≤0.045%, and the rest is Fe;

[0032] 1. The present application sets the double high bar rolling temperature at 950-1000℃, which can prevent grain growth during heating process and refine austenite grains. The rolling piece temperature rises significantly during rolling process. In order to prevent grain growth caused by temperature rise during rolling process and to prevent the roll ring from being easily collapsed, the two water tanks before the finishing rolling machine are opened at 40%-80% water, and the double high bar temperature entering the finishing rolling machine is controlled at 900-930℃. In order to reduce the cooling intensity and make the radial steel temperature uniform, the two water tanks before the reducing machine are opened at 20%-50% water, and the temperature entering the reducing machine is controlled at 830-870℃, and then the steel is naturally cooled on the cooling bed. In addition, by not setting the water tank after the reducing and the recovery section, or although the water tank after the reducing and the recovery section is set, the water in the water tank after the reducing is not opened when the steel passes through the water tank after the reducing and the recovery section, so as to avoid the formation of water penetration or strong cooling. Because the water penetration cooling opens a large amount of water, the cooling intensity is large, which will cause the steel surface to have tempered sorbite structure. The present application controls the temperature during the rolling process, especially the weak cooling after rolling, so that the steel surface only has ferrite and pearlite, and does not have tempered sorbite structure or martensite structure.

[0033] 2. The double high bar process (two splitting) is: blast furnace molten iron smelting→molten iron desulfurization pretreatment→ converter molten steel smelting→ billet continuous casting→ heating furnace heating→ rough rolling→ medium rolling→ water tank and recovery section→ finishing rolling→ water tank and recovery section→ reducing→ shear multiple lengths→ cooling bed→ shear fixed length→ collection, bundling, weighing, labeling and warehousing.

[0034] 3. After the molten iron is blown by BOF, the molten iron is discharged by a slide plate slag dam, then alloy and deoxidizer are added, so that the C content is 0.21%-0.25%, the Si content is 0.40%-0.70%, the Mn content is 1.10%-1.30%, and the P and S contents are ≤0.045%, then the molten iron is sent to an argon station for argon blowing, appropriate two-cooling parameters are selected, and the molten iron is poured by adopting a whole-process protective pouring process.

[0035] 4. The billet continuously cast is heated by a heating furnace, the temperature of a first heating section is controlled at 1000-1060℃, the temperature of a second heating section is controlled at 1060-1120℃, the temperature of a soaking section is controlled at 1040-1100℃, the rolling temperature is controlled at 950-1000℃, and then the temperature entering the finishing rolling is controlled at 900-930℃, the temperature entering the reducing is controlled at 830-870℃, and the steel is naturally cooled on the cooling bed.

[0036] Table 1: Composition of the steel of each example

[0037] Example Production line Specification C Si Mn P S Example 1 Double high bar Φ 10 0.22 0.48 1.18 0.027 0.031 Example 2 Double high bar Φ 12 0.22 0.50 1.19 0.030 0.025 Example 3 Double high bar Φ 14 0.23 0.45 1.18 0.041 0.026 Example 4 Double high bar Φ 16 0.23 0.47 1.20 0.031 0.021 Example 5 Double high bar Φ 18 0.22 0.45 1.19 0.020 0.022 Example 6 Double high bar Φ 20 0.22 0.44 1.18 0.029 0.020

[0038] Table 2: Heating process of the steel of each example

[0039] Example Production line Specification Furnace temperature First heating temperature Second heating temperature Soaking temperature Heating time Example 1 Double high bar Φ 10 682 1012 1097 1059 82 Example 2 Double high bar Φ 12 633 1027 1079 1062 80 Example 3 Double high bar Φ 14 642 1029 1085 1058 79 Example 4 Double high bar Φ 16 695 1018 1096 1049 75 Example 5 Double high bar Φ 18 701 1023 1076 1048 78 Example 6 Double high bar Φ 20 642 1019 1092 1066 81

[0040] Table 3: Rolling process of each example steel bar

[0041] Example Production line Cutting Specification Opening temperature Entry temperature of finishing rolling Entry temperature of reducing Example 1 Double high bar 2 Φ 10 971 915 845 Example 2 Double high bar 2 Φ 12 975 903 851 Example 3 Double high bar 2 Φ 14 984 919 835 Example 4 Double high bar 2 Φ 16 983 913 838 Example 5 Double high bar 2 Φ 18 973 911 833 Example 6 Double high bar 2 Φ 20 990 916 839

[0042] Table 4: Mechanical properties of each example steel

[0043] Example Production line Specification Yield strength Mpa Tensile strength Mpa A(％) Agt (%) Strength yield ratio Example 1 Double high bar Φ 10 460 630 31 17.6 1.37 Example 2 Double high bar Φ 12 455 620 29 14.5 1.36 Example 3 Double high bar Φ 14 455 620 27 14.2 1.36 Example 4 Double high bar Φ 16 445 615 28 15.3 1.38 Example 5 Double high bar Φ 18 450 610 28 13.9 1.36 Example 6 Double high bar Φ 20 455 610 29 14.6 1.34

[0044] A is the elongation at break, unit: %, Agt is the total elongation of maximum force, unit: %

[0045] Table 5: Metallographic structure of each example steel

[0046] Example Production line Specification Macrostructure Surface structure 1 / 4 structure 1 / 4 grain size 1 / 4 P content Center structure Example 1 Double high bar Φ 10 No ring P + F P + F 11.5 39％ P + F Example 2 Double high bar Φ 12 No ring P + F P + F 11.5 34％ P + F Example 3 Double high bar Φ 14 No ring P + F P + F 11.5 36％ P + F Example 4 Double high bar Φ 16 No ring P + F P + F 11.0 41％ P + F Example 5 Double high bar Φ 18 No ring P + F P + F 11.0 38％ P + F Example 6 Double high bar Φ 20 No ring P + F P + F 11.0 35％ P + F

[0047] From examples 1-6, it can be seen that by reasonable chemical composition control, using suitable rolling process, the use amount of micro-alloy such as Nb, V and Ti can be reduced, the alloy cost per ton of steel is reduced by 65 yuan, at the same time, the amount of alloy manually input by converter can be reduced, the labor intensity is reduced, at the same time, the steel bar also has good mechanical properties, and the metallographic structure meets the requirements of GB / T 1499.2-2018.

[0048] The above description is only a specific embodiment of the present application, and is not intended to limit the scope of the present application. The components of the present application can be combined with each other under the condition of no conflict, and any equivalent changes and modifications made by any person skilled in the art without departing from the concept and principle of the present application shall fall within the scope of protection of the present application.

Claims

1. A hot-rolled ribbed steel bar produced from double high bars, characterized in that, The hot-rolled ribbed steel bar has the following components in percentage by weight: C: 0.22% to 0.23%, Si: 0.44% to 0.48%, Mn: 1.18% to 1.20%, P≤0.045%, S≤0.045%, and the rest is Fe; The hot-rolled ribbed steel bar has a specification of φ10 to φ20 mm and is rolled by two-cutting; The hot-rolled ribbed steel bar has a yield strength of ≥440 MPa, a tensile strength of ≥600 MPa, an elongation after breaking A of ≥25%, a maximum force total elongation Agt of ≥13%, and a strength-yield ratio of ≥1.33; The hot-rolled ribbed steel bar has the following microstructure: macrostructure: no ring; surface layer structure: pearlite + ferrite; 1 / 4 structure: pearlite + ferrite; 1 / 4 grain size: 11.0-12 grade; 1 / 4 pearlite content: 34%-41%; Central structure: pearlite + ferrite; The production method of the hot-rolled ribbed steel bar produced by the double-high-rod method comprises the following steps: the production method adopts two-cutting and high-speed rod rolling; the production method comprises the following steps: blast furnace molten iron smelting, molten iron desulfurization pretreatment, converter molten steel smelting, bloom continuous casting, heating furnace heating, rough rolling, intermediate rolling, pre-precision rolling water tank and recovery section, precision rolling, pre-reducing water tank and recovery section, reducing, cutting length, cooling bed, cutting length, collecting, and bundling; The opening rolling temperature is 950-1000℃, the precision rolling temperature is 903-919℃, the reducing temperature is controlled at 830-870℃, and the post-rolling natural cooling is performed; The two water tanks before the precision rolling machine are opened at 40%-80% water, and the two water tanks before the reducing machine are opened at 20%-50% water; The rolling speed is 14 m / s-42 m / s.

2. The double high ribbed rolled steel bar produced by the method as claimed in claim 1, wherein, The finished product specification is φ10 mm, and the rolling speed is 40 m / s.

3. The double high ribbed rolled steel bar produced by the method as claimed in claim 1, wherein, The finished product specification is φ12 mm, and the rolling speed is 36 m / s.

4. The double high ribbed rolled steel bar produced by the method as claimed in claim 1, wherein, The finished product specification is φ14 mm, and the rolling speed is 27 m / s.

5. The double high ribbed rolled steel bar produced by the method as claimed in claim 1, wherein, The finished product specification is φ16 mm, and the rolling speed is 23 m / s.

6. The double high ribbed rolled steel bar produced by hot rolling as claimed in claim 1, wherein, The finished product specification is φ18 mm, and the rolling speed is 16 m / s.

7. The double high ribbed rolled steel bar produced by the method as claimed in claim 1, wherein, The finished product specification is φ20 mm, and the rolling speed is 15 m / s.

8. The double high ribbed rolled steel bar produced by hot rolling as claimed in claim 1, wherein, The hot-rolled ribbed steel bar has the following components: C: 0.22%, Si: 0.48%, Mn: 1.18%, P: 0.027%, S: 0.031%, and the rest is Fe.

9. The double high ribbed rolled steel bar produced by hot rolling as claimed in claim 1, wherein C： C: 0.23%, Si: 0.45%, Mn: 1.18%, P: 0.041%, S: 0.026%, and the rest is Fe.