Production method of HRB400E and Q355B blank flexible rolling

Abstract

The application provides a production method of HRB400E and Q355B blank flexible rolling, the HRB400E and Q355B blank chemical component content ratio is as follows: C: 0.20%-0.24%, Si: 0.20%-0.35%, Mn: 1.05%-1.25%, Nb: 0.017%-0.027%, P: less than or equal to 0.035%, S: less than or equal to 0.035%, the hot-rolled ribbed steel bar and the round steel in the application use the same blank, the performance requirements of different steel grades are met through flexible rolling, the production efficiency is greatly improved, the mixed blank is reduced, the production cost is reduced, and the performance of the finished product is not caused by the human operation error and the mixed blank.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of steel production, in particular to a production method for flexible rolling of steel billets, in particular a production method for flexible rolling of HRB400E and Q355B billets. BACKGROUND

[0002] At present, the bar production line mainly produces hot-rolled ribbed steel bars and large-specification straight round steel, and the hot-rolled ribbed steel bars are widely used in highways, bridges and various buildings, so the annual output of hot-rolled ribbed steel bars in China is very large, and the products of the normal rolling are also hot-rolled ribbed steel bars, and occasionally a small amount of large-specification straight round steel is rolled. At present, special steel grades for ribbed steel bars are used for rolling hot-rolled ribbed steel bars, and special steel grades for round steel are used for rolling round steel, which will bring certain difficulties to production control. When producing these two special steel grades, continuous casting cannot avoid the situation of mixed pouring of billets, and the composition of the mixed pouring billets is not uniform, which leads to the mixed pouring billets being judged as waste, thereby increasing the production cost. Moreover, round steel is only occasionally rolled, and in order to ensure the delivery quantity, the special billets for producing round steel are often larger than the required quantity, which will lead to a small part of the remaining billets being stacked in the warehouse, thereby occupying the space of the warehouse. Sometimes the warehouse is tight, and the billets for round steel are also stacked together with the billets for hot-rolled ribbed steel bars, although the billets are well marked, but there will still be human operation errors, and the wrong billets are used for production, thereby leading to the performance not meeting the requirements.

[0003] In summary, the existing technology has the following problems: special steel grades are used for rolling hot-rolled ribbed steel bars and round steel respectively, and the problem of mixed pouring of billets caused by human operation errors or in the production process cannot be avoided, thereby leading to the performance of the finished products not meeting the requirements and increasing the production cost. SUMMARY

[0004] The present application provides a production method for flexible rolling of steel billets, in particular a production method for flexible rolling of HRB400E and Q355B billets, to solve the problem in the above-mentioned existing technology that special steel grades are used for rolling hot-rolled ribbed steel bars and round steel respectively, which leads to the situation of mixed pouring of billets caused by human operation errors or in the production process, thereby leading to the performance of the finished products not meeting the requirements and increasing the production cost.

[0005] Therefore, the present application provides a production method for flexible rolling of HRB400E and Q355B billets, which uses the same kind of billets, and the chemical composition content ratio (in terms of weight percentage) of the HRB400E and Q355B billets is as follows: C: 0.20% to 0.24%, Si: 0.20% to 0.35%, Mn: 1.05% to 1.25%, Nb: 0.017% to 0.027%, P ≤ 0.035%, and S ≤ 0.035%.

[0006] The production method of the HRB400E and Q355B blank flexible rolling comprises the following process steps which are sequentially performed:

[0007] Blast furnace molten iron smelting→ molten iron desulfurization pretreatment→ converter molten steel smelting→ bloom continuous casting→ heating furnace heating→ rough rolling→ medium rolling→ finishing mill set→ large cooling bed→ fixed-length cold shearing→ small cooling bed→ bundling, weighing, labeling and warehousing;

[0008] When the HRB400E steel bar is rolled, the preheating section temperature is ≤900℃, the first heating section temperature is 1040±30℃, the second heating section temperature is 1100±30℃, and the soaking section temperature is 1080±30℃; when the Q355B round steel is rolled, the preheating section temperature is ≤900℃, the first heating section temperature is 1060±30℃, the second heating section temperature is 1120±30℃, and the soaking section temperature is 1100±30℃.

[0009] Further, when the HRB400E steel bar is rolled, the opening rolling temperature is 1000±30℃; the water tank cooling is used to control the temperature of entering the finishing mill to be 880±20℃.

[0010] Further, when the Q355B round steel is rolled, the opening rolling temperature is 1020±30℃; the water tank cooling is used to control the temperature of entering the finishing mill to be 930±20℃.

[0011] Further, when the HRB400E steel bar is rolled, the grain size is ≥11 grade by using controlled rolling to refine the grain, and the water tank cooling is used to control the temperature of the upper cooling bed to be 880±20℃.

[0012] Further, when the Q355B round steel is rolled, the grain size is ≥10 grade by using controlled rolling to refine the grain, and the water tank cooling is used to control the temperature of the upper cooling bed to be 900±20℃.

[0013] Further, the HRB400E steel bar specification is 10-25mm.

[0014] Further, the Q355B round steel specification is 50mm.

[0015] Further, the converter molten steel smelting: after the molten iron is blown by the oxygen top-blown converter, the molten steel is tapped by using the slide plate slag stopping, then the deoxidizer and alloy are added, and then the argon station is blown.

[0016] Further, the bloom continuous casting adopts the full-process protective casting process for casting, and the bloom size is 165mm×165mm×10000mm.

[0017] The beneficial effects of the present application are: the production method of the HRB400E and Q355B blank flexible rolling uses the same blank, the HRB400E and Q355B blank chemical composition content ratio is: C: 0.20%-0.24%, Si: 0.20%-0.35%, Mn: 1.05%-1.25%, Nb: 0.017%-0.027%, P≤0.035%, S≤0.035%; based on the process steps under the above reasonable component design, when rolling the HRB400E steel bar, the preheating section temperature is ≤900℃, the first heating section temperature is 1040±30℃, the second heating section temperature is 1100±30℃, and the soaking section temperature is 1080±30℃; when rolling the Q355B round steel, the preheating section temperature is ≤900℃, the first heating section temperature is 1060±30℃, the second heating section temperature is 1120±30℃, and the soaking section temperature is 1100±30℃, the hot-rolled ribbed steel bar and the round steel in the application use the same blank, the performance requirements of different steel grades are met through flexible rolling, the production efficiency is greatly improved, the mixed blank is reduced, and the production cost is reduced, and the performance of the finished product is not affected by the human operation error. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is the metallographic structure photo (500 times magnification) of example 1 of the present application;

[0019] Figure 2 It is the metallographic structure photo (500 times magnification) of example 2 of the present application;

[0020] Figure 3 It is the metallographic structure photo (500 times magnification) of example 3 of the present application;

[0021] Figure 4 It is the metallographic structure photo (500 times magnification) of example 4 of the present application;

[0022] Figure 5 It is the metallographic structure photo (500 times magnification) of example 5 of the present application. DETAILED DESCRIPTION

[0023] In order to have a clearer understanding of the technical features, objects and effects of the present application, the present application will be described.

[0024] The purpose of the present application is to provide a production method of HRB400E and Q355B blank flexible rolling, so that the hot-rolled ribbed steel bar and the round steel use the same blank, the performance requirements of different steel grades are met through flexible rolling, the production efficiency is improved, the production cost is reduced, and the performance of the finished product is not affected by the mixed blank.

[0025] I. The principle of the present application is:

[0026] On the basis of HRB400E composition, the content of C is controlled at 0.20% to 0.24%, which meets the composition requirement of Q355B; without adding ferrosilicon, the content of Si in the steel is reduced from 0.50% to 0.75% to 0.20% to 0.35%, so as to reduce the tensile strength of the steel and prevent the tensile strength from being too high to meet the performance requirement of Q355B; the content of Mn is reduced from 1.30% to 1.50% to 1.05% to 1.25%, so as to improve the elongation after fracture and impact energy performance of Q355B; the content of Nb is increased from 0.012% to 0.022% to 0.017% to 0.027%, so as to fully utilize the fine-grain strengthening effect of Nb and improve the strength and plasticity and toughness of the steel; the content of P and S is controlled to be less than or equal to 0.035%, so as to reduce the influence of P and S on plasticity and toughness.

[0027] Due to the large reduction of the contents of Si and Mn, if the conventional process is adopted for rolling HRB400E, the performance of the finished product will be low, therefore, the controlled rolling and controlled cooling process is required, the opening rolling temperature is reduced from 1040±30°C to 1000±30°C, so as to prevent the grains from growing too much during the heating process; the entry temperature of the finishing rolling is reduced from 950±20°C to 880±20°C, so as to make the grains be rolled in the unrecrystallization zone and be refined; the temperature on the cooling bed after rolling is reduced from 950±20°C to 880±20°C, so as to prevent the grains from growing again after rolling, and the strength and plasticity and toughness of the steel bar are improved by refining the grains.

[0028] The yield strength of Q355B only needs to be greater than or equal to 335MPa, and the tensile strength is in the range of 470 to 630MPa, therefore, the rolling temperature cannot be too low, so as to prevent the tensile strength from exceeding the maximum value of 630MPa, the opening rolling temperature is reduced from 1040±30°C to 1020±30°C, so as to prevent the grains from growing too much during the heating process; the entry temperature of the finishing rolling is reduced from 950±20°C to 930±20°C, so as to prevent the grains from growing too much during the rolling process; the temperature on the cooling bed is reduced from 950±20°C to 920±20°C, so as to improve the strength and plasticity and toughness of the Q355B round steel by refining the grains.

[0029] II. Based on the above principle, the application provides a production method for flexible rolling of HRB400E and Q355B billets, and the specific technical measures include:

[0030] 1. The process is as follows: blast furnace molten iron smelting→ molten iron desulfurization pretreatment→ converter molten steel smelting→ square billet continuous casting→ heating furnace heating→ rough rolling→ medium rolling→ finishing rolling unit→ large cooling bed→ fixed-length cold shearing→ small cooling bed→ bundling, weighing, labeling and warehousing.

[0031] 2. After the hot metal is blown by oxygen top-blown converter (BOF), the slag is blocked by slide plate, then deoxidizer and alloy are added to make the content of C 0.20%-0.24%, the content of Si 0.20%-0.35%, the content of Mn 1.05%-1.25%, the content of Nb 0.017%-0.027%, the content of P and S ≤0.035%, then the hot metal is sent to argon station to be blown by argon, the appropriate secondary cooling parameters are selected for continuous casting, and the full-range protective casting process is adopted to cast, and the billet size is 165mm*165mm*10000mm.

[0032] 3. When the HRB400E steel bar is rolled, the billet is heated by a heating furnace, the preheating section temperature is ≤900℃, the first heating section temperature is 1040±30℃, the second heating section temperature is 1100±30℃, the soaking section temperature is 1080±30℃, the rolling temperature is 1000±30℃, the water tank cooling is adopted to control the temperature of entering the finishing rolling to be 880±20℃, the controlled rolling is adopted to refine the grain, the water tank cooling is adopted to control the temperature of the upper cooling bed to be 880±20℃, the controlled cooling is adopted to prevent the grain from growing, the grain size is ≥11 grade, and the performance of the steel bar is improved.

[0033] 4. When the Q355B round steel is rolled, the billet is heated by a heating furnace, the preheating section temperature is ≤900℃, the first heating section temperature is 1060±30℃, the second heating section temperature is 1120±30℃, the soaking section temperature is 1100±30℃, the rolling temperature is 1020±30℃, the water tank cooling is adopted to control the temperature of entering the finishing rolling to be 930±20℃, the controlled rolling is adopted to refine the grain, the water tank cooling is adopted to control the temperature of the upper cooling bed to be 920±20℃, the controlled cooling is adopted to prevent the grain from growing, the grain size is ≥10 grade, and the plasticity performance of the Q355B round steel is improved.

[0034] Three, examples

[0035] 1. The production method of the HRB400E and Q355B billet flexible rolling of the present application adopts the following component proportion. Table 1 is the chemical component content ratio of the products of each example, wherein examples 1-4 are the chemical component content ratio of HRB400E; and example 5 is the chemical component content ratio of Q355B (in terms of weight percentage).

[0036] Table 1: Chemical component content ratio of each example steel (%)

[0037] Examples Grade C Si Mn P S Nb Example 1 HRB400E 0.22 0.28 1.15 0.021 0.020 0.023 Example 2 HRB400E 0.23 0.27 1.14 0.027 0.027 0.024 Example 3 HRB400E 0.23 0.27 1.12 0.027 0.027 0.023 Example 4 HRB400E 0.21 0.30 1.19 0.019 0.015 0.025 Example 5 Q355B 0.21 0.30 1.19 0.019 0.015 0.025

[0038] 2. The production method of the HRB400E and Q355B billet flexible rolling of the present application adopts the following specific heating process, and the corresponding process parameters of each example product are shown in Table 2.

[0039] Table 2: Heating process of each example steel

[0040]

[0041] 3. The specific process parameters of the production method of flexible rolling of HRB400E steel bars with rolling size of 10-25 mm and Q355B round steel billet with rolling size of 50 mm are shown in Table 3, which is the process parameters corresponding to each example of Table 1 and Table 2.

[0042] Table 3: Rolling process of each example steel

[0043]

[0044] 4. The HRB400E steel bars and Q355B round steel produced according to the above process technology have excellent performance, Figures 1-4 The metallographic structure photos of HRB400E corresponding to Examples 1-4, the grain size is ≥ 11 levels by using controlled rolling to refine the grains; Figure 5 The metallographic structure photos of Q355B corresponding to Example 5, the grain size is ≥ 10 levels by using controlled rolling to refine the grains. The yield strength ReL of the HRB400E steel bars is 445-460 MPa, the tensile strength Rm is 605-625 MPa, the elongation A after fracture is 22-24%, and the maximum total elongation Agt of the steel bars is 13.9-15.1%; the yield strength ReL of the Q355B round steel is 366-403 MPa, the tensile strength Rm is 560-607 MPa, the elongation A after fracture is 23-26%, and the impact energy of the three samples of Example 5 is 42.7-75.6 J, and the detailed mechanical properties are shown in Table 4.

[0045] Table 4: Mechanical properties of each example steel

[0046]

[0047] As can be seen from Tables 1-4, by using the present application, the same billet can be used for hot-rolled ribbed steel bars and round steel, and the performance requirements of HRB400E and Q355B can be met by flexible rolling, the production efficiency is improved, the production cost is reduced, and the mixing of billets to cause the performance of finished products to be inconsistent is avoided.

[0048] The application provides a production method of HRB400E and Q355B blank flexible rolling, the application first controls the content of each chemical component, on the basis of HRB400E component, the content of C is controlled to be 0.20% to 0.24%, silicon iron is not added, the content of Si in the steel is reduced to 0.20% to 0.35%, the content of Mn is reduced to 1.05% to 1.25%, the content of Nb is increased to 0.017% to 0.027%, the content of P and S is controlled to be less than or equal to 0.035%, so that the component requirement of Q355B is met, the tensile strength of Q355B is reduced, the elongation after fracture and impact work performance of Q355B is improved, the strength and plasticity of Q355B steel are improved, the same blank is used for hot-rolled ribbed steel bars and round steel, then the HRB400E and Q355B are separately controlled in heating process and rolling process to perform flexible rolling, so that the performance requirement of HRB400E and Q355B is met, the production efficiency is improved, the production cost is reduced, and the mixed blank is avoided to cause the performance of finished products to be inconsistent.

[0049] The above description is merely illustrative of the application and is not intended to limit the scope of the application. The various components of the application can be combined or integrated in other ways without departing from the scope of the application. Any modifications of the application by those skilled in the art, which are not described as preferred or essential to implementation, are also intended to be within the scope of the application.

Claims

1. A production method of HRB400E and Q355B blank flexible rolling, characterized in that, The HRB400E and Q355B billet chemical composition contents are: C: 0.20%-0.24%, Si: 0.20%-0.35%, Mn: 1.05%-1.25%, Nb: 0.017%-0.027%, P≤0.035%, and S≤0.035% using the same billet. The HRB400E and Q355B billet flexible rolling production method comprises the following process steps in sequence: Blast furnace hot metal smelting→hot metal desulfurization pretreatment→converter molten steel smelting→billet continuous casting→heating furnace heating→rough rolling→medium rolling→finishing rolling unit→large cooling bed→fixed-length cold shearing→small cooling bed→bundling, weighing, labeling, and warehousing; When rolling the HRB400E steel bar, the preheating temperature is ≤900℃, the first heating temperature is 1040±30℃, the second heating temperature is 1100±30℃, and the soaking temperature is 1080±30℃; when rolling the Q355B round steel, the preheating temperature is ≤900℃, the first heating temperature is 1060±30℃, the second heating temperature is 1120±30℃, and the soaking temperature is 1100±30℃; when rolling the HRB400E steel bar, the rough rolling temperature is 1000±30℃; the water tank cooling is used to control the temperature of entering the finishing rolling to be 880±20℃; When rolling the Q355B round steel, the rough rolling temperature is 1020±30℃; the water tank cooling is used to control the temperature of entering the finishing rolling to be 930±20℃.

2. The method for producing HRB400E and Q355B blank flexible rolling according to claim 1, characterized in that, When rolling the HRB400E steel bar, the controlled rolling is used to refine the grain, so that the grain size is ≥11 grade, and the water tank cooling is used to control the temperature of entering the large cooling bed to be 880±20℃.

3. The method of production of HRB400E and Q355B billet flexible rolling according to claim 1, characterized in that, When rolling the Q355B round steel, the controlled rolling is used to refine the grain, so that the grain size is ≥10 grade, and the water tank cooling is used to control the temperature of entering the large cooling bed to be 900±20℃.

4. The production method of HRB400E and Q355B blank flexible rolling according to claim 1, characterized in that, The HRB400E steel bar specification is 10-25mm.

5. The method of production of HRB400E and Q355B billet flexible rolling according to claim 1, characterized in that, The Q355B round steel specification is 50mm.

6. The production method of HRB400E and Q355B blank flexible rolling according to claim 1, characterized in that, The converter molten steel smelting: after the hot metal is blown and refined by the oxygen top-blown converter, the slide plate is used to block the slag for tapping, then the deoxidizer and alloy are added, and then the argon station is used to blow argon.

7. The method of production of HRB400E and Q355B billet flexible rolling according to claim 1, characterized in that, The billet continuous casting adopts the full-process protective casting process for pouring, and the billet size is 165mm×165mm×10000mm.

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