Angle-crack-resistant Q235B carbon structural steel hot rolled steel strip and production method thereof

Abstract

The invention discloses a corner-crack-resistant Q235B carbon structural steel hot-rolled steel strip and a production method thereof.According to the production method, on the basis of medium-carbon and low-manganese carbon steel Q235B in the prior art, chemical components of the medium-carbon and low-manganese carbon steel Q235B are optimized, and the corner-crack-resistant Q235B carbon structural steel hot-rolled steel strip is obtained in combination with the optimized casting blank heating process, rolling process and coiling process. According to the method, the casting blank corner crack phenomenon does not occur in the production process, and the product corner crack resistance target is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel materials, and in particular relates to a Q235B carbon structural steel hot-rolled steel strip resistant to corner cracking and a production method thereof. Background Art

[0002] Q235B steel, which is a representative of carbon structural steel with medium carbon and low manganese composition design, is one of the steel products with the largest production volume and the widest market application in steel enterprises. Due to its good cost performance, Q235B steel plate has become the main material in the engineering machinery industry. With the long-term high-load continuous service of 1650mm and 2150mm continuous casting machines in the production plant, the accuracy of its equipment has been continuously reduced. For the production of medium carbon and low manganese carbon steel Q235B (chemical composition and weight percentage: C: 0.17 ~ 0.19, Si ≤ 0.15, Mn: 0.20 ~ 0.30, P ≤ 0.025, S ≤ 0.020, the balance is Fe and incidental inclusions), the corner crack defects are prone to occur in the billet, which increases the workload of artificial flame cleaning of corner defects. On the one hand, it reduces the yield rate; on the other hand, the offline processing of billet defects seriously affects the production of hot charging and increases the heating energy consumption. It has become a difficult problem that steel mills urgently need to solve. At the beginning of 2023, the Q235B products produced by the manufacturer frequently experienced corner cracking problems. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention provides a production method of a Q235B carbon structural steel hot-rolled steel strip with resistance to corner cracking, which optimizes the chemical composition of the medium-carbon and low-manganese carbon steel Q235B in the prior art, and combines the optimized ingot heating process, rolling process and coiling process to obtain the Q235B carbon structural steel hot-rolled steel strip with resistance to corner cracking; wherein:

[0004] The chemical composition of the medium carbon and low manganese carbon steel Q235B is calculated by mass percentage: C: 0.17-0.19, Si≤0.15, Mn: 0.20-0.30, P≤0.025, S≤0.020, and the balance is Fe and accompanying inclusions. The chemical composition of the anti-corner crack Q235B carbon structural steel hot-rolled steel strip after chemical composition optimization is calculated by mass percentage: C: 0.06-0.08, Si: 0.10-0.20, Mn: 0.20-0.30, P:≤0.020, S≤0.015, Ti: 0.030-0.040, and the balance is Fe and accompanying inclusions;

[0005] The casting billet heating process comprises: the casting billet heating temperature is 1245±20°C, and the temperature is kept for 25 to 60 minutes;

[0006] The rolling process includes: the starting rolling temperature is 1225±10°C, the rough rolling process adopts a 3+3 mode, and the final rolling temperature is 885±20°C;

[0007] The coiling process includes: a coiling temperature of 670±20°C.

[0008] In some embodiments, the production method includes the following steps based on a 2250mm hot rolling production line: heating the ingot - high-pressure water descaling - fixed-width press - E1R1 roughing mill rolling - E2R2 roughing mill rolling - flying shear - high-pressure water descaling - F1~F7 finishing mill rolling - encrypted laminar cooling - coiling - pallet transportation system - warehousing - sampling, inspection - weighing, and packaging.

[0009] In some embodiments, the thickness of the ingot is 230 mm.

[0010] In some embodiments, the continuous casting speed for obtaining the cast billet is 1.0 to 1.6 m / min.

[0011] In some embodiments, the thickness of the corner crack resistant Q235B carbon structural steel hot rolled steel strip is 9.8 mm.

[0012] The corner crack resistant Q235B carbon structural steel hot-rolled steel strip obtained by the above production method also belongs to the content of the present invention.

[0013] The beneficial effects of the present invention are as follows: the present invention provides a production method of Q235B hot-rolled steel strip resistant to corner cracking, which can save 80 yuan in manual corner clearing costs per ton of steel on the basis of a 2250mm hot rolling process, and can improve hot charging rate and production efficiency. Through microstructure and performance analysis, the various performances of the product meet the standard requirements, thereby improving the quality and competitiveness of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the metallographic structure diagram of Q235B (normal composition) produced in Example 1, volume number: 244112458.

[0015] Figure 2 This is the metallographic structure diagram of Q235B (anti-corner cracking component) produced in Example 1, volume number: 236117524. DETAILED DESCRIPTION

[0016] In view of the problems existing in the prior art, the present invention adjusts the composition of Q235B products and replaces the current product's "medium carbon + Mn" composition system (C: 0.17-0.19, Si ≤ 0.15, Mn ≤ 0.20, P ≤ 0.020, S ≤ 0.015, Ti: 0.030-0.040, the balance is Fe and incidental inclusions) with the design concept of "low carbon + Ti" (C: 0.06-0.08, Si: 0.10-0.20, Mn: 0.20-0.30, P ≤ 0.020, S ≤ 0.015, Ti: 0.030-0.040, the balance is Fe and incidental inclusions). Mn: 0.20~0.30, P≤0.025, S≤0.020, the balance is Fe and incidental inclusions), the high-temperature liquid precipitation TiN second phase particles of Ti microalloying are used to fix the free N atoms in the molten steel, reduce or avoid the precipitation of AlN second phase particles along the primary ferrite grain boundary when the low-temperature austenite transforms to ferrite, and improve the toughness of the high-temperature third brittle zone of the steel, thereby improving the toughness of the material in the straightening zone of the ingot, and eliminating the corner crack defects of the carbon-manganese steel ingot represented by Q235B structural steel.

[0017] The objective of the present invention is achieved through the following technical solutions:

[0018] A method for producing a corner crack resistant Q235B carbon structural steel hot-rolled steel strip, comprising the following steps:

[0019] (1) Steelmaking process: Based on the chemical composition of the medium-carbon and low-manganese Q235B product in the prior art (C: 0.17-0.19, Si≤0.15, Mn: 0.20-0.30, P≤0.025, S≤0.020, the balance being Fe and incidental inclusions), the C content is reduced by 0.11%, and 0.030-0.040 Ti is added to obtain a continuous casting billet of the corner crack-resistant Q235B carbon structural steel hot-rolled steel strip of the present invention; wherein the steelmaking process comprises the following processes: blast furnace → KR desulfurization → converter → LF refining → slab continuous casting, the continuous casting billet drawing speed is 1.0-1.6 m / min, and the resulting billet thickness is 230 mm.

[0020] (2) Billet heating, rolling and coiling process:

[0021] Specifically, it includes the following steps based on the 2250mm hot rolling production line: heating of ingots - high-pressure water descaling - fixed width press - E1R1 roughing mill rolling - E2R2 roughing mill rolling - flying shear - high-pressure water descaling - F1~F7 finishing mill rolling - encrypted laminar cooling - coiling - pallet transport system - storage - sampling, inspection - weighing and packaging;

[0022] Among them: the heating temperature of the ingot is 1245±20℃, and the insulation time is 25 to 60min; the starting rolling temperature is 1225±10℃, the rough rolling process adopts the 3+3 mode, the final rolling temperature is 885±20℃; the coiling temperature is 670±20℃.

[0023] Finally, a 9.8mm thick, corner-crack-resistant 235MPa grade carbon structural steel hot-rolled steel strip was obtained.

[0024] (3) Analyze the microstructure and properties of the corner crack resistant 235 MPa grade carbon structural steel hot-rolled steel strip prepared in step (2) to determine whether the microstructure, grain size grade and performance thereof meet the requirements.

[0025] The present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the present invention.

[0026] Example 1

[0027] (1) For the Q235B product that has corner cracks (including the following chemical components in weight percentage: C: 0.17-0.19, Si≤0.15, Mn: 0.20-0.30, P≤0.025, S≤0.020, the balance is Fe and accompanying inclusions), the chemical composition of the corner crack-resistant 235MPa grade carbon structural steel hot-rolled steel strip of the present invention (C: 0.06-0.08, Si: 0.10-0.20, Mn: 0.20-0.30, P≤0.020, S≤0.015, Ti: 0.030-0.040, the balance is Fe and accompanying inclusions) is developed and designed, as shown in Table 1 below.

[0028] Table 1: Chemical composition of hot rolled steel strip (by mass percentage)

[0029] Volume Number C Si Mn P S Ti 244112458 0.18 0.13 0.24 0.013 0.008 - 23A108527 0.17 0.12 0.22 0.011 0.002 - 236117524 0.06 0.13 0.24 0.013 0.008 0.033 236115818 0.07 0.12 0.22 0.011 0.002 0.035

[0030] (2) The continuous casting billet drawing speed is 1.0-1.6 m / min, and a slab with a thickness of 230 mm is obtained. The process conditions for billet heating are: billet heating temperature is 1245±20°C, and the insulation time is 25-60 min; the rolling process conditions are: the starting rolling temperature is 1225±10°C, the rough rolling process adopts the 3+3 mode, the final rolling temperature is 885±20°C; and the coiling temperature is 670±20°C. The specific process parameters are shown in Table 2.

[0031] Table 2: Process parameters for each example

[0032]

[0033] (3) The above-mentioned production process can solve the corner crack problem of Q235B ingot. The hot-rolled microstructure is ferrite and pearlite, and the microstructure before and after adjustment is similar. Figure 1 (244112458) and Figure 2From the performance test results feedback, as shown in Table 3, in the tensile test and +20℃ impact test, the standard requirements are met before and after the composition adjustment. However, in the subsequent production, when the anti-corner cracking component of the present invention is used, no corner cracking of the ingot occurs, and the goal of product anti-corner cracking is achieved.

[0034] Table 3: Q235B performance distribution

[0035]

[0036] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for producing a corner crack resistant Q235B carbon structural steel hot-rolled steel strip, which is obtained by optimizing the chemical composition of the medium carbon and low manganese carbon steel Q235B in the prior art, and combining the optimized billet heating process, rolling process and coiling process; wherein: The chemical composition of the medium carbon and low manganese carbon steel Q235B is calculated by mass percentage: C: 0.17-0.19, Si≤0.15, Mn: 0.20-0.30, P≤0.025, S≤0.020, and the balance is Fe and accompanying inclusions. The chemical composition of the anti-corner crack Q235B carbon structural steel hot-rolled steel strip after chemical composition optimization is calculated by mass percentage: C: 0.06-0.08, Si: 0.10-0.20, Mn: 0.20-0.30, P:≤0.020, S≤0.015, Ti: 0.030-0.040, and the balance is Fe and accompanying inclusions; The casting billet heating process comprises: the casting billet heating temperature is 1245±20°C, and the temperature is kept for 25 to 60 minutes; The rolling process includes: the starting rolling temperature is 1225±10°C, the rough rolling process adopts a 3+3 mode, and the final rolling temperature is 885±20°C; The coiling process includes: a coiling temperature of 670±20°C.

2. The production method according to claim 1 includes the following steps based on a 2250mm hot rolling production line: heating the ingot - high-pressure water descaling - fixed-width press - E1R1 roughing mill rolling - E2R2 roughing mill rolling - flying shear - high-pressure water descaling - F1~F7 finishing mill rolling - encrypted laminar cooling - coiling - pallet transportation system - warehousing - sampling, inspection - weighing and packaging.

3. The production method according to claim 2, wherein the thickness of the cast slab is 230 mm.

4. The production method according to claim 2 or 3, wherein the continuous casting speed for obtaining the cast billet is 1.0 to 1.6 m / min.

5. The production method according to any one of claims 1 to 4, wherein the thickness of the corner crack resistant Q235B carbon structural steel hot-rolled steel strip is 9.8 mm.

6. A Q235B carbon structural steel hot-rolled strip resistant to corner cracking, produced by the method according to any one of claims 1 to 5.

Images