A production method of low-carbon niobium-titanium microalloyed Q235B

Abstract

The application discloses a production method of low-carbon Nb-Ti micro-alloyed Q235B, which comprises the following steps: in the first step, 25kg vacuum induction furnace is used to smelt the experimental steel, and the maximum diameter of the ingot is 100mm; in the second step, the ingot is heated by a heating furnace and then is subjected to blooming, the heating temperature is 1150 DEG C, and the blooming thickness is 72mm; in the third step, the ingot is rolled by using a two-high reversible rolling mill, and then is subjected to laminar flow cooling, the rolling temperature is greater than or equal to 1000 DEG C, the final rolling temperature is greater than or equal to 850 DEG C, the final cooling temperature is 520 DEG C to 560 DEG C, and pass reduction is strictly implemented in the rolling process, and the temperature control in the process of ingot heating and rolling is shown as follows: the heating temperature is 1150 DEG C plus or minus 50 DEG C, the rolling temperature is 1050 DEG C plus or minus 50 DEG C, the final rolling temperature is 880 DEG C plus or minus 50 DEG C, and the final cooling temperature is 550 DEG C plus or minus 50 DEG C. The application aims to provide the production method of the low-carbon Nb-Ti micro-alloyed Q235B, and effectively improves the surface micro-crack defects of the finished steel plate.

Description

Technical Field

[0001] This invention relates to the field of metallurgical plate production technology, and in particular to a production method for low-carbon niobium-titanium microalloyed Q235B. Background Technology

[0002] Q235B is one of the most commonly used carbon structural steels in China. Due to its certain elongation, strength, and toughness, ease of stamping and welding, and low price, it is used extensively, primarily in structural components and engineering construction. It is used to build factory frames, small bridges, iron towers, agricultural vehicles, small boilers, and simple containers. It can also be used for mechanical parts with low requirements for mechanical and technological properties. The conventional chemical composition of Q235B generally adopts a medium-carbon, low-manganese design, with a carbon content of 0.14%–0.18% and a manganese content of 0.4%–0.6%. However, the carbon content between 0.14% and 0.18% is in a crack-sensitive zone, and micro-cracks are prone to appear on the surface of the finished steel plate. These defects are extremely difficult to detect with the naked eye, and after a 180° bending test, the defects are magnified, leading to slight cracking of the steel plate. This patented Q235B adopts a low-carbon (0.05%~0.07%) niobium-titanium microalloying composition design concept to avoid carbon content crack sensitive areas. At the same time, the rolling process adopts controlled rolling and controlled cooling process to produce Q235B that meets the standard requirements, effectively improving the surface crack defects of the finished steel plate. Summary of the Invention

[0003] The purpose of this invention is to provide a production method for low-carbon niobium-titanium microalloyed Q235B, which effectively improves the microcrack defects on the surface of the finished steel plate.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for producing low-carbon niobium-titanium microalloyed Q235B, comprising:

[0006] Step 1: The experimental steel was smelted in a 25 kg vacuum induction furnace, and the maximum diameter of the steel ingot was 100 mm.

[0007] Step 2: After the steel ingot is heated in a heating furnace, it is shaped into billets at a heating temperature of 1150℃ and a billet thickness of 72mm.

[0008] Step 3: Rolling is carried out using a laboratory two-roll reversible rolling mill. After rolling, laminar flow cooling is performed. The initial rolling temperature is ≥1000℃, the final rolling temperature is ≥850℃, and the final cooling temperature is 520℃~560℃. During the rolling process, the reduction of each pass is strictly implemented. The temperature control during the heating and rolling of the steel ingot is as follows: heating temperature 1150±50℃, initial rolling temperature 1050±50℃, final rolling temperature 880±50℃, and final cooling temperature 550±50℃.

[0009] Step 4: After rolling, the steel plates are sampled according to standards, and the samples are subjected to impact performance testing, mechanical property testing, and process performance testing.

[0010] Furthermore, the chemical composition of the Q235B is C: ≤0.07%, Si: ≤0.10%, Mn: ≤0.30%, P: ≤0.020%, S: ≤0.005%, Nb: ≤0.020%, Ti: ≤0.020%, with the remainder being Fe and unavoidable inclusions.

[0011] Furthermore, the rolling thickness is 6-20mm.

[0012] Furthermore, the chemical composition of the Q235B is C: 0.05%, Si: 0.06%, Mn: 0.25%, P: 0.017%, S: 0.002%, Nb: 0.015%, Ti: 0.020%, with the remainder being Fe and unavoidable inclusions.

[0013] Furthermore, the chemical composition of the Q235B is C: 0.06%, Si: 0.04%, Mn: 0.27%, P: 0.015%, S: 0.003%, Nb: 0.018%, Ti: 0.015%, with the remainder being Fe and unavoidable inclusions.

[0014] Furthermore, the chemical composition of the Q235B is C: 0.07%, Si: 0.05%, Mn: 0.30%, P: 0.015%, S: 0.001%, Nb: 0.020%, Ti: 0.017%, with the remainder being Fe and unavoidable inclusions.

[0015] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0016] This invention employs a low-carbon niobium-titanium microalloying composition design concept and a controlled rolling and cooling process to produce a Q235B steel. This Q235B not only meets the standard requirements for all mechanical properties but also effectively avoids microcrack defects on the surface of the finished steel plate. Furthermore, the preparation method of this invention is simple and suitable for industrial production and widespread application. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings.

[0018] Figure 1 Metallographic photographs of Examples 1-3 of the present invention;

[0019] Figure 2 This is a photograph of the bending test in Embodiment 2 of the present invention. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to comparative examples and specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way. The chemical composition and related properties of the comparative examples are based on industrial-scale production data.

[0021] The chemical composition of the experimental steel used in the embodiments of this invention is shown in Table 1, and the composition of the comparative example is also shown in Table 1. The preparation method includes:

[0022] Step 1: The experimental steel was smelted in a 25 kg vacuum induction furnace, and the maximum diameter of the steel ingot was 100 mm.

[0023] Step 2: After the steel ingot is heated in a heating furnace, it is shaped into billets at a heating temperature of 1150℃ and a billet thickness of 72mm.

[0024] Step 3: Rolling is performed using a laboratory two-roll reversible rolling mill, followed by laminar flow cooling. The initial rolling temperature is ≥1000℃, the final rolling temperature is ≥850℃, and the final cooling temperature is 520℃~560℃. Strict pass reduction is enforced during the rolling process. Temperature control during ingot heating and rolling is shown in Table 2, and pass reduction is shown in Table 3.

[0025] Step 4: After rolling, the steel plates are sampled according to standards, and the samples are subjected to impact performance testing, mechanical property testing, and technological property testing. See Tables 4 and 5 for details.

[0026] It can be seen that the impact performance of Examples 1-3 meets the requirements of the national standard GB / T700-2006, and the yield strength, tensile strength, and elongation also meet the standard requirements. After the 180° bending test, the surfaces of Examples 1-3 are intact without cracks. Although the mechanical properties of the comparative example also meet the standard requirements, slight cracks appear on the surface. It is evident that Q235B produced by adopting the low-carbon niobium-titanium microalloying composition design concept and using controlled rolling and controlled cooling process not only meets the standard requirements for various mechanical properties, but also effectively avoids micro-crack defects on the surface of the finished steel plate.

[0027] Table 1. Chemical composition (wt%) of the embodiments and comparative examples of the present invention.

[0028] Chemical elements C Si Mn P S Nb Ti Example 1 0.05 0.06 0.25 0.017 0.002 0.015 0.020 Example 2 0.06 0.04 0.27 0.015 0.003 0.018 0.015 Example 3 0.07 0.05 0.30 0.015 0.001 0.020 0.017 Comparative Example 0.17 0.25 0.40 0.025 0.025 / /

[0029] Table 2 Temperature control parameters of embodiments of the present invention

[0030]

[0031] Table 3. Number of passes and pressure in embodiments of the present invention

[0032]

[0033] Table 4 Impact test values ​​of embodiments of the present invention

[0034]

[0035] Table 5 Mechanical and process performance of embodiments and comparative examples of the present invention

[0036]

[0037]

[0038] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing low-carbon niobium-titanium microalloyed Q235B, characterized in that, include: Step 1: The experimental steel was smelted in a 25 kg vacuum induction furnace, and the maximum diameter of the steel ingot was 100 mm. Step 2: After the steel ingot is heated in a heating furnace, it is shaped into billets at a heating temperature of 1150℃ and a billet thickness of 72mm. Step 3: Rolling is carried out using a laboratory two-roll reversible rolling mill, followed by laminar flow cooling; heating temperature 1150℃, initial rolling temperature 1030℃, final rolling temperature 900℃, and final cooling temperature 540℃. The rolling passes and reduction are controlled as follows: Step 4: After rolling, the steel plates are sampled according to standards, and the samples are subjected to impact performance testing, mechanical property testing, and process performance testing. The chemical composition of Q235B is C: 0.05%, Si: 0.06%, Mn: 0.25%, P: 0.017%, S: 0.002%, Nb: 0.015%, Ti: 0.020%, with the remainder being Fe and unavoidable inclusions.

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