Ultralow-temperature high-impact-toughness girder steel 700L and production method thereof

Abstract

The invention discloses ultralow-temperature high-impact-toughness girder steel 700L and a production method thereof. The ultralow-temperature high-impact-toughness girder steel 700L comprises the following chemical components in percentage by mass: 0.04 to 0.07 percent of C, 0.05 to 0.25 percent of Si, 1.4 to 1.8 percent of Mn, less than or equal to 0.01 percent of P, less than or equal to 0.003 percent of S, 0.06 to 0.08 percent of Nb, 0.01 to 0.03 percent of V, 0.05 to 0.09 percent of Ti, 0.10 to 0.25 percent of Ni, 0.015 to 0.045 percent of Als, less than or equal to 0.004 percent of N and the balance of Fe and impurities within an allowable range. The production method comprises the working procedures of converter smelting, LF + RH refining, continuous casting, slab heating, rough rolling, finish rolling and coiling. The 700L girder steel provided by the invention has good ultralow-temperature impact toughness, and the full-size impact energy at-40 DEG C is 120 J or above.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy, and particularly relates to a super-low-temperature high-impact-toughness girder steel 700L and a production method thereof. BACKGROUND

[0002] The girder steel 700L is mainly used in the field of commercial vehicles. With the implementation of a series of energy-saving and emission-reducing measures of the country, the girder steel 700L produced in China is widely used in the field of commercial vehicles. However, with the gradual increase of the export quantity to the high-cold region, higher requirements are put forward for the impact toughness of the girder steel in the super-low-temperature environment. The impact performance of the currently produced girder steel 700L is generally that the impact energy at-20 DEG C is greater than or equal to 47J. When such girder steel enters the high-cold region, the general environmental temperature reaches-40 DEG C or even lower. The temperature is lower than the ductile-brittle transition temperature of the girder steel, the impact toughness of the steel rapidly decreases, the fracture risk sharply increases when subjected to a certain impact load, and the safe use of the product cannot be guaranteed. SUMMARY

[0003] The purpose of the application is to provide a super-low-temperature high-impact-toughness girder steel 700L, which has good super-low-temperature impact performance.

[0004] To achieve the above-mentioned purpose, the technical scheme provided by the application is as follows.

[0005] A super-low-temperature high-impact-toughness girder steel 700L, the chemical components and the mass percentage contents thereof are as follows: C: 0.04-0.07%, Si: 0.05-0.25%, Mn: 1.4-1.8%, P≤0.01%, S≤0.003%, Nb: 0.06-0.08%, V: 0.01-0.03%, Ti: 0.05-0.09%, Ni: 0.10-0.25%, Als: 0.015-0.045%, N≤0.004%, and the balance is Fe and impurities within the allowable range.

[0006] The girder steel 700L has a metallographic structure of ferrite and a small amount of pearlite, and the grain size is 12-13 levels; the full-size impact energy at-40 DEG C is greater than or equal to 120J.

[0007] The application also provides a production method of the super-low-temperature high-impact-toughness girder steel 700L, which comprises the steps of converter smelting, LF+RH refining, continuous casting, slab heating, rolling and laminar cooling.

[0008] The converter smelting process adopts 250t converter blowing, and the converter end-point temperature is 1600-1660 DEG C.

[0009] The LF+RH refining process controls the LF outlet temperature at 1610-1650 DEG C, and the RH outlet temperature is 1560-1580 DEG C.

[0010] The continuous casting process adopts dynamic soft reduction, increases the solidification end reduction amount, and improves the center quality of the casting blank.

[0011] The slab heating process controls the discharge temperature at 1230-1260 DEG C, and the slab holding time is greater than or equal to 40 min.

[0012] The rolling process adopts 3+3 passes in the first stage of rough rolling, and adopts F1-F7 finishing rolling mill groups in the second stage of finishing rolling, the finishing rolling inlet temperature is controlled at 940-1020 DEG C, and the finish rolling temperature is controlled at 840-890 DEG C.

[0013] The laminar cooling process adopts a front concentrated mode, the cooling water temperature is controlled at 22-30 DEG C, the cooling speed is controlled at 35-65 DEG C / s, and the cooling is performed to 550-600 DEG C for coiling.

[0014] The invention principle of the technical scheme is as follows:

[0015] The present application realizes the improvement of the low-temperature impact performance of the large beam steel 700L by the new component design, the low-C component system, the addition of multiple alloy strengthening, the LF+RH double refining, the strict control of P, S and H elements, and the optimization of the rolling process according to the component design and the impact performance requirements.

[0016] The technical scheme has the following beneficial technical effects:

[0017] (1) The present application is produced by the double refining LF-RH process, effectively controls the harmful elements P, S and gases N, H, and ensures the cleanliness of the molten steel.

[0018] (2) The present application controls the higher discharge temperature to ensure the alloy melting, realizes the grain refinement by the controlled rolling and controlled cooling, and improves the strength and toughness of the product.

[0019] (3) The large beam steel 700L provided by the present application has good ultra-low temperature impact toughness, and the full-size impact energy is greater than or equal to 120 J at-40 DEG C.

[0020] (4) The large beam steel 700L provided by the present application has a metallographic structure of ferrite and a small amount of pearlite, and the grain size is 12-13 levels. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a typical metallographic photo of the steel of Example 1;

[0022] Figure 2 It is a typical metallographic photo of the steel of Example 2;

[0023] Figure 3 Typical metallographic photo of the steel of Example 3;

[0024] Figure 4 Typical metallographic photo of the steel of Example 4;

[0025] Figure 5 Typical metallographic photo of the steel of Example 5;

[0026] Figure 6 Typical metallographic photo of the steel of Example 6; DETAILED DESCRIPTION

[0027] The application will be further described in detail below in combination with the drawings and specific examples.

[0028] The application provides a super-low-temperature high-impact-toughness girder steel 700L, which has the following chemical components and mass percentages: C: 0.04-0.07%, Si: 0.05-0.25%, Mn: 1.4-1.8%, P≤0.01%, S≤0.003%, Nb: 0.06-0.08%, V: 0.01-0.03%, Ti: 0.05-0.09%, Ni: 0.10-0.25%, Als: 0.015-0.045%, N≤0.004%, and the balance of Fe and impurities within a permissible range.

[0029] The application also provides a production method of the super-low-temperature high-impact-toughness girder steel 700L, which comprises the following steps: converter smelting, LF+RH refining, continuous casting, slab heating, rolling and laminar cooling.

[0030] The converter smelting step adopts 250t converter blowing, and the converter end-point temperature is 1600-1660℃.

[0031] The LF+RH refining step controls the LF off-site temperature at 1610-1650℃, and the RH off-site temperature is 1560-1580℃.

[0032] The continuous casting step adopts dynamic soft reduction, and increases the solidification end reduction amount to improve the center quality of the casting blank; constant speed casting is adopted, and the casting speed is controlled at 1.0-1.4m / min, and the hydrogen content is ≤2ppm.

[0033] The slab heating step controls the discharge temperature at 1230-1260℃, and the slab holding time is ≥40min.

[0034] The rolling step comprises the following two stages: the first stage is rough rolling, and 3+3 passes are adopted; the second stage is finish rolling, and 7 passes are adopted by using F1-F7 finish rolling mill groups, the finish rolling inlet temperature is controlled at 940-1020℃, and the finish rolling temperature is controlled at 840-890℃.

[0035] Laminar flow cooling process: adopts a front-end centralized mode, with cooling water temperature controlled at 22-30℃, cooling rate controlled at 35-65℃ / s, and winding at 550-600℃.

[0036] Examples 1-6:

[0037] The steel plate composition of each embodiment is shown in Table 1.

[0038] The smelting, refining and continuous casting process parameters for each embodiment are shown in Table 2.

[0039] The parameters for the heating, rolling, and laminar flow cooling processes in each embodiment are shown in Table 3.

[0040] The properties of the high impact toughness beam steel 700L in each embodiment are shown in Table 4.

[0041] Table 1. Steel plate composition (wt%) for each embodiment

[0042]

[0043]

[0044] The balance in Table 1 represents Fe and impurities within the allowable range.

[0045] Table 2. Parameters of smelting, refining, and continuous casting processes in each embodiment.

[0046]

[0047] Table 3. Parameters of heating, rolling, and laminar flow cooling processes in each embodiment.

[0048]

[0049] Table 4. Performance of High Impact Toughness Beam Steel 700L in Each Example at -40℃

[0050] Examples Thickness / mm Impact work 1 / J Impact work 2 / J Impact work 3 / J Average impact work / J Full-scale impact work / J 1 6.0 87 72 71 76.5 153 2 7.8 85 72 89 82 164 3 9.0 143 166 147 152 203 4 10.0 145 130 118 131 175 5 12.0 177 194 196 189 189 6 16.0 116 121 129 122 122

[0051] As can be seen from Table 4, the 700L beam steel provided by this invention has good ultra-low temperature impact toughness, with a full-size impact energy ≥120J at -40℃.

[0052] Metallographic images of the 700L ultra-low temperature high impact toughness main beam steel provided in each embodiment are shown below. Figures 1-6 .from Figures 1-6 It can be seen that the metallographic structure consists of ferrite and a small amount of pearlite, with a grain size of 12 to 13.

Claims

1. A 700L ultra-low temperature high impact toughness main beam steel, characterized in that, Its chemical composition and mass percentage are as follows: C: 0.04-0.07%, Si: 0.05-0.25%, Mn: 1.4-1.8%, P≤0.01%, S≤0.003%, Nb: 0.06-0.08%, V: 0.01-0.03%, Ti: 0.05-0.09%, Ni: 0.10-0.25%, Als: 0.015-0.045%, N≤0.004%, with the balance being Fe and impurities within the allowable range.

2. The 700L ultra-low temperature high impact toughness beam steel according to claim 1, characterized in that, The metallographic structure of the 700L main beam steel is ferrite and a small amount of pearlite, with a grain size of 12-13.

3. The 700L ultra-low temperature high impact toughness beam steel according to claim 1, characterized in that, The main beam steel 700L has a full-size impact energy ≥120J at -40℃.

4. The production method of 700L ultra-low temperature high impact toughness beam steel as described in claim 1, characterized in that, It includes converter smelting, LF+RH refining, continuous casting, slab heating, rolling, and laminar flow cooling processes.

5. The production method of 700L ultra-low temperature high impact toughness beam steel according to claim 5, characterized in that, The converter smelting process uses a 250t converter for blowing, with the final converter temperature being 1600-1660℃.

6. The production method of 700L ultra-low temperature high impact toughness main beam steel according to claim 5, characterized in that, In the LF+RH refining process, the LF outlet temperature is controlled at 1610~1650℃; the RH outlet temperature is controlled at 1560~1580℃.

7. The production method of 700L ultra-low temperature high impact toughness main beam steel according to claim 5, characterized in that, In the continuous casting process, the billet pulling speed is controlled at 1.0 to 1.4 m / min, and the hydrogen content is ≤2 ppm.

8. The production method of 700L ultra-low temperature high impact toughness beam steel according to claim 5, characterized in that, In the slab heating process, the furnace exit temperature is controlled at 1230-1260℃, and the slab holding time is ≥40min.

9. The production method of ultra-low temperature high-toughness beam steel 700L according to claim 5, characterized in that, The rolling process consists of two stages: the first stage is rough rolling, which uses 3+3 passes; the second stage is finish rolling, which uses 7 passes on F1-F7 finish rolling mills, with the finish rolling inlet temperature controlled at 940-1020℃ and the final rolling temperature controlled at 840-890℃.

10. The production method of ultra-low temperature high-toughness beam steel 700L according to claim 5, characterized in that, The laminar flow cooling process adopts a front-end centralized mode, with the cooling water temperature controlled at 22-30℃, the cooling rate controlled at 35-65℃ / s, and the coiling performed after cooling to 550-600℃.

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