A production method for solving the large strength fluctuation range of a hot continuous rolling plate coil of high-titanium steel with a thickness of less than or equal to 8 mm

Abstract

The application discloses a production method for solving the large strength fluctuation range of a high Ti steel hot continuous rolling plate coil with a thickness of less than or equal to 8 mm, and the method comprises the following steps: 1) smelting; 2) casting blank heating; 3) rough rolling; 4) finish rolling; 5) post-rolling cooling; and 6) coiling. The low-alloy high-strength steel product with a thickness of 4-8 mm, a Ti content of 0.093% and no Nb, V and other micro-alloying elements is successfully prepared. The detection result shows that the strength fluctuation of the yield strength and the tensile strength of the whole coil steel is within 15-25 MPa, the elongation is greater than or equal to 18%, the Kv2 at-20 DEG C is greater than 100 J, the performance stability is good, the problem of the large strength fluctuation of the high Ti steel is solved, and the impact toughness is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel metallurgy, and in particular to a production method for solving the large strength fluctuation range of a high-Ti steel hot continuous rolling coil with a thickness of less than or equal to 8 mm. BACKGROUND

[0002] With the continuous increase in the prices of resource commodities, the cost pressure on the production and operation of enterprises is increasing, and therefore, in order to reduce production costs, when developing steel products, each steel enterprise tries to reduce or remove the addition of alloy elements in product design as much as possible on the basis of ensuring mechanical properties and user performance, especially in the development of high-strength steel products, cheap Ti is used to replace expensive Nb, V, Mo, and Cr for alloying, and in recent years, the design of single high-Ti high-strength steel has been paid more and more attention. However, due to the Ti yield control level during smelting, the combination of Ti and impurities resulting in the fluctuation of effective Ti, the narrow Ti precipitation strengthening process window, and the high requirement for rolling process control, the performance of high-Ti high-strength hot continuous rolling coils fluctuates greatly along the length of the coil, the strength distribution is uneven, the strength fluctuation range of the head, middle, and tail of the coil is 100-200 MPa, the fluctuation range is too large, and the impact toughness is poor, which results in the application quality risks such as cutting and bending, warping, difficulty in cold bending forming, and easy cracking during use, and cannot meet the user's requirements. Therefore, the performance stability of Ti-containing steel hot continuous rolling coils is an important difficulty in the development process of this series of steel, and the solution to this problem can greatly promote the development and application of this series of steel. SUMMARY

[0003] The present application aims to overcome the deficiencies of the background art, and provides a production method for solving the large strength fluctuation range of a high-Ti steel hot continuous rolling coil with a thickness of less than or equal to 8 mm, which controls the strength fluctuation range of a single high-Ti high-strength steel hot continuous rolling coil with a thickness of less than or equal to 8 mm within 25 MPa, and solves the problem that the strength fluctuation range of a single high-Ti high-strength steel hot continuous rolling coil reaches 100-200 MPa.

[0004] To achieve the above-mentioned purpose, the present application designs a production method for solving the large strength fluctuation range of a high-Ti steel hot continuous rolling coil with a thickness of less than or equal to 8 mm, which includes the following steps:

[0005] 1) Smelting: control the S, N, and O contents in the steel to meet S≤0.005%, N≤55ppm, and O≤30ppm, and continuously cast into a billet;

[0006] 2) Billet heating: heat the billet, and control the billet heating temperature at 1160-1240℃ to obtain a slab;

[0007] 3) rough rolling: the slab is discharged from the heating furnace and enters the rough rolling mill group to be rolled, the intermediate slab thickness is controlled according to the thickness of the finished product, and then the intermediate slab is sent to the finishing rolling;

[0008] 4) finishing rolling: the finishing rolling slab enters the hot continuous rolling mill group to be rolled, the rough rolling temperature is controlled to be not more than 1140℃, the finish rolling temperature is 840-920℃, and the pass distribution is automatically distributed according to the computer model;

[0009] 5) post-rolling cooling: after being discharged from the finishing rolling mill group, the slab directly enters the rapid cooling mode, the cooling speed is controlled to be 46-88℃ / S, and the cooling time is 2-6S; then the slab enters the low-speed cooling mode, the cooling speed is controlled to be 8-30℃ / S, and the cooling time is 2-8S;

[0010] 6) coiling: the coiling temperature is 500-600℃.

[0011] Further, in the step 1), the thickness of the cast slab is 210-250mm.

[0012] Further, in the step 2), the heating temperature of the cast slab is controlled to be 1160-1200℃.

[0013] Further, in the step 3), the thickness of the intermediate slab is controlled to be 30-50mm.

[0014] Further, in the step 4), the rough rolling temperature is not more than 1120℃, and the finish rolling temperature is 880-910℃.

[0015] Further, in the step 5), the cooling speed in the rapid cooling mode is controlled to be 50-88℃ / S, and the cooling time in the ultra-fast cooling section is 2-6S.

[0016] Further, in the step 5), the cooling speed in the low-speed cooling mode is controlled to be 12-20℃ / S, and the cooling time in the low-speed cooling section is 3-8S.

[0017] Further, in the step 6), the coiling temperature is 520-560℃.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] Firstly, the present application successfully prepares a low-alloy high-strength steel product with a thickness of ≥4-8mm, a Ti content of 0.093% and no Nb, V and other micro-alloying elements, the detection results show that the strength fluctuation of the yield strength and tensile strength of the whole steel is within 15-25MPa, the elongation is ≥18%, the Kv2 at-20℃ is greater than 100J, the performance stability is very good, the problem of large strength fluctuation of high-Ti steel is solved, and the impact toughness is greatly improved.

[0020] Secondly, the strength fluctuation range of the existing single high Ti high strength hot continuous rolling plate coil reaches 100-200MPa, mainly because the length of the steel coil with thickness of 4-8mm reaches 250-600m, the existing production method causes TiC to precipitate unevenly along the full length of the steel coil after the steel coil is coiled, and the existing single high Ti steel is designed mainly based on the precipitation strengthening of TiC, the precipitation window of TiC is relatively narrow, and the existing coiling temperature is generally controlled at about 620℃, thereby causing the strength of the full length of the steel coil to fluctuate greatly. Although the present application is also designed based on single high Ti, the design principle is different from the existing design idea, and the precipitation strengthening and microstructure strengthening of TiC are matched, thereby achieving the control of the uniformity of the full length strength of the steel coil, the design principle is realized through the innovative production method, the two-stage cooling is innovatively adopted, the cooling speed is controlled in sections, the cooling interval process time is controlled, the coiling temperature is controlled at 500-580℃, the process window is wide, which is beneficial to the microstructure transformation and uniform precipitation of TiC, and thereby the full length strength of the steel coil is controlled within 25MPa.

[0021] Thirdly, the production method of the present application has simple process steps, can be continuously batch-produced and manufactured with stable quality, and further enriches the product types. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is the metallographic structure diagram of the steel product of Example 1 of the present application.

[0023] Figure 2 It is the metallographic structure diagram of the steel product of Comparative Example 1. DETAILED DESCRIPTION

[0024] The implementation of the present application will be described in detail below in combination with the implementation examples, but they do not constitute the limitation of the present application, but only serve as examples. At the same time, the advantages of the present application will become clearer and easier to understand through the description.

[0025] The application is a production method for solving the large strength fluctuation range of high Ti steel hot continuous rolling plate coil with thickness ≤8mm, the chemical composition of the steel is as follows in percentage (%): C: 0.01-0.12%, Si ≤0.5%, Mn: 0.2-2.50%, Ti: 0.055-0.15%, the balance is balanced iron and inevitable impurities, and no other precious alloy elements are needed to be added in the steel.(1) Smelting: strictly control the content of S, N and O in the steel, meet S ≤0.005%, N: ≤55ppm, O ≤30ppm, and the continuous casting is formed into a billet with thickness: 210-250mm.(2) Heating the billet and controlling the heating temperature at 1160-1240℃;(4) Rough rolling: the billet is out of the heating furnace and enters the rough rolling mill organization, according to the thickness of the finished product, the thickness of the intermediate billet is controlled at 30-50mm, and then is sent to the finishing rolling;(4) Finishing rolling: the finishing rolling billet enters the 7-stand hot continuous rolling mill group for rolling, the opening rolling temperature is controlled to be not more than 1140℃, the final rolling temperature is at 840-920℃, and the pass distribution is automatically distributed according to the computer model;(5) Cooling after rolling: after out of the finishing rolling mill group, directly enter the rapid cooling mode, the cooling speed is controlled at 46-88℃ / S, and the cooling time is 2-6S; then enter the low speed cooling mode, the cooling speed is controlled at 8-30℃ / S, and the cooling time is 2-8S;(6) Coiling: the coiling temperature is 500-600℃.

[0026] The chemical composition of the steel of the application examples 1-3 and the comparative examples 1-3 is shown in table 1, the production process parameters are shown in table 2, and the properties of the high Ti hot continuous rolling steel produced according to different processes are shown in table 3. Referring to the composition of the steel in table 1, the 250-ton rolling furnace is smelted, the continuous casting is formed into a billet, then the billet is heated, and the steel coil with thickness specifications of 4, 6 and 8mm is rolled, and then the rough rolling, finishing rolling, cooling and coiling are carried out according to different processes, and finally the product of the examples and the comparative examples is obtained.

[0027] Table 1 Chemical composition of the steel (wt%)

[0028] Ingredients C Si Mn P S Ti N O Content 0.06 0.13 1.03 0.016 0.003 0.093 48 ppm 26 ppm 26 ppm

[0029] Table 2 Process parameters for production of the application examples and the comparative examples

[0030]

[0031] Table 3 Performance comparison table of high Ti hot continuous rolling steel products with different specifications

[0032]

[0033] Note: Tensile, bending is transverse sampling, impact is longitudinal sampling (specifications <6mm steel plate does not do impact test; specifications 6mm steel plate impact sample size: 5×10×55mm, specifications 8mm steel plate impact sample size: 7.5×10×55mm).

[0034] As can be seen from Table 3, although the hot-rolled steel products prepared in Examples 1-3 have the yield strength fluctuation range of the head, middle and tail of the steel coil within 20 MPa, the tensile strength fluctuation range within 25 MPa, the yield strength fluctuation range of the head, middle and tail of the steel coil in Comparative Examples 1-3 within 90-202 MPa, the tensile strength fluctuation range within 94-181 MPa, the stability of the strength of the examples is obviously superior to that of the comparative examples; the elongation and -20°C Kv2 of the examples are also obviously superior to those of the comparative examples.

[0035] The above is only a specific embodiment of the present application, it should be noted that any skilled person in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application, and the rest not described in detail is the prior art.

Claims

1. A production method for solving the problem of large strength fluctuations in hot-rolled high-Ti steel coils with a thickness ≤8mm, characterized in that: Includes the following steps: 1) Smelting: The chemical composition of the steel by mass percentage is: C: 0.01~0.12%, Si ≤0.5%, Mn: 0.2~2.50%, Ti: 0.055~0.15%, with the balance being balance iron and unavoidable impurities. No other precious alloying elements need to be added to the steel. The mass percentage content of S, N, and O in the steel is controlled to meet the following requirements: S≤0.005%, N:≤55ppm, O≤30ppm. The steel is continuously cast into billets; the thickness of the billets is 210~250mm. 2) Billet heating: The billet is heated, and the heating temperature is controlled at 1160-1240℃ to obtain a slab; 3) Rough rolling: After the slab exits the heating furnace, it enters the rough rolling mill for rolling. Depending on the thickness of the finished product, the thickness of the intermediate slab is controlled to be 30~50mm during rough rolling, and then it is sent to the finish rolling mill. 4) Finishing: The finishing billet enters the hot continuous rolling mill for rolling. The initial rolling temperature is controlled to be no more than 1140℃, and the final rolling temperature is 840~920℃. The number of passes is automatically allocated according to the computer model. 5) Post-rolling cooling: After exiting the finishing mill, it directly enters the rapid cooling mode, controlling the cooling rate at 46~50℃ / S and the cooling time at 2~6S; then it enters the low-speed cooling mode, controlling the cooling rate at 8~12℃ / S and the cooling time at 2~8S. 6) Winding: Winding temperature 500~520℃.

2. The production method according to claim 1, characterized in that: In step 2), the heating temperature of the billet is controlled at 1160~1200℃.

3. The production method according to claim 1, characterized in that: In step 4), the initial rolling temperature of the finishing mill does not exceed 1120℃, and the final rolling temperature is 880~910℃.

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