Production and preparation method for producing Q420C hot-rolled round steel with diameter of more than 180mm from 280mm*380mm rectangular blank section

Abstract

The invention discloses a production and preparation method for producing Q420C hot-rolled round steel with the diameter of 180 mm or above through a 280 mm * 380 mm rectangular blank section. The production and preparation method comprises a steelmaking technological process and a steel rolling technological process. The steel comprises the following chemical components in percentage by mass: 0.17%-0.22% of C, 0.40%-0.50% of Si, 1.30%-1.40% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.08%-0.10% of V, 0.04%-0.06% of Nb, 0.02%-0.04% of Ti, more than or equal to 0.015% of Al, 0.011%-0.015% of N and the balance of iron and impurities. The performance of the round steel in the hot rolling state meets the requirements that the yield strength is larger than or equal to 420 MPa, the tensile strength is larger than or equal to 520 MPa, the ductility is larger than or equal to 21%, and the Charpy V-type impact toughness at 0 DEG C is larger than or equal to 34 J.

Description

Technical Field

[0001] The invention belongs to the technical field of material metallurgy, and in particular relates to a production method for producing Q420C hot-rolled round steel with a diameter of more than 180 mm from a 280 mm×380 mm rectangular billet cross section. Background Art

[0002] Low alloy high strength Q420C steel is widely used in the fields of engineering machinery steel and plant structure production. The national standard requires that the impact energy of Q420C steel is greater than 34J at 0℃, requiring high strength and good toughness. The room temperature and low temperature structure of Q420C steel is generally ferrite + pearlite. A certain amount of microalloys such as Nb, V, Ti, etc. are often added to the C-Mn composition to ensure the matching of strength and toughness; or through a large cooling rate after rolling and a very low final cooling temperature, the ferrite grains are fully refined to improve the strength and toughness of the steel plate; or through heat treatment to improve the mechanical properties of the steel and improve toughness and plasticity.

[0003] The compression ratio of hot-rolled round steel directly affects the grain size and hot-rolled mechanical properties of the round steel. The compression ratio of a round steel with a 280mm×380mm cross-section and a rolling diameter of 180mm is 4.2. The grain size after rolling is relatively coarse, and the strength and toughness of the hot-rolled round steel will not meet the standard requirements.

[0004] If the mechanical properties of large-size hot-rolled round steel are to meet the standard requirements, the C content needs to be reduced and a large amount of alloying elements need to be added to the steel to refine the grains. In this way, when the molten steel undergoes peritectic reaction and solidifies during the casting process, the rapid cooling in the crystallizer forms a primary solidified billet shell. In this process, high-temperature ferrite transforms to austenite. The high-temperature ferrite itself has a volume shrinkage of 3.5% to 4.0%. More importantly, the density of high-temperature ferrite is 0.5% to 1.0% smaller than that of austenite. The process of transformation from ferrite to austenite at high temperature is manifested as linear shrinkage, and at 25 to 100°C below the solidus temperature, the average linear shrinkage suddenly increases, and the primary billet shell in the crystallizer separates from the copper plate of the crystallizer to form an air gap, which slows down the heat transfer, makes the billet shell thinner, and makes the surface of the casting sensitive to cracks and depression defects.

[0005] Patent No. 202011502583.X discloses "A low alloy high strength steel Q420C steel plate and its production method", with the chemical composition by mass percentage, in wt%: C: 0.16-0.20, Si: 0.15-0.30, Mn: 0.70-0.90, P: <0.020, S: <0.012, Ti: 0.055-0.065, Als: 0.010-0.03, and the rest are Fe and residual elements. The preparation method for Q420C steel plate is not suitable for the production of Q420C hot-rolled round steel due to different compression ratios and post-rolling cooling methods.

[0006] Patent No. 202310036479.3 discloses "A production method for solving Q420C cracks", which only improves the cracks of Q420C hot-rolled round steel from the aspect of steel rolling heating, but does not clarify parameters such as the mechanical properties and steelmaking process of Q420C.

[0007] Patent No. 201410271652.9 discloses the "Production Method of Low-alloy High-strength Q420C Medium-thick Steel Plate". The chemical composition by weight percentage includes: C 0.16-0.18%, Si 0.35-0.45%, Mn 1.45-1.55%, P≤0.02%, S≤0.015%, Als 0.015-0.03%, and the rest is iron and impurities. The mechanical properties of Q420C are achieved through subsequent controlled rolling and controlled cooling of the steel plate, and its production process is not applicable to Q420C hot-rolled round steel. Summary of the invention

[0008] The purpose of the present invention is to provide a production method for producing Q420C hot-rolled round steel with a diameter of more than 180 mm from a 280 mm × 380 mm rectangular billet cross section. The method can effectively reduce the cracks in the rectangular billet through reasonable chemical composition design and production process control so that the performance of the round steel in the hot-rolled state meets the following requirements: yield strength ≥420 MPa, tensile strength ≥520 MPa, elongation ≥21%, and 0°C Charpy V-type impact toughness ≥34 J.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0010] The present invention discloses a production method for producing Q420C hot-rolled round steel with a diameter of 180 mm or more from a rectangular billet section of 280 mm×380 mm. The steelmaking process includes: molten iron—molten iron pretreatment—converter—refining outside the furnace—rectangular billet continuous casting; the steel rolling process includes: billet heating—high-pressure water dephosphorization—Ф850 billet opening machine—Ф700 mm×3+Ф550 mm×4 continuous rolling mill group rolling—sawing (sampling)—inspection—grinding—bundling—warehousing—delivery; the steelmaking process parameters are controlled as follows:

[0011] 1) Converter tapping C ≥ 0.10%, tapping temperature ≥ 1600℃;

[0012] 2) Refining time ≥40min, white slag basicity ≥3.0;

[0013] 3) The water volume of the crystallizer is controlled at 3100L / min, the secondary cooling water is low-cooling, and the protective slag is the special protective slag for peritectic steel;

[0014] 4) The temperature of the billet entering the straightening machine is ≥980℃;

[0015] 5) Continuous casting superheat ≤ 30°C, casting machine speed between 0.63-0.66m / min;

[0016] The steel rolling process parameters are controlled as follows:

[0017] 1) Heating temperature is between 1200-1250℃ and heating time is 3-4h;

[0018] 2) Rolling temperature ≤ 1050℃;

[0019] 3) Final rolling temperature ≤850℃;

[0020] The chemical composition mass percentage of the hot-rolled round steel is: C: 0.17%-0.22%, Si: 0.40%-0.50%, Mn: 1.30%-1.40%, P≤0.015%, S≤0.010%, V: 0.08%-0.10%, Nb: 0.04%-0.06%, Ti: 0.02%-0.04%, Al: ≥0.015%, N: 0.011%-0.015%, and the rest is Fe and other trace impurity elements.

[0021] Furthermore, the chemical composition mass percentage of the hot-rolled round steel is: C: 0.19%, Si: 0.47%, Mn: 1.33%, P: 0.012%, S: 0.007%, V: 0.09%, Nb: 0.04%, Ti: 0.03%, Al: 0.022%, N: 0.0145%, and the rest is Fe and other trace impurity elements.

[0022] Furthermore, the chemical composition mass percentage of the hot-rolled round steel is: C: 0.18%, Si: 0.46%, Mn: 1.35%, P: 0.014%, S: 0.007%, V: 0.09%, Nb: 0.04%, Ti: 0.03%, Al: 0.022%, N: 0.0125%, and the rest is Fe and other trace impurity elements.

[0023] Furthermore, the chemical composition mass percentage of the hot-rolled round steel is: C: 0.20%, Si: 0.46%, Mn: 1.38%, P: 0.012%, S: 0.009%, V: 0.10%, Nb: 0.05%, Ti: 0.04%, Al: 0.021%, N: 0.0138%, and the rest is Fe and other trace impurity elements.

[0024] Furthermore, the casting speed of the casting machine is controlled at 0.65m / min.

[0025] Furthermore, the steel rolling process parameters are: heating temperature 1243°C, heating time 3.5h, starting rolling temperature 1035°C, and final rolling temperature 832°C.

[0026] Furthermore, the rolling process parameters are as follows: heating temperature 1244°C, heating time 3.5h, start rolling temperature 1041°C, and final rolling temperature 830°C.

[0027] Furthermore, the steel rolling process parameters are: heating temperature 1243°C, heating time 3.5h, starting rolling temperature 1033°C, and final rolling temperature 834°C.

[0028] The functions of some elements in the steel of the present invention are as follows:

[0029] C: It is the main element that determines the strength of steel and the main substance that forms pearlite. The form and amount of carbides in steel determine the hardness and strength of steel. That is, as the C content increases, the strength and hardness of steel increase, while the plasticity and toughness of steel decrease. Therefore, the C content should not be too high, and carbon is the most effective element for improving strength, so the C content should not be too low. Therefore, the C content is controlled within the range of 0.17-0.22%.

[0030] Si: It can improve the corrosion resistance of steel and is often added to stainless steel, low alloy steel, and corrosion-resistant alloys to improve the corrosion resistance of these alloys, so that they have the properties of resistance to chloride stress corrosion cracking, pitting corrosion, hot concentrated nitric acid corrosion, oxidation resistance, and seawater corrosion resistance. Studies have shown that in a hot and humid atmospheric environment, Si can significantly improve the atmospheric corrosion resistance of carbon steel and low alloy steel. In addition, Si can also improve the corrosion resistance of low alloy steel in the splash zone of seawater. The Si element content of the steel of the present invention is designed to be 0.40-0.50%.

[0031] Mn: It is an important strengthening element with low composition. With the increase of manganese content, the strength of steel is significantly improved, the processing performance of steel is improved, and the ductile-brittle transition temperature hardly changes. However, if the manganese content is too high, it will inhibit the transformation of ferrite, affect the yield strength of steel, and be unfavorable for the control of yield strength ratio. The Mn element content of the steel of the present invention is designed to be 1.30-1.40%.

[0032] P and S are impurity elements in steel. P has a certain effect of improving corrosion resistance, but P is an element that is easy to segregate. It will cause serious segregation in parts of the steel, reduce plasticity and toughness, and is extremely harmful to low-temperature toughness. The S element is easy to segregate and enrich in steel, and is an element that is harmful to corrosion resistance. The steel of the present invention strictly controls the sulfur and phosphorus content levels in terms of metallurgical quality, that is, P: ≤0.015%, S: ≤0.010% to meet the requirements of steel grade for purity, impact toughness, welding performance and corrosion resistance.

[0033] V: V has strong bonding ability with C, O and N, and forms extremely stable compounds with them, thus refining the grains, reducing the thermal sensitivity and temper brittleness of steel. It can significantly improve the welding performance of ordinary low alloy steel. The V content of the steel of the present invention is designed to be 0.08-0.10%.

[0034] Nb: During the rolling process, the niobium carbonitride particles that are solid-dissolved in austenite and induced by deformation can significantly increase the austenite non-recrystallization temperature, refine the austenite grains and then refine the grains of ferrite, etc., and improve the strength. Nb solid-dissolved in austenite can also improve the hardenability. The carbide Nb particles precipitated during the quenching process or combined with V and Mo to precipitate the second phase, which improves the high-temperature strength. Therefore, the Nb element content in the steel of the present invention is designed to be 0.04-0.06%.

[0035] Ti: The compound of titanium and carbon (TiC) has a strong bonding force and high stability. It will only slowly dissolve into the solid solution of iron when heated to above 1000°C. TiC particles have the effect of preventing the growth and coarsening of steel grains. Titanium is one of the strong ferrite-forming elements, which reduces the austenite phase area. Solid solution titanium improves the hardenability of steel, while the presence of TiC particles reduces the hardenability of steel. Therefore, the Ti element content in the steel of the present invention is designed to be 0.02-0.04%.

[0036] Al: Al has a strong affinity with O and N, and is a deoxidizing and nitrogen fixing agent during steelmaking. Aluminum can strongly reduce the austenite phase region in steel, refine the intrinsic grain size of steel, reduce the notch sensitivity of steel, reduce and eliminate the aging phenomenon of steel, especially reduce the toughness-brittleness transition temperature of steel, and improve the low-temperature toughness of steel. However, when the solid-solution Al content in steel exceeds a certain value, the austenite grains tend to grow and coarsen. The Al element content of the steel of the present invention is designed to be ≥0.015%.

[0037] N: Nitrogen can dissolve in steel to form a solid solution. In addition, nitrogen can also form nitrides in steel, which preferentially nucleate in steel and increase the dislocation of ferrite, which can effectively increase the strength and toughness of steel. The N content of the steel of the present invention is designed to be 0.011-0.015%.

[0038] Compared with the prior art, the beneficial technical effects of the present invention are:

[0039] According to the role of microalloying elements in steel, Ti element refines the as-cast structure of the ingot during the high-temperature steelmaking process, and V and Nb precipitate to refine the grain size during the rolling stage;

[0040] The N element works on steel and forms nitrides with Al, V, Nb and Ti to precipitate and refine the grain size, thus improving the strength and toughness of Q420C.

[0041] Reasonably control the process parameters of smelting, refining, continuous casting, etc. to control the occurrence of cracks in the casting. DETAILED DESCRIPTION

[0042] The present invention is further described below by means of specific examples. The examples are only for the purpose of explanation, and the protection scope of the present invention is not limited to these examples.

[0043] The present invention is further described below:

[0044] Tables 1, 2, 3 and 4 show the weight percentage contents of chemical components and process parameters such as steelmaking and steel rolling in various embodiments of the present invention. The specification of the rolled round steel is 180 mm.

[0045] Table 1 Chemical composition and weight percentage content of the examples

[0046]

[0047]

[0048] Table 2 Steelmaking process parameters of the embodiment

[0049]

[0050] Table 3 Steel rolling process parameters of the embodiment

[0051] Example Heating temperature / ℃ Heating time / h Rolling temperature / ℃ Final rolling temperature / ℃ 1 1243 3.5 1035 832 2 1244 3.5 1041 830 3 1243 3.5 1033 834

[0052] Table 4 Mechanical properties of the examples

[0053] Example <![CDATA[R el / MPa]]> <![CDATA[R m / MPa]]> A / ％ 0℃ impact value / J 1 451 547 22 51 2 457 551 23 48 3 463 543 22 51

[0054] It can be seen from Table 1 that the chemical composition and steelmaking process of Examples 1 and 2 are within the scope required by the patent of the present invention, and the smelting composition is well controlled.

[0055] Through the test data analysis in Table 3 and Table 4 and the rolling process, all performance indicators meet the technical requirements.

[0056] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A production method for producing Q420C hot-rolled round steel with a cross section of 280mm×380mm rectangular billet and a diameter of 180mm or more, the steelmaking process flow: molten iron - molten iron pretreatment - converter - refining outside the furnace - rectangular billet continuous casting, steel rolling process flow: billet heating - high-pressure water dephosphorization - Ф850 billet opening machine - Ф700mm×3+Ф550mm×4 continuous rolling mill group rolling - sawing (sampling) - inspection - grinding - bundling - storage - delivery; it is characterized in that, Steelmaking process parameters are controlled as follows: 1) Converter tapping C ≥ 0.10%, tapping temperature ≥ 1600℃; 2) Refining time ≥40min, white slag basicity ≥3.0; 3) The water volume of the crystallizer is controlled at 3100L / min, the secondary cooling water is low-cooling, and the protective slag is the special protective slag for peritectic steel; 4) The temperature of the billet entering the straightening machine is ≥980℃; 5) Continuous casting superheat ≤ 30°C, casting machine speed between 0.63-0.66m / min; The steel rolling process parameters are controlled as follows: 1) Heating temperature is between 1200-1250℃ and heating time is 3-4h; 2) Rolling temperature ≤ 1050℃; 3) Final rolling temperature ≤850℃; The chemical composition mass percentage of the hot-rolled round steel is: C: 0.17%-0.22%, Si: 0.40%-0.50%, Mn: 1.30%-1.40%, P≤0.015%, S≤0.010%, V: 0.08%-0.10%, Nb: 0.04%-0.06%, Ti: 0.02%-0.04%, Al: ≥0.015%, N: 0.011%-0.015%, and the rest is Fe and other trace impurity elements.

2. The method for producing Q420C hot-rolled round steel with a diameter of 180 mm or more from a rectangular billet section of 280 mm×380 mm according to claim 1, characterized in that: The chemical composition mass percentage of the hot-rolled round steel is: C: 0.19%, Si: 0.47%, Mn: 1.33%, P: 0.012%, S: 0.007%, V: 0.09%, Nb: 0.04%, Ti: 0.03%, Al: 0.022%, N: 0.0145%, and the rest is Fe and other trace impurity elements.

3. The method for producing Q420C hot-rolled round steel with a diameter of 180 mm or more from a rectangular billet section of 280 mm×380 mm according to claim 1, characterized in that: The chemical composition mass percentage of the hot-rolled round steel is: C: 0.18%, Si: 0.46%, Mn: 1.35%, P: 0.014%, S: 0.007%, V: 0.09%, Nb: 0.04%, Ti: 0.03%, Al: 0.022%, N: 0.0125%, and the rest is Fe and other trace impurity elements.

4. The method for producing Q420C hot-rolled round steel with a diameter of 180 mm or more from a rectangular billet section of 280 mm×380 mm according to claim 1, characterized in that: The chemical composition mass percentage of the hot-rolled round steel is: C: 0.20%, Si: 0.46%, Mn: 1.38%, P: 0.012%, S: 0.009%, V: 0.10%, Nb: 0.05%, Ti: 0.04%, Al: 0.021%, N: 0.0138%, and the rest is Fe and other trace impurity elements.

5. The method for producing Q420C hot-rolled round steel with a diameter of 180 mm or more from a rectangular billet section of 280 mm×380 mm according to claim 1, characterized in that: The casting machine speed is controlled at 0.65m / min.

6. The method for producing Q420C hot-rolled round steel with a diameter of 180 mm or more from a rectangular billet section of 280 mm×380 mm according to claim 1, characterized in that: Steel rolling process parameters: heating temperature 1243℃, heating time 3.5h, starting rolling temperature 1035℃, final rolling temperature 832℃.

7. The method for producing Q420C hot-rolled round steel with a diameter of 180 mm or more from a rectangular billet section of 280 mm×380 mm according to claim 1, characterized in that: Steel rolling process parameters: heating temperature 1244℃, heating time 3.5h, starting rolling temperature 1041℃, final rolling temperature 830℃.

8. The method for producing Q420C hot-rolled round steel with a diameter of 180 mm or more from a rectangular billet section of 280 mm×380 mm according to claim 1, characterized in that: Steel rolling process parameters: heating temperature 1243℃, heating time 3.5h, starting rolling temperature 1033℃, final rolling temperature 834℃.

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