A low alloy HRB400E steel billet and its preparation method

Abstract

The present application relates to the technical field of iron and steel metallurgy, and specifically discloses a low-alloy HRB400E steel billet and a preparation method thereof, wherein the steel billet comprises the following elements in percentage by weight: 0.22wt%≤C≤0.25wt%, 0.27wt%≤Si≤0.42wt%, 0.65wt%≤Mn≤0.77wt%, 0<P≤0.045wt%, 0<S≤0.045wt%, and the balance being iron and inevitable impurities; by adjusting the cooling process, the molten steel is precisely cooled from 1515-1525°C to 950-1050°C, and is directly rolled without reheating, thereby reducing costs and improving production efficiency. The yield strength, tensile strength, strength-to-yield ratio, elongation after fracture, and maximum total elongation of the prepared steel billet are 520MPa, 646MPa, 1.56, 23.0%, and 11.48%, respectively, and the yield ratio is 0.85.

Description

Technical Field

[0001] This application belongs to the technical field of steel smelting, and particularly relates to a low-alloy HRB400E steel billet and a preparation method thereof. Background Art

[0002] Low-alloy steel is a type of steel manufactured through processes such as smelting, cooling, and rolling, which is based on ordinary carbon steel and added with low amounts of alloying elements below 3%. Since the strength of this type of steel is significantly higher than that of carbon steel with the same carbon content, it is called High-strength Low-alloy Steel (HSLA).

[0003] High-strength low-alloy steel is a type of steel that uses as few alloying elements as possible to obtain the highest possible comprehensive mechanical properties, in order to achieve the purpose of meeting usage requirements and having low costs. The low-alloy HRB400E steel billet used for rolling is obtained by cooling alloyed molten steel, and the low-alloy HRB400E steel billet used for rolling requires good internal quality of the low-alloy HRB400E steel billet, and the macrostructure grade is less than 2.5 levels to ensure stable rolling.

[0004] Among the existing alloying elements of low-alloy HRB400E steel billets, especially when the manganese content reaches 1.1% - 1.35%, it will cause the macrostructure quality of the low-alloy HRB400E steel billet to be poor, and the cooling temperature cannot be accurately controlled during preparation. After cooling, the low-alloy HRB400E steel billet needs to enter the heating furnace for heating before it can enter the rolling mill for rolling, increasing costs and having low production efficiency. Summary of the Invention

[0005] In order to improve production efficiency while ensuring the quality of the low-alloy HRB400E steel billet, this application provides a low-alloy HRB400E steel billet and a preparation method thereof.

[0006] In the first aspect, this application provides a low-alloy HRB400E steel billet, and the technical solution adopted is as follows:

[0007] A low-alloy HRB400E steel billet, the chemical composition components of the low-alloy HRB400E steel billet include: 0.22wt% ≤ C ≤ 0.25wt%, 0.27wt% ≤ Si ≤ 0.42wt%, 0.65wt% ≤ Mn ≤ 0.77wt%, 0 < P ≤ 0.045wt%, 0 < S ≤ 0.045wt%, and the balance is iron and unavoidable impurities.

[0008] The chemical composition of the low-alloy HRB400E steel billet in this application includes: 0.22wt% ≤ C ≤ 0.25wt%, 0.27wt% ≤ Si ≤ 0.42wt%, 0.65wt% ≤ Mn ≤ 0.77wt%, 0 < P ≤ 0.045wt%, 0 < S ≤ 0.045wt%, and the balance is iron and inevitable impurities; the raw materials can select any value within their respective ranges, and the obtained low-alloy HRB400E steel billets all have high quality.

[0009] By adopting the above technical solution, the element composition content of the low-alloy HRB400E steel billet is controlled, that is, 0.22wt% ≤ C ≤ 0.25wt%, 0.27wt% ≤ Si ≤ 0.42wt%, 0.65wt% ≤ Mn ≤ 0.77wt%, 0 < P ≤ 0.045wt%, 0 < S ≤ 0.045wt%, and the rest is iron and other inevitable impurities.

[0010] Carbon (C): It is the main element affecting the structure and properties in steel, having the function of strengthening the solid solution and ensuring hardenability. The content of carbon directly affects the strength, hardness, toughness of steel, and thus affects the wear resistance of steel. When the carbon content in steel increases, the yield point and tensile strength increase, but the plasticity and impact resistance decrease. A high carbon content will also reduce the atmospheric corrosion resistance of steel. In addition, carbon can increase the cold brittleness and aging sensitivity of steel.

[0011] Silicon (Si): In the steelmaking process, adding silicon as a reducing agent and deoxidizer can significantly ensure the elastic limit, yield point and tensile strength of steel. The deoxidizer in smelting can increase the overheating and decarburization sensitivity of steel. Adding Si not only cooperates with Mn to significantly ensure hardenability, but can also inhibit the overheating sensitivity brought by Mn to a certain extent.

[0012] Manganese (Mn): In the steelmaking process, it is a good deoxidizer and desulfurizer, ensuring the hardenability of steel and improving the hot processing performance of steel. However, if the Mn content is too high, it will increase the overheating sensitivity of the low-alloy HRB400E steel billet and easily reduce the toughness.

[0013] Phosphorus (P): Generally, phosphorus is a harmful element in steel, making the steel produce cold brittleness and reducing the impact toughness of steel.

[0014] Sulfur (S): Sulfur is also a harmful element under normal circumstances. It makes the steel produce hot brittleness, reduces the ductility and toughness of steel, and causes cracks during forging and rolling. P and S are easy to form grain boundary inclusions in steel, increasing the brittleness of steel and the cracking tendency of castings during casting and heat treatment.

[0015] Especially by controlling the contents of Si and Mn elements, the low-alloy HRB400E steel billet meets the requirements of high-strength HRB400E steel.

[0016] Preferably: a low-alloy HRB400E steel billet, which comprises elements with the following weight percentages: C: 0.23wt%; Si: 0.30wt%; Mn: 0.65wt%; 0 < P ≤ 0.021wt%; 0 < S ≤ 0.026wt%, P + S = 0.047wt%, and the balance is iron and inevitable impurities.

[0017] For the low-alloy HRB400E of this application, when it comprises elements with the following weight percentages: C: 0.23wt%; Si: 0.30wt%; Mn: 0.65wt%; 0 < P ≤ 0.021wt%; 0 < S ≤ 0.026wt%, P + S = 0.047wt%, the effect is the best.

[0018] Preferably: the carbon equivalent of the low-alloy HRB400E steel billet ≥ 0.35wt%.

[0019] The carbon equivalent refers to the influence of various alloying elements in steel on the crack sensitivity, that is, according to the size of the influence on crack sensitivity, it is converted into the influence of carbon element. The carbon equivalent can be used to predict the degree of cold crack occurrence in steel.

[0020] By adopting the above technical solution, controlling the carbon equivalent of the low-alloy HRB400E steel billet ≥ 0.35wt% indicates that the low-alloy HRB400E steel billet has low cold crack sensitivity, thus ensuring the quality of the low-alloy HRB400E steel billet.

[0021] Preferably: the total oxygen content of the low-alloy HRB400E steel billet is controlled to be ≤ 80ppm.

[0022] By adopting the above technical solution, the total oxygen content of the low-alloy HRB400E steel billet is controlled to be ≤ 80ppm, reducing the inclusion content in the low-alloy HRB400E steel billet, improving the cleanliness of the molten steel, and further ensuring the quality of the low-alloy HRB400E steel billet.

[0023] In the second aspect, this application provides a preparation method of a low-alloy HRB400E steel billet, which adopts the following technical solution: a manufacturing method of a low-alloy HRB400E steel billet, which comprises the following operating steps:

[0024] Step S1: Charge the raw materials of the low-alloy HRB400E steel billet into a converter for smelting and alloying in an argon station to obtain molten steel; Step S2: Pour the molten steel into a tundish at a temperature of 1515 - 1525°C, let the molten steel stay for 12 - 15 minutes, and cool it to 950 - 1050°C through primary water cooling and secondary water cooling at a drawing speed of 3.5 - 4.5 m / min, and then roll it to obtain the low-alloy HRB400E steel billet.

[0025] By adopting the above technical solution, the molten steel obtained by converter smelting and argon station alloying is cast into a tundish at a molten steel temperature of 1515-1525°C. The molten steel stays for 12-15 minutes, and is cooled to 950-1050°C through primary and secondary water cooling at a pulling speed of 3.5-4.5m / min. The steel is then rolled to obtain a low-alloy HRB400E steel billet. The molten steel is poured into the tundish at a temperature of 1515-1525℃, and the molten steel is retained for 12-15 minutes. The temperature and retention time of the molten steel are controlled so that the various alloy elements are evenly dispersed in the molten steel in a completely molten state, and the heat is slowly and evenly dissipated and cooled in a sufficient retention time, providing conditions for the growth and refinement of internal grains. The drawing speed is controlled at 3.5-4.5m / min. A higher drawing speed can promote grain growth. Combined with primary and secondary water cooling to refine the grains, a low-alloy HRB400E steel billet with good internal quality can be obtained. At the same time, it is cooled to 950-1050℃, so that the cooled low-alloy HRB400E steel billet can be directly rolled into the rolling mill without passing through a heating furnace, reducing the baking cost of the heating furnace and improving production efficiency.

[0026] As a preference: the primary water cooling in step S2 adopts crystallizer cooling, the water temperature of the crystallizer cooling is 30-40 ° C, and the water supply volume is 160-180m 3 / h, water flow rate is 16-20m / s, and the shell thickness of low alloy HRB400E steel billet is ≥12mm.

[0027] By adopting the above technical solution, the water temperature of the primary water cooling crystallizer is controlled to be 30-40℃ and the water supply volume is 160-180m 3 / h, the water flow rate is 16-20m / s, which can enhance the convective heat transfer of molten steel to the solidification interface, improve the heat conduction in the solidified shell, further enhance the convective heat exchange between the outer wall of the copper plate and the cooling water, accelerate the heat exchange rate, and make the low-alloy HRB400E steel billet quickly form a shell; at the same time, it breaks the gas layer film formed by water vapor in the air during the cooling process, so that the moisture directly contacts the low-alloy HRB400E steel billet, reduces the air gap between the shell and the crystallizer, and further enhances the heat transfer in the air gap between the shell and the crystallizer, which can make the molten steel exchange a lot of heat, enhance the uniformity of shell solidification, ensure that the shell thickness of the low-alloy HRB400E steel billet is ≥12mm, has sufficient strength, and will not cause the shell to be too thin, the low-alloy HRB400E steel billet to bulge and deform, or even leak, thereby ensuring the quality of the low-alloy HRB400E steel billet and further improving production efficiency.

[0028] As a preference: in the secondary water cooling process in step S2, the water temperature is 30-35°C, and the cooling is carried out in a staged cooling mode of zero, one, two, three and four stages. The zero and one stages are cooled by solid cone nozzles, and the water distribution volume is 16-17m3 / min、20-26m 3 / min, the second, third and fourth stages are cooled by high-strength giant nozzles, with water distribution volumes of 13-15m 3 / min、7-11m 3 / min、4-7m 3 / min, and the temperature difference between the core temperature and the surface temperature of the low alloy HRB400E steel billet is ≤100℃ during the whole process.

[0029] During the solidification process, as solute redistribution occurs within the low-alloy HRB400E billet, the solidification front continuously advances, closing the distance between the two solidification fronts. The rapid growth of columnar crystals on either side causes them to intersect prematurely before solidification, a phenomenon known as solidification bridging. This solidification bridging creates a "small ingot" structure within the low-alloy HRB400E billet, hindering the downward flow of molten steel from above, resulting in porosity and shrinkage cavities. Furthermore, since the solute-rich molten steel concentrates within the "small ingot," the quality of the low-alloy HRB400E billet is compromised once it fully solidifies. Columnar crystal formation typically occurs in the secondary water-cooling zone. Uneven cooling in this zone can cause the columnar crystals in the low-alloy HRB400E billet to grow at varying speeds, increasing the risk of interdendritic bridging.

[0030] By adopting the above technical solution, the secondary water cooling is divided into five sections, and the water distribution amount of each section is different, so that the low-alloy HRB400E steel billet can be cooled evenly, and the temperature difference between the core temperature and the surface temperature in the whole process is ≤100°C. The thermal stress of the low-alloy HRB400E steel billet during solidification can be reduced, and the formation of inter-dendritic bridges in the steel core part in the middle of the low-alloy HRB400E steel billet can be reduced. The heat is evenly reduced, and the low-magnification defects in the interior of the low-alloy HRB400E steel billet are reduced. The composition uniformity of the finished product is good, the internal quality of the low-alloy HRB400E steel billet is improved, and the production efficiency is further improved.

[0031] Preferably, the specific water volume of the secondary water cooling in step S2 is 0.1-0.2 L / kg.

[0032] The specific water volume is the ratio of cooling water consumption per unit time to the mass of the steel billet passing through the secondary water cooling zone, and is an indicator of the water spray intensity of the secondary water cooling in continuous casting.

[0033] By adopting the above technical solution, the water content in the secondary water cooling process is controlled, making the cooling process relatively gentle. The temperature gradient inside the low-alloy HRB400E steel billet is low and stable, which is conducive to the formation of equiaxed crystals, reduces the distance between dendrites, refines the grains, improves the internal quality of the low-alloy HRB400E steel billet, and further improves production efficiency.

[0034] Preferably, the superheat of the molten steel is ≤20°C.

[0035] The melting temperature of low alloy steel is a range, which is composed of the starting melting temperature and the ending melting temperature. The superheat of molten steel is the temperature difference between the actual temperature and the melting temperature.

[0036] By adopting the above technical solution, the superheat of the molten steel is controlled, and the cooling differences between each section in the primary water cooling and secondary water cooling can be reduced, so as to achieve the purpose of small temperature difference and uniform cooling of the surface temperature of the low-alloy HRB400E steel billet. Combined with a higher drawing speed, cracks caused by excessive thermal stress can be prevented. At the same time, matching the cooling process of this application, the low-alloy HRB400E steel billet can be uniformly solidified, which is conducive to grain refinement, improving the internal quality of the low-alloy HRB400E steel billet, and further improving production efficiency.

[0037] Preferably, the water pressure of the primary water cooling and the secondary water cooling in step S2 are both 1.4-1.8 MPa.

[0038] During the solidification process of molten steel, the liquid steel in the center of the low-alloy HRB400E billet will continuously release heat to the surface of the low-alloy HRB400E billet. When the cooling water on the surface cannot take away the heat released from the center of the low-alloy HRB400E billet, the temperature of the surface of the low-alloy HRB400E billet will rise, and a large expansion stress will be generated at the solidification front of the low-alloy HRB400E billet, resulting in uneven distribution of elements inside the low-alloy HRB400E billet and poor quality.

[0039] By adopting the above technical solution, the water pressure of the primary water cooling and the secondary water cooling in step S2 is controlled, so that there is no temperature reversal during the entire cooling process, the expansion stress is reduced, the internal quality of the low-alloy HRB400E steel billet is improved, and the production efficiency is further improved.

[0040] In this application, the capacity of the steel tundish is expanded to 60-80 tons, so that the molten steel has sufficient floating time in the ladle, ensuring the purity of the molten steel, which is beneficial to ensuring the processing performance of the low-alloy HRB400E steel billet.

[0041] In summary, this application includes at least one of the following beneficial technical effects:

[0042] (1) The low alloy HRB400E steel billet of the present application is prepared by adjusting the following weight percentages of elements: 0.22wt%≤C≤0.25wt%, 0.27wt%≤Si≤0.42wt%, 0.65wt%≤Mn≤0.77wt%, 0<P≤0.045wt%, 0<S≤0.045wt%, and the balance being iron and unavoidable impurities; and at the same time, adjusting the cooling process parameters in the preparation method so that the molten steel is cooled from 1515-1525°C to 950- 1050℃, which ensures the quality of low-alloy HRB400E steel billet. The yield strength, tensile strength, strength-to-yield ratio, elongation after fracture and maximum total elongation of the prepared low-alloy HRB400E steel billet are 520MPa, 646MPa, 1.56, 23.0% and 11.48% respectively, and the yield ratio is as low as 0.85. The quality is good. The low-alloy HRB400E steel billet can go directly into the rolling mill without passing through the heating furnace, which reduces the baking cost of the heating furnace and improves production efficiency.

[0043] (2) The present application can promote grain growth and ensure the quality of the low-alloy HRB400E steel billet by adjusting the cooling pulling speed of the low-alloy HRB400E steel billet, so that the yield strength, tensile strength, strength-to-yield ratio, elongation after fracture and maximum total elongation of the finished low-alloy HRB400E steel billet are 491 MPa, 617 MPa, 1.47, 21.6% and 10.75% respectively, and the yield-to-yield ratio is 0.90.

[0044] (3) The present application controls the uniform cooling of the low-alloy HRB400E steel billet by adjusting the water distribution of the secondary water cooling, and further controls the water ratio of the secondary water cooling to make the cooling process of the low-alloy HRB400E steel billet relatively smooth, which is conducive to the formation of equiaxed crystals, refines the grains, and improves the quality of the low-alloy HRB400E steel billet. The yield strength, tensile strength, strength-to-yield ratio, elongation after fracture and maximum total elongation of the obtained low-alloy HRB400E steel billet product are 501 MPa, 627 MPa, 1.5, 22.1% and 11.00%, respectively, and the yield-to-yield ratio is 0.88.

[0045] (4) The present application controls the superheat of molten steel, thereby reducing the surface temperature cooling difference of the low-alloy HRB400E steel billet, so that the yield strength, tensile strength, strength-to-yield ratio, elongation after fracture and maximum total elongation of the finished low-alloy HRB400E steel billet are 506 MPa, 632 MPa, 1.52, 22.3% and 11.13% respectively, and the yield-to-yield ratio is 0.87. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The low alloy HRB400E steel billet product prepared in Example 1 of the present application;

[0047] Figure 2 This is a high-magnification image of the finished low-alloy HRB400E steel billet prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0048] The present application is further described in detail below with reference to specific embodiments.

[0049] The following raw materials in this application are all commercially available products. They are all for the purpose of fully disclosing the raw materials of this application and should not be understood as restricting the sources of the raw materials. Specifically, manganese is derived from metallic manganese; iron is derived from ferroferric oxide; silicon is derived from silicon dioxide; carbon is derived from zirconium carbide; phosphorus is derived from phosphorus pentoxide; and sulfur is derived from pyrite.

[0050] Example 1

[0051] The low alloy HRB400E steel billet of Example 1 was prepared by the following preparation method:

[0052] Step S1: The raw materials of low alloy HRB400E steel billet, whose chemical compositions are shown in Table 1, are charged into a converter for smelting and alloying in an argon station to obtain molten steel, wherein the oxygen content of the molten steel is 78 ppm;

[0053] Step S2: Pour the molten steel at 1525℃ into the tundish, and keep the molten steel for 13 minutes. The water pressure is 1.2MPa, and the average superheat of the molten steel is 27℃. At a casting speed of 3.5m / min, it first enters the primary water cooling mode, using the crystallizer cooling. The average water temperature of the crystallizer cooling is 35℃, and the water supply is 170m3. 3 / h, the water flow rate is 18m / s, and the shell thickness of the low alloy HRB400E steel billet is 15mm;

[0054] Then it enters the secondary water cooling zone, where the water temperature is 33°C on average and the water volume is 0.23L / kg. The zero and first sections are cooled by solid cone nozzles, with water volumes of 16.5m3 respectively. 3 / min、26m 3 / min, the second, third and fourth stages are cooled by high-strength giant nozzles, with a water supply capacity of 14m 3 / min、11m 3 / min、4m 3 / min, and the average temperature difference between the core temperature and the surface temperature of the low alloy HRB400E steel billet during the whole process is 97℃;

[0055] After cooling to an average temperature of 1012℃, it is directly rolled to obtain a 165mm*165mm low alloy HRB400E steel billet product. Figure 1 The low alloy HRB400E steel billet product prepared in Example 1 of the present application; Figure 2This is a high-magnification image of the finished low-alloy HRB400E steel billet prepared in Example 1 of the present application, showing high purity and good grain refinement.

[0056] Examples 2-4

[0057] The preparation methods of the low alloy HRB400E steel billets of Examples 2-4 are the same as that of Example 1, except that the weight percentages of the chemical elements of the raw materials are different, as shown in Table 1 for details.

[0058] Table 1 Weight percentage of each chemical element and carbon equivalent (wt%)

[0059]

[0060] Examples 5-6

[0061] The chemical composition content of the low alloy HRB400E steel billets of Examples 5-6 is the same as that of Example 4, except that the drawing speed in step S2 of the preparation method is different, as shown in Table 2 for details.

[0062] Examples 7-8

[0063] The chemical composition content of the low alloy HRB400E steel billets of Examples 7-8 is the same as that of Example 5, except that the water distribution amount in the primary water cooling in step S2 of the preparation method is different, as shown in Table 2 for details.

[0064] Table 2 Step parameters of Examples 5-8

[0065]

[0066] Example 9

[0067] The chemical composition content of the low-alloy HRB400E steel billet of Example 9 is the same as that of Example 5, except that the water distribution amount in the secondary water cooling in step S2 of the preparation method is different, as shown in Table 3 for details.

[0068] Examples 10-12

[0069] The chemical composition content of the low alloy HRB400E steel billets of Examples 10-12 is the same as that of Example 9, except that the water distribution amount in the secondary water cooling in step S2 of the preparation method is different, as shown in Table 3 for details.

[0070] Table 3 Step parameter table of Examples 9-12

[0071]

[0072] Examples 13-14

[0073] The chemical composition content of the low alloy HRB400E steel billets of Examples 13-14 is the same as that of Example 11, except that the superheat degree of the molten steel in the preparation method is different, as shown in Table 4 for details.

[0074] Examples 15-18

[0075] The chemical composition content of the low-alloy HRB400E steel billets of Examples 15-18 is the same as that of Example 13, except that the water pressures of the primary water cooling and the secondary water cooling in step S2 of the preparation method are different, as shown in Table 4 for details.

[0076] Table 4 Step parameter table of Examples 13-18

[0077]

[0078] Comparative Examples 1-4

[0079] The preparation methods of the low alloy HRB400E steel billets of Examples 1-4 are the same as that of Example 1, except that the weight percentages of the chemical elements of the raw materials are different, as shown in Table 5 for details.

[0080] Table 5 Weight percentage of each chemical element and carbon equivalent (wt%)

[0081]

[0082] Comparative Example 5

[0083] The chemical composition of the low alloy HRB400E steel billet of Comparative Example 5 is the same as that of Example 1, except that in step S2 of the preparation method, specifically, at a drawing speed of 3 m / min, the molten steel is subjected to a water distribution of 170 m 3 / min primary water cooling and water distribution volume is 67m 3 After secondary water cooling at a rate of / min, the cooled steel billet is obtained, and the average temperature is measured to be 800℃. The steel billet is then heated to 980℃ in a heating furnace and then enters the rolling mill for rolling.

[0084] Performance test (I)

[0085] The following testing standards or methods were used to perform performance tests on the low alloy HRB400E steel billets obtained in different Examples 1-18 and Comparative Examples 1-5. The test results are shown in Table 6.

[0086] Internal quality low-level grade: The internal quality low-level grade of low-alloy HRB400E steel billet was rated according to GB / T1979-2001 standard. The results are shown in Table 6 below.

[0087] Processing time: The time required from converter smelting to rolling into finished products when preparing low alloy HRB400E billets in Examples 1-18 and Comparative Examples 1-5 was recorded. The results are shown in Table 6 below.

[0088] Table 6 Performance test results of different low alloy HRB400E billets

[0089]

[0090] The test results in Table 6 show that the internal quality low-multiple grade of the low-alloy HRB400E steel billet obtained in the present application is ≤level 2, which ensures the internal quality of the low-alloy HRB400E steel billet and has high rolling performance; at the same time, the process time of the preparation method of the low-alloy HRB400E steel billet using the present application is 20 minutes, which is 10 minutes shorter than the traditional low-speed water cooling and then furnace heating, and then hot rolling, with a total process time of 30 minutes. This not only reduces the heating furnace baking cost, but also improves production efficiency.

[0091] Performance Testing (II)

[0092] The low alloy HRB400E steel billets prepared in Examples 1-18 and Comparative Examples 1-5 were tested for yield strength, tensile strength, elongation after fracture, strength-to-yield ratio, and yield-to-yield ratio according to GB / T 228.1-2010. The results are shown in Table 7.

[0093] Table 7 Performance test results of different low alloy HRB400E billets

[0094]

[0095] The test results in Table 7 show that the yield strength, tensile strength, strength-to-yield ratio, elongation after fracture and maximum total elongation of the low-alloy HRB400E steel billet obtained in this application are 520 MPa, 646 MPa, 1.56, 23.0% and 11.48% respectively, and the yield ratio is as low as 0.85. It has high mechanical properties and the quality of the low-alloy HRB400E steel billet is good.

[0096] In Examples 1-3, the yield strength, tensile strength, strength-to-yield ratio, elongation after fracture and maximum total elongation of the low-alloy HRB400E steel billet prepared in Example 3 are 451 MPa, 577 MPa, 1.35, 19.6% and 9.75%, respectively, all of which are higher than those in Example 1-2. The yield ratio is 0.98, which is lower than that in Example 1-2, indicating that when the weight percentage of the chemical elements C, Si, Mn, P and S in the raw materials are controlled to be 0.23wt%, 0.3wt%, 0.65wt%, 0.021wt% and 0.026wt%, respectively, the steel has better mechanical properties and improves the quality of the low-alloy HRB400E steel billet.

[0097] In Examples 3-4, the yield strength, tensile strength, strength-to-yield ratio, elongation after fracture and maximum total elongation of the low-alloy HRB400E steel billet prepared in Example 4 are 459 MPa, 585 MPa, 1.38, 20.0% and 9.95%, respectively, which are all higher than those in Examples 1-2, and the yield ratio is 0.96, which is lower than that in Example 3, indicating that when the carbon equivalent in the weight percentage of chemical elements is controlled to be greater than 0.35wt%, it has better mechanical properties and improves the quality of the low-alloy HRB400E steel billet.

[0098] Among Examples 4-6, the yield strength, tensile strength, strength-to-yield ratio, elongation after fracture, and maximum total elongation of the low-alloy HRB400E steel billet prepared in Example 5 were 491 MPa, 617 MPa, 1.47%, 21.6%, and 10.75%, respectively, all higher than those in Example 4 and Example 6. The yield ratio was 0.90, lower than those in Example 4 and Example 6. This indicates that controlling the drawing speed of the low-alloy HRB400E steel billet during cooling to 4 m / min resulted in better mechanical properties and improved quality. This may be due to the fact that a higher drawing speed promotes grain growth, resulting in a low-alloy HRB400E steel billet with good internal quality.

[0099] Combined with the mechanical property test data of the low alloy HRB400E steel billet of Example 5 and Examples 7-8, it is found that the yield strength, tensile strength, strength-to-yield ratio, elongation after fracture and maximum total elongation of the low alloy HRB400E steel billet prepared in Example 5 are 491MPa, 617MPa, 1.47, 21.6% and 10.75%, respectively, which are higher than those of Examples 7 and 8, and the yield ratio is 0.90, which is lower than that of Examples 7 and 8, indicating that when the water distribution rate of the primary water cooling in the cooling of the low alloy HRB400E steel billet is controlled to be 170m 3 / min, it has better mechanical properties and improves the quality of low alloy HRB400E steel billet.

[0100] Combined with the mechanical property test data of the low alloy HRB400E steel billets of Examples 5 and 9-12, it was found that the yield strength, tensile strength, strength-to-yield ratio, elongation after fracture and maximum total elongation of the low alloy HRB400E steel billets prepared in Examples 10-12 were 495-501 MPa, 621-627 MPa, 1.49-1.50, 21.8-22.1% and 10.85-11.00%, respectively, which were higher than those in Example 5 and Example 9, and the yield ratio was 0.88-0.89, which was lower than that in Example 5 and Example 9. Example 9 shows that controlling the water distribution amount in the secondary water cooling during the cooling of the low-alloy HRB400E steel billet has an impact on the mechanical properties of the steel billet, especially when the water distribution amount of the secondary water cooling is adjusted to control its specific water amount to 0.1-0.2L / kg, the mechanical properties are further improved. This may be related to the fact that controlling the secondary water cooling makes the cooling process of the low-alloy HRB400E steel billet relatively gentle, and the temperature gradient inside the steel billet is low and stable, which is conducive to the formation of equiaxed crystals, reduces the distance between dendrites, refines the grains, and improves the quality of the low-alloy HRB400E steel billet.

[0101] Combining the mechanical property test data of the low-alloy HRB400E steel billets of Example 11 and Examples 13-14, it was found that the yield strength, tensile strength, strength-to-yield ratio, elongation after fracture and maximum total elongation of the low-alloy HRB400E steel billets prepared in Examples 13-14 were 504-506 MPa, 630-632 MPa, 1.51-1.52, 22.2-22.3% and 11.08-11.13%, respectively, all of which were higher than that of Example 11. The yield ratio was 0.87, which was lower than that of Example 14, indicating that when the superheat of the molten steel was controlled to be ≤20°C, it had better mechanical properties, which may be related to the fact that the cooling difference of the surface temperature of the low-alloy HRB400E steel billet was small, thereby improving the quality of the low-alloy HRB400E steel billet.

[0102] Combining the mechanical property test data of the low-alloy HRB400E steel billets of Example 13 and Examples 15-18, it was found that the yield strength, tensile strength, strength-to-yield ratio, elongation after fracture and maximum total elongation of the low-alloy HRB400E steel billets prepared in Examples 15-17 were 513-520 MPa, 639-646 MPa, 1.54-1.56, 22.7-23.0% and 11.30-11.48%, respectively, all of which were higher than those in Example 13 and Example 18, and the yield ratio was 0.85-0.86, which was lower than that in Example 13 and Example 18, indicating that when the water pressure of the primary water cooling and secondary water cooling of the molten steel were controlled to be 1.4-1.8 MPa, better mechanical properties were obtained, which may be related to the fact that the cooling process was controlled without reheating, thereby improving the quality of the low-alloy HRB400E steel billet.

[0103] In addition, by combining the mechanical property test data of the low-alloy HRB400E steel billets in Comparative Examples 1-5 and Example 1, it is found that the weight percentage content of chemical elements in the raw materials of the low-alloy HRB400E steel billets of the present application is 0.22 wt% ≤ C ≤ 0.25 wt%, 0.27 wt% ≤ Si ≤ 0.42 wt%, 0.65 wt% ≤ Mn ≤ 0.77 wt%, 0 < P ≤ 0.045 wt%, 0 < S ≤ 0.045 wt%, and the balance is iron and inevitable impurities. By controlling the low-alloy elements and配合 the preparation method, especially the adjustment of the cooling process parameters, the molten steel can be accurately temperature-controlled and cooled from 1515 - 1525 °C to 950 - 1050 °C, ensuring the quality of the low-alloy HRB400E steel billets, enabling the low-alloy HRB400E steel billets to directly enter the rolling mill for rolling without passing through a heating furnace, reducing the heating furnace baking cost, and improving the production efficiency.

[0104] This specific embodiment is only an explanation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment that do not contribute creatively as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law. It should be noted that there is an unclear expression "配合" in the original text. I translated it as "配合" as it is in the original, but it might need to be adjusted according to the actual context for a more accurate translation.

Claims

1. A low alloy HRB400E steel billet, characterized in that: It has the following percentage content of elements: 0.22wt%≤C≤0.25wt%, 0.27wt%≤Si≤0.42wt%, 0.65wt%≤Mn≤0.77wt%, 0<P≤0.045wt%, 0<S≤0.045wt%, and the balance is iron and unavoidable impurities; The method for preparing the low-alloy HRB400E steel billet comprises the following steps: Step S1: loading the raw materials of low-alloy HRB400E steel billet into a converter for smelting, alloying in an argon station, and obtaining molten steel; Step S2, pouring molten steel at 1515-1525° C. into a tundish, allowing the molten steel to remain there for 12-15 minutes, cooling to 950-1050° C. through primary and secondary water cooling at a drawing speed of 3.5-4.5 m / min, and rolling to obtain a low alloy HRB400E steel billet; The water temperature in the secondary water cooling process in step S2 is 30-35°C, and the cooling is carried out in a staged cooling mode of zero, one, two, three and four stages. The zero and one stages are cooled by solid cone nozzles, and the water distribution volume is 16-17m 3 / min、20-26m 3 / min, the second, third and fourth stages are cooled by high-strength giant nozzles, with water distribution volumes of 13-15m 3 / min、7-11m 3 / min、4-7m 3 / min, the temperature difference between the core temperature and the surface temperature of the low alloy HRB400E steel billet during the whole process is ≤100°C; the specific water volume of the secondary water cooling in step S2 is 0.1-0.2L / kg; The primary water cooling in step S2 is performed by crystallizer cooling, the water temperature of the crystallizer cooling is 30-40°C, and the water supply volume is 160-180m 3 / h, water flow rate is 16-20m / s, and the shell thickness of low alloy HRB400E steel billet is ≥12mm.

2. The low alloy HRB400E steel billet according to claim 1, characterized in that: The elements have the following content percentages: C: 0.23 wt%; Si: 0.30 wt%; Mn: 0.65 wt%; 0<P≤0.021 wt%; 0<S≤0.026 wt%, P+S=0.047 wt%, and the balance is iron and unavoidable impurities.

3. The low alloy HRB400E steel billet according to claim 1, characterized in that: The carbon equivalent of the low alloy HRB400E steel billet is ≥0.35wt%.

4. The low alloy HRB400E steel billet according to claim 1, characterized in that: The total oxygen content of the low alloy HRB400E steel billet is controlled to be ≤80ppm.

5. The low alloy HRB400E steel billet according to claim 1, characterized in that: The superheat of the molten steel is ≤20°C.

6. The low alloy HRB400E steel billet according to claim 1, characterized in that: The water pressure of the primary water cooling and the secondary water cooling in step S2 are both 1.4-1.8 MPa.

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