V-Nb-Ce composite microalloyed large-specification low-temperature-resistant angle steel and production method thereof

Abstract

The invention provides V-Nb-Ce composite microalloyed large-size low-temperature-resistant angle steel and a production method thereof. The V-Nb-Ce composite microalloyed large-size low-temperature-resistant angle steel comprises the following chemical components in percentage by weight: 0.15 to 0.18 percent of C, 1.25 to 1.45 percent of Mn, 0.25 to 0.50 percent of Si, 0.04 to 0.05 percent of V, 0.015 to 0.030 percent of Nb, less than or equal to 0.015 percent of P, less than or equal to 0.007 percent of S, less than or equal to 1.8 ppm of [H], 0.010 to 0.017 percent of Ce, 0.010 to 0.018 percent of Als and the balance of Fe and inevitable impurities. Compared with the prior art, a trace amount of rare earth element Ce is added, soft reduction in the continuous casting process is combined to refine an as-cast structure, element segregation is relieved, and a banded structure is eliminated; low-content niobium (less than or equal to 0.030%) and vanadium (less than or equal to 0.05%) are adopted for composite microalloying, comprehensive regulation and control of the production process are combined, and finally the strength and toughness of the super-large-specification angle steel are improved through the comprehensive effect of grain refinement and dispersion precipitation strengthening. The large-size low-temperature-resistant angle steel produced through the scheme reaches the E-grade quality grade, namely the core impact toughness Akv of the angle steel is larger than or equal to 58J (the test temperature is minus 40 DEG C).

Description

Technical Field

[0001] The invention relates to the technical field of hot-rolled steel sections, and in particular to a V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel and a production method thereof. Background Art

[0002] Angle steel is widely used in steel structures, and large-size angle steel is mainly used for tower manufacturing and building structures. At present, my country's electric energy ultra-high voltage and UHV transmission line construction projects are booming. Due to the strong rigid demand for UHV construction, transmission towers are developing towards large-scale and high-strength, leading the rapid progress of the downstream raw material manufacturing industry. The development of China's angle steel production capacity is strongly positively correlated with the development of national ultra-high voltage transmission. The State Grid plans to build 38 ultra-high voltage lines, involving more than 30,000 kilometers of lines, a transformer capacity of 340 million KVA, and a total investment of 380 billion yuan, which provides a broad market prospect for angle steel for power towers.

[0003] In order to meet the needs of a large number of multi-circuit lines, ultra-high voltage and large-section conductive wires, it is necessary to develop large-scale power tower structures, and the loads designed on power towers will also become larger and larger, which requires large-size and high-strength angle steels to meet the structural design requirements of angle steels for power towers. Therefore, the strength grade of angle steels used in manufacturing tower materials has also been upgraded from Q345 to Q420 or even Q460. In addition, the quality grades of angle steels commonly used in power towers in my country are usually Class B and Class C, so angle steels for power towers are prone to fracture accidents under low temperature and bad weather conditions. However, the climate change in northern and remote mountainous areas of my country is extremely harsh, and the service conditions of angle steels are becoming more and more demanding. In order to ensure the safety of equipment operation, the requirements for their low-temperature impact toughness are becoming higher and higher. Therefore, in the T / CEC 352 "Hot-rolled Equal Angle Steels for Transmission Line Towers" standard launched by the Electric Power Enterprise Federation, two quality grades, D and E, were added to the strength levels of Q420 and Q460 to meet the needs of the State Grid for large-size, high-strength and low-temperature impact-resistant angle steels.

[0004] At present, high-strength angle steel is generally strengthened by adding vanadium iron or vanadium nitrogen alloy. Most large-size high-strength angle steels have a V content of more than 0.07%. The main problems are: carbon equivalent limits the flexible design of C, Mn, and V components; adding higher contents of nitrogen, vanadium and other elements causes the appearance of a low-temperature plasticity valley in the steel billet, and large-size angle steels have serious cracking; the increase in manganese content easily causes banded structure in the angle steel, thereby deteriorating the mechanical properties of the angle steel, especially the low-temperature impact toughness; when the niobium content is too high (> 0.045%), niobium compounds will aggregate, the grain boundary brittleness will increase, and the toughness of the steel will also be reduced. Therefore, it is urgent to develop a chemical composition system of ultra-large-size high-strength and tough angle steels with low-temperature toughness resistance and related supporting production process technologies. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel and a production method thereof, using 0.015% to 0.030% niobium to replace part of vanadium, with an upper limit of vanadium content of 0.05%, optimizing the elemental components such as V and Nb and their corresponding production processes. Since the precipitation of niobium compounds in austenite can increase the recrystallization temperature, non-recrystallization rolling can effectively refine the grains, and the carbides of niobium and vanadium are precipitated in the ferrite in the form of fine dispersion, the strength and toughness of the ultra-large-size angle steel are finally improved through the combined effects of grain refinement and precipitation, which will greatly solve the problems of cracking of large-size angle steel and low-temperature impact toughness not meeting the standards. The large-size angle steel produced by the scheme of the present invention reaches the E-grade quality grade, that is, the impact toughness of the sample taken at the center of the thickness of the angle steel (core): Akv ≥ 58J (test temperature -40°C).

[0006] To achieve this technical purpose, the present invention adopts the following scheme: In a first aspect, the present invention provides a V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel, the chemical composition of which, by weight percentage, comprises: C: 0.15-0.18%, Mn: 1.25-1.45%, Si: 0.25-0.50%, V: 0.04-0.05%, Nb: 0.015-0.030%, P: ≤0.015%, S: ≤0.007%, [H] ≤1.8ppm, Ce: 0.010-0.017%, Als: 0.010-0.018%, and the remainder Fe and unavoidable impurities.

[0007] Furthermore, the low temperature resistant angle steel structure is a uniform and fine ferrite + degenerate pearlite structure, and the average grain size is 6 to 8 μm.

[0008] Furthermore, the technical indicators of mechanical properties of low-temperature resistant angle steel are: tensile strength: Rm≥580MPa, yield strength: Rel≥470MPa, elongation: A≥25%, -40℃ angle steel core impact toughness: Akv≥58J.

[0009] In a second aspect, the present invention provides a method for producing a V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel, comprising the steps of converter smelting → refining → continuous casting → heating in a heating furnace → rough rolling → finishing rolling → cooling, wherein the process control of the smelting and continuous casting steps is as follows: The converter smelting is carried out according to the smelting process system of conventional low alloy steel. The refining adopts RH vacuum treatment. The converter smelting end temperature is controlled at 1630-1670℃, and the temperature of the refined molten steel is controlled at 1570-1610℃. The casting temperature of the continuous casting process is controlled at 1550-1560℃, the billet drawing speed is 0.75-0.9m / min, the secondary cooling speed is controlled at 100-120℃ / min, the light pressure reduction during the continuous casting process is controlled at 5-8mm, and the billet cross-sectional size is 320×460mm. Light pressure is used in the continuous casting process to break up dendrites and reduce element segregation.

[0010] The process parameters of the rolling and cooling process are controlled as follows: the rectangular billet obtained by continuous casting is heated to 1180-1220°C in a heating furnace and then subjected to rough rolling. The starting rolling temperature of the rough rolling mill is controlled at 1070-1090°C, the inlet temperature of the first finishing mill (F1) is controlled at 970-980°C, and the inlet temperature of the second finishing mill (F2) is controlled at 870-880°C. A total of 10-15 rolling passes are performed, the compression ratio is greater than 5.5, water cooling is used after rolling, and the cooling rate is controlled at 7-12°C / s.

[0011] During the whole rolling process, the rough rolling adopts austenite recrystallization rolling, and the second finishing mill (F2) adopts non-recrystallization rolling to ensure that the hardened austenite phase changes to obtain a uniform and fine ferrite + pearlite structure. The low temperature resistant angle steel structure is a uniform and fine ferrite + degenerate pearlite structure with an average grain size of 6 to 8 μm. Its mechanical properties reach tensile strength: R m ≥580MPa, yield strength: R el ≥470MPa, elongation: A≥25%, core impact toughness: A kv ≥58J (test temperature -40℃).

[0012] Only by adopting the chemical composition and production process parameters of the present invention can the final room temperature structure of the hot-rolled angle steel be a uniform and fine ferrite + degenerate pearlite structure, and the ferrite grain size is 6 to 8 μm; and there are no banded structures and sharp-angled inclusions in the steel, thereby significantly improving the toughness and strength of the large-size angle steel of the present invention.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1) The chemical composition formula of V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel is provided.

[0014] 2) The reason why the angle steel produced by the present invention has both high strength and high toughness: (1) The main purpose of light pressure reduction during continuous casting is to break dendrites, increase the nucleation rate during solidification, refine the cast structure, reduce the segregation of elements such as Mn, thereby reducing or eliminating the banded structure in the final product structure. Refining adopts RH vacuum treatment to reduce [H]≤1.8ppm in the steel to avoid a large number of fine cracks in the angle steel, which significantly reduces the plasticity and impact toughness of the angle steel. (2) Adding a trace amount of rare earth element Ce to the steel can effectively improve the morphology and distribution of inclusions, making the inclusions spherical or nearly spherical, and the distribution is also more diffuse. Compared with long strips or angular inclusions, spherical inclusions have less effect on the continuity of the steel matrix, thereby reducing the probability of steel fracture caused by inclusions as crack initiation factors; on the other hand, after rare earth elements are added to steel, they will react with other elements to achieve microalloying and refine the grains, thereby also improving the strength and toughness of steel to a certain extent. (3) The strengthening effect of vanadium on steel is mainly precipitation strengthening, and the effect of fine grain strengthening is very weak. Niobium has a dual effect of fine grain strengthening and dispersed precipitation strengthening on steel. The precipitation of niobium in austenite can hinder the growth of austenite grains on the one hand, and increase the recrystallization temperature on the other hand. Combined with non-recrystallization rolling, it can effectively refine the grains, thereby achieving fine grain strengthening; niobium can also achieve dispersed distribution of precipitates by inducing precipitation and controlling the cooling rate after rolling, thereby adjusting the toughness level of steel in a wider range; as the strengthening effect decreases significantly with the increase of niobium content in steel, and the strengthening effect of low niobium content (≤0.030%) is very significant, the niobium content in the composition design of the present invention is ≤0.030%.

[0015] 3) The organization and performance tests show that the V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel produced according to the chemical ratio and process parameters of the present invention has a microstructure composed of uniform and fine ferrite + degenerate pearlite, and no banded structure appears in the organization; its mechanical performance indicators can fully meet the standard requirements of Q420E or Q460E, and various performance indicators are better than existing products, and the product has excellent low-temperature impact toughness, that is, core impact toughness: Akv ≥ 58J (test temperature -40°C). BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The scanning electron microscope organization diagram in Example 1; Figure 2 The morphology and distribution diagram of inclusions in Example 1; Figure 3 This is the scanning electron microscope organization diagram in Comparative Example 1; Figure 4 The morphology and distribution diagram of inclusions in Comparative Example 1; Figure 5 This is the scanning electron microscope organization diagram in Comparative Example 2; Figure 6 is the morphology of the aggregated niobium compounds in Comparative Example 2; Figure 7 This is the scanning electron microscope organization diagram in comparative example 3. DETAILED DESCRIPTION

[0017] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific implementation methods, but the present invention is not limited thereto.

[0018] The invention provides a V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel and a production method thereof, comprising the steps of converter smelting→refining→continuous casting→heating in a heating furnace→rough rolling→finishing rolling→cooling, which are specifically carried out in the following steps. Example 1

[0019] According to the chemical composition of the V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel of the present invention, smelting and casting into a rectangular billet are carried out, and the chemical composition thereof is as follows in weight percentage: C: 0.15%, Mn: 1.45%, Si: 0.25%, V: 0.05%, Nb: 0.020%, Ce: 0.011%, Als: 0.012%, S: 0.005%, P: 0.013%, [H]: 1.6ppm, and the remainder is Fe and unavoidable impurities.

[0020] The final temperature of converter smelting is 1630℃, and the temperature of refined molten steel is 1570℃; the casting temperature of continuous casting process is 1550℃, the casting speed is 0.9m / min, the secondary cooling speed is 100℃ / min, the soft reduction is 6mm, and the cross-sectional size of the casting is 320×460mm (the cross-sectional size of the casting in subsequent embodiments is the same). The rectangular billet obtained by continuous casting is heated to 1200℃ in a heating furnace and then rough rolled. The starting rolling temperature of the rough rolling mill is 1075℃, the inlet temperature of the first finishing mill (F1) is 970℃, and the inlet temperature of the second finishing mill (F2) is 875℃. A total of 10 passes are rolled, the compression ratio is 5.6, and the cooling rate after rolling is 8℃ / s.

[0021] The room temperature structure of the low temperature resistant hot rolled angle steel is uniform and fine ferrite + degenerate pearlite structure, the average grain size is 6.5μm, there is no banded structure in the structure, most of the inclusions are spherical or ellipsoidal and the size of the inclusions is small (see Figure 1 and Figure 2 ). The tensile strength of the tested product is R m =635MPa, yield strength R el =495MPa, elongation A=28%, core impact toughness A kv =74J (test temperature -40℃). Example 2

[0022] According to the chemical composition of the V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel of the present invention, smelting and casting into a rectangular billet are carried out, and the chemical composition thereof is as follows in weight percentage: C: 0.16%, Mn: 1.30%, Si: 0.30%, V: 0.04%, Nb: 0.030%, Ce: 0.013%, Als: 0.010%, S: 0.003%, P: 0.015%, [H]: 1.8ppm, and the remainder is Fe and unavoidable impurities.

[0023] The final temperature of converter smelting is 1640℃, and the temperature of refined molten steel is 1585℃; the casting temperature of continuous casting process is 1553℃, the casting speed is 0.85m / min, the secondary cooling speed is 105℃ / min, and the light reduction is 5mm. The rectangular billet obtained by continuous casting is heated to 1180℃ in the heating furnace and then rough rolled. The starting rolling temperature of the rough rolling mill is 1070℃, the inlet temperature of the first finishing mill (F1) is 975℃, and the inlet temperature of the second finishing mill (F2) is 870℃. A total of 12 passes are rolled, the compression ratio is 5.9, and the cooling rate after rolling is 7℃ / s.

[0024] The room temperature structure of the low temperature resistant hot rolled angle steel is uniform and fine ferrite + degenerate pearlite structure, and the average grain size is 8μm. The tensile strength R m =580MPa, yield strength R el =470MPa, elongation A=25%, core impact toughness A kv =58J (test temperature -40℃). Example 3

[0025] According to the chemical composition of the V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel of the present invention, smelting and casting into a rectangular billet are carried out, and the chemical composition thereof is as follows in weight percentage: C: 0.18%, Mn: 1.25%, Si: 0.35%, V: 0.043%, Nb: 0.025%, Ce: 0.010%, Als: 0.018%, S: 0.007%, P: 0.010%, [H]: 1.5ppm, and the remainder is Fe and unavoidable impurities.

[0026] The final temperature of converter smelting is 1670℃, and the temperature of refined steel out of the station is 1610℃; the casting temperature of the continuous casting process is 1560℃, the billet pulling speed is 0.80m / min, the secondary cooling rate is 120℃ / min, and the light reduction is 8mm. The rectangular billet obtained by continuous casting is heated to 1220℃ in a heating furnace and then rough rolled. The starting rolling temperature of the rough rolling mill is 1090℃, the inlet temperature of the first finishing mill (F1) is 980℃, and the inlet temperature of the second finishing mill (F2) is 880℃. A total of 15 passes are rolled, the compression ratio is 6.3, and the cooling rate after rolling is 12℃ / s.

[0027] The room temperature structure of the low temperature resistant hot rolled angle steel is uniform and fine ferrite + degenerate pearlite structure, and the average grain size is 6μm. The tensile strength R m =650MPa, yield strength R el =515MPa, elongation A=32%, core impact toughness A kv =86J (test temperature -40℃). Example 4

[0028] According to the chemical composition of the V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel of the present invention, smelting and casting into a rectangular billet are carried out, and the chemical composition thereof is as follows in weight percentage: C: 0.17%, Mn: 1.40%, Si: 0.50%, V: 0.045%, Nb: 0.015%, Ce: 0.017%, Als: 0.016%, S: 0.004%, P: 0.013%, [H]: 1.7ppm, and the remainder is Fe and unavoidable impurities.

[0029] The final temperature of converter smelting is 1650℃, and the temperature of refined steel out of the station is 1590℃; the casting temperature of the continuous casting process is 1557℃, the billet pulling speed is 0.87m / min, the secondary cooling rate is 110℃ / min, and the light reduction is 7mm. The rectangular billet obtained by continuous casting is heated to 1210℃ in a heating furnace and then rough rolled. The starting rolling temperature of the rough rolling mill is 1080℃, the inlet temperature of the first finishing mill (F1) is 976℃, and the inlet temperature of the second finishing mill (F2) is 877℃. A total of 13 passes are rolled, the compression ratio is 6.1, and the cooling rate after rolling is 10℃ / s.

[0030] The room temperature structure of the low temperature resistant hot rolled angle steel is uniform and fine ferrite + degenerate pearlite structure, and the average grain size is 7.5μm. The tensile strength R m =595MPa, yield strength R el =475MPa, elongation A=26%, core impact toughness A kv =65J (test temperature -40℃). Example 5

[0031] According to the chemical composition of the V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel of the present invention, smelting and casting into a rectangular billet are carried out, and the chemical composition thereof is as follows in weight percentage: C: 0.16%, Mn: 1.37%, Si: 0.40%, V: 0.047%, Nb: 0.027%, Ce: 0.015%, Als: 0.014%, S: 0.006%, P: 0.009%, [H]: 1.4ppm, and the remainder is Fe and unavoidable impurities.

[0032] The final temperature of converter smelting is 1655℃, and the temperature of refined steel out of the station is 1600℃; the casting temperature of the continuous casting process is 1552℃, the billet pulling speed is 0.75m / min, the secondary cooling rate is 112℃ / min, and the light reduction is 6mm. The rectangular billet obtained by continuous casting is heated to 1190℃ in a heating furnace and then rough rolled. The starting rolling temperature of the rough rolling mill is 1085℃, the inlet temperature of the first finishing mill (F1) is 974℃, and the inlet temperature of the second finishing mill (F2) is 873℃. A total of 11 passes are rolled, the compression ratio is 5.8, and the cooling rate after rolling is 9℃ / s.

[0033] The room temperature structure of the low temperature resistant hot rolled angle steel is uniform and fine ferrite + degenerate pearlite structure, and the average grain size is 7μm. The tensile strength R m =625MPa, yield strength R el =490MPa, elongation A=27.5%, core impact toughness A kv =72J (test temperature -40℃). Example 6

[0034] According to the chemical composition of the V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel of the present invention, smelting and casting into a rectangular billet are carried out, and the chemical composition thereof is as follows in weight percentage: C: 0.17%, Mn: 1.35%, Si: 0.29%, V: 0.049%, Nb: 0.019%, Ce: 0.014%, Als: 0.017%, S: 0.005%, P: 0.011%, [H]: 1.0 ppm, and the remainder is Fe and unavoidable impurities.

[0035] The final temperature of converter smelting is 1648℃, and the temperature of refined molten steel is 1595℃; the casting temperature of continuous casting process is 1553℃, the casting speed is 0.82m / min, the secondary cooling speed is 114℃ / min, and the light reduction is 7mm. The rectangular billet obtained by continuous casting is heated to 1205℃ in the heating furnace and then rough rolled. The starting rolling temperature of the rough rolling mill is 1078℃, the inlet temperature of the first finishing mill (F1) is 972℃, and the inlet temperature of the second finishing mill (F2) is 871℃. A total of 14 passes are rolled, the compression ratio is 6.2, and the cooling rate after rolling is 11℃ / s.

[0036] The room temperature structure of the low temperature resistant hot rolled angle steel is uniform and fine ferrite + degenerate pearlite structure, and the average grain size is 6.3μm. The tensile strength R m =655MPa, yield strength R el =510MPa, elongation A=30.5%, core impact toughness A kv =82J (test temperature -40℃). Comparative Example 1

[0037] This comparative example does not use soft reduction in the continuous casting process, and rare earth Ce is not added to the steel. Its chemical composition is as follows in terms of weight percentage: C: 0.17%, Mn: 1.41%, Si: 0.31%, V: 0.045%, Nb: 0.019%, Als: 0.017%, S: 0.007%, P: 0.012%, [H]: 3.4ppm, and the balance is Fe and unavoidable impurities.

[0038] The final temperature of converter smelting is 1650℃, and the temperature of refined molten steel is 1593℃; the casting temperature of continuous casting process is 1555℃, the casting speed is 0.83m / min, and the secondary cooling rate is 113℃ / min. The rectangular billet obtained by continuous casting is heated to 1206℃ in the heating furnace and then kept warm for rough rolling. The starting rolling temperature of the rough rolling mill is 1080℃, the inlet temperature of the first finishing mill (F1) is 973℃, and the inlet temperature of the second finishing mill (F2) is 874℃. A total of 14 rolling passes are performed, the compression ratio is 6.2, and the cooling rate after rolling is 11℃ / s.

[0039] In this comparative example, soft reduction was not used in the continuous casting process of the experimental steel, which was prone to dendrite growth and caused element segregation, resulting in a serious banded structure in the angle steel product (see Figure 3 ); In addition, no rare earth Ce was added during the smelting process, resulting in the presence of irregular triangular, rectangular and other morphological inclusions in the steel, and the size was large (see Figure 4 ), the above is the main reason for the coarse grains and reduced impact toughness of the experimental steel in Comparative Example 1. The room temperature structure of the hot-rolled angle steel in this comparative example is ferrite + pearlite structure, and the average grain size is 13.5μm. The tensile strength R of this comparative product was tested. m =585MPa, yield strength R el =475MPa, elongation A=19%, core impact toughness A kv =43J (test temperature -40℃). Comparative Example 2

[0040] 0.055% Nb is added to the steel in this comparative example, and the chemical composition of other elements is as follows in weight percentage: C: 0.16%, Mn: 1.34%, Si: 0.32%, V: 0.040%, Nb: 0.055%, Ce: 0.012%, Als: 0.018%, S: 0.006%, P: 0.011%, [H]: 1.7ppm, and the balance is Fe and unavoidable impurities.

[0041] The final temperature of converter smelting is 1655℃, and the temperature of refined steel out of the station is 1600℃; the casting temperature of the continuous casting process is 1558℃, the billet pulling speed is 0.85m / min, and the secondary cooling rate is 110℃ / min. The rectangular billet obtained by continuous casting is heated to 1210℃ in a heating furnace and then rough rolled. The starting rolling temperature of the rough rolling mill is 1085℃, the inlet temperature of the first finishing mill (F1) is 976℃, and the inlet temperature of the second finishing mill (F2) is 876℃. A total of 13 rolling passes are performed, the compression ratio is 6.1, and the cooling rate after rolling is 10℃ / s.

[0042] The microalloying element Nb content in the experimental steel of this comparative example 2 is relatively high. On the one hand, it is easy to produce aggregated and distributed undissolved niobium, which increases the brittleness of the grain boundaries; on the other hand, it weakens the fine grain strengthening and dispersion precipitation strengthening effects of niobium, resulting in a certain degree of increase in the grain size (see Figure 5 and Figure 6 ), which will also reduce the plasticity and toughness of the steel. The room temperature structure of the hot-rolled angle steel in this comparative example is ferrite + pearlite structure, and the average grain size is 10.5μm. The tensile strength R of the tested product m =620MPa, yield strength R el =495MPa, elongation A=22.5%, core impact toughness A kv =50J (test temperature -40℃). Comparative Example 3

[0043] The chemical composition of the steel in this comparative experiment is as follows in weight percentage: C: 0.17%, Mn: 1.35%, Si: 0.39%, V: 0.046%, Nb: 0.026%, Ce: 0.015%, Als: 0.014%, S: 0.006%, P: 0.014%, [H]: 1.5ppm, and the balance is Fe and unavoidable impurities.

[0044] The final temperature of converter smelting is 1660℃, and the temperature of refined steel out of the station is 1605℃; the casting temperature of the continuous casting process is 1558℃, the billet pulling speed is 0.83m / min, the secondary cooling rate is 116℃ / min, and the light reduction is 6mm. The rectangular billet obtained by continuous casting is heated to 1250℃ in a heating furnace and then rough rolled. The starting rolling temperature of the rough rolling mill is 1110℃, the inlet temperature of the first finishing mill (F1) is 1030℃, and the inlet temperature of the second finishing mill (F2) is 953℃. A total of 11 passes are rolled, the compression ratio is 5.8, and the cooling rate after rolling is 9℃ / s.

[0045] The heating temperature, the start rolling temperature of the roughing mill, and the inlet temperatures of the first and second finishing mills of the experimental steel of this comparative example 3 are all higher than those of the steel of the present invention, resulting in the inability to perform non-recrystallization rolling in the final rolling, which weakens the grain refinement effect. Although a certain strength value is maintained, the plasticity and toughness are reduced, which does not meet the requirements of the present invention. The room temperature structure of the hot-rolled angle steel of this comparative example is ferrite + pearlite structure, and the average grain size is 12.2μm (see Figure 7 ). The tensile strength of the tested product is R m =600MPa, yield strength R el =485MPa, elongation A=20.5%, core impact toughness A kv =45J (test temperature -40℃).

[0046] In summary, this embodiment has ultra-high strength and good plasticity matching, which is achieved due to the combined effects of the ferrite and pearlite structures being uniform and fine, the absence of banded structures in the structures, and the inclusions being mostly spherical or ellipsoidal and having small sizes.

[0047] Finally, it should be noted that the above are only preferred embodiments of the present invention. Of course, those skilled in the art can make changes and modifications to the present invention. If these modifications and variations fall within the scope of the claims of the present invention and their equivalent technologies, they should be considered to be within the scope of protection of the present invention.

Claims

1. A V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel, characterized in that: The chemical composition, by weight percentage, includes: C: 0.15-0.18%, Mn: 1.25-1.45%, Si: 0.25-0.50%, V: 0.04-0.05%, Nb: 0.015-0.030%, P: ≤0.015%, S: ≤0.007%, [H] ≤1.8ppm, Ce: 0.010-0.017%, Als: 0.010-0.018%, and the balance Fe and unavoidable impurities.

2. The V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel according to claim 1, characterized in that The low temperature resistant angle steel structure is uniform and fine ferrite + degenerate pearlite structure, and the average grain size is 6 to 8μm.

3. The V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel according to claim 1, characterized in that: The technical indicators of mechanical properties of low-temperature resistant angle steel are: tensile strength: Rm≥580MPa, yield strength: Rel≥470MPa, elongation: A≥25%, -40℃ angle steel core impact toughness: Akv≥58J.

4. A method for producing a V-Nb-Ce composite microalloyed large-size low-temperature resistant angle steel according to any one of claims 1 to 3, comprising the steps of converter smelting → refining → continuous casting → heating in a heating furnace → rough rolling → finishing rolling → cooling, characterized in that: The process parameters of smelting and continuous casting are controlled as follows: the end temperature of converter smelting is controlled at 1630-1670°C, the temperature of refined molten steel out of the station is controlled at 1570-1610°C; the casting temperature of the continuous casting process is controlled at 1550-1560°C, the billet drawing speed is 0.75-0.9m / min, the secondary cooling speed is controlled at 100-120°C / min, the soft reduction in the continuous casting process is controlled at 5-8mm, and the billet cross-sectional size is 320×460mm; The rolling and cooling process parameters are controlled as follows: the ingot obtained by continuous casting is heated to 1180-1220°C in a heating furnace and then subjected to rough rolling. The starting rolling temperature of the rough rolling mill is controlled at 1070-1090°C, the inlet temperature of the first finishing mill is controlled at 970-980°C, and the inlet temperature of the second finishing mill is controlled at 870-880°C. A total of 10-15 rolling passes are performed, the compression ratio is greater than 5.5, and the water cooling rate after rolling is controlled at 7-12°C / s.

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