A Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C and a production method thereof

Abstract

The present invention discloses a Q355-grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C and a production method thereof. The Q355-grade hot-rolled H-shaped steel comprises the following chemical components: C, Si, Mn, Nb, V, Ni, and Fe, wherein: 0.020%≤Nb+V≤0.06%; Nb+V+Ni≤0.30%. The present invention adopts Ni, Nb, and V alloy elements, obtains a refined grain structure through reasonable continuous casting and rolling processes, and cooperates with a universal rolling controlled rolling process to obtain a hot-rolled H-shaped steel product with excellent longitudinal and transverse impact resistance, and further controls various factors affecting the low-temperature toughness of the hot-rolled H-shaped steel in formula a. The hot-rolled H-shaped steel product thus produced has a low-temperature impact temperature of up to -100°C and excellent transverse impact toughness.

Description

Technical Field

[0001] The invention belongs to the technical field of H-shaped steel, and particularly relates to a Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100 DEG C and a production method thereof. Background Art

[0002] At present, the application field of H-shaped steel is constantly expanding, and has expanded from the steel structure industry to the machinery industry, special railway vehicles, offshore oil platforms and other fields. The hot-rolled H-shaped steel used in projects such as extremely cold regions and offshore oil platforms has high requirements for mechanical properties, especially low-temperature impact requirements.

[0003] In the production process of H-beam, low-temperature impact control has always been a difficult point, and there are many influencing factors. The main reasons are: 1. Composition design and the purity of molten steel. If there are too many impurities such as S and P remaining in the steel, it will lead to poor low-temperature toughness; the second reason is that for thick-gauge H-beam, the temperature of the rolled piece is high during the rolling process. While ensuring the strength, it is necessary to control the cooling. Uneven cooling of thick gauges will lead to unstable low-temperature toughness. At present, the hot-rolled H-beam products disclosed in the prior art can achieve a minimum low-temperature impact toughness of -50°C, but this type of hot-rolled H-beam is still difficult to meet higher requirements. Therefore, there is an urgent need to find a method for producing hot-rolled H-beams with higher requirements for low-temperature impact toughness to meet the application needs of some special fields.

[0004] Chinese patent CN112359289A discloses an ultra-thick Q355-grade hot-rolled H-beam with excellent low-temperature toughness and a production method. This patent primarily controls the H-beam's composition, specifically containing C, Si, Mn, P, S, Nb, Al, Ti, and N. The flange thickness t is 80 to 150 mm, with a CEV ≤ 0.42% and a Pcm ≤ 0.25%. The invention proposes a low-cost composition design scheme using Nb and Al microalloying, coupled with a rational continuous casting and rolling process, to regulate the distribution of AlN and NbC in the continuous casting billet and H-beam. This improves the microstructure of the billet and refines the H-beam structure, resulting in excellent mechanical properties and economic benefits. However, this patent utilizes a Nb and Ti alloy system, adding a large amount of alloy, resulting in high production costs and unfavorable product economics.

[0005] Chinese patent CN112410667A discloses a low-cost, heavy Q355E hot-rolled H-beam and its manufacturing method. This patent primarily utilizes rationally controlled H-beam composition, specifically containing C, Si, Mn, Nb, Ti, and N. During the production process, the total number of universal mill finish rolling passes is controlled to 9 to 13, with the rolling deformation in the fifth to third passes of the finish rolling process controlled to 7% to 8%, and the rolling deformation temperature to 880°C to 930°C. This invention targets heavy Q335E hot-rolled H-beam with flange thicknesses of 50mm to 80mm. It proposes a low-cost composition design without the addition of Ni and V alloying elements, combined with controlled austenite grain size after rough rolling, to produce a hot-rolled H-beam with high strength and low-temperature toughness. However, this patent utilizes a Nb and Ti alloy system, which adds a large amount of alloys, resulting in high production costs and unfavorable product economics.

[0006] Chinese patent CN112030070A discloses a 420MPa hot-rolled H-beam with excellent low-temperature toughness and its production method. This patent primarily utilizes controlled rolling and cooling processes to develop a 420MPa hot-rolled H-beam with excellent overall performance by rationally controlling the H-beam's composition, specifically including C, Si, Mn, P, S, Ni, V, and N. However, this patent primarily targets high-strength steel, and its low-temperature toughness only reaches -20°C.

[0007] Chinese patent CN107227430A discloses a hot-rolled H-beam with excellent low-temperature toughness at -60°C and a production method thereof. The steel contains the following elements by weight: carbon 0.07-0.15%, silicon 0.15-0.35%, manganese 1.00-1.45%, phosphorus ≤ 0.020%, sulfur ≤ 0.015%, vanadium 0.020-0.060%, niobium 0.010-0.060%, nickel 0.10-0.25%, aluminum ≥ 0.015%, with the balance being iron and unavoidable impurities. Compared to existing technologies, the H-beam produced by this invention exhibits an extremely low ductile-brittle transition temperature and excellent low-temperature toughness. It also reduces welding steps, post-weld visual inspection, and weld flaw detection, reducing production costs by over 500 yuan per ton of steel. However, this patent utilizes a Nb and Ni alloy system, resulting in a low-temperature toughness rating of only -60°C.

[0008] Chinese patent CN107868910A discloses a low-temperature-resistant and tough H-beam and its production process. By rationally controlling the H-beam's composition, specifically including C, Si, Mn, P, S, and Nb, and combining this with process rolling control, the H-beam exhibits an extremely low ductile-brittle transition temperature and excellent low-temperature impact resistance in cold regions and low-temperature environments at temperatures of -40°C or below. However, this patent uses a Nb alloy, which has a low-temperature toughness of -40°C. Summary of the Invention

[0009] In order to solve the above technical problems, the present invention provides a Q355 grade hot-rolled H-beam with good low-temperature toughness at -100°C and a production method thereof. The hot-rolled H-beam product produced using the method of the present invention has a low-temperature impact temperature of -100°C and excellent transverse impact toughness.

[0010] The technical solution adopted by the present invention is as follows:

[0011] The invention discloses a Q355-grade hot-rolled H-shaped steel with good low-temperature toughness at -100 DEG C. The Q355-grade hot-rolled H-shaped steel comprises the following chemical components in weight percentage: C: 0.07-0.12%, Si: 0.10-0.30%, Mn: 1.15-1.55%, P≤0.020%, S≤0.025%, Nb: 0.005-0.02%, V: 0.01-0.05%, Ni: 0.05-0.25%, and the remainder is Fe and impurity elements, wherein: 0.020%≤Nb+V≤0.06%; Nb+V+Ni≤0.30%.

[0012] Furthermore,

[0013] a=-174.87×C+12.32×Si+12.99×Mn-304.07×P-86.75×S+160.07×Nb+22.09×V+18.53×Ni+2.1×k1-0.13×k2+0.003×k3+0.52×k4+113.9, a value ≥ 100; where k1 is

[0014] The roughing pass reduction rate in the temperature range of 1100-1200℃, k2 is the rolling temperature of the third finishing pass, k3 is the finishing pass reduction rate in the temperature range of 900-950℃, and k4 is the finishing pass reduction rate in the temperature range of 750-850℃. When calculating the a value, ignore the units or percentages of each parameter and directly take the numerical value for calculation.

[0015] The metallographic structure of the Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C is ferrite+pearlite+bainite, and the grain size grade is 11.

[0016] The Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C has an average longitudinal impact energy of greater than 200J and an average transverse impact energy of greater than 150J at -40 to -80°C; the average longitudinal impact energy at -100°C is greater than 100J and the average transverse impact energy is greater than 50J.

[0017] The present invention also provides a production method of the Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C, which comprises the following steps: smelting → refining → continuous casting → heating in a heating furnace → descaling → rough rolling → finishing rolling → air cooling.

[0018] During the heating step in the heating furnace, the atmosphere in the furnace is a weakly reducing atmosphere, and the furnace is heated to 1200-1250°C for 90-130 minutes to ensure that the alloy elements are fully dissolved, while avoiding overburning, oxidation and burning, and excessive coarsening of austenite grains, and avoiding bending and deformation of the steel billet in the heating furnace.

[0019] In the descaling step, the descaling water pressure is 16-25 MPa and the roller speed is 1-3 m / s to ensure that the iron oxide scale on the surface of the blank is completely removed.

[0020] In the rough rolling step, the starting rolling temperature is controlled at 1000-1200°C, the finishing rolling temperature is greater than 980°C, the web pass reduction rate is controlled at 50-60%, and the strain rate is 4-6s -1 This stage is within the austenite recrystallization temperature range. The pass reduction rate and strain rate within this temperature range are designed to trigger dynamic recrystallization of austenite within this temperature range, so that the percentage of austenite recrystallization in the rough rolling stage reaches more than 50%. Through large rolling deformation and repeated recrystallization of austenite, the austenite grains are continuously refined, so that the grain size of the final product reaches level 11.0 or above, meeting the final comprehensive mechanical performance requirements of the product.

[0021] In the finishing rolling step, the starting rolling temperature of the universal rolling mill is ≥950°C, and the final rolling temperature is controlled at ≥750°C. The universal rolling mill performs temperature-controlled rolling in the third pass, and the temperature control temperature is 910-950°C. At this stage, the austenite is further dynamically recrystallized and the austenite grains are refined. If the rolling temperature is too high, the grains will be coarse, which will affect the low-temperature impact performance. If the temperature is low, the rolling load of the finishing mill will be large, which will affect the overall dimensions.

[0022] In the finishing rolling step, the temperature range is 900-950°C, the pass reduction rate is controlled at 10-25%, and the strain rate is 3-5s -1 In the temperature range of 750-850℃, the pass reduction rate is controlled at 15-35%, and the strain rate is 5-7s -1 The remaining deformation of the billet is completed in this stage. Since the appropriate Nb element is added to this product to increase the non-recrystallization temperature of austenite, the starting rolling temperature of the universal rolling mill during H-beam rolling is ≥950℃, and the final rolling temperature is controlled at ≥750℃. In order to meet the mechanical property requirements of low-temperature steel, the finishing rolling stage is divided into two stages. In the first stage, the pass reduction rate is controlled at 10-25% in the temperature range of 900-950℃, and the strain rate is 3-5s -1 In this stage, the austenite is further dynamically recrystallized and the austenite grains are refined. In the second stage, the temperature range is 750-850℃, the pass reduction rate is controlled at 15-35%, and the strain rate is 5-7s -1In this stage, the austenite is within the non-recrystallization temperature range. Austenite recrystallization does not occur in this temperature range. The accumulated deformation formed by low temperature and high pressure can elongate the original austenite grains, forming a large number of deformation bands and dislocations within the grains. The increase in grain boundary area increases the nucleation density of austenite, further refines the grain size, increases the strength of the steel, and improves the toughness of the steel. At the same time, the elongated austenite and the large number of deformation bands and dislocations also provide a large number of landing points for the precipitation of carbonitride second phase particles. The stored energy formed by low temperature and high pressure also provides sufficient kinetic energy for the precipitation of carbonitride second phase particles. Nb and V, as strong carbide-forming elements, form a large number of VC and NbC dispersoids distributed in the matrix at this stage, further improving the strength and toughness of the steel.

[0023] The flange thickness of the Q355 grade hot-rolled H-shaped steel provided by the present invention, which has good low-temperature toughness at -100°C, is ≤40mm.

[0024] The Q355-grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C provided by the present invention adopts Ni, Nb, and V alloy elements, obtains a refined grain structure through reasonable continuous casting and rolling processes in conjunction with a universal rolling controlled rolling process, and obtains a hot-rolled H-shaped steel product with excellent longitudinal and transverse impact strength. In addition, various factors affecting the low-temperature toughness of the hot-rolled H-shaped steel are further controlled in formula a, where a=-174.87×C+12.32×Si+12.99×Mn-304.07×P-86.75×S+160.07×Nb+22.09×V+18.53×Ni+2.1×k1-0.13×k2+0.003×k3+0.52×k4+113.9. Only in this way can the Q355-grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C be obtained.

[0025] The effects of the factors in the above formula a on low-temperature toughness are as follows:

[0026] In the solid solution, as iron carbide Fe3C, carbon is the primary controlling element for strength and hardness. As the carbon content in steel increases, the strength, hardness and hardenability of the steel can be improved, but the plasticity and toughness will be reduced; silicon and manganese elements are mainly deoxidation and desulfurization, which improves the tensile strength and is beneficial to the low-temperature toughness of the steel; sulfur and phosphorus elements will form a brittle body in the steel. Sulfur has the most harmful effect on steel by forming brittle sulfide FeS, which will reduce the low-temperature toughness of the steel. Phosphorus in the solution has an important hardening effect. Since phosphorus increases brittleness, it increases non-metallic inclusions in the steel, which reduces the strength and plasticity of the steel; vanadium is a very important grain refining element, which inhibits the growth of austenite. As little as 0.1% vanadium will It effectively inhibits grain growth during the hardening process, has a strong solid solution strengthening effect when dissolved in ferrite, and has a grain refinement effect, which is beneficial to low-temperature impact toughness; nickel strengthens ferrite by forming a simple substitutional solid solution. As an austenite-forming element, nickel stabilizes austenite by increasing the A4 temperature and reducing the A3 temperature, which is beneficial to low-temperature toughness; niobium can improve strength and toughness through precipitation hardening and further refinement of ferrite grains; controlling the pass reduction rate can effectively increase the degree of grain crushing, refine the grains, and is beneficial to low-temperature toughness; the universal third pass rolling temperature is to roll at the austenite dynamic recrystallization temperature to refine the grains. The lower the temperature, the better the refinement effect. This application further ensures the low-temperature toughness of hot-rolled H-beam by comprehensively controlling the various factors that affect the low-temperature toughness of hot-rolled H-beam in formula a.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] Compared with the current hot-rolled H-shaped steel with low-temperature impact toughness of -60℃, the low-temperature toughness of the Q355 grade hot-rolled H-shaped steel provided by the present invention can reach -100℃, and the longitudinal impact performance is that the average longitudinal impact energy at -100℃ is greater than 100J, the average transverse impact energy is greater than 50J, and the transverse impact toughness is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the metallographic structure diagram of the hot-rolled H-beam produced in Example 1;

[0030] Figure 2 This is the grain size diagram of the hot-rolled H-beam produced in Example 1;

[0031] Figure 3 This is the metallographic structure diagram of the hot-rolled H-beam produced in Example 2;

[0032] Figure 4 This is the grain size diagram of the hot-rolled H-beam produced in Example 2. DETAILED DESCRIPTION

[0033] The present invention provides a Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C. The Q355 grade hot-rolled H-shaped steel comprises the following chemical components in weight percentage: C: 0.07-0.12%, Si: 0.10-0.30%, Mn: 1.15-1.55%, P≤0.020%, S≤0.025%, Nb: 0.005-0.02%, V: 0.01-0.05%, Ni: 0.05-0.25%, and the remainder is Fe and impurity elements.

[0034] in:

[0035] 0.020%≤Nb+V≤0.06%;

[0036] Nb+V+Ni≤0.30%.

[0037] Furthermore,

[0038] a=55.22×C-31.59×Si-5.54×Mn-62.4×P+153.61×S+294.89×Nb-85.39×V+18.53×Ni+2.1×k1-0.11×k2-0.003×k3-0.52×k4+130.21, a value ≥ 100; wherein k1 is the roughing pass reduction in the temperature range of 1100-1200°C, k2 is the third finishing pass rolling temperature, k3 is the finishing pass reduction in the temperature range of 900-950°C, and k4 is the finishing pass reduction in the temperature range of 750-850°C; when calculating the a value, ignore the units or percentages of each parameter and directly take the numerical value for calculation.

[0039] The production method of the Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C comprises the following steps: smelting→refining→continuous casting→heating in a heating furnace→descaling→rough rolling→finishing rolling→air cooling.

[0040] In the heating step of the heating furnace, the atmosphere in the furnace is a weak reducing atmosphere, and the temperature is heated to 1200-1250° C. in the heating furnace, and the entire heating time is 90-130 minutes.

[0041] In the descaling step, the descaling water pressure is 16-25 MPa and the roller speed is 1-3 m / s.

[0042] In the rough rolling step, the starting rolling temperature is controlled at 1000-1200°C, the finishing rolling temperature is greater than 980°C, the web pass reduction rate is controlled at 50-60%, and the strain rate is 4-6s -1 .

[0043] In the finishing rolling step, the starting rolling temperature of the universal rolling mill is ≥950°C, and the final rolling temperature is controlled at ≥750°C, wherein the third pass of the universal rolling mill is temperature-controlled rolling at a temperature of 910-950°C;

[0044] Furthermore, in the finishing rolling step, in the temperature range of 900-950°C, the pass reduction rate is controlled at 10-25%, and the strain rate is 3-5s-1; in the temperature range of 750-850°C, the pass reduction rate is controlled at 15-35%, and the strain rate is 5-7s-1. -1 .

[0045] The present invention is described in detail below with reference to the embodiments.

[0046] Example 1

[0047] A Q355 grade hot-rolled H-beam with good low-temperature toughness at -100°C, the chemical composition and weight percentage of which are shown in Table 1.

[0048] The method for producing Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C comprises the following steps:

[0049] 1) Hot metal pretreatment: Hot metal pretreatment process time ≤ 30 minutes, argon blowing station argon front temperature 1550 ~ 1590 ℃, argon blowing station time ≤ 10 minutes;

[0050] 2) LF refining: LF refining process time: 60 to 90 minutes, smelting in a converter, argon blowing to uniform composition, the chemical composition of the molten steel after LF refining meets the requirements of the present invention for the chemical composition of the molten steel;

[0051] 3) Continuous casting: The beam blank continuous casting machine casts beam blanks with a cross-section of 750×450×120mm, and the H-beam rolling mill rolls the national standard H500×200×10×16 specifications;

[0052] 4) Heating in the heating furnace: The temperature of the heating section of the heating furnace is 1235-1240°C, the temperature of the soaking section is 1227-1231°C, and the heating time is 98 minutes;

[0053] 5) Descaling: Descaling water pressure is 18MPa, roller speed is 2m / s;

[0054] 6) Hot rolling: The slab mill was reciprocatingly rolled for 13 passes, with the flange thickness reduced by 20% and the web thickness reduced by 52%. The universal rolling mill performed temperature-controlled rolling in the third pass at a controlled temperature of 930°. The universal rolling mill was then rolled for 7 passes. The product was air-cooled after rolling. The specific process control of the hot rolling process is shown in Table 2.

[0055] The H-shaped steel product produced in this embodiment has good appearance, size, surface quality, good mechanical properties, and high low-temperature impact resistance at -100°C. The performance data are shown in Table 3.

[0056] Example 2

[0057] A Q355 grade hot-rolled H-beam with good low-temperature toughness at -100°C, the chemical composition and weight percentage of which are shown in Table 1.

[0058] The method for producing Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C comprises the following steps:

[0059] 1) Hot metal pretreatment: Hot metal pretreatment process time ≤ 32 minutes, argon blowing station argon front temperature 1560 ~ 1600 ℃, argon blowing station time ≤ 10 minutes;

[0060] 2) LF refining: LF refining process time: 60 to 90 minutes, after converter smelting, argon blowing to homogenize the composition, LF refining, the chemical composition of the molten steel meets the requirements of the present invention for the chemical composition of the molten steel;

[0061] 3) Continuous casting: The beam blank continuous casting machine casts beam blanks with a cross-section of 750×450×120mm, and the H-beam rolling mill rolls the European standard 305×305×223 specifications;

[0062] 4) Heating in the heating furnace: The temperature of the heating section of the heating furnace is 1239-1244°C, the temperature of the soaking section is 1232-1236°C, and the heating time is 118 minutes;

[0063] 5) Descaling: Descaling water pressure 17MPa, roller speed 1.5m / s;

[0064] 6) Hot rolling: The slab mill was used for 15 reciprocating passes, with the flange thickness reduced by 25% and the web thickness reduced by 60%. The universal mill was used for the third temperature-controlled rolling at 910°C. The universal mill was used for 7 passes. The product was air-cooled after rolling. The specific process control of the hot rolling process is shown in Table 2.

[0065] The H-shaped steel product produced in this embodiment has good appearance, size, surface quality, good mechanical properties, and high low-temperature impact resistance at -100°C. The performance data are shown in Table 3.

[0066] Example 3

[0067] A Q355 grade hot-rolled H-beam with good low-temperature toughness at -100°C, the chemical composition and weight percentage of which are shown in Table 1.

[0068] The method for producing Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C comprises the following steps:

[0069] 1) Hot metal pretreatment: Hot metal pretreatment process time ≤ 28 minutes, argon blowing station argon front temperature 1540 ~ 1570 ℃, argon blowing station time ≤ 8 minutes;

[0070] 2) LF refining: LF refining process time: 50 to 80 minutes, after converter smelting, argon blowing to homogenize the composition, LF refining, the chemical composition of the molten steel meets the requirements of the present invention for the chemical composition of the molten steel;

[0071] 3) Continuous casting: The beam blank continuous casting machine casts beam blanks with a cross-section of 500×300×120mm, and the H-beam rolling mill rolls the national standard H400×200×8×13 specifications;

[0072] 4) Heating in the heating furnace: The temperature of the heating section of the heating furnace is 1211-1225°C, the temperature of the soaking section is 1209-1215°C, and the heating time is 90 minutes;

[0073] 5) Descaling: Descaling water pressure 18MPa, roller speed 2m / s;

[0074] 6) Hot rolling: The slab mill was used for 9 reciprocating rolling passes, with the flange thickness reduced by 22% and the web thickness reduced by 55%. The universal rolling mill was used for the third temperature-controlled rolling pass at 950°C. The universal rolling mill was used for 5 passes. The product was air-cooled after rolling. The specific process control of the hot rolling process is shown in Table 2.

[0075] The H-shaped steel product produced in this embodiment has good appearance, size, surface quality, good mechanical properties, and high low-temperature impact resistance at -100°C. The performance data are shown in Table 3.

[0076] Example 4

[0077] A Q355 grade hot-rolled H-beam with good low-temperature toughness at -100°C, the chemical composition and weight percentage of which are shown in Table 1.

[0078] The method for producing Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C comprises the following steps:

[0079] 1) Hot metal pretreatment: Hot metal pretreatment process time ≤ 31 minutes, argon blowing station argon front temperature 1540 ~ 1580 ℃, argon blowing station time ≤ 10 minutes;

[0080] 2) LF refining: LF refining process time: 60 to 90 minutes, after converter smelting, argon blowing to homogenize the composition, LF refining, the chemical composition of the molten steel meets the requirements of the present invention for the chemical composition of the molten steel;

[0081] 3) Continuous casting: The beam blank continuous casting machine casts beam blanks with a cross section of 750×450×120mm, and the H-beam rolling mill rolls the national standard H700×300×13×24.

[0082] 4) Heating in the heating furnace: The temperature of the heating section of the heating furnace is 1240-1247°C, the temperature of the soaking section is 1235-1242°C, and the heating time is 110 minutes;

[0083] 5) Descaling: Descaling water pressure 19MPa, roller speed 3m / s;

[0084] 6) Hot rolling: The slab mill was used for 13 reciprocating passes, with the flange thickness reduced by 22% and the web thickness reduced by 58%. The universal rolling mill performed the third temperature-controlled rolling at 950°C. The universal rolling mill was used for 7 passes. The product was air-cooled after rolling. The specific process control of the hot rolling process is shown in Table 2.

[0085] The H-shaped steel product produced in this embodiment has good appearance, size, surface quality, good mechanical properties, and high low-temperature impact resistance at -100°C. The performance data are shown in Table 3.

[0086] Example 5

[0087] A Q355 grade hot-rolled H-beam with good low-temperature toughness at -100°C, the chemical composition and weight percentage of which are shown in Table 1.

[0088] The method for producing Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C comprises the following steps:

[0089] 1) Hot metal pretreatment: Hot metal pretreatment process time ≤ 30 minutes, argon blowing station argon front temperature 1560 ~ 1600 ℃, argon blowing station time ≤ 10 minutes;

[0090] 2) LF refining: LF refining process time: 60 to 90 minutes, after converter smelting, argon blowing to homogenize the composition, LF refining, the chemical composition of the molten steel meets the requirements of the present invention for the chemical composition of the molten steel;

[0091] 3) Continuous casting: The beam blank continuous casting machine casts beam blanks with a cross-section of 750×450×120mm, and the H-beam rolling mill rolls the European standard HEM300 specifications;

[0092] 4) Heating in the heating furnace: The temperature of the heating section of the heating furnace is 1235-1240°C, the temperature of the soaking section is 1227-1231°C, and the heating time is 108 minutes;

[0093] 5) Descaling: Descaling water pressure 20MPa, roller speed 2.5m / s;

[0094] 6) Hot rolling: The slab mill was reciprocatingly rolled for 13 passes, with the flange thickness reduced by 23% and the web thickness reduced by 56%. The universal rolling mill performed temperature-controlled rolling in the third pass at a controlled temperature of 920°. The universal rolling mill was then rolled for 7 passes. The product was air-cooled after rolling. The specific process control of the hot rolling process is shown in Table 2.

[0095] The H-shaped steel product produced in this embodiment has good appearance, size, surface quality, good mechanical properties, and high low-temperature impact resistance at -100°C. The performance data are shown in Table 3.

[0096] Example 6

[0097] A Q355 grade hot-rolled H-beam with good low-temperature toughness at -100°C, the chemical composition and weight percentage of which are shown in Table 1.

[0098] The method for producing Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C comprises the following steps:

[0099] 1) Hot metal pretreatment: Hot metal pretreatment process time ≤ 25 minutes, argon blowing station argon front temperature 1520 ~ 1550 ℃, argon blowing station time ≤ 8 minutes;

[0100] 2) LF refining: LF refining process time: 40 to 70 minutes, after converter smelting, argon blowing to homogenize the composition, LF refining, the chemical composition of the molten steel meets the requirements of the present invention for the chemical composition of the molten steel;

[0101] 3) Continuous casting: The beam blank continuous casting machine casts beam blanks with a cross-section of 430×300×90mm, and the H-beam rolling mill rolls the American standard W14*48 specifications;

[0102] 4) Heating in the heating furnace: The temperature of the heating section of the heating furnace is 1210-1224°C, the temperature of the soaking section is 1209-1215°C, and the heating time is 90 minutes;

[0103] 5) Descaling: Descaling water pressure 16MPa, roller speed 1.5m / s;

[0104] 6) Hot rolling: The slab mill was used for 9 reciprocating rolling passes, with the flange thickness reduced by 20% and the web thickness reduced by 50%. The universal rolling mill was used for the third temperature-controlled rolling pass at 950°C. The universal rolling mill was used for 5 passes. The product was air-cooled after rolling. The specific process control of the hot rolling process is shown in Table 2.

[0105] The H-shaped steel product produced in this embodiment has good appearance, size, surface quality, good mechanical properties, and high low-temperature impact resistance at -100°C. The performance data are shown in Table 3.

[0106] Comparative Example 1

[0107] A hot-rolled H-shaped steel, the chemical composition and weight percentage of which are shown in Table 1.

[0108] The production method of the hot-rolled H-beam comprises the following steps:

[0109] 1) Hot metal pretreatment: Hot metal pretreatment process time ≤ 30 minutes, argon blowing station argon front temperature 1550 ~ 1590 ℃, argon blowing station time ≤ 10 minutes;

[0110] 2) LF refining: LF refining process time: 60 to 90 minutes, after converter smelting, argon blowing to homogenize the composition, LF refining, the chemical composition of the molten steel meets the requirements of the present invention for the chemical composition of the molten steel;

[0111] 3) Continuous casting: The beam blank continuous casting machine casts beam blanks with a cross-section of 750×450×120mm, and the H-beam rolling mill rolls the national standard H500×200×10×16 specifications;

[0112] 4) Heating in the heating furnace: The temperature of the heating section of the heating furnace is 1235-1240°C, the temperature of the soaking section is 1227-1231°C, and the heating time is 98 minutes;

[0113] 5) Descaling: Descaling water pressure 18MPa, roller speed 2m / s;

[0114] 6) Hot rolling: The slab mill was reciprocatingly rolled for 13 passes, with the flange thickness reduced by 20% and the web thickness reduced by 52%. The universal rolling mill performed temperature-controlled rolling in the third pass at a controlled temperature of 990°. The universal rolling mill was then rolled for 7 passes. The product was air-cooled after rolling. The specific process control of the hot rolling process is shown in Table 2.

[0115] The H-shaped steel product produced in this comparative example has good appearance, size and surface quality, but poor low-temperature impact resistance at -100°C. The performance data are shown in Table 3.

[0116] Comparative Example 2

[0117] A hot-rolled H-shaped steel, the chemical composition and weight percentage of which are shown in Table 1.

[0118] The production method of the hot-rolled H-beam comprises the following steps:

[0119] 1) Hot metal pretreatment: Hot metal pretreatment process time ≤ 30 minutes, argon blowing station argon front temperature 1550 ~ 1590 ℃, argon blowing station time ≤ 10 minutes;

[0120] 2) LF refining: LF refining process time: 60 to 90 minutes, after converter smelting, argon blowing to homogenize the composition, LF refining, the chemical composition of the molten steel meets the requirements of the present invention for the chemical composition of the molten steel;

[0121] 3) Continuous casting: The beam blank continuous casting machine casts beam blanks with a cross-section of 750×450×120mm, and the H-beam rolling mill rolls the national standard H500×200×10×16 specifications;

[0122] 4) Heating in the heating furnace: The temperature of the heating section of the heating furnace is 1235-1240°C, the temperature of the soaking section is 1227-1231°C, and the heating time is 98 minutes;

[0123] 5) Descaling: Descaling water pressure 18MPa, roller speed 2m / s;

[0124] 6) Hot rolling: The slab mill was reciprocatingly rolled for 13 passes, with the flange thickness reduced by 20% and the web thickness reduced by 40%. The universal rolling mill performed temperature-controlled rolling in the third pass at a controlled temperature of 930°. The universal rolling mill was then rolled for 7 passes. The product was air-cooled after rolling. The specific process control of the hot rolling process is shown in Table 2.

[0125] The H-shaped steel product produced in this comparative example has good appearance, size and surface quality, but poor low-temperature impact resistance at -100°C. The performance data are shown in Table 3.

[0126] Comparative Example 3

[0127] A hot-rolled H-shaped steel, the chemical composition and weight percentage of which are shown in Table 1.

[0128] The production method of the hot-rolled H-beam comprises the following steps:

[0129] 1) Hot metal pretreatment: Hot metal pretreatment process time ≤ 30 minutes, argon blowing station argon front temperature 1550 ~ 1590 ℃, argon blowing station time ≤ 10 minutes;

[0130] 2) LF refining: LF refining process time: 60 to 90 minutes, after converter smelting, argon blowing to homogenize the composition, LF refining, the chemical composition of the molten steel meets the requirements of the present invention for the chemical composition of the molten steel;

[0131] 3) Continuous casting: The beam blank continuous casting machine casts beam blanks with a cross-section of 750×450×120mm, and the H-beam rolling mill rolls the national standard H500×200×10×16 specifications;

[0132] 4) Heating in the heating furnace: The temperature of the heating section of the heating furnace is 1235-1240°C, the temperature of the soaking section is 1227-1231°C, and the heating time is 98 minutes;

[0133] 5) Descaling: Descaling water pressure 18MPa, roller speed 2m / s;

[0134] 6) Hot rolling: The slab mill was used for 13 reciprocating passes, with the flange thickness reduced by 20% and the web thickness reduced by 40%. The universal mill was used for the third temperature-controlled rolling pass at 970°C. The universal mill was used for 7 passes. The product was air-cooled after rolling. The specific process control of the hot rolling process is shown in Table 2.

[0135] The H-shaped steel product produced in this comparative example has good appearance, size and surface quality, but poor low-temperature impact resistance at -100°C. The performance data are shown in Table 3.

[0136] Comparative Example 4

[0137] A hot-rolled H-shaped steel, the chemical composition and weight percentage of which are shown in Table 1.

[0138] The production method of the hot-rolled H-beam comprises the following steps:

[0139] 1) Hot metal pretreatment: Hot metal pretreatment process time ≤ 30 minutes, argon blowing station argon front temperature 1550 ~ 1590 ℃, argon blowing station time ≤ 10 minutes;

[0140] 2) LF refining: LF refining process time: 60 to 90 minutes, after converter smelting, argon blowing to homogenize the composition, LF refining, the chemical composition of the molten steel meets the requirements of the present invention for the chemical composition of the molten steel;

[0141] 3) Continuous casting: The beam blank continuous casting machine casts beam blanks with a cross-section of 750×450×120mm, and the H-beam rolling mill rolls the national standard H500×200×10×16 specifications;

[0142] 4) Heating in the heating furnace: The temperature of the heating section of the heating furnace is 1235-1240°C, the temperature of the soaking section is 1227-1231°C, and the heating time is 98 minutes;

[0143] 5) Descaling: Descaling water pressure 17MPa, roller speed 2m / s;

[0144] 6) Hot rolling: The slab mill was reciprocatingly rolled for 13 passes, with the flange thickness reduced by 20% and the web thickness reduced by 52%. The universal rolling mill performed temperature-controlled rolling in the third pass at a controlled temperature of 930°. The universal rolling mill was then rolled for 7 passes. The product was air-cooled after rolling. The specific process control of the hot rolling process is shown in Table 2.

[0145] The H-shaped steel product produced in this comparative example has good appearance, size and surface quality, but poor low-temperature impact resistance at -100°C. The performance data are shown in Table 3.

[0146] Comparative Example 5

[0147] A hot-rolled H-shaped steel, the chemical composition and weight percentage of which are shown in Table 1.

[0148] The production method of the hot-rolled H-beam comprises the following steps:

[0149] 1) Hot metal pretreatment: Hot metal pretreatment process time ≤ 30 minutes, argon blowing station argon front temperature 1550 ~ 1590 ℃, argon blowing station time ≤ 10 minutes;

[0150] 2) LF refining: LF refining process time: 60 to 90 minutes, after converter smelting, argon blowing to homogenize the composition, LF refining, the chemical composition of the molten steel meets the requirements of the present invention for the chemical composition of the molten steel;

[0151] 3) Continuous casting: The beam blank continuous casting machine casts beam blanks with a cross-section of 750×450×120mm, and the H-beam rolling mill rolls the national standard H500×200×10×16 specifications;

[0152] 4) Heating in the heating furnace: The temperature of the heating section of the heating furnace is 1235-1240°C, the temperature of the soaking section is 1227-1231°C, and the heating time is 98 minutes;

[0153] 5) Descaling: Descaling water pressure 18MPa, roller speed 2m / s;

[0154] 6) Hot rolling: The slab mill was used for 13 reciprocating passes, with the flange thickness reduced by 20% and the web thickness reduced by 35%. The universal mill was used for the third temperature-controlled rolling at 930°C. The universal mill was used for 7 passes. The product was air-cooled after rolling. The specific process control of the hot rolling process is shown in Table 2.

[0155] The H-shaped steel product produced in this comparative example has good appearance, size and surface quality, but poor low-temperature impact resistance at -100°C. The performance data are shown in Table 3.

[0156] Table 1 Steel composition (wt%) of each embodiment and comparative example

[0157] serial number C Si Mn P S Nb V Ni V+Nb V+Nb+Ni Example 1 0.10 0.21 1.30 0.015 0.007 0.015 0.020 0.16 0.035 0.195 Example 2 0.08 0.23 1.25 0.010 0.005 0.012 0.025 0.18 0.037 0.217 Example 3 0.12 0.14 1.19 0.010 0.007 0.009 0.013 0.20 0.022 0.222 Example 4 0.09 0.25 1.35 0.008 0.003 0.010 0.033 0.15 0.043 0.193 Example 5 0.10 0.20 1.27 0.013 0.002 0.013 0.022 0.17 0.035 0.205 Example 6 0.10 0.21 1.29 0.011 0.005 0.012 0.022 0.20 0.034 0.234 Comparative Example 1 0.10 0.21 1.30 0.015 0.007 0.015 0.020 0.16 0.035 0.195 Comparative Example 2 0.10 0.21 1.30 0.015 0.007 0.015 0.020 0.16 0.035 0.195 Comparative Example 3 0.10 0.21 1.30 0.015 0.007 0.015 0.020 0.16 0.035 0.195 Comparative Example 4 0.10 0.25 1.33 0.010 0.005 0 0.030 0 0.030 0.030 Comparative Example 5 0.17 0.20 1.30 0.015 0.010 0.001 0.01 0.01 0.011 0.021

[0158] Table 2 Main rolling process parameters of each embodiment and comparative example

[0159]

[0160]

[0161] The performance test results of the H-beams produced in the embodiments and comparative examples according to the above formula and method are shown in Table 3.

[0162] Table 3 Properties of steel sections produced in the examples and comparative examples

[0163]

[0164]

[0165] The results of the series of temperature shocks on the H500×200×10×16 hot-rolled H-beam produced in Example 1 are shown in Table 4:

[0166] Table 4 Temperature shock of H500×200×10×16 series

[0167] Shock temperature / ℃ Vertical 1 / J Vertical 2 / J Vertical 3 / J Horizontal 1 / J Horizontal 2 / J Horizontal 3 / J -40 389 397 367 301 288 282 -60 306 311 317 309 249 236 -80 241 233 242 156 162 198 -100 167 152 147 62 59 67

[0168] The hot rolled H-beam produced in Examples 1 and 2 was subjected to metallographic analysis through microstructure analysis. The results are shown in Table 5. Figures 1 to 4 As shown, the product produced by the method of the present invention has a higher grain size and a uniform structure, and the finished product structure is ferrite, pearlite and a small amount of bainite.

[0169] Table 2

[0170] microstructure Actual grain size Example 1 Ferrite + pearlite + a small amount of bainite ( Figure 1 ) 11( Figure 2 ) Example 2 Ferrite + pearlite + a small amount of bainite ( Figure 3 ) 11( Figure 4 )

[0171] From the above, it can be seen that according to the technical solution provided by the present invention, it is possible to produce hot-rolled H-shaped steel having a metallographic structure of ferrite + pearlite + a small amount of bainite, with an average longitudinal impact energy of greater than 200 J and an average transverse impact energy of greater than 150 J at -40 to -80°C, and an average longitudinal impact energy of greater than 100 J and an average transverse impact energy of greater than 50 J at -100°C. The steel also has a pearlite lamella spacing of ≤4 μm, a yield strength of 380 to 430 MPa, a tensile strength of 500 to 540 MPa, a NbC volume fraction of ≥6.5%, and an elongation of ≥29%.

[0172] In Comparative Example 1, although the contents of the chemical components in the H-beam are controlled according to the requirements of the present invention, the universal third rolling temperature is not appropriate, resulting in poor mechanical properties and low-temperature toughness of the H-beam.

[0173] In Comparative Examples 2 and 3, although the contents of various chemical components in the H-beams were controlled in accordance with the requirements of the present invention, the mechanical properties and low-temperature toughness of the H-beams were poor due to the inappropriate reduction rate of the roughing web pass and the inappropriate universal third pass rolling temperature.

[0174] In Comparative Example 4, since Nb and Ni were not added to the H-beam formula for alloying, the mechanical properties and low-temperature toughness of the H-beam were poor.

[0175] In Comparative Example 5, since the C content in the H-beam formula is relatively high and the Nb and V contents are too low, the a value is not properly controlled, and the mechanical properties and low-temperature toughness of the H-beam finally produced are relatively poor.

[0176] The above-mentioned reference embodiments provide a detailed description of a Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C and its production method. This is illustrative rather than restrictive, and several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A Q355 grade hot-rolled H-beam with good low temperature toughness at -100°C, characterized in that: The Q355 grade hot-rolled H-beam comprises the following chemical composition in weight percentage: C: 0.07-0.12%, Si: 0.10-0.30%, Mn: 1.15-1.55%, P≤0.020%, S≤0.025%, Nb: 0.005-0.02%, V: 0.01-0.05%, Ni: 0.05-0.25%, and the remainder is Fe and impurity elements, wherein: 0.020%≤Nb+V≤0.06%; Nb+V+Ni≤0.30%; a=-174.87×C+12.32×Si+12.99×Mn-304.07×P-86.75×S+160.07×Nb+22.09×V+18.53×Ni+2.1×k1-0.13×k2+0.003×k3+0.52×k4+113.9, a value ≥ 100; wherein k1 is the roughing pass reduction in the temperature range of 1100-1200°C, k2 is the third finishing pass rolling temperature, k3 is the finishing pass reduction in the temperature range of 900-950°C, and k4 is the finishing pass reduction in the temperature range of 750-850°C; when calculating the a value, ignore the units or percentages of each parameter and directly take the numerical values ​​for calculation.

2. The Q355 grade hot-rolled H-beam with good low temperature toughness at -100°C according to claim 1, characterized in that: The metallographic structure of the Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C is ferrite+pearlite+bainite, and the grain size grade is 11.

3. The Q355 grade hot-rolled H-beam with good low temperature toughness at -100°C according to claim 1, characterized in that: The Q355 grade hot-rolled H-shaped steel with good low-temperature toughness at -100°C has an average longitudinal impact energy of greater than 200J and an average transverse impact energy of greater than 150J at -40 to -80°C; the average longitudinal impact energy at -100°C is greater than 100J and the average transverse impact energy is greater than 50J.

4. The method for producing Q355 grade hot-rolled H-beam with good low temperature toughness at -100°C according to any one of claims 1 to 3, characterized in that: The production method comprises the following steps: smelting→refining→continuous casting→heating in a heating furnace→descaling→rough rolling→finishing rolling→air cooling.

5. The production method according to claim 4, characterized in that In the heating step of the heating furnace, the atmosphere in the furnace is a weak reducing atmosphere, and the temperature is heated to 1200-1250° C. in the heating furnace, and the entire heating time is 90-130 minutes.

6. The production method according to claim 4, characterized in that In the descaling step, the descaling water pressure is 16-25 MPa and the roller speed is 1-3 m / s.

7. The production method according to claim 4, characterized in that In the rough rolling step, the starting rolling temperature is controlled at 1000-1200°C, the finishing rolling temperature is greater than 980°C, the web pass reduction rate is controlled at 50-60%, and the strain rate is 4-6s -1 .

8. The production method according to claim 4, characterized in that In the finishing rolling step, the starting rolling temperature of the universal rolling mill is ≥950°C, and the final rolling temperature is controlled at ≥750°C. The third pass of the universal rolling mill is temperature-controlled rolling, and the temperature is controlled at 910-950°C.

9. The production method according to claim 8, characterized in that In the finishing rolling step, the temperature range is 900-950°C, the pass reduction rate is controlled at 10-25%, and the strain rate is 3-5s- 1 In the temperature range of 750-850℃, the pass reduction rate is controlled at 15-35%, and the strain rate is 5-7s -1 .

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