Low-cost high-toughness structural steel and preparation method thereof

Abstract

The invention discloses low-cost high-toughness structural steel and a preparation method thereof, belongs to the technical field of structural steel, and solves the problems that the structural steel in the prior art is high in high-cost element content and high in cost; the welding performance is poor, and the toughness and the performance uniformity are poor. The low-cost and high-toughness structural steel comprises the following components in percentage by mass: 0.03%-0.04% of C, 0.25%-0.30% of Si, 0.4%-0.5% of Mn, 1.5%-2.0% of Ni, 0.7%-0.9% of Cr, 0.15%-0.25% of Mo, 0.03%-0.05% of V and the balance of Fe and other inevitable impurities. The low-cost high-toughness structural steel is high in strength, good in toughness and good in isotropic uniformity.

Description

Technical Field

[0001] The present invention relates to the technical field of structural steel, and in particular to a low-cost high-strength and toughness structural steel and a preparation method thereof. Background Art

[0002] High-strength, low-alloy steel is a new type of structural steel. It can not only greatly improve the utilization rate of steel resources and achieve the goals of energy saving, economy and environmental protection, but also has high strength, good low-temperature toughness and excellent welding performance. It is currently widely used in engineering machinery, coal mining, ships and marine engineering steel. With the development of engineering machinery and hull structures towards large-scale and lightweight, higher requirements are also placed on the mechanical properties and welding properties of high-strength and toughness structural steel.

[0003] In recent years, domestic scholars have conducted some research on high-strength structural steel. For example, 202310608399.0 discloses a thin-gauge low-yield ratio 690MPa grade marine engineering steel and its manufacturing method, but its C content is high, weldability is poor, and the impact energy at -40℃ is ≥100J, and the toughness is low. Existing low-alloy structural steels generally require a higher C content to ensure strength, resulting in poor weldability, and existing low-alloy structural steels often have problems such as low toughness and large differences in the longitudinal and transverse properties of steel plates. Summary of the invention

[0004] In view of the above situation, the present invention aims to provide a low-cost, high-strength and toughness structural steel and a preparation method thereof, which is used to solve one of the following technical problems: the existing structural steel has a high content of high-cost elements and high cost; poor welding performance, poor toughness and performance uniformity.

[0005] The purpose of the present invention is mainly achieved through the following technical solutions:

[0006] The invention provides a low-cost high-strength and toughness structural steel. The components of the low-cost high-strength and toughness structural steel include, by mass percentage, C 0.03%-0.04%, Si 0.25%-0.30%, Mn 0.4%-0.5%, Ni 1.5%-2.0%, Cr 0.7%-0.9%, Mo 0.15%-0.25%, V 0.03%-0.05%, and the rest are Fe and other inevitable impurities.

[0007] Furthermore, among the components of low-cost, high-strength and toughness structural steel, there is the following relationship: C+Mn / 6+(Cr+Mo) / 5+Ni / 15≤0.50; wherein C, Mn, Cr, Mo, and Ni refer to the mass percentage of the corresponding elements × 100.

[0008] Furthermore, among the components of low-cost and high-strength structural steel, there is the following relationship: C+Si / 30+Ni / 60+(Mn+Cr) / 20+Mo / 15+V / 10≤0.18; wherein C, Si, Mn, Cr, Mo, Ni, and V refer to the mass percentage of the corresponding elements × 100.

[0009] Furthermore, among the components of low-cost, high-strength and toughness structural steel, the following relationship exists: 0.4≤C+Mn / 6+(Cr+Mo) / 5+Ni / 15≤0.46.

[0010] Furthermore, the calculated recrystallization temperature Tnr of the low-cost, high-strength and toughness structural steel is ≤792°C.

[0011] The present invention also provides a method for preparing low-cost high-strength and toughness structural steel, which is used to prepare the above-mentioned low-cost high-strength and toughness structural steel. The preparation method comprises the following steps:

[0012] Step 1, smelting and casting into billet;

[0013] Step 2, subjecting the blank to controlled rolling to obtain a hot rolled plate, wherein the controlled rolling includes two stages: rough rolling and finish rolling;

[0014] Step 3, directly quenching the hot-rolled plate;

[0015] Step 4: Perform tempering heat treatment to obtain low-cost, high-strength and toughness structural steel.

[0016] Furthermore, in step 2, the rolling temperature is controlled to always remain in the recrystallization temperature range.

[0017] Furthermore, in step 2, the final rolling temperature of the rough rolling is controlled to be 1050-950°C.

[0018] Furthermore, in step 2, the rough rolling reduction is 60% to 70%.

[0019] Furthermore, in step 2, the finishing rolling reduction is 55% to 65%.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] The low-cost high-strength and toughness structural steel of the present invention reduces the alloy cost of the structural steel while improving the welding performance by precisely controlling the contents of elements such as C, Si, Ni, Mn, Cr, Mo, V, etc., especially reducing the contents of alloying elements such as C and Ni, thereby improving the welding efficiency in the manufacturing process and reducing the manufacturing cost; low-cost high-strength and toughness structural steel with low cost, high strength, good toughness, easy welding and good isotropic uniformity can be obtained.

[0022] In the preparation method of the low-cost, high-strength and toughness structural steel of the present invention, the rolling temperature is controlled to always be maintained in the recrystallization temperature range, so that the rolling process is all recrystallization rolling, and "recrystallization, large reduction" rolling is achieved. The steel of the present invention obtains an equiaxed and fine structure through recrystallization rolling, and is retained by direct quenching. The toughness of the steel plate is improved by tempering, and excellent strength and toughness are obtained by fine grain strengthening as the main strengthening means. At the same time, the equiaxed fine grain structure also has good mechanical properties in the horizontal and vertical directions after tempering. Finally, a thin-gauge, low-cost, easy-to-weld, high-strength and toughness structural steel with tempered martensite as the main structure, which has both mechanical properties and welding properties, is obtained, which meets the development needs of the machinery, shipbuilding and other industries in the future stage.

[0023] The low-cost, high-strength and toughness structural steel of the present invention has excellent performance, with a yield strength of more than 604MPa, for example, a yield strength of 604-650MPa; a tensile strength of more than 670MPa, for example, a tensile strength of 670-730MPa; an elongation after fracture of more than 20%, for example, 21%-26%; an impact absorption energy of more than 200J at -84°C, for example, 200-230J; the above-mentioned low-cost, high-strength and toughness structural steel has good isotropic uniformity and good welding performance.

[0024] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the contents particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0026] Figure 1 is a process route diagram of the preparation method of the present invention;

[0027] Figure 2 This is the original austenite metallographic photograph of the steel in Example 2;

[0028] Figure 3 is a scanning electron microscope photograph of the steel of Example 3;

[0029] Figure 4 This is an electron backscatter diffraction electron microscope photograph of the steel in Example 4. DETAILED DESCRIPTION

[0030] Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used to explain the principles of the present invention together with the embodiments of the present invention.

[0031] The present invention provides a low-cost high-strength and toughness structural steel. The components of the low-cost high-strength and toughness structural steel include, by mass percentage: C 0.03%-0.04%, Si 0.25%-0.35%, Mn 0.4%-0.5%, Ni 1.5%-2.0%, Cr 0.7%-0.9%, Mo 0.15%-0.25%, V 0.03%-0.05%, and the rest are Fe and other inevitable impurities.

[0032] The functions and dosages of the components in the present invention are described in detail below.

[0033] C is a basic element in steel and has a strong solid solution strengthening effect, which can improve the strength and hardenability of steel, but the increase of C content is not good for weldability. Therefore, the present invention controls the C content to 0.03% to 0.04%.

[0034] Si has a certain solid solution strengthening effect, mainly plays a deoxidation role in the steelmaking process. A high content of Si is unfavorable to the low-temperature toughness and weldability of steel. Taking comprehensive considerations, the Si content in the present invention is controlled to be 0.25% to 0.30%.

[0035] Mn is a solid solution strengthening element and also an austenite stabilizing element, which can expand the austenite phase region. Too high a Mn content can easily lead to structural segregation and reduce the weldability of the material. Taking all factors into consideration, the present invention controls the Mn content to 0.4% to 0.5%.

[0036] Ni has a certain solid solution strengthening effect, and can improve the hardenability and low temperature toughness of steel, and can also improve the corrosion resistance of steel. However, the cost of Ni element alloy is relatively high. Considering the economic cost of steel, the present invention controls the Ni content to 1.5% to 2.0%.

[0037] Cr has a certain solid solution strengthening effect and is also a hardenability element, which can improve the hardenability of steel and obtain a martensitic structure after direct quenching. Taking all factors into consideration, the Cr content in the present invention is controlled to be 0.7% to 0.9%.

[0038] Mo can improve the hardenability of steel and also has a precipitation strengthening effect. During the tempering process, Mo-containing carbides are formed to reduce the precipitation of cementite that reduces low-temperature toughness, while improving the strength and toughness of the steel. Taking all factors into consideration, the Mo content in the present invention is controlled to be 0.15% to 0.25%.

[0039] V precipitates during the rolling process, which can improve the grain refinement during the rolling process. At the same time, carbides are formed during the tempering process to improve the strength and toughness of the steel. Taking all factors into consideration, the V content in the present invention is controlled to be 0.03% to 0.05%.

[0040] Specifically, among the components of the above-mentioned low-cost and high-strength and toughness structural steel, there is the following relationship: C+Mn / 6+(Cr+Mo) / 5+Ni / 15≤0.50; wherein C, Mn, Cr, Mo, and Ni refer to the mass percentage of the corresponding elements × 100.

[0041] Preferably, 0.4≤C+Mn / 6+(Cr+Mo) / 5+Ni / 15≤0.46.

[0042] Specifically, among the components of the above-mentioned low-cost and high-strength structural steel, there is the following relationship: C+Si / 30+Ni / 60+(Mn+Cr) / 20+Mo / 15+V / 10≤0.18; wherein C, Si, Mn, Cr, Mo, Ni, and V refer to the mass percentage of the corresponding elements × 100.

[0043] Preferably, 0.14≤C+Si / 30+Ni / 60+(Mn+Cr) / 20+Mo / 15+V / 10≤0.17.

[0044] Specifically, the calculated recrystallization temperature Tnr of the above low-cost high-strength and toughness structural steel is ≤792°C.

[0045] On the other hand, the present invention also provides a method for preparing the above-mentioned low-cost high-strength and toughness structural steel, comprising the following steps:

[0046] Step 1, smelting and casting into billet;

[0047] Step 2, subjecting the blank to controlled rolling to obtain a hot rolled plate, wherein the controlled rolling includes two stages: rough rolling and finish rolling;

[0048] Step 3, directly quenching the hot-rolled plate;

[0049] Step 4: Perform tempering heat treatment to obtain low-cost, high-strength and toughness structural steel.

[0050] Specifically, in the above step 2, the rolling temperature is controlled to always remain in the recrystallization temperature range.

[0051] Specifically, the preparation method of the present invention ensures that the rolling temperature is always controlled to be maintained in the recrystallization temperature range, dynamically recrystallizes and refines the original austenite grains, and retains the equiaxed fine-grained structure through subsequent direct quenching, thereby avoiding the reduction in toughness and anisotropy caused by the flattened elongated structure caused by the combination of rolling in the non-crystallization zone and direct quenching, thereby ensuring the strength and toughness of the steel and the uniformity of performance in all directions.

[0052] Specifically, in the above step 2, considering that too high final rolling temperature of rough rolling may easily cause grain coarsening of the rolling structure, the final rolling temperature of rough rolling is controlled to be 1050-950°C, for example, 960°C, 970°C, 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, and 1040°C.

[0053] Specifically, in the above step 2, the rough rolling reduction is controlled to be 60% to 70%, for example, 63%, 65%, or 67%.

[0054] Specifically, in the above step 2, considering that the final rolling temperature of the finishing rolling is too low, a certain degree of non-recrystallization rolling will occur, the degree of recrystallization refinement will be reduced, and the non-recrystallization rolling will form an anisotropic flattened and elongated structure. Therefore, the final rolling temperature of the finishing rolling is controlled to be 900-800°C, for example, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, and 890°C.

[0055] Specifically, in the above step 2, the finishing rolling reduction is controlled to be 55% to 65%, for example, 57%, 59%, 61%, or 63%.

[0056] Specifically, in the above step 3, the quenching cooling method is water cooling. Considering that if the cooling rate is too low, the martensite structure cannot be generated and the strength is reduced, the cooling rate is controlled to be 60 to 90°C / s, such as 65°C / s, 70°C / s, 75°C / s, 80°C / s, and 85°C / s.

[0057] Specifically, in the above step 3, the final cooling temperature of the steel plate surface is controlled to be ≤50°C.

[0058] Specifically, in the above step 4, considering that the holding temperature of the tempering heat treatment is too high, the temperature range of the two-phase zone is entered, the microstructure type changes, and the holding time is too long, over-aging occurs, and the precipitate size is too large to damage the mechanical properties. The holding temperature is too low and the holding time is too short, the internal stress cannot be eliminated, and the precipitation strengthening effect cannot be obtained. Therefore, the controlled tempering heat treatment includes: heating the steel plate to 600-700°C for holding, holding for 1-2 hours, and then air cooling to room temperature.

[0059] Specifically, in the above step 2, the microstructure of the hot-rolled plate after rolling is controlled to be equiaxed fine austenite, and the original austenite grain size is ≤8 μm.

[0060] Specifically, in the above step 4, the structure of the low-cost high-strength and toughness structural steel is tempered martensite, and the width of the tempered martensite lath is 50 to 200 nm.

[0061] Specifically, in the above step 4, the low-cost high-strength and toughness structural steel obtained is a thin-gauge steel plate, for example, the thickness of the steel plate is 5 to 10 mm.

[0062] Specifically, the low-cost high-strength and toughness structural steel has excellent performance, with a yield strength of more than 604MPa, for example, a yield strength of 604-650MPa; a tensile strength of more than 670MPa, for example, a tensile strength of 670-730MPa; an elongation of more than 20%, for example, 21%-26%; an impact absorption energy of more than 200J at -84°C, for example, 200-230J; the low-cost high-strength and toughness structural steel has good isotropic uniformity, for example, the difference in yield strength between the transverse and longitudinal directions is less than 13MPa, for example, 1-13MPa; the difference in tensile strength between the transverse and longitudinal directions is less than 10MPa, for example, 1-10MPa; the difference in elongation between the transverse and longitudinal directions is less than 2%, for example, 0-2%; the difference in -84°C impact absorption energy between the transverse and longitudinal directions is less than 16J, for example, 3-16J. The low-cost high-strength and toughness structural steel has low C content, low alloying element content, low carbon equivalent, and excellent welding performance.

[0063] The low-cost high-strength and toughness structural steel of the present invention reduces the alloy cost of the structural steel while improving the welding performance and reducing the recrystallization temperature by precisely controlling the contents of elements such as C, Si, Ni, Mn, Cr, Mo, V, etc., especially reducing the contents of alloy elements such as C and Ni, and regulating the contents of elements such as C, V, Si, etc., thereby improving the welding efficiency in the manufacturing process and reducing the manufacturing cost; and can obtain low-cost high-strength and toughness structural steel with low cost, high strength, good toughness, easy welding and good isotropic uniformity.

[0064] In the preparation method of the low-cost, high-strength and toughness structural steel of the present invention, the rolling temperature is controlled to always be maintained in the recrystallization temperature range, so that the rolling process is all recrystallization rolling, and "recrystallization, large reduction" rolling is achieved. The steel of the present invention obtains an equiaxed and fine structure through recrystallization rolling, and is retained by direct quenching. The toughness of the steel plate is improved by tempering, and excellent strength and toughness are obtained by fine grain strengthening as the main strengthening means. At the same time, the equiaxed fine grain structure also has good mechanical properties in the horizontal and vertical directions after tempering. Finally, a thin-gauge, low-cost, easy-to-weld, high-strength and toughness structural steel with tempered martensite as the main structure, which has both mechanical properties and welding properties, is obtained, which meets the development needs of the machinery, shipbuilding and other industries in the future stage.

[0065] The low-cost, high-strength and toughness structural steel of the present invention has excellent performance, with a yield strength of more than 604MPa, for example, a yield strength of 604-650MPa; a tensile strength of more than 670MPa, for example, a tensile strength of 670-730MPa; an elongation after fracture of more than 20%, for example, 21%-26%; an impact absorption energy of more than 200J at -84°C, for example, 200-230J; the above-mentioned low-cost, high-strength and toughness structural steel has good isotropic uniformity and good welding performance.

[0066] The advantages of precise control of the composition and process parameters of the steel of the present invention are demonstrated below with specific examples and comparative examples.

[0067] Examples 1-5 of the present invention provide a low-cost, high-strength and toughness structural steel and a preparation method thereof. The chemical compositions of the steels of Examples 1-5 are shown in Table 1.

[0068] The method for preparing the steel of Examples 1-5 comprises:

[0069] Step 1, smelting and casting into billet;

[0070] Step 2, the blank is subjected to controlled rolling to obtain a hot-rolled plate, wherein the controlled rolling includes two stages: rough rolling and finish rolling; the thickness of the hot-rolled plate after final rolling is 5 to 10 mm;

[0071] Step 3, directly quenching the hot-rolled plate; the quenching cooling method is water cooling, and the cooling rate is 60-90°C / s;

[0072] Step 4: Perform tempering heat treatment to obtain low-cost, high-strength and toughness structural steel.

[0073] The calculated recrystallization temperature Tnr of the steel of Examples 1-5 is ≤ 792°C.

[0074] The specific process parameters of rolling of Examples 1-5 are shown in Table 2; the specific process parameters of quenching and tempering are shown in Table 3; the microstructure of the low-cost high-strength and toughness structural steel is shown in Table 4, and the mechanical properties test results of the low-cost high-strength and toughness structural steel are shown in Table 5.

[0075] Figure 1 is a process route diagram of the preparation method of the present invention; Figure 2 This is the original austenite metallographic photograph of the steel in Example 2; Figure 3 is a scanning electron microscope photograph of the steel of Example 3; Figure 4 This is an electron backscatter diffraction electron microscope photograph of the steel in Example 4.

[0076] The inventor has conducted a large number of experimental studies during the research process, and now uses some solutions with poor performance as comparative examples.

[0077] Comparative Example 1

[0078] This comparative example provides a structural steel and a preparation method thereof. The components thereof are shown in Table 1, and the specific process parameters of the preparation method are shown in Table 2.

[0079] Comparative Example 1 has higher C and V contents and lower Si content, resulting in a higher recrystallization temperature of about 836°C; therefore, the process of the comparative example is a two-stage rolling of recrystallization rolling + non-recrystallization rolling. After two-stage rolling + direct quenching, the high-density dislocation formed by non-recrystallization rolling of Comparative Example 1 improves the strength of the material, but the larger grain size and higher dislocation density compared to the recrystallized structure result in poor toughness of the steel plate. At the same time, the flattened and elongated organizational morphology formed by non-recrystallization rolling also affects the uniformity of the performance of the steel plate, resulting in large differences in the transverse and longitudinal properties of the steel plate.

[0080] Comparative Example 2

[0081] This comparative example provides a structural steel and a preparation method thereof, wherein the components are the same as those in Example 1, the final rolling thickness is 20 mm, and the specific process parameters of the preparation method are shown in Table 2.

[0082] The microstructure and main performance test results of the comparative steel are shown in Tables 3 and 4 above.

[0083] Table 1 Chemical composition, wt%

[0084] C Si Mn Ni Cr Mo V Example 1 0.04 0.25 0.4 2.0 0.7 0.15 0.03 Example 2 0.04 0.29 0.4 1.5 0.8 0.20 0.03 Example 3 0.03 0.27 0.5 1.9 0.7 0.16 0.05 Example 4 0.04 0.25 0.4 1.8 0.9 0.24 0.04 Example 5 0.04 0.35 0.5 2.0 0.7 0.25 0.04 Comparative Example 1 0.06 0.20 0.4 1.8 0.9 0.24 0.08

[0085] Table 2 Specific process parameters

[0086]

[0087] Table 4 Microstructure of steel

[0088]

[0089]

[0090] Table 5 Mechanical properties of steel

[0091]

[0092] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A low-cost, high-strength and tough structural steel, characterized in that: The components of the low-cost high-strength and toughness structural steel include, by mass percentage, C 0.03%-0.04%, Si 0.25%-0.30%, Mn 0.4%-0.5%, Ni 1.5%-2.0%, Cr 0.7%-0.9%, Mo 0.15%-0.25%, V 0.03%-0.05%, and the rest are Fe and other inevitable impurities.

2. The low-cost, high-strength and tough structural steel according to claim 1, characterized in that: The components of the low-cost high-strength and toughness structural steel have the following relationship: C+Mn / 6+(Cr+Mo) / 5+Ni / 15≤0.50; wherein C, Mn, Cr, Mo, and Ni refer to the mass percentage of the corresponding elements×100.

3. The low-cost, high-strength and tough structural steel according to claim 1, characterized in that: The components of the low-cost, high-strength and toughness structural steel have the following relationship: C+Si / 30+Ni / 60+(Mn+Cr) / 20+Mo / 15+V / 10≤0.18; wherein C, Si, Mn, Cr, Mo, Ni and V refer to the mass percentage of the corresponding elements × 100.

4. The low-cost, high-strength and tough structural steel according to claim 2, characterized in that: Among the components of the low-cost, high-strength and toughness structural steel, the following relationship exists: 0.4≤C+Mn / 6+(Cr+Mo) / 5+Ni / 15≤0.

46.

5. The low-cost, high-strength and tough structural steel according to any one of claims 1 to 4, characterized in that: The calculated recrystallization temperature Tnr of the low-cost high-strength and toughness structural steel is ≤792°C.

6. A method for preparing low-cost high-strength and tough structural steel, characterized in that: The preparation method is used to prepare the low-cost high-strength and toughness structural steel according to any one of claims 1 to 5, and the preparation method comprises the following steps: Step 1, smelting and casting into billet; Step 2, subjecting the blank to controlled rolling to obtain a hot rolled plate, wherein the controlled rolling includes two stages: rough rolling and finish rolling; Step 3, directly quenching the hot-rolled plate; Step 4: Perform tempering heat treatment to obtain low-cost, high-strength and toughness structural steel.

7. The preparation method according to claim 6, characterized in that: In step 2, the rolling temperature is controlled to always be kept in the recrystallization temperature range.

8. The preparation method according to claim 6, characterized in that: In the step 2, the final rolling temperature of the rough rolling is controlled to be 1050-950°C.

9. The preparation method according to claim 6, characterized in that: In the step 2, the rough rolling reduction is 60% to 70%.

10. The preparation method according to any one of claims 6 to 9, characterized in that: In the step 2, the finishing rolling reduction is 55% to 65%.

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