Steel with high shock resistance, high strength and high toughness and production method thereof

Abstract

The invention provides steel with high shock resistance, high strength and high toughness and a production method thereof. The steel comprises the following chemical components in percentage by mass: 0.14 to 0.20 percent of C, 0.10 to 0.30 percent of Si, 1.20 to 1.80 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.005 percent of S, 0.010 to 0.060 percent of Als, 0.010 to 0.035 percent of Nb and the balance of Fe and inevitable impurities. The production method comprises the steps of molten iron desulphurization, converter smelting, LF refining, slab continuous casting, continuous casting slab hot direct loading and heating, slab rolling, laminar cooling, coiling and forced cooling delivery. And the laminar cooling is front section sectional type cooling. By optimizing the chemical components of the steel and combining with an improved production process, especially a rolling and laminar cooling control process, energy conservation and emission reduction are achieved while the mechanical property and the machining and using performance of the steel are improved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of steel production and manufacturing, and in particular to a high-seismic-resistance, high-strength and high-toughness steel and a production method thereof. Background Art

[0002] In recent years, the production of domestic high-rise building steel materials has gradually increased. High-strength, low yield ratio, high seismic resistance, and high toughness high-rise building steel materials are mainly used for high-rise building columns, railway station waiting room load-bearing beams, large factory structure frames, mechanical base beams and other products. The steel grades used to produce high-strength, low yield ratio, and high toughness high-rise building steel are mainly Q345GJ, Q390GJ, Q420GJ, Q460GJ, Q500GJ and other series of products. Each product is divided into different grades of B, C, D, and E. Among them, the output of high-strength, low yield ratio, and high toughness high-rise building steel materials of large manufacturers in developed areas of China reaches 10,000 tons / year.

[0003] At present, steel materials for high-rise buildings have the following four main performance problems: (1) poor processing formability; (2) high yield strength ratio; (3) low strength; (4) poor welding performance. In addition, the manufacturing cost is relatively high. The steel material production methods in the existing technology usually only solve part of these problems, and there is no production method that can obtain steel materials with excellent comprehensive performance and low cost. For example, the mechanical properties of Q420GJ medium and thick steel plates are usually solved mainly through component design and process control in the existing technology, but more alloy elements (such as Nb, V and Ti) are added to the components, which increases the production cost. Summary of the invention

[0004] The problem solved by the present invention is how to produce a high-vibration-resistant, high-strength and high-toughness steel at a low cost.

[0005] In order to solve the above problems, the present invention provides a method for producing high-seismic resistance, high-strength and high-toughness steel, wherein the chemical composition of the high-seismic resistance, high-strength and high-toughness steel is as follows in terms of mass percentage:

[0006] C: 0.14-0.20%, Si: 0.10-0.30%, Mn: 1.20-1.80%, P≤0.025%, S≤0.005%, Als: 0.010-0.060%, Nb: 0.010-0.035%, the balance is Fe and unavoidable impurities;

[0007] The production method comprises: molten iron desulfurization, converter smelting, LF refining, slab continuous casting, hot direct charging and heating of continuous casting slabs, slab rolling, laminar cooling, coiling and forced cooling before delivery; the laminar cooling is front-stage segmented cooling.

[0008] Optionally, during the converter smelting, nitrogen and argon switching is used for bottom blowing, and the alloy is directly added when the converter is tapping steel.

[0009] Optionally, the slab continuous casting adopts full-process protective casting, and the temperature of the molten steel in the middle package is controlled at 1536-1542°C.

[0010] Optionally, the slab rolling includes rough rolling and finish rolling, and the thickness of the intermediate slab before finish rolling is above 45 mm.

[0011] Optionally, the slab rolling includes seven finishing passes; for steel plates with a thickness of 3.0-7.0 mm, the reduction amount of each pass during the finishing rolling process is 16 mm, 10 mm, 7 mm, 4 mm, 2 mm, 1 mm, and 1 mm, respectively; for steel plates with a thickness of 7.0-16.0 mm, the reduction amount of each pass during the finishing rolling process is 14 mm, 8 mm, 5 mm, 3 mm, 2 mm, 1 mm, and 1 mm, respectively.

[0012] Optionally, during the heating process, for steel plates with a thickness of 2.0-3.6 mm, the furnace temperature is 1230±30°C; for steel plates with a thickness of 3.61-5.0 mm, the furnace temperature is 1220±30°C.

[0013] Optionally, in the finish rolling, for steel plates with a thickness of 3.0-7.0 mm, the reference temperature at the finish rolling entrance is 1040±30°C, and the final rolling temperature is 880±20°C; for steel plates with a thickness of 7.0-16.0 mm, the reference temperature at the finish rolling entrance is 1060±30°C, and the final rolling temperature is 890±20°C.

[0014] Optionally, the front-stage segmented cooling is performed in the 2nd, 3rd and 5th stages of the cooling process.

[0015] Optionally, in the coiling step, for a steel plate with a thickness of 3.0-7.0 mm, the coiling temperature is 590±20°C; for a steel plate with a thickness of 7.0-16.0 mm, the coiling temperature is 580±20°C.

[0016] The advantages of the production method of the present invention compared with the prior art are:

[0017] In the chemical composition design of steel, the present invention adopts a manganese-silicon component system of a high-cost-effective alloy to replace a low-cost-effective alloy system (carbon-manganese-iron), because the cost per ton of steel of the manganese-silicon alloy is more advantageous, that is, the cost of the manganese-silicon alloy is lower when the molten steel increases by 0.1% Mn, and no strong precipitation and solidification elements such as titanium (Ti) and vanadium (V) are added to the chemical composition, further reducing the raw material cost of the alloy. In addition, in addition to the advantage of reducing costs, such a component design also reduces harmful elements that affect the performance of steel, and is also conducive to reducing the yield strength and yield strength ratio of steel.

[0018] The steel of the present invention adopts a composite of C, Si, Mn, P, S, Als and Nb, and is designed with a content ratio, and the slab is rolled by direct hot furnace charging, and the laminar cooling process is precisely controlled, especially the front-stage segmented cooling is adopted in the laminar cooling process, so as to achieve the purpose of reducing mixed crystals and improving performance uniformity, and at the same time, it is beneficial to the grain transformation speed, improve the tensile strength and toughness, and reduce the yield strength ratio. The present invention improves the mechanical properties and processing performance of the steel as a whole, and the subsequent good welding performance, reduces the yield strength ratio, and the low yield strength ratio is conducive to improving the toughness and shock resistance of the material, and also solves the problem of poor processing performance and bending cracking that is easy to occur during the cold bending process, and also achieves energy saving and emission reduction.

[0019] The present invention is the first to use medium carbon, low manganese and a small amount of microalloy as components, through laminar cooling, especially the front-stage segmented cooling control means, using the interaction between the dispersion precipitation of microalloy carbonitrides and dislocations to obtain a significant strengthening effect, and prepare a low-cost, high-performance high-rise building steel with qualified welding performance, good processing formability, and pressure burst test that meets standard requirements.

[0020] The present invention also provides a high-strength, high-toughness steel with high shock resistance, which is prepared by the above production method. The steel prepared by the present invention has good strength and toughness, a hot coil yield strength of more than 420MP, a tensile strength of more than 540MP, a yield strength ratio of less than 0.80, an elongation of more than 22%, and a -20°C low-temperature impact test detection of more than 120J. The steel prepared by the present invention meets the Q420GJ grade standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a flowchart of a method for producing high-seismic-resistance, high-strength and high-toughness steel in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0023] In the description of this specification, the description with reference to the terms "embodiment", "one embodiment", "some embodiments" and "an implementation" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or implementation are included in at least one embodiment or implementation of the invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or implementation. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or implementations in a suitable manner.

[0024] An embodiment of the present invention provides a method for producing high-seismic resistance, high-strength and high-toughness steel, wherein the chemical composition of the high-seismic resistance, high-strength and high-toughness steel is, by mass percentage, C: 0.14-0.20%, Si: 0.10-0.30%, Mn: 1.20-1.80%, P≤0.025%, S≤0.005%, Als: 0.010-0.060%, Nb: 0.010-0.035%, and the remainder is Fe and unavoidable impurities.

[0025] In the chemical composition design of the present invention, the role of each element is as follows:

[0026] Carbon (C) is the most basic strengthening element and one of the main elements that affect the mechanical properties of steel. It mainly plays a role in solid solution strengthening. If the C content is too high, the ductility, toughness and welding performance of the steel will deteriorate. If the C content is too low, the strength of the steel will deteriorate. The carbon content of the present invention is controlled between 0.14-0.20%, which belongs to medium carbon content.

[0027] Silicon (Si) is a deoxidizing element in steel and also has a solid solution strengthening effect, which helps to improve the tensile strength of steel. Too high Si content will affect the welding performance and low temperature toughness of steel. The Si content of the present invention is controlled between 0.10-0.30%.

[0028] Manganese (Mn) can improve the strength and low temperature toughness of steel, and also has the effect of refining the structure. It is a relatively economical strengthening element. Too high Mn content is easy to cause segregation of continuous casting billets. The manganese content of the present invention is controlled between 1.20-1.80%.

[0029] Aluminum (Al) is an element with deoxidizing effect. A proper amount of Al is beneficial to grain refinement, reducing inclusions in steel, and improving the strength and toughness of steel. Excessive Al will cause surface cracks in the continuous casting billet. The Al content of the present invention is controlled between 0.010-0.060%, which is the weight percentage of acid-melted aluminum (Als) in steel.

[0030] Niobium (Nb) is a microalloying element. Trace amounts of niobium have a pinning effect on austenite grain boundaries, which inhibits the growth of deformed austenite, forms precipitates during cooling or tempering, improves strength and toughness, and plays a role in precipitation strengthening. If the Nb content is too low, the dispersion precipitation effect is not obvious, and the effect of grain refinement and matrix strengthening is not achieved. If the Nb content is too high, cracks on the surface of the continuous casting billet are easily generated, and the welding performance will be deteriorated. Therefore, the Nb content of the present invention is controlled at 0.010-0.035%.

[0031] Sulfur (S) and phosphorus (P) are impurity elements in steel, and the lower their content, the better. Too high a content will seriously damage the low-temperature toughness of the steel and increase the segregation degree of the continuous casting billet. The S content of the present invention should be controlled below 0.005%, and the P content should be controlled below 0.025%.

[0032] The production method of the high-strength, high-toughness steel with high shock resistance includes a smelting process and a rolling process. Specifically, Figure 1 As shown, the process steps include:

[0033] Step S1, desulfurization of molten iron;

[0034] Step S2, converter smelting;

[0035] Step S3, LF refining;

[0036] Step S4, slab continuous casting;

[0037] Step S5, hot direct loading and heating of the continuous casting billet;

[0038] Step S6, slab rolling;

[0039] Step S7, laminar cooling (front section segmented cooling);

[0040] Step S8, coiling;

[0041] Step S9, forced cooling before leaving the factory.

[0042] In some embodiments, step S1 is to desulfurize molten iron from blast furnace until [S]≤0.005wt%; in a specific embodiment, KR desulfurization is used.

[0043] In some embodiments, the molten iron after desulfurization treatment is sent to the converter for smelting. During the converter smelting, nitrogen / argon switching is used (50% nitrogen blowing before blowing and 50% nitrogen blowing after blowing) for bottom blowing. The converter endpoint controls the steel tapping, and the alloy is directly added when the converter taps the steel.

[0044] In a specific embodiment, Si, Mn alloy and carbon powder balls are added during the steel tapping process for smelting to ensure that the alloy can be completely melted; in a specific embodiment, the alloy is added for smelting when 1 / 2-2 / 3 of the steel is tapped.

[0045] In some embodiments, during the process of transferring the molten steel obtained by smelting into the ladle, slag blocking is used for tapping, and the amount of slag discharged from the converter is strictly controlled.

[0046] In some embodiments, during LF refining, good argon blowing is required at the bottom of the ladle; the LF furnace (Ladle Furnace) is used to treat the white slag produced by the ladle furnace and desulfurize to [S] ≤ 0.005%; the LF furnace is used to fine-tune the composition and treat spherical inclusions according to the target composition requirements.

[0047] In some embodiments, LF refining includes calcium treatment, specifically, feeding a silicon-calcium wire at the end of LF refining to increase the Ca content in the molten steel to 0.0015-0.0040% and improve the inclusion level in the molten steel; narrow composition control and cleanliness control are performed during the refining process.

[0048] In some embodiments, the slab continuous casting in step S4 adopts full-process protection casting. During continuous casting, the liquidus temperature TL=1518° C. The temperature of the molten steel in the tundish is controlled to be about 10-15° C. higher than the liquidus temperature.

[0049] In some embodiments, the temperature of the molten steel in the middle ladle in step S4 is controlled to be 1536-1542° C. In a specific embodiment, the temperature of the molten steel in the middle ladle is 1538° C.

[0050] In some embodiments, the crystallizer protection slag uses a special medium-carbon protection slag.

[0051] In some embodiments, hot direct charging of continuous casting slabs means that the continuous casting slabs are directly charged into the furnace for hot rolling without cooling treatment, so as to maximize the utilization of hot slab energy and reduce the time the slabs are in the furnace; the slabs that are not hot-charged into the furnace are stacked and slowly cooled, and hot charging requires that the minimum charging temperature be ≥200°C.

[0052] In some embodiments, the continuous casting slab is sent to a heating furnace for heating, and then subjected to hot rolling treatment after being taken out of the furnace. During the heating process, for a steel plate with a thickness of 2.0-3.6 mm, the furnace temperature is 1230±30°C; for a steel plate with a thickness of 3.61-5.0 mm, the furnace temperature is 1220±30°C. The specific process parameters for heating the slab are shown in Table 1.

[0053] Table 1. Heating process parameters

[0054]

[0055] In some embodiments, the slab rolling includes rough rolling and finish rolling. After heating, the continuous casting slab is subjected to rough rolling and finish rolling in sequence, and the thickness of the intermediate slab before finish rolling (the slab after continuous casting) is greater than 45 mm. When the thickness of the intermediate slab is increased to greater than 45 mm before finish rolling, the reduction rate can be increased for the subsequent finish rolling, thereby increasing the strength of the steel.

[0056] In some embodiments, the slab rolling includes seven passes of finishing rolling; for a steel plate with a thickness of 3.0-7.0 mm, the reduction amount of each pass during the finishing rolling process is 16 mm, 10 mm, 7 mm, 4 mm, 2 mm, 1 mm, and 1 mm, respectively; for a steel plate with a thickness of 7.0-16.0 mm, the reduction amount of each pass during the finishing rolling process is 14 mm, 8 mm, 5 mm, 3 mm, 2 mm, 1 mm, and 1 mm, respectively.

[0057] In the finishing rolling process, the reasonable distribution of the reduction of each stand is helpful to improve the mechanical properties of the product including strength and toughness.

[0058] In some embodiments, in the finish rolling, for steel plates with a thickness of 3.0-7.0 mm, the reference temperature at the finish rolling entrance is 1040±30°C, and the final rolling temperature is 880±20°C; for steel plates with a thickness of 7.0-16.0 mm, the reference temperature at the finish rolling entrance is 1060±30°C, and the final rolling temperature is 890±20°C. In this embodiment, the final rolling temperature is increased by about 20°C compared with the conventional process, reaching 880-890°C, which can increase the proportion of ferrite in the steel structure and improve the overall toughness. The process parameters for slab finish rolling are shown in Table 2 below.

[0059] Table 2. Rolling process parameters

[0060] Thickness range(mm) Finishing rolling entrance reference temperature (℃) Finishing rolling temperature(℃) 3.0-7.0 1040±30 880±20 7.0-16.0 1060±30 890±20

[0061] Through the intelligent control of the self-learning rolling model, the cooling water distribution between the finishing mill stands is accurately controlled, the final rolling temperature hit rate is improved, and the performance homogeneity of the entire coil is greatly improved.

[0062] In some embodiments, laminar cooling treatment is performed after rolling, and the laminar cooling adopts front-stage segmented cooling, and the front-stage segmented cooling is cooling in the front section and the 1st, 2nd, 3rd and 17th, 18th sections of the cooling process. Laminar cooling is divided into 18 sections in total, and most of the domestic back-end cooling methods are adopted. In this embodiment of the present invention, front-stage segmented cooling is adopted in the laminar cooling process to achieve the purpose of reducing mixed crystals and improving performance uniformity. The use of front-stage segmented rapid cooling can be beneficial to the grain transformation speed, improve tensile strength and toughness, and reduce the yield ratio (the yield ratio can generally be controlled to be rolled below 0.80). The yield ratio of the conventional cooling method is likely to exceed 0.83.

[0063] In some embodiments, after laminar cooling, the steel is rolled into a coil by a coiler, and the coiling temperature ensures that the phase change is substantially completed at the end of the coiling. In some embodiments, in the coiling step, for a steel plate with a thickness of 3.0-7.0 mm, the coiling temperature is 590±20°C; for a steel plate with a thickness of 7.0-16.0 mm, the coiling temperature is 580±20°C. The cooling process and coiling temperature parameters are shown in Table 3 below.

[0064] Table 3. Cooling and coiling process parameters

[0065]

[0066] In some embodiments, the forced cooling before leaving the factory is the cooling stage after coiling, and the hot coil is slowly cooled in a closed environment after coiling to achieve the purpose of uniform coiling performance.

[0067] The Q420GJ steel of the present invention can be produced by a steelmaking workshop and a hot rolling mill unit equipped with LF or RH refining equipment.

[0068] The steel produced by the embodiment of the present invention was tested for performance, and the test results are shown in Tables 4 and 5. Table 6 shows the mechanical performance requirements of Q420GJ national standard.

[0069] Table 4. Test results of mechanical properties of Q420GJ hot coil

[0070]

[0071] Table 5. Mechanical properties test results of Q420GJ processed pipe products

[0072]

[0073] Table 6. Mechanical properties requirements of Q420GJ national standard

[0074]

[0075] The present embodiment will be further described below in conjunction with Examples 1-3 according to the embodiments of the present invention. Obviously, the described Examples 1-3 are only part of the embodiments of the present invention, but not all of the embodiments.

[0076] Examples 1-3

[0077] A Q420GJ steel with high seismic resistance, high strength and high toughness, whose chemical composition is shown in Table 7 by mass percentage, and the balance is Fe and inevitable impurities.

[0078] Table 7. Chemical composition of Examples 1-3

[0079]

[0080] The steel production method comprises: hot metal desulfurization, converter smelting, LF refining, slab continuous casting, hot direct charging and heating of continuous casting slabs, slab rolling, laminar cooling, coiling and forced cooling before delivery;

[0081] The specific process parameters during the production process are as follows:

[0082] Table 8. Desulfurization of molten iron in Example 1-3

[0083]

[0084] Table 9. Converter smelting of Example 1-3

[0085]

[0086] Table 10. LF refining of Examples 1-3

[0087]

[0088]

[0089] Table 11. Slab continuous casting of Examples 1-3

[0090]

[0091] Table 12. Heating, slab rolling, and laminar cooling of Examples 1-3

[0092]

[0093] Table 12. Finishing rolling reduction

[0094]

[0095] The mechanical properties of Q420GJ produced in Examples 1-3 are shown in Table 13.

[0096] Table 13. Mechanical properties test results of Q420GJ of Examples 1-3

[0097]

[0098]

[0099] Comparative Example

[0100] The mechanical properties of Q420GJ produced by Shagang and Magang on the market are shown in Table 14 below.

[0101] Table 14. Mechanical properties of Q420GJ

[0102]

[0103] Compared with Q420GJ of Shagang and Magang, the Q420GJ of the present invention adopts medium carbon plus Nb, Si, Mn, S, Als composite lean component design, meets the steel standard requirements of Q420GJ for high-rise buildings with low yield ratio, high strength and high toughness, ensures that the steel coil has excellent cold processing performance, strength, low yield ratio and good welding performance for subsequent welding, and realizes direct hot loading organization, energy saving and emission reduction. It avoids the problems of strip distortion of low carbon and high manganese design, poor processing and pipe forming, high yield ratio after pipe making, and substandard performance detection of welding area. In addition, the quality design production cost of medium carbon, low manganese and a small amount of micro-alloy steel is reduced by more than 20% by means of controlled rolling and controlled cooling.

[0104] Finally, it should be noted that the detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention, and they are not intended to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to examples, ordinary technicians in the field should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for producing high-strength, high-toughness steel with high seismic resistance, characterized in that: The chemical composition of the high-seismic-resistance, high-strength and high-toughness steel is as follows in terms of mass percentage: C: 0.14-0.20%, Si: 0.10-0.30%, Mn: 1.20-1.80%, P≤0.025%, S≤0.005%, Als: 0.010-0.060%, Nb: 0.010-0.035%, the balance is Fe and unavoidable impurities; The production method comprises: molten iron desulfurization, converter smelting, LF refining, slab continuous casting, hot direct charging and heating of continuous casting slabs, slab rolling, laminar cooling, coiling and forced cooling before delivery; the laminar cooling is front-stage segmented cooling.

2. The method for producing high-seismic-resistance, high-strength and high-toughness steel according to claim 1, characterized in that: During the converter smelting, nitrogen and argon are switched for bottom blowing, and the alloy is directly added when the converter is tapping steel.

3. The method for producing high-seismic-resistance, high-strength and high-toughness steel according to claim 1, characterized in that: The slab continuous casting adopts full-process protection casting, and the temperature of the molten steel in the middle package is controlled at 1536-1542°C.

4. The method for producing high-strength, high-toughness steel with high seismic resistance according to claim 1, characterized in that: The slab rolling includes rough rolling and finish rolling, and the thickness of the intermediate slab before finish rolling is more than 45 mm.

5. The method for producing high-seismic-resistance, high-strength and high-toughness steel according to claim 1 or 4, characterized in that: The slab rolling includes seven finishing passes; for steel plates with a thickness of 3.0-7.0 mm, the reduction amount of each pass during the finishing rolling process is 16 mm, 10 mm, 7 mm, 4 mm, 2 mm, 1 mm, and 1 mm, respectively; for steel plates with a thickness of 7.0-16.0 mm, the reduction amount of each pass during the finishing rolling process is 14 mm, 8 mm, 5 mm, 3 mm, 2 mm, 1 mm, and 1 mm, respectively.

6. The method for producing high-seismic-resistance, high-strength and high-toughness steel according to claim 1, characterized in that: During the heating process, for steel plates with a thickness of 2.0-3.6 mm, the furnace temperature is 1230±30° C.; for steel plates with a thickness of 3.61-5.0 mm, the furnace temperature is 1220±30° C.

7. The method for producing high-seismic-resistance, high-strength and high-toughness steel according to claim 4, characterized in that: In the finishing rolling, for steel plates with a thickness of 3.0-7.0 mm, the reference temperature at the finishing rolling entrance is 1040±30°C, and the final rolling temperature is 880±20°C; for steel plates with a thickness of 7.0-16.0 mm, the reference temperature at the finishing rolling entrance is 1060±30°C, and the final rolling temperature is 890±20°C.

8. The method for producing high-seismic-resistance, high-strength and high-toughness steel according to claim 1, characterized in that: The front stage segmented cooling is performed in the 2nd, 3rd and 5th stages of the cooling process.

9. The method for producing high-seismic-resistance, high-strength and high-toughness steel according to claim 1, characterized in that: In the coiling step, for the steel plate with a thickness of 3.0-7.0 mm, the coiling temperature is 590±20°C; for the steel plate with a thickness of 7.0-16.0 mm, the coiling temperature is 580±20°C.

10. A high-strength, high-toughness steel with high seismic resistance, characterized in that: The steel is prepared by the production method of high-seismic-resistance, high-strength and high-toughness steel as described in any one of claims 1-9.

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