Production method of Q355-grade low-cost hot-rolled H-shaped steel

Abstract

The invention discloses a production method of Q355-grade low-cost hot-rolled H-shaped steel. The production process comprises the steps of converter smelting, LF refining, beam blank continuous casting and rolling. The low-cost hot-rolled H-shaped steel comprises the following chemical components in percentage by mass: 0.15%-0.25% of C, 0.30%-0.60% of Si, 1.20%-1.70% of Mn, less than or equal to 0.025% of P, less than or equal to 0.020% of S, 0.020%-0.040% of Ti and the balance of Fe and inevitable impurities, and the total mass fraction is 100%. According to the production method, on the basis that the production cost is reduced, high yield strength and tensile strength are kept, and meanwhile good plasticity and impact toughness are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting and rolling, and in particular relates to a production method of Q355 grade low-cost hot-rolled H-shaped steel. Background Art

[0002] Q355 grade hot-rolled H-beam has a wide range of application needs in many fields such as construction, machinery manufacturing, and bridges. With the continuous advancement of infrastructure construction and the continuous development of industry, the demand for this product is expected to maintain steady growth. Low-cost Q355 grade hot-rolled H-beam will have stronger market competitiveness, attract more customers, and further expand market share. Ti, V, and Nb all have the function of refining grains and improving strength in steel. The carbides and nitrides formed by Ti combined with carbon, nitrogen and other elements in steel can effectively hinder grain growth, which is similar to the mechanism of action of V and Nb. This provides a theoretical possibility for replacing V and Nb with Ti. Ti is relatively abundant in nature, and its price is more stable and generally lower than that of V and Nb. Using Ti instead of V and Nb can significantly reduce the procurement cost of alloy elements, thereby reducing the production cost of Q355 grade hot-rolled H-beam, which is of great significance for improving the competitiveness of products in the market. The existing production equipment and process flow of steel mills can adapt to the addition of Ti after appropriate adjustments. In the steelmaking process, by adjusting the timing and method of alloy addition, as well as optimizing the refining and continuous casting process parameters, it is possible to ensure that Ti is evenly distributed in the steel and plays its due strengthening role. It is highly feasible for steel mills to use alloying elements Ti to replace V and Nb to produce low-cost Q355 grade hot-rolled H-beams, and it has good prospects in terms of market, technology and sustainable development.

[0003] Publication No. CN 103966507 A introduces a 275MPa yield strength ultra-thick low-temperature hot-rolled H-beam and its production method, introduces its chemical composition, and meets the technical requirements of ultra-thick low-temperature hot-rolled H-beam through converter smelting, refining and other processes. This patent introduces a Q355-grade low-cost hot-rolled H-beam production method, which uses converter smelting, LF refining and other processes to replace Nb or V with Ti microalloying to reduce costs and meet the performance requirements of Q355-grade hot-rolled H-beam. This patent can better reflect its advantages in comprehensive mechanical properties and quality stability through more sophisticated process control, and the developed hot-rolled H-beam has a unique design in alloying treatment and process route, which can better meet the needs of low-cost production.

[0004] Publication No. CN 110016611 A introduces a weather-resistant and low-temperature-resistant hot-rolled H-beam with a yield strength of 355MPa and its production method, introduces its chemical composition, and develops hot-rolled H-beam with good low-temperature toughness and corrosion resistance through converter smelting, LF refining and other processes. This patent introduces a production method for Q355-grade low-cost hot-rolled H-beam. Through a series of processes such as specific chemical composition and converter smelting, LF refining, etc., Ti microalloying is used to replace Nb or V to reduce costs and develop hot-rolled H-beam with excellent comprehensive mechanical properties. This patent focuses on the production of low-cost hot-rolled H-beam, and conducts a more detailed and in-depth study of the chemical composition and process parameters. Through example comparison, it comprehensively demonstrates the performance changes under different conditions, can more accurately optimize the production process and ensure product quality, and the hot-rolled H-beam developed has more advantages in cost control and comprehensive performance optimization.

[0005] Publication No. CN 104032217 A introduces a hot-rolled H-beam and its production method, introduces its chemical composition, can be used for semi-trailer beams, and produces hot-rolled steel that meets the requirements through processes such as molten iron pretreatment and selective cooling methods. This patent introduces a production method for Q355 grade low-cost hot-rolled H-beam. Through specific chemical composition and a series of processes such as converter smelting and LF refining, Ti microalloying is used to replace Nb or V to reduce costs and develop hot-rolled H-beam with excellent comprehensive mechanical properties, emphasizing the fine control and optimization of each link in the production process. This patent focuses on the production of low-cost hot-rolled H-beam, conducts a more in-depth study of chemical composition and process parameters, and comprehensively demonstrates the performance changes under different conditions through example comparison. It can more effectively optimize the production process and ensure product quality, and the hot-rolled H-beam developed has more advantages in cost control and comprehensive performance optimization. Summary of the invention

[0006] In order to solve the above technical problems, the purpose of the present invention is to provide a production method of Q355 grade low-cost hot-rolled H-shaped steel, which not only maintains a high yield strength and tensile strength, but also has good plasticity and impact toughness on the basis of reducing production costs.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The present invention discloses a method for producing Q355 grade low-cost hot-rolled H-shaped steel, the production process of which comprises: converter smelting, LF refining, profiled blank continuous casting, and rolling; wherein:

[0009] For combined-blowing converter smelting, the total charge volume is controlled within the range of 105±2 tons; the low-high-low gun position control method is adopted, and the gun position is between 1.1-1.5m; when the Si content of the molten iron entering the furnace is less than or equal to 0.5%, single slag operation is adopted; and when the Si content is greater than 0.5%, double slag operation is adopted; the terminal basicity must be controlled within the range of 2.7-3.5, and the terminal carbon content C is required to be ≥0.06%, and the temperature T is required to be ≥1620℃; the final deoxidation adopts the Al-containing deoxidation method, and 280-320kg of top slag lime is added during steel tapping. The slide plate slag blocking technology is used during the steel tapping process, and slag is strictly prohibited;

[0010] Refining, the ladle enters the LF furnace for argon blowing smelting, and the time is controlled at 7-12 minutes; when the top slag of the ladle is fully melted and in good condition, the initial sample is extracted for component analysis, and then titanium wire is fed into it according to the target composition. The wire feeding speed is between 2.5-4.5m / s, and the position where the titanium wire is inserted is located above the bottom blowing hole; the bottom blowing argon stirring is carried out throughout the whole process, and the bottom blowing intensity is set to strong blowing in the early stage, and the blowing volume is in the range of 80-120L / min; when the titanium wire is started to be fed, the bottom blowing intensity is adjusted to normal, that is, 60-100L / min; low-pressure soft blowing is used before the ladle leaves the station, and the soft blowing flow is controlled at 20-30L / min to ensure that inclusions can float up, and the refining soft blowing argon time is greater than 12 minutes;

[0011] The whole process adopts protective pouring, the baking temperature of the tundish needs to be controlled between 900-920℃, and the baking time is 3.5-5.5 hours; a sealing ring should be added to the water inlet of the large ladle, and protective pouring measures should be implemented throughout the pouring process. The crystallizer adopts the sleeve type protective pouring method, and the crystallizer is an H-type crystallizer; the secondary cooling stage adopts the weak cooling mode to ensure that the straightening temperature is above 800℃; the tundish uses a sizing ladle and is covered with carbonized rice husks to ensure that the liquid surface is well covered;

[0012] The special-shaped continuous casting billet is heated in a digitally controlled heating furnace, the heating temperature of the billet is 1210-1270°C, the holding time is 2.5-3.5 hours, and the billet is descaled by high-pressure water after being taken out of the furnace;

[0013] The rough rolling temperature is 1120-1180℃, and water cooling is used for controlled cooling. The rolling passes are 3-5 times, and then the rough rolled profile is sent to the finishing mill for rolling; the finishing rolling temperature is 910-970℃, and the finishing rolling adopts warm rolling and water cooling controlled rolling, and the rolling passes are 5-7 times; the final rolling temperature is 850-880℃, and the total reduction of the two-stage rolling is ≥75%; after the rolling is completed, air cooling is carried out and the profile is sent to the cooling bed for centralized cooling; after the temperature drops below 100℃, it is straightened in the straightening machine, and finally cut to size and bundled;

[0014] The mass percentage of the chemical composition of the low-cost hot-rolled H-beam includes: C 0.15%-0.25%, Si 0.30%-0.60%, Mn 1.20%-1.70%, P≤0.025%, S≤0.020%, Ti 0.020%-0.040%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

[0015] Furthermore, the cross-sectional dimensions of the continuous casting billet are H290mm×100mm×350mm.

[0016] Furthermore, the surface quality of Q355 grade low-cost hot-rolled H-beam special-shaped continuous casting ingots was inspected, and the internal quality was tested by low-power hot acid test and the quality of H-beam was tracked and inspected.

[0017] Furthermore, no obvious surface and internal quality defects of the ingot were found during the inspection. The quality of the ingot was good, and the surface crack rate of the ingot was less than 1%.

[0018] Furthermore, the finished product size is H300×300×10×15×12000mm.

[0019] Furthermore, the mass percentage of the chemical composition of the low-cost hot-rolled H-beam includes: C 0.17%, Si 0.37%, Mn 1.32%, P 0.017%, S 0.011%, Ti 0.032%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

[0020] Furthermore, the mass percentage of the chemical composition of the low-cost hot-rolled H-beam includes: C 0.19%, Si 0.40%, Mn 1.37%, P 0.018%, S 0.008%, Ti 0.031%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

[0021] Furthermore, the mass percentage of the chemical composition of the low-cost hot-rolled H-beam includes: C 0.17%, Si 0.38%, Mn 1.33%, P 0.022%, S 0.009%, Ti 0.030%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

[0022] Furthermore, the mass percentage of the chemical composition of the low-cost hot-rolled H-beam includes: C 0.18%, Si 0.43%, Mn 1.36%, P 0.020%, S 0.011%, Ti 0.029%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

[0023] The surface quality of the finished product of Q355 low-cost hot-rolled H-beam was inspected, and the mechanical properties were tested. No obvious surface quality defects were found during the inspection, the surface quality was good, and all the properties of the H-beam after rolling met the standard requirements.

[0024] Compared with the prior art, the beneficial technical effects of the present invention are:

[0025] (1) By using Ti microalloying to replace Nb or V, the procurement cost of alloying elements is significantly reduced. Ti is stable and cheap, and can reduce the production cost of a ton of steel by 50-80 yuan compared with Nb and V, greatly improving the market competitiveness of the product.

[0026] (2) The Ti microalloyed steel of the present invention not only maintains a high yield strength and tensile strength, but also has good plasticity and impact toughness. The strength and toughness of the Ti microalloyed steel are comparable to those of Nb and V microalloyed steels, fully meeting the performance requirements of Q355 steel.

[0027] (3) The carbonitrides of Ti microalloying can be evenly distributed at the grain boundaries of steel, effectively preventing grain growth, thereby significantly reducing the incidence of inclusions and cracks during the production process. The crack rate of the ingot is lower than that of Nb microalloying steel and is comparable to that of V microalloying steel. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with specific embodiments.

[0029] Table 1 shows the chemical composition of each example, and Table 2, Table 3 and Table 4 further illustrate the present invention in combination with the embodiments and comparative examples.

[0030] Table 1 Chemical composition of each example (mass percentage / %)

[0031] Examples C Si Mn P S Ti Nb V Example 1 0.17 0.37 1.32 0.017 0.011 0.032 —— —— Example 2 0.19 0.40 1.37 0.018 0.008 0.031 —— —— Example 3 0.17 0.38 1.33 0.022 0.009 0.030 —— —— Example 4 0.18 0.43 1.36 0.020 0.011 0.029 —— —— Comparative Example 1 0.18 0.40 1.31 0.023 0.007 —— 0.028 —— Comparative Example 2 0.19 0.39 1.35 0.024 0.010 —— —— 0.030 Comparative Example 3 0.20 0.42 1.34 0.016 0.014 —— —— ——

[0032] Embodiment 1:

[0033] The present invention provides a method for producing Q355 grade low-cost hot-rolled H-shaped steel, wherein the production process is carried out according to the following steps:

[0034] The converter uses low-sulfur molten iron, top and bottom double blowing, and controls the final slag basicity to 2.8. Slag is blocked during steel tapping, and the final deoxidation adopts Al-containing deoxidation method.

[0035] Refining white slag operation, argon blowing time 8 minutes. According to the target composition, titanium wire is fed into it, and the feeding speed is 3.0m / s. The soft blowing flow rate is 25L / min, and argon is blown at the bottom throughout the process, and the soft blowing time is 15min.

[0036] The continuous casting adopts a full protection pouring process, the baking temperature of the tundish needs to be controlled at 900℃, and the baking time is 3.8 hours. The secondary cooling stage adopts a weak cooling mode to ensure the straightening temperature is 830℃.

[0037] The cross-sectional dimensions of the continuous casting profiled billet are H290mm×100mm×350mm. The surface crack rate of the billet is 0.5%.

[0038] The special-shaped continuous casting billet is heated in a digitally controlled heating furnace. The heating temperature of the billet is 1230°C and the insulation time is 2.8 hours. After being taken out of the furnace, it is descaled using high-pressure water.

[0039] The rough rolling temperature is 1150℃, and water cooling is used for controlled cooling. The rolling passes are 5 times, and then the rough rolled profile is sent to the finishing mill for rolling. The finishing rolling temperature is 930℃, and the finishing rolling adopts warm rolling and water cooling controlled rolling, and the rolling passes are 7 times. The final rolling temperature is 880℃.

[0040] The finished product size is H300×300×10×15×12000mm.

[0041] The surface quality of the finished product of Q355 low-cost hot-rolled H-beam was inspected, and the mechanical properties were tested. No obvious surface quality defects were found during the inspection, the surface quality was good, and all the properties of the H-beam after rolling met the standard requirements.

[0042] Example 2-4: Except for some specific process parameters that are different from those in Example 1, the rest of Example 2-4 is exactly the same as Example 1. See Table 2 for specific process parameters.

[0043] Table 2 Process parameters of each embodiment

[0044]

[0045] Comparative Example 1:

[0046] Comparative Example 1 is completely the same as Example 1 except that Nb element is used to replace Ti element for microalloying, and the surface crack rate of the ingot is 1.5%, which is different from Example 1. The Nb content of this comparative example is 0.028%. Adding one Ti increases the cost by 5.65 yuan; adding one Nb increases the cost by 35.17 yuan. Example 1 adds 3.2 Ti, and Comparative Example 1 adds 2.8 Nb. Compared with Comparative Example 1, the cost of a ton of steel in Example 1 is reduced by 80.4 yuan.

[0047] Comparative Example 2:

[0048] Comparative Example 2 is completely the same as Example 1 except that V is used to replace Ti for microalloying, which is different from Example 1. The V content of this comparative example is 0.030%. Adding one Ti increases the cost by 5.65 yuan; adding one V increases the cost by 23.29 yuan. Example 1 adds 3.2 Ti, and Comparative Example 1 adds 3.0 V. Compared with Comparative Example 2, the cost of one ton of steel in Example 1 is reduced by 51.8 yuan.

[0049] Comparative Example 3:

[0050] Comparative Example 3 is completely the same as Example 1 except that no alloying elements are added, which is different from Example 1.

[0051] Table 3 Non-metallic inclusions and austenite grain size of each embodiment and comparative example

[0052]

[0053] Table 4 Mechanical properties of H-beam after rolling in each example

[0054]

[0055] It can be seen from the above table that the Ti microalloying scheme in the embodiment not only has obvious advantages in reducing costs, but also achieves a lower quality defect rate while maintaining mechanical properties. These advantages are due to the uniform distribution of carbonitrides formed by Ti, carbon and nitrogen at the grain boundaries, which avoids the problem that Nb and V are easy to aggregate and difficult to control at high temperatures. In addition, the price of Ti is more stable and is suitable for existing equipment and processes. Using Ti instead of Nb or V is an innovation in the technical field.

[0056] It can be seen from the above embodiments and comparative examples that:

[0057] (1) Although Nb has a similar grain refining effect as Ti, its price fluctuates greatly and its procurement cost is high. Experimental data show that the cost of using Ti in the embodiment is reduced by about 80 yuan / ton compared with Nb. In terms of mechanical properties, the mechanical properties of Example 1 are equivalent to those of Comparative Example 1, and the strengthening effect of Ti microalloying is equivalent to that of Nb. However, since the carbonitride distribution of Ti is more uniform, the product yield is higher, and the quality defects in the production process are significantly reduced, the comprehensive effect brought by Ti microalloying is significantly better than Nb in terms of production stability.

[0058] (2)(2) V also has the effect of refining grains, but its price is more expensive than Ti. In this case, Ti is used instead of V. The cost of using Ti in the embodiment is reduced by about 50 yuan / ton compared with V. The mechanical properties of the embodiment and comparative example 2 are not much different.

[0059] (3) Comparative Example 3 does not use Ti, V or Nb at all. Although the production cost is the lowest, its mechanical properties are significantly reduced and the impact toughness is also poor, indicating that the same mechanical properties cannot be achieved without adding microalloying elements. This comparison fully proves the significant strengthening effect of Ti microalloying.

[0060] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing Q355 grade low-cost hot-rolled H-beam, characterized in that: Its production process includes: converter smelting, LF refining, profiled billet continuous casting, rolling; among which: For combined-blowing converter smelting, the total charge volume is controlled within the range of 105±2 tons; the low-high-low gun position control method is adopted, and the gun position is between 1.1-1.5m; when the Si content of the molten iron entering the furnace is less than or equal to 0.5%, single slag operation is adopted; and when the Si content is greater than 0.5%, double slag operation is adopted; the terminal basicity must be controlled within the range of 2.7-3.5, and the terminal carbon content C is required to be ≥0.06%, and the temperature T is required to be ≥1620℃; the final deoxidation adopts the Al-containing deoxidation method, and 280-320kg of top slag lime is added during steel tapping. The slide plate slag blocking technology is used during the steel tapping process, and slag is strictly prohibited; Refining, the ladle enters the LF furnace for argon blowing smelting, and the time is controlled at 7-12 minutes; when the top slag of the ladle is fully melted and in good condition, the initial sample is extracted for component analysis, and then titanium wire is fed into it according to the target composition. The wire feeding speed is between 2.5-4.5m / s, and the position where the titanium wire is inserted is located above the bottom blowing hole; the bottom blowing argon stirring is carried out throughout the whole process, and the bottom blowing intensity is set to strong blowing in the early stage, and the blowing volume is in the range of 80-120L / min; when the titanium wire is started to be fed, the bottom blowing intensity is adjusted to normal, that is, 60-100L / min; low-pressure soft blowing is used before the ladle leaves the station, and the soft blowing flow is controlled at 20-30L / min to ensure that inclusions can float up, and the refining soft blowing argon time is greater than 12 minutes; The whole process adopts protective pouring, the baking temperature of the tundish needs to be controlled between 900-920℃, and the baking time is 3.5-5.5 hours; a sealing ring should be added to the water inlet of the large ladle, and protective pouring measures should be implemented throughout the pouring process. The crystallizer adopts the sleeve type protective pouring method, and the crystallizer is an H-type crystallizer; the secondary cooling stage adopts the weak cooling mode to ensure that the straightening temperature is above 800℃; the tundish uses a sizing ladle and is covered with carbonized rice husks to ensure that the liquid surface is well covered; The special-shaped continuous casting billet is heated in a digitally controlled heating furnace, the heating temperature of the billet is 1210-1270°C, the holding time is 2.5-3.5 hours, and the billet is descaled by high-pressure water after being taken out of the furnace; The rough rolling temperature is 1120-1180℃, and water cooling is used for controlled cooling. The rolling passes are 3-5 times, and then the rough rolled profile is sent to the finishing mill for rolling; the finishing rolling temperature is 910-970℃, and the finishing rolling adopts warm rolling and water cooling controlled rolling, and the rolling passes are 5-7 times; the final rolling temperature is 850-880℃, and the total reduction of the two-stage rolling is ≥75%; after the rolling is completed, air cooling is carried out and the profile is sent to the cooling bed for centralized cooling; after the temperature drops below 100℃, it is straightened in the straightening machine, and finally cut to size and bundled; The mass percentage of the chemical composition of the low-cost hot-rolled H-beam includes: C 0.15%-0.25%, Si 0.30%-0.60%, Mn 1.20%-1.70%, P≤0.025%, S≤0.020%, Ti 0.020%-0.040%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

2. The method for producing Q355 grade low-cost hot-rolled H-beam according to claim 1, characterized in that: The cross-sectional dimensions of the continuous casting billet are H290mm×100mm×350mm.

3. The method for producing Q355 grade low-cost hot-rolled H-beam according to claim 1, characterized in that: The surface quality of Q355 grade low-cost hot-rolled H-beam special-shaped continuous casting ingot is inspected, and the internal quality is tested by hot acid at low magnification and the quality of H-beam is tracked and inspected.

4. The method for producing Q355 grade low-cost hot-rolled H-beam according to claim 1, characterized in that: No obvious surface and internal quality defects of the ingot were found during the inspection. The quality of the ingot was good, and the surface crack rate of the ingot was less than 1%.

5. The method for producing Q355 grade low-cost hot-rolled H-beam according to claim 1, characterized in that: The finished product size is H300×300×10×15×12000mm.

6. The method for producing Q355 grade low-cost hot-rolled H-beam according to claim 1, characterized in that: The mass percentage of the chemical composition of the low-cost hot-rolled H-beam includes: C 0.17%, Si 0.37%, Mn 1.32%, P 0.017%, S 0.011%, Ti 0.032%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

7. The method for producing Q355 grade low-cost hot-rolled H-beam according to claim 1, characterized in that: The mass percentage of the chemical composition of the low-cost hot-rolled H-beam includes: C 0.19%, Si 0.40%, Mn 1.37%, P 0.018%, S 0.008%, Ti 0.031%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

8. The method for producing Q355 grade low-cost hot-rolled H-beam according to claim 1, characterized in that: The mass percentage of the chemical composition of the low-cost hot-rolled H-beam includes: C 0.17%, Si 0.38%, Mn 1.33%, P 0.022%, S 0.009%, Ti 0.030%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

9. The method for producing Q355 grade low-cost hot-rolled H-beam according to claim 1, characterized in that: The mass percentage of the chemical composition of the low-cost hot-rolled H-beam includes: C 0.18%, Si 0.43%, Mn 1.36%, P 0.020%, S 0.011%, Ti 0.029%, and the rest is Fe and unavoidable impurities, with a total mass fraction of 100%.

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