Low-cost low-alloy high-strength structural steel q460c hot-rolled steel strip and production method thereof

Abstract

The application discloses a low-cost low-alloy high-strength structural steel Q460C hot-rolled steel strip and a production method thereof, wherein the chemical components are as follows in percentage by mass: C: 0.16-0.18%, Si: 0.15-0.25%, Mn: 0.65-0.85%, P: 0.020% or less, S: 0.010% or less, Ti: 0.040-0.055%, the balance being Fe and inevitable impurities, and Nb is not contained. The production method comprises the following steps: a casting blank heating process, a hot rolling process and a cooling and coiling process. By adopting the "C-Mn-Ti" low-cost alloy design system, the traditional "C-Mn-Nb" system is completely replaced, and the optimized controlled rolling and controlled cooling process is matched, so that the alloy cost is significantly reduced under the premise of guaranteeing the mechanical properties of the Q460C, the ton steel cost is reduced by about 162 yuan, and good economic benefits and market competitiveness are achieved.

Description

Technical Field

[0001] This invention belongs to the field of steel materials technology, specifically relating to a low-cost, low-alloy, high-strength structural steel Q460C hot-rolled steel strip and its production method. Background Technology

[0002] With the transformation and upgrading of the steel industry, low-cost, high-efficiency, and high-quality production models have become key for enterprises to enhance their core competitiveness. Q460C, as a representative grade of low-alloy high-strength structural steel, is widely used in engineering machinery, bridge construction, vehicle manufacturing, and other fields, with huge market demand.

[0003] Traditional Q460C products often employ a "C-Mn-Nb" or "C-Mn-V" microalloying system, which refines the grain and improves strength by adding precious microalloying elements such as Nb and V. However, in recent years, the prices of alloys such as Nb and V have continued to rise, resulting in persistently high alloy costs per ton of steel and severely squeezing the profit margins of steel companies.

[0004] To reduce production costs, some studies have attempted to partially replace Nb or V with relatively inexpensive Ti. For example, existing technology (CN104651716A) discloses a method for producing low-alloy Q460C steel plates using a composite addition of Nb and Ti, where the Mn content is still as high as 1.45–1.55%. However, this approach still cannot completely eliminate the dependence on expensive Nb, and the high Mn content adversely affects the weldability and low-temperature toughness of the steel.

[0005] Therefore, how to develop a low-cost production method that completely eliminates Nb, significantly reduces Mn content, and still ensures the strength and toughness matching of Q460C is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-cost, low-alloy, high-strength structural steel Q460C hot-rolled steel strip and its production method. Through precise “C-Mn-Ti” composition design and optimized controlled rolling and cooling process, it can completely replace Nb-based alloys, significantly reduce alloy costs, and maintain excellent mechanical properties.

[0007] Specifically, this invention provides a method for producing low-cost, low-alloy, high-strength structural steel Q460C hot-rolled strip. This method optimizes the chemical composition of existing C-Mn-Nb series low-alloy high-strength structural steel Q460C and combines optimized billet heating, rolling, and coiling processes to obtain the low-cost, low-alloy, high-strength structural steel Q460C hot-rolled strip.

[0008] The chemical composition of the C-Mn-Nb series low-alloy high-strength structural steel Q460C, by mass percentage, is: C: 0.06~0.08%, Si: 0.10~0.20%, Mn: 1.30~1.50%, P≤0.018%, S≤0.008%, Nb: 0.025~0.035%, with the balance being Fe and associated inclusions. The chemical composition of the optimized C-Mn-Ti series low-cost low-alloy high-strength structural steel Q460C hot-rolled steel strip, by mass percentage, is: C: 0.16~0.18%, Si: 0.15~0.25%, Mn: 0.65~0.85%, P≤0.020%, S≤0.010%, Ti: 0.040~0.055%, with the balance being Fe and associated inclusions.

[0009] The production method includes the following steps:

[0010] Billet heating process: The billet is heated to 1230±20℃ and held for 24~60min. This temperature range ensures sufficient TiC solution while avoiding excessive coarsening of austenite grains. The holding time ensures uniform billet temperature.

[0011] The rolling process is as follows: the initial rolling temperature is 1220~1260℃, the rough rolling process adopts a 3+3 mode, and the final rolling temperature is 835~890℃; the initial rolling temperature is connected with the heating temperature, utilizing recrystallization in the rough rolling stage to refine the grains. The final rolling temperature is controlled in the higher range of 835~890℃ to roll in the non-recrystallized (or partially recrystallized) austenite region, increasing the dislocation density and providing more nucleation sites for subsequent TiC precipitation;

[0012] The winding process involves a winding temperature of 575~620℃; the winding temperature is crucial for controlling TiC precipitation. 575~620℃ is the "window temperature" for the large-scale dispersion and precipitation of TiC. If the winding temperature is below 575℃, the TiC precipitation momentum is insufficient, resulting in poor strengthening effect; if it is above 620℃, the precipitated particles coarsen, weakening the strengthening effect.

[0013] The core of this invention lies in employing a "high carbon-low manganese-titanium microalloying" composition system, completely eliminating the nitrogen (Nb) element. The roles and rationale for each element are as follows:

[0014] C (carbon): 0.16–0.18%

[0015] Carbon is the most economical element for improving the strength of steel, mainly through solid solution strengthening and precipitation strengthening by forming TiC with Ti. This application controls the C content at 0.16–0.18%, higher than the 0.06–0.08% of the traditional C-Mn-Nb system. The higher C content compensates for the strength loss caused by Nb removal and Mn reduction, and also allows for the formation of sufficient TiC particles with Ti, which precipitate during the coiling process, resulting in a significant precipitation strengthening effect. If the C content is below 0.16%, the precipitation strengthening effect is insufficient; if it is above 0.18%, it adversely affects weldability and toughness.

[0016] Mn (manganese): 0.65–0.85%

[0017] This application significantly reduces the Mn content from 1.30–1.50% in the traditional system to 0.65–0.85%. Although Mn can strengthen through solid solution and expand the austenite phase region, high Mn content reduces the weldability of steel, increases segregation tendency, and is relatively expensive. This invention compensates for the strength loss caused by low Mn content through TiC precipitation strengthening, achieving the effect of "replacing Mn with Ti". If the Mn content is below 0.65%, the strength is difficult to guarantee; if it is above 0.85%, the cost advantage is weakened, and the improvement in weldability is not significant.

[0018] Ti (Titanium): 0.040~0.055%

[0019] Titanium is the core microalloying element in this invention. In steel, Ti can form two important types of second-phase particles: TiN precipitated at high temperatures (liquid precipitation) pins grain boundaries, inhibiting austenite grain growth; TiC particles precipitated during low-temperature coiling produce significant precipitation strengthening. This application precisely controls the Ti content to 0.040–0.055% and limits the Ti / C mass ratio to 0.25–0.32 to ensure sufficient TiC precipitation. If the Ti content is too low, the precipitation strengthening effect is insufficient; if the Ti content is too high, coarse TiN inclusions are easily formed, impairing toughness.

[0020] Nb, V: 0% (excluding)

[0021] This application completely eliminates expensive alloying elements such as Nb and V, significantly reducing alloy costs.

[0022] In some embodiments, the mass percentages of Ti and C in the chemical composition of the hot-rolled steel strip satisfy the following: Ti / C = 0.25 to 0.32.

[0023] In some embodiments, the thickness of the hot-rolled steel strip is 2.0 to 13.0 mm, and the microstructure of the hot-rolled steel strip is ferrite + pearlite, with the ferrite grain size ≥ 11.

[0024] In some embodiments, the thickness of the billet is 230 mm, and the continuous casting speed is 1.0 to 1.5 m / min.

[0025] In some embodiments, the production method is based on a 2250mm hot rolling production line and includes, in sequence: billet heating → high-pressure water descaling → width-fixing press → E1R1 roughing → E2R2 roughing → flying shear → high-pressure water descaling → F1~F7 finishing rolling → dense laminar flow cooling → coiling.

[0026] Another aspect of the present invention provides a low-cost, low-alloy, high-strength structural steel Q460C hot-rolled steel strip prepared by the above method, with a yield strength ≥460MPa, a tensile strength of 520~720MPa, an elongation ≥17%, and an impact energy at 0℃ (5×5×10mm specimen) ≥34J.

[0027] The beneficial effects of this invention are:

[0028] 1. Significantly reduced costs: By completely eliminating the expensive Nb element and significantly reducing the Mn content, the cost per ton of steel alloy is reduced by approximately 162 yuan compared to the traditional C-Mn-Nb system.

[0029] 2. Excellent performance: The product has a yield strength ≥460MPa (preferably ≥500MPa), tensile strength 520~720MPa (preferably 600~720MPa), elongation ≥17% (preferably ≥23%), and impact energy at 0℃ ≥34J (preferably ≥70J), fully meeting the requirements of GB / T 1591-2018 standard for Q460C.

[0030] 3. Good process adaptability: Based on a conventional 2250mm hot continuous rolling production line, no additional equipment investment is required, making it easy to promote. Detailed Implementation

[0031] To address the problems existing in the prior art, this invention adjusts the composition of the Q460C product by replacing the current product's "C-Mn-Nb" composition system (C: 0.06~0.08%, Si: 0.10~0.20%, Mn: 0.65~0.85%, P≤0.020%, S≤0.010%, Ti: 0.040~0.055%, balance Fe and associated inclusions) with a "C-Mn-Ti" composition system (C: 0.16~0.18%, Si: 0.15~0.25%, Mn: 1.30~1.50%, P≤0.018%, S≤0.008%, Nb: 0.025~0.035%, balance Fe and associated inclusions) design concept.

[0032] The objective of this invention is achieved through the following technical solution:

[0033] A method for producing low-cost, low-alloy, high-strength structural steel hot-rolled strip, comprising the following steps:

[0034] (1) Steelmaking process: Based on the chemical composition of the existing "C-Mn-Nb" composition system of Q460C products (C: 0.06~0.08%, Si: 0.10~0.20%, Mn: 1.30~1.50%, P≤0.018%, S≤0.008%, Nb: 0.025~0.035%, with the balance being Fe and accompanying inclusions), the content of Mn element is reduced by about 0.65%, Nb element is eliminated, and about 0.10% of C element and about 0.05% of Ti element are added to obtain the continuous casting billet of the low-cost low-alloy high-strength structural steel hot-rolled steel strip of the present invention; wherein the steelmaking process includes the following steps: blast furnace → KR desulfurization → converter → LF refining → slab continuous casting, the continuous casting speed is 1.0~1.5m / min, and the billet thickness is 230mm.

[0035] (2) Billet heating, rolling and coiling processes:

[0036] Specifically, the process includes the following steps based on a 2250mm hot rolling production line: billet heating, high-pressure water descaling, width-fixing press, E1R1 roughing mill rolling, E2R2 roughing mill rolling, flying shear, high-pressure water descaling, F1~F7 finishing mill rolling, dense laminar flow cooling, coiling, pallet transport system, warehousing, sampling and inspection, weighing and packaging.

[0037] The billet heating temperature is 1230±20℃, and the holding time is 24~60min; the initial rolling temperature is 1220~1260℃, the rough rolling process adopts the 3+3 mode, the final rolling temperature is 835~890℃; and the coiling temperature is 575~620℃.

[0038] The final product is a thick, low-cost, low-alloy, high-strength Q460C hot-rolled steel strip.

[0039] (3) Analyze the microstructure and properties of the low-cost, low-alloy, high-strength Q460C hot-rolled steel strip prepared in step (2) to determine whether its microstructure, grain size grade and properties meet the requirements.

[0040] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0041] Example 1

[0042] (1) For the old composition Q460C product (C: 0.06~0.08%, Si: 0.10~0.20%, Mn: 1.30~1.50%, P≤0.018%, S≤0.008%, Nb: 0.025~0.035%, balance is Fe and accompanying inclusions), the chemical composition of the low-cost low alloy high-strength Q460C steel strip of the present invention (C: 0.16~0.18%, Si: 0.15~0.25%, Mn: 0.65~0.85%, P≤0.020%, S≤0.010%, Ti: 0.040~0.055%, balance is Fe and accompanying inclusions) is developed and designed as shown in Table 1 below.

[0043] Table 1: Chemical composition of hot-rolled steel strip (by mass percentage)

[0044]

[0045] (2) The continuous casting speed is 1.0~1.5m / min, and a slab with a thickness of 230mm is obtained.

[0046] The heating conditions for the original low-alloy high-strength Q460C billet are as follows: billet heating temperature is 1240±20℃, and holding temperature is 25~60min; the rolling conditions are as follows: rough rolling adopts 3+3 mode, final rolling temperature is 855~895℃; coiling temperature is 605~635℃. Specific process parameters are shown in Table 2 below.

[0047] The heating process conditions for low-cost, low-alloy, high-strength Q460C billets are as follows: billet heating temperature is 1230±20℃, holding temperature is 24~60min; the rolling process conditions are as follows: rough rolling adopts 3+3 mode, final rolling temperature is 835~890℃; coiling temperature is 575~620℃. Specific process parameters are shown in Table 2 below.

[0048] Table 2: Process Parameters for Each Example

[0049]

[0050] (3) The production cost of Q460C can be reduced by adopting the above-mentioned production process. According to the performance feedback from the chemical testing, as shown in Table 3, the composition before and after the adjustment met the standard requirements in the tensile test and the +20℃ impact test, but the cost of the new composition alloy was about 162 yuan lower than the original cost per ton of steel.

[0051] Table 3: Performance Distribution of Q460C

[0052]

[0053] As shown in Table 3, the mechanical properties of Q460C produced using cost-reducing components all meet the requirements of the Q460C standard, and all have a large margin, indicating that the technical solution of the present invention is stable and feasible.

[0054] Comparative Example 1

[0055] The 8mm thick Q460C steel plate was produced using the typical composition and process disclosed in the existing technology CN104651716A. It should be noted that CN104651716A produces steel plates (thick plate line), which differs from the hot strip rolling line used in this invention in terms of equipment. However, for the purpose of comparing alloy design concepts, this comparative example 1 was verified and reproduced on the hot strip rolling line with the process parameters disclosed therein.

[0056] Chemical composition: C 0.16%, Si 0.35%, Mn 1.50%, Nb 0.025%, Ti 0.018%, Al 0.03%, V-free; Process: Initial rolling temperature 1120℃, final rolling temperature 820℃, coiling temperature 640℃. Performance test results are shown in Table 4 below, with alloy cost calculated based on current market prices (2026).

[0057] Table 4: Performance and Cost of Comparative Example 1

[0058]

[0059] As can be seen from the results in Table 4 above, although Comparative Example 1 can also meet the performance requirements, its alloy cost is much higher than that of the embodiments of the present invention, and it still relies on Nb element, which does not meet the ultimate requirement of cost reduction.

[0060] Comparative Example 2

[0061] The operation is the same as that of 254116138 (cost-reduction component), the only difference being the chemical composition design. Specifically, the Ti content in this comparative example 2 is 0.030%, while the contents of other elements are the same. The performance test results are shown in Table 5 below.

[0062] Table 5: Performance of Comparative Example 2

[0063]

[0064] As shown in Table 5 above, due to the low Ti content and insufficient TiC precipitation, the yield strength is lower than 460 MPa, which does not meet the Q460C requirement.

[0065] Comparative Example 3

[0066] The operation is the same as that of 254116138 (cost reduction component), except for the winding temperature. Specifically, the winding temperature of this comparative example 3 is 650℃. The performance test results are shown in Table 6 below.

[0067] Table 6: Performance of Comparative Example 3

[0068]

[0069] If the winding temperature is too high, the TiC particles coarsen, the precipitation strengthening effect weakens, the yield strength approaches the lower limit of the standard, and the performance margin is insufficient.

[0070] Comparative Example 4 (winding temperature exceeds the lower limit of this invention)

[0071] The operation is the same as that of 254116138 (cost reduction component), except for the winding temperature. Specifically, the winding temperature of this comparative example 3 is 550℃. The performance test results are shown in Table 7 below.

[0072] Table 7: Performance of Comparative Example 4

[0073]

[0074] If the winding temperature is too low, TiC precipitation will be insufficient, and the impact toughness will decrease significantly. The impact energy at 0℃ will not meet the requirements.

[0075] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing low-cost, low-alloy, high-strength structural steel Q460C hot-rolled strip, characterized in that, The chemical composition of the hot-rolled steel strip, by mass percentage, is: C: 0.16–0.18%, Si: 0.15–0.25%, Mn: 0.65–0.85%, P≤0.020%, S≤0.010%, Ti: 0.040–0.055%, with the balance being Fe and unavoidable impurities; and the chemical composition does not contain Nb. The production method includes the following steps: Billet heating process: heating temperature is 1230±20℃, holding time is 24~60min; Hot rolling process: The initial rolling temperature is 1220~1260℃, the roughing rolling mode is 3+3, and the final rolling temperature is 835~890℃; Cooling and winding process: Laminar flow cooling is adopted, and the winding temperature is 575~620℃.

2. The production method according to claim 1, characterized in that, The chemical composition of the hot-rolled steel strip has a Ti / C mass percentage of 0.25 to 0.

32.

3. The production method according to claim 1, characterized in that, The thickness of the hot-rolled steel strip is 2.0 to 13.0 mm, and the microstructure of the hot-rolled steel strip is ferrite + pearlite, with the ferrite grain size ≥ 11.

4. The production method according to claim 1, characterized in that, The thickness of the billet is 230 mm, and the continuous casting speed is 1.0 to 1.5 m / min.

5. The production method according to claim 1, characterized in that, The production method is based on a 2250mm hot rolling production line and includes the following steps in sequence: billet heating → high-pressure water descaling → width-fixing press → E1R1 rough rolling → E2R2 rough rolling → flying shear → high-pressure water descaling → F1~F7 finish rolling → dense laminar flow cooling → coiling.

6. A low-cost, low-alloy, high-strength structural steel Q460C hot-rolled strip, characterized in that, It is produced by the production method according to any one of claims 1 to 5.

7. The hot-rolled steel strip according to claim 6, characterized in that, Its yield strength is ≥500MPa, tensile strength is 600~720MPa, elongation is ≥17%, and impact energy at 0℃ (5×5×10mm specimen) is ≥75J.

Images