A continuous casting method of heavy section beam blank with high ratio of secondary dendrite arm spacing

Abstract

The application discloses a continuous casting method of heavy section beam blank with high axis crystal rate, which comprises the following steps: controlling the superheat of the molten steel ΔT; controlling the pouring speed of the molten steel Vc; carrying out electromagnetic stirring on the web and the flange of the secondary cooling zone; controlling the secondary cooling intensity, the cooling water amount of each section and the distribution of the cooling water amount of each surface; and reasonably distributing the cooling area of each section to produce the heavy section beam blank with the axis crystal rate of 40-55%. The method is suitable for the heavy section beam blank with the weight of more than 1.5 tons per meter.

Description

Technical Field

[0001] This invention belongs to the field of special-shaped billet production technology, specifically relating to a continuous casting method for heavy special-shaped billets with high axial crystal ratio. Background Technology

[0002] Hot-rolled H-beams are profiled steel products with excellent mechanical properties and superior performance. Due to their economical and reasonable cross-section, superior performance, and simple, convenient, and quick processing, fabrication, and installation, they have become "high-efficiency and energy-saving pioneers" in building steel structure systems, serving as the backbone of large buildings. They are widely used in beams and columns of industrial and civil building steel structures, steel structural supports for industrial buildings, steel piles and support structures for underground engineering, and structures for industrial equipment in petrochemical and power industries. Simultaneously, their application is further promoted in aircraft terminal construction, shipbuilding, offshore oil and gas platforms, machinery manufacturing frame structures, and railway, highway, and bridge construction. With the continuous development of high-rise buildings and heavy equipment, H-beams are evolving towards heavier, higher-strength, and more versatile applications. Currently, Maanshan Iron & Steel has developed H-beam specifications with flange thicknesses exceeding 100mm. The mechanical properties of H-beams are continuously improving, and special-purpose H-beams also have requirements for low-temperature performance and Z-axis performance.

[0003] Hot-rolled H-beams are formed by hot rolling shaped billets. With the increasing size, weight, and variety of H-beams, the quality requirements for shaped billets are also constantly rising. Shaped billets are becoming increasingly heavy. Maanshan Iron & Steel's heavy shaped billet has a maximum cross-section of 1300mm×510mm×140mm×215mm, which is currently the largest shaped billet cross-section in China, with a weight per meter reaching 2.8t / m and a flange thickness of 215mm. With the increasing weight of shaped billets, the difficulty of quality control for continuously cast billets has increased, especially the internal quality. Furthermore, heavy H-beams produced using heavy shaped billets have flange thicknesses exceeding 100mm, resulting in a very small flange compression ratio of only around 2.0, and even less than 2.0 for the extreme thickness specifications. This further places higher demands on the internal quality of heavy shaped billets. Therefore, the internal quality of heavy shaped billets is crucial, and it is imperative to improve the internal quality by increasing the equiaxed crystal ratio.

[0004] H-beams require excellent cross-sectional properties, meaning good web and flange properties. Therefore, shaped billets need good internal quality across the entire cross-section. Improving the equiaxed grain ratio of continuously cast billets is the fundamental method for improving their internal quality. Currently, some methods successfully applied to slab continuous casting machines to improve equiaxed grain ratio are not applicable to shaped billet continuous casting machines. For example, light reduction technology is unsuitable because the shaped billet has an H-shaped structure; light reduction of the web inevitably leads to flange deformation or even tearing. Furthermore, since there are no support rollers on the inner side of the flanges during continuous casting, light reduction technology cannot be applied to the web. Another example is electromagnetic stirring technology. In shaped billet continuous casting machines, stirring the molten steel in both the web and flange areas, as well as considering their interactions, results in a fundamentally different electromagnetic stirring structure compared to slab continuous casting machines, making it unsuitable for direct application. Therefore, improving the equiaxed grain ratio of heavy shaped billets is more challenging than that of slabs, requiring the development of high equiaxed grain ratio control technologies specifically tailored to the characteristics of heavy shaped billet continuous casting machines.

[0005] However, no existing technology has disclosed a strategy for improving the axial ratio of irregularly shaped blanks. Summary of the Invention

[0006] The purpose of this invention is to provide a continuous casting method for heavy shaped billets with high axial crystal ratio. This method is applicable to heavy shaped billets with a weight of more than 1.5 tons per meter, especially H-beam billets with a width of 900-1300 mm, a height of 400-550 mm, a web thickness of 120-140 mm, and a flange thickness of 100-220 mm. Using this method, heavy shaped billets with a high axial crystal ratio of 40-55% can be obtained.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A continuous casting method for heavy shaped billets with high axial crystal ratio is disclosed. In the continuous casting step of the heavy shaped billet, the superheat of molten steel ΔT is controlled between 15 and 30°C; the pouring speed Vc, the superheat of molten steel ΔT, and the weight per meter of the shaped billet Q are controlled to satisfy: 1.37≤Q*Vc=(1.67-0.01ΔT)≤1.52, where Vc is in m / min, ΔT is in °C, and Q is in t / m; the secondary cooling water ratio is controlled between 0.5 and 0.55 L / kg; and electromagnetic stirring is performed on the web and flanges of the secondary cooling zone.

[0009] The secondary cooling water distribution ratio is as follows: Foot roller zone: Moving section zone: Zone 1: Zone 2: Zone 3: 10-12%: 13-17%: 38-42%: 18-22%: 12-16%.

[0010] The water distribution for the inner and outer arcs and sides of each section of the secondary cooling system is as follows: the water volume for the foot roller, moving section, and Zone 1 is the same for both inner and outer arcs, and the water volume for both sides is 50% of the total water volume for both inner and outer arcs; the water volume for the inner arc in Zone 2 is 67-72% of the water volume for the outer arc, and the water volume for both sides is 60-67% of the total water volume for both inner and outer arcs; the water volume for the inner arc in Zone 3 is 57-62% of the water volume for the outer arc, and the water volume for both sides is the same as the total water volume for both inner and outer arcs.

[0011] Different cooling area ratios are adopted for different parts of the secondary cooling zone. The cooling area ratios for the foot roller area, moving section area, Zone 1, Zone 2, and Zone 3, and the inner and outer arcs are 100%, 100%, 72%–77%, 57%–62%, and 55%–60%, respectively; the cooling area ratios for the sides are 100%, 100%, 75%–80%, 60%–65%, and 47%–52%, respectively.

[0012] The electromagnetic stirring rollers on the web and flanges are installed in a sector-shaped section of Zone 1.

[0013] The parameters for the electromagnetic stirring of the web plate are: current 300-400A, frequency 2-7Hz, and stirring method is butterfly.

[0014] The parameters for the flange electromagnetic stirrer are: current 350-450A, frequency 2-7Hz, and stirring method is butterfly-shaped.

[0015] The equiaxed crystallinity of the heavy-duty irregular blank is 40-55%.

[0016] The heavy-duty special-shaped billet has a weight of more than 1.5 tons per meter, a width of 900-1300 mm, a height of 400-550 mm, a web thickness of 120-140 mm, and a flange thickness of 100-220 mm.

[0017] The key control points and effects of each process parameter in the continuous casting method for high axial crystal ratio heavy irregular billets provided by this invention are as follows:

[0018] The superheat ΔT of continuously cast steel has a significant impact on the formation of equiaxed crystals in irregularly shaped billets. Reducing the superheat of continuously cast steel can decrease the temperature gradient between the liquid steel inside the solidified billet shell and the steel at the solidification front, forming a compositionally subcooled zone at the crystallization front of columnar crystals. This generates a large number of new crystal nuclei that grow into equiaxed crystals, blocking the growth of columnar crystals and increasing the nucleation and growth area of ​​equiaxed crystals. However, the superheat of continuously cast steel also affects the smooth pouring of molten steel and the melting of the protective slag. Too low a superheat can lead to the inability to pour the steel, poor melting of the protective slag, and the generation of leaks or surface defects in the billet. Therefore, it is necessary to control the superheat of continuously cast steel appropriately. In this invention, the superheat ΔT of continuously cast steel is controlled between 15 and 30°C.

[0019] The pouring speed (Vc) of molten steel directly affects the growth rate of the solidified billet shell. Since the heat transfer rate of the solid billet shell is lower than that of the liquid molten steel, it affects the temperature gradient of the liquid molten steel within the solidified shell. A faster pouring speed means the molten steel temperature within the shell cannot be transferred quickly enough, resulting in a larger temperature gradient between the liquid molten steel inside the solidified shell and the molten steel at the solidification front. This is unfavorable for equiaxed crystal growth. Therefore, a lower pouring speed is beneficial for increasing the equiaxed crystal ratio. Simultaneously, the pouring speed is also related to the cross-section and superheat of the shaped billet. A larger cross-section requires a slower pouring speed; a higher superheat results in a higher temperature of the molten steel within the solidified shell, requiring more heat transfer time and thus a lower pouring speed. Therefore, the pouring speed, the weight per meter of the shaped billet, and the superheat of the continuously cast molten steel interact and must satisfy the following condition: 1.37 ≤ Q * Vc = (1.67 - 0.01ΔT) ≤ 1.52, where Vc is in m / min, ΔT is in °C, and Q is in t / m.

[0020] The intensity of the secondary cooling process directly affects the temperature gradient between the liquid steel inside the solidified billet shell and the steel at the solidification front within the secondary cooling section. Stronger cooling results in a larger temperature gradient, which is more conducive to columnar crystal growth and less conducive to increasing the equiaxed crystal ratio. Therefore, a weak cooling process with a lower cooling intensity and a water volume controlled at 0.5–0.55 L / kg is adopted. The distribution ratio of cooling water volume in each section of the secondary cooling process must meet the following requirements: Foot roll area: Moving section area: Zone 1: Zone 2: Zone 3: 10–12%: 13–17%: 38–42%: 18–22%: 12–16%.

[0021] Furthermore, due to the shape characteristics of the irregular billet, the cooling water sprayed onto the inner arc will remain on the web and flow downwards along the length of the billet, while the cooling water sprayed onto the outer arc will detach from the billet surface due to gravity. The cooling efficiency of the inner arc cooling water is higher than that of the outer arc. To ensure the uniformity of billet shell cooling, the water distribution must meet the following requirements: the water volume of the foot roller, the moving section area, and the inner and outer arcs of Zone 1 is the same, and the water volume of the two sides is 50% of the total water volume of the inner and outer arcs; the water volume of the inner arc in Zone 2 is 67-72% of the water volume of the outer arc, and the water volume of the two sides is 60-67% of the total water volume of the inner and outer arcs; the water volume of the inner arc in Zone 3 is 57-62% of the water volume of the outer arc, and the water volume of the two sides is the same as the total water volume of the inner and outer arcs.

[0022] Furthermore, due to the varying thickness of the irregularly shaped billet at different locations, different cooling area ratios (the proportion of cooling area to the surface area of ​​the billet in that area) are adopted for each part to reduce the differences in cooling intensity. The cooling area ratios for the foot roll, moving section, Zone 1, Zone 2, and the inner and outer arcs of Zone 3 are 100%, 100%, 72%–77%, 57%–62%, and 55%–60%, respectively; the side cooling area ratios are 100%, 100%, 75%–80%, 60%–65%, and 47%–52%, respectively.

[0023] The secondary cooling electromagnetic stirring is installed in the secondary cooling section of the heavy-duty shaped billet continuous casting machine. In this area, columnar crystals in the shaped billet grow vigorously. The electromagnetic stirrer can homogenize the composition and temperature of the molten steel within the billet shell, breaking up or inhibiting columnar crystal growth. Stirring also breaks up dendrite bridging within the liquid phase cavity; these broken dendrites become nuclei for equiaxed crystals, expanding the equiaxed crystal region. To fully utilize the electromagnetic stirring effect in the secondary cooling zone, the stirring zone must have a certain liquid core thickness. Therefore, the electromagnetic stirring rollers on the web and flanges are installed within a fan-shaped section of the first zone. The electromagnetic stirring force is directly proportional to the magnitude of the magnetic induction intensity, which is directly proportional to the electromagnetic stirring current and inversely proportional to the frequency. At a constant frequency, a larger current results in a larger magnetic induction intensity and stronger stirring. Conversely, at a constant current, the magnetic induction intensity decreases with increasing frequency, and the stirring intensity weakens. For carbon structural steel, the required electromagnetic stirring force depends on the carbon content; the higher the carbon content, the greater the required electromagnetic stirring force. Since the carbon content of the carbon structures produced from heavy shaped billets is relatively low, between 0.08% and 0.23%, a particularly large electromagnetic stirring force is not required. Considering the thickness of the billet in different parts of the heavy shaped billet, the electromagnetic stirring current and frequency must meet the following requirements:

[0024] Electromagnetic stirring of the web plate: current 300-400A, frequency 2-7Hz.

[0025] Flange electromagnetic stirring: current 350~450A, frequency 2-7Hz.

[0026] Electromagnetic stirring can employ either a single-ring butterfly stirring method or a double-ring butterfly stirring method. The double-ring butterfly method is more conducive to the exchange of heat between the high-temperature molten steel at the top and the low-temperature molten steel at the bottom over a longer distance, which helps to uniformly heat the molten steel within the billet shell, reduce superheat, and improve the equiaxed crystal ratio. Therefore, the double-ring butterfly stirring method is adopted.

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

[0028] The heavy-duty irregular billet produced using the process of this invention has an equiaxed crystal ratio of 40-55%, which is more than 10% higher than that produced without this process, greatly improving the internal quality of the heavy-duty irregular billet. Attached Figure Description

[0029] Figure 1 The image shows the heavy irregular-shaped billet in Example 3, with an equiaxed crystallinity of 46.9%.

[0030] Figure 2 The image shows a heavy-duty irregular billet in Comparative Example 2, with an equiaxed crystal ratio of 30.3%.

[0031] Figure 3 This is a schematic diagram of the irregular blank shape. Detailed Implementation

[0032] This invention provides a continuous casting method for heavy special-shaped billets with high axial crystal ratio. In the continuous casting step of heavy special-shaped billets, the superheat of molten steel ΔT is controlled; the pouring speed of molten steel Vc is controlled; electromagnetic stirring is performed on the web and flange of the secondary cooling zone; the intensity of secondary cooling is controlled; the cooling water volume of each section of secondary cooling and the distribution of cooling water volume of each surface are controlled; and the cooling area of ​​different parts of each section is reasonably allocated.

[0033] The specific controls are as follows:

[0034] The superheat ΔT of continuously cast steel is controlled between 15 and 30°C.

[0035] The pouring speed of molten steel Vc, the superheat of molten steel ΔT, and the weight per meter of the special-shaped billet Q satisfy the following: 1.37≤Q*Vc=(1.67-0.01ΔT)≤1.52, where Vc is in m / min, ΔT is in ℃, and Q is in t / m.

[0036] The secondary cooling water volume is controlled at 0.5–0.55 L / kg. The cooling water distribution for each section is as follows: foot roller area: moving section area: zone 1: zone 2: zone 3: 10–12% : 13–17% : 38–42% : 18–22% : 12–16%.

[0037] Furthermore, the water distribution for each section of the inner and outer arcs and sides is as follows: the water volume of the foot roller, the moving section area, and the inner and outer arcs of Zone 1 is the same, and the water volume of the two sides is 50% of the total water volume of the inner and outer arcs; the water volume of the inner arc in Zone 2 is 67-72% of the water volume of the outer arc, and the water volume of the two sides is 60-67% of the total water volume of the inner and outer arcs; the water volume of the inner arc in Zone 3 is 57-62% of the water volume of the outer arc, and the water volume of the two sides is the same as the total water volume of the inner and outer arcs.

[0038] Furthermore, different cooling area ratios (the ratio of cooling area to the surface area of ​​the billet in that area) are adopted for different parts of the secondary cooling zone. The cooling area ratios for the foot roll, moving section, Zone 1, Zone 2, and the inner and outer arcs of Zone 3 are 100%, 100%, 72%–77%, 57%–62%, and 55%–60%, respectively; the side cooling area ratios are 100%, 100%, 75%–80%, 60%–65%, and 47%–52%, respectively.

[0039] The second cooling plate and the flange electromagnetic stirring roller are installed in the sector section of Zone 1.

[0040] Controlling the electromagnetic stirring current and frequency parameters:

[0041] Electromagnetic stirring of the web plate: current 300-400A, frequency 2-7Hz.

[0042] Flange electromagnetic stirring: current 350~450A, frequency 2-7Hz.

[0043] The electromagnetic stirring method employs a double-ring butterfly stirring mechanism.

[0044] The equiaxed crystallinity of the heavy-duty irregular blank is 40-55%.

[0045] The present invention will now be described in detail with reference to the embodiments.

[0046] Table 1 shows the process parameters and equiaxed crystal ratio values ​​of the H-beam billets produced in each embodiment and comparative example during the continuous casting process.

[0047] Table 1

[0048]

[0049]

[0050] In the table, the dimensions of the BB5 section are H×B×T1×T2=910mm×510mm×130mm×165mm; the dimensions of the BB6 section are H×B×T1×T2=1030mm×440mm×130mm×112.5mm; and the dimensions of the BB7 section are H×B×T1×T2=1300mm×510mm×140mm×215mm; where H is the width, B is the height, T1 is the web thickness, and T2 is the flange thickness. Figure 3 As shown.

[0051] Table 2, following Table 1

[0052]

[0053]

[0054] In the above cases, the distribution ratio of cooling water in each section of the secondary cooling system in Comparative Example 1 was not controlled according to the requirements of this invention; the cooling area of ​​each section of the secondary cooling system in Comparative Example 2 was not controlled according to the requirements of this invention; the superheat of molten steel ΔT in the tundish in Comparative Example 3 was not controlled within the range of 15-30℃ as required by this invention; the secondary cooling intensity water volume in Comparative Example 4 was not controlled according to the requirement of 0.5-0.55 L / kg for secondary cooling water volume as required by this invention; the relationship between the superheat of molten steel ΔT, molten steel pouring speed, and the weight per meter of the shaped billet Q in Comparative Example 5 was not controlled according to the requirement of Q*Vc=(1.67-0.01ΔT); and electromagnetic stirring of the web and flange was not used as required by this invention in Comparative Example 6. Due to the lack of control according to the requirements of this invention in Comparative Examples 1 to 6, the equiaxed crystal ratio of the heavy shaped billets was less than 35%, which was significantly lower than that of the embodiments and did not meet the high equiaxed crystal ratio requirement of 40-55% of this invention.

[0055] The above detailed description of a continuous casting method for a heavy-duty irregular billet with high axial crystal ratio, with reference to the embodiments, is illustrative rather than limiting. Several embodiments can be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A continuous casting method for heavy-duty irregular billets with high equiaxed crystal ratio, characterized in that, In the continuous casting process of heavy special-shaped billets, the superheat of molten steel ΔT is controlled between 15 and 30°C; the pouring speed Vc, superheat of molten steel ΔT, and weight per meter of special-shaped billet Q are controlled to meet the following conditions: 1.37≤Q*Vc=(1.67-0.01ΔT)≤1.52, where Vc is in m / min, ΔT is in °C, and Q is in t / m; the secondary cooling water volume is controlled between 0.5 and 0.55 L / kg; electromagnetic stirring is performed on the web and flanges of the secondary cooling zone.

2. The continuous casting method for high-equiaxed heavy-duty irregular billets according to claim 1, characterized in that, The secondary cooling water distribution ratio is as follows: Foot roller zone: Moving section zone: Zone 1: Zone 2: Zone 3: 10-12%: 13-17%: 38-42%: 18-22%: 12-16%.

3. The continuous casting method for high-equiaxed heavy-duty irregular billets according to claim 2, characterized in that, The water distribution for the inner and outer arcs and sides of each section of the secondary cooling system is as follows: the water volume for the foot roller, moving section, and Zone 1 is the same for both inner and outer arcs, and the water volume for both sides is 50% of the total water volume for both inner and outer arcs; the water volume for the inner arc in Zone 2 is 67-72% of the water volume for the outer arc, and the water volume for both sides is 60-67% of the total water volume for both inner and outer arcs; the water volume for the inner arc in Zone 3 is 57-62% of the water volume for the outer arc, and the water volume for both sides is the same as the total water volume for both inner and outer arcs.

4. The continuous casting method for high-equiaxed heavy-duty irregular billets according to claim 2 or 3, characterized in that, Different cooling area ratios are adopted for different parts of the secondary cooling zone. The cooling area ratios for the foot roller area, moving section area, Zone 1, Zone 2, and Zone 3, and the inner and outer arcs are 100%, 100%, 72%–77%, 57%–62%, and 55%–60%, respectively; the cooling area ratios for the sides are 100%, 100%, 75%–80%, 60%–65%, and 47%–52%, respectively.

5. The continuous casting method for high-equiaxed heavy-duty irregular billets according to claim 1, characterized in that, The electromagnetic stirring rollers on the web and flanges are installed in a sector-shaped section of Zone 1.

6. The continuous casting method for high-equiaxed heavy-duty irregular billets according to claim 1, characterized in that, The parameters for the electromagnetic stirring of the web plate are: current 300-400A, frequency 2-7Hz, and stirring method is butterfly.

7. The continuous casting method for high-equiaxed heavy-duty irregular billets according to claim 1, characterized in that, The parameters for the flange electromagnetic stirrer are: current 350-450A, frequency 2-7Hz, and stirring method is butterfly-shaped.

8. The continuous casting method for high-equiaxed heavy-duty irregular billets according to claim 1, characterized in that, The equiaxed crystallinity of the heavy-duty irregular blank is 40-55%.

9. The continuous casting method for high-equiaxed heavy-duty irregular billets according to claim 1, characterized in that, The heavy-duty special-shaped billet has a weight of more than 1.5 tons per meter, a width of 900-1300 mm, a height of 400-550 mm, a web thickness of 120-140 mm, and a flange thickness of 100-220 mm.

Images