Duplex stainless steel cold-rolled coil for welding strip and continuous casting production process of duplex stainless steel cold-rolled coil

Abstract

The invention discloses a duplex stainless steel cold-rolled coil for a welding strip and a continuous casting production process of the duplex stainless steel cold-rolled coil, the continuous casting production process comprises the steps of smelting, continuous casting, hot rolling, cold rolling and the like, silicon iron is adopted for pre-reduction in AOD reduction so as to fully reduce Cr2O3 in slag, and the yield of chromium is increased. After AOD reduction, deslagging is conducted, the slag thickness is smaller than 100 mm, it is guaranteed that Al2O3 in the slag is larger than 20%, SiO2 in the slag is smaller than 10%, and the yield of aluminum is increased. The aluminum content is 0.03-0.04% so as to ensure the low total oxygen content, and the calcium content is 0.0015-0.0025% so as to ensure the good calcium treatment effect. The low carbon and nitrogen content in the component design can guarantee the high ferrite content in the hot rolling process, and the thermoplasticity is improved. After the duplex stainless steel hot wire is annealed and pickled, the chromium-passing steel wire is used for removing the defects of surface color difference, poor pickling and the like, one-time pickling of a cold wire is ensured, and the production efficiency is improved. And the 20-roller rolling mill is used for rolling 11 passes, the pass reduction rate is 10.7-18%, and the excellent mechanical property and plate shape are guaranteed. The duplex stainless steel cold-rolled coil for the welding strip is produced by adopting a continuous casting process, the production process is simple, and the cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel smelting, and in particular relates to a duplex stainless steel cold-rolled coil for welding strip and a continuous casting production process thereof. Background Art

[0002] Due to its high yield strength and good corrosion resistance, duplex stainless steel is widely used in petroleum, chemical industry, desulfurization and denitrification, seawater desalination and other fields. In 2022, the market demand for duplex stainless steel has exceeded 200,000 tons. As the demand for duplex stainless steel continues to increase, the demand for special welding materials for duplex stainless steel is also increasing.

[0003] Duplex stainless steel for welding strips is usually produced by die casting because of its low carbon, low phosphorus requirements, high alloy content and great difficulty in hot working. However, it has the problems of high die casting cost and long production cycle. Summary of the invention

[0004] The purpose of the present invention is to provide a continuous casting production process of duplex stainless steel cold-rolled coils for welding strips, so as to solve the problems of high production cost and long production cycle of the existing die casting process.

[0005] In order to achieve the above objectives, the present invention adopts the following technical solutions: The present invention provides a continuous casting production process of a duplex stainless steel cold-rolled coil for welding strip, wherein the chemical composition of the duplex stainless steel is as follows by weight percentage: C≤0.018%, Si 0.45-0.65%, Mn 1.50-1.75%, P≤0.020%, S≤0.001%, Cr 23.0-23.5%, Ni 7.50-8.00%, Mo 3.00-3.50%, N 0.12-0.14%, and the rest are Fe and residual elements; the production process comprises the following steps: (1) Smelting Duplex stainless steel for welding strip is produced by electric furnace-AOD converter-LF refining process; the sulfur content after AOD converter treatment is ≤10ppm; the target value of aluminum content in LF refining process is 0.03-0.04%, and the target value of calcium content is 0.0015-0.0025%; (2) Continuous casting The superheat of the tundish is controlled at 20-30°C, electromagnetic stirring is applied, and the current intensity is 1770A to obtain a duplex stainless steel ingot for welding strip; (3) Hot rolling Hot rolling is carried out according to the conventional process of duplex stainless steel, and the process flow is: heating - rough rolling - finishing rolling by Steckel mill - coiling to obtain hot rolled black coil; (4) Cold rolling The duplex stainless steel cold-rolled coil for welding strip is produced according to the process of hot annealing and pickling - online 6-roller rolling mill - hot annealing and pickling - chrome steel wire pickling - 20-roller rolling mill - cold annealing and pickling.

[0006] As a further preferred embodiment of the technical solution of the present invention, in step (1), the AOD converter is decarburized by oxygen blowing, and when the carbon content is ≤0.01%, ferrosilicon is used for reduction, the amount of ferrosilicon added is 35-40 kg / ton of steel, and the reduction time is 5 min; after reduction, the slag is poured, the slag thickness is ≤100 mm, and then 5-6 kg / t steel of aluminum blocks, 10-12 kg / t steel of lime and 3-5 kg / t steel of fluorite are added for desulfurization.

[0007] Furthermore, after the LF enters the station and is electrified for slag slagging, aluminum wire is fed in. After argon blowing and stirring for 15 minutes, pure calcium wire is fed in. After weak blowing for 15-20 minutes, the molten steel is put into the continuous casting machine for casting.

[0008] Furthermore, the specifications of the duplex stainless steel ingot for the welding strip in step (2) are: 220 mm×1040 mm×(10000-10500) mm.

[0009] Furthermore, in step (3), the thickness of the hot-rolled black coil is 3.5 mm.

[0010] Furthermore, in step (4), the target thickness of the welding strip after rolling with the duplex stainless steel on-line 6-roll mill is 2.8 mm.

[0011] Furthermore, in step (4), the chromium steel wire is pickled with sulfuric acid and mixed acid (nitric acid + hydrofluoric acid), with the sulfuric acid concentration of 265-268 g / L, metal ions of 43-45 g / L, and temperature of 80-85°C; the nitric acid concentration of 61-63 g / L, the hydrofluoric acid concentration of 6.0-7.0 g / L, the metal ions of 21-23 g / L, and the temperature of 39-40°C.

[0012] Furthermore, in step (4), the 20-high rolling mill is rolled for 11 passes, the rolling target thickness is 0.5 mm, and the pass reduction rate is 10.7-18%.

[0013] The duplex stainless steel cold-rolled coil for welding strip that meets the requirements can be obtained by utilizing the above production process.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts a continuous casting process to produce duplex stainless steel cold-rolled coils for welding strips, and the production process is simple and the cost is low. 1. Using AOD reduction and ferrosilicon pre-reduction can ensure the full reduction of Cr2O3 in the slag and improve the chromium recovery rate. In addition, the lower the Cr2O3 content in the slag, the easier it is to desulfurize.

[0015] 2. After AOD reduction, the slag is poured, and the slag thickness is less than 100mm, which can ensure that the Al2O3 content in the slag is greater than 20%, and the SiO2 content is less than 10%, thereby improving the aluminum recovery rate.

[0016] 3. The target value of aluminum content is 0.03-0.04%, which can ensure low total oxygen content. The target value of calcium content is 0.0015-0.0025%, which can ensure good calcium treatment effect. In addition, it can fix the S content in molten steel and improve thermoplasticity.

[0017] 4. The low carbon and nitrogen content in the composition design can ensure a high ferrite content during hot rolling and good thermoplasticity.

[0018] 5. After the welding strip is annealed and pickled by hot wire of duplex stainless steel, it is passed through chrome steel wire to remove surface color difference, poor pickling and other defects, ensuring that the cold wire is pickled once to improve production efficiency.

[0019] 6. The 20-roll mill rolls the steel plate in 11 passes with a reduction rate of 10%-18% per pass, ensuring excellent mechanical properties and plate shape. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a metallographic structure diagram of a duplex stainless steel cold-rolled coil for welding strip produced in Example 1 of the present invention; Figure 2 This is a metallographic structure diagram of a duplex stainless steel cold-rolled coil for welding strip produced in Example 2 of the present invention; Figure 3 This is the metallographic structure diagram of the duplex stainless steel cold-rolled coil for welding strip produced in Example 3 of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with specific embodiments and drawings, but the implementation manner of the present invention is not limited thereto.

[0022] Example 1 1. Smelting Duplex stainless steel for welding strip is produced by electric furnace-AOD converter-LF refining process. The electric furnace melts nickel iron and scrap steel. AOD blows oxygen for decarburization, and reduction is carried out when the carbon content is 0.01%. Pre-reduction is carried out with ferrosilicon, and the addition amount is 35kg / ton of steel, and the reduction time is 5min. After reduction, the slag is poured, and the slag thickness is 100mm. Then 6kg / t steel aluminum blocks, 12kg / t steel lime and 5kg / t steel fluorite are added for desulfurization. The sulfur content after AOD treatment is 10ppm. After the LF enters the station and is electrified for slag, aluminum wire is fed in, and the aluminum content target value is 0.04%. After argon blowing and stirring for 15min, pure calcium wire is fed in, and the calcium content target value is 0.0025%. After weak blowing for 20min, the molten steel is cast on the continuous casting machine.

[0023] 2. Continuous casting The superheat of the tundish is controlled at 30°C, electromagnetic stirring is applied, and the current intensity is 1770A; the specifications of the duplex stainless steel ingot for welding strip are: 220mm×1040mm×10000mm; the weight percentage of the duplex stainless steel composition for welding strip is: C 0.018%, Si 0.45%, Mn 1.50%, P 0.020%, S0.001%, Cr 23.0%, Ni 7.50%, Mo 3.00%, N0.12%, others are Fe and residual elements. The slab is ground after it comes off the line, first grinding the edge 200mm, grinding depth 2.0mm, and then the whole is ground first with 16# grinding wheel grinding 2.5mm, and then with 20# grinding wheel grinding 0.5mm.

[0024] 3. Hot rolling Hot rolling is carried out according to the conventional process of duplex stainless steel. The process flow is: heating - rough rolling - finishing rolling by Steckel mill - coiling, and hot rolled black coil is obtained. The thickness of the black coil is 3.5mm.

[0025] 4. Cold rolling The production is carried out according to the process of hot annealing and pickling - online 6-roller rolling mill - hot annealing and pickling - chrome steel wire pickling - 20-roller rolling mill - cold annealing and pickling.

[0026] The target thickness of the welding strip is 2.8 mm after rolling with a 6-roll online rolling mill using duplex stainless steel.

[0027] Chromium steel wire pickling is carried out by sulfuric acid and mixed acid (nitric acid + hydrofluoric acid) in sequence. Sulfuric acid concentration is 265g / L, metal ion is 43g / L, temperature is 80℃. Nitric acid concentration is 61g / L, hydrofluoric acid concentration is 6.0g / L, metal ion is 21g / L, temperature is 39℃.

[0028] The 20-roll mill was rolled for 11 passes, with a target thickness of 0.5 mm. The pass reduction ratios are shown in Table 1.

[0029] Table 1: The metallographic structure diagram of the duplex stainless steel cold-rolled coil for welding strip obtained by the method of this embodiment is shown in Figure 1 ,from Figure 1 It can be seen that the austenite content is 55%. The mechanical properties of duplex stainless steel for welding strip are shown in Table 2 below.

[0030] Table 2: The yield strength of the duplex stainless steel cold-rolled coil for welding strip is greater than 450MPa, the tensile strength is greater than 650MPa, and the elongation is greater than or equal to 25%.

[0031] Example 2 1. Smelting Duplex stainless steel for welding strip is produced by electric furnace-AOD converter-LF refining process. The electric furnace melts nickel iron and scrap steel. AOD blows oxygen for decarburization, and reduction is carried out when the carbon content is 0.009%. Ferrosilicon is used for pre-reduction, and the addition amount is 40kg / ton of steel, and the reduction time is 5min. After reduction, the slag is poured, and the slag thickness is 90mm. Then 5kg / t steel aluminum blocks, 10kg / t steel lime and 3kg / t steel fluorite are added for desulfurization. The sulfur content after AOD treatment is 8ppm. After the LF enters the station and is electrified for slag, aluminum wire is fed in, and the aluminum content target value is 0.03%. After blowing argon and stirring for 15min, pure calcium wire is fed in, and the calcium content target value is 0.0015%. After weak blowing for 15min, the molten steel is cast on the continuous casting machine.

[0032] 2. Continuous casting The superheat of the tundish is controlled at 20°C, electromagnetic stirring is applied, and the current intensity is 1770A; the specifications of the duplex stainless steel ingot for welding strip are: 220mm×1040mm×10500mm; the weight percentage of the duplex stainless steel composition for welding strip is: C 0.015%, Si 0.65%, Mn 1.75%, P 0.018%, S0.0005%, Cr 23.5%, Ni8.00%, Mo 3.50%, N0.14%, others are Fe and residual elements. The slab is ground after it comes off the line, first grinding the edge 200mm, grinding depth 2.0mm, and then the whole grinding, first grinding 2.5mm with 16# grinding wheel, then grinding 0.5mm with 20# grinding wheel.

[0033] 3. Hot rolling Hot rolling is carried out according to the conventional process of duplex stainless steel. The process flow is: heating - rough rolling - finishing rolling by Steckel mill - coiling, and hot rolled black coil is obtained. The thickness of the black coil is 3.5mm.

[0034] 4. Cold rolling The production is carried out according to the process of hot annealing and pickling - online 6-roller rolling mill - hot annealing and pickling - chrome steel wire pickling - 20-roller rolling mill - cold annealing and pickling.

[0035] The target thickness of the welding strip is 2.8 mm after rolling with a 6-roll online rolling mill using duplex stainless steel.

[0036] Chromium steel wire pickling is carried out by sulfuric acid and mixed acid (nitric acid + hydrofluoric acid) in sequence. Sulfuric acid concentration is 268g / L, metal ion is 45g / L, temperature is 85℃. Nitric acid concentration is 63g / L, hydrofluoric acid concentration is 7.0g / L, metal ion is 23g / L, temperature is 40℃.

[0037] The 20-roll mill rolled the steel in 11 passes, with a target thickness of 0.5 mm. The reduction ratios for each pass are shown in Table 3.

[0038] Table 3: The metallographic structure diagram of the duplex stainless steel cold-rolled coil for welding strip obtained by the method of this embodiment is shown in Figure 2 ,from Figure 2 It can be seen that the austenite content is 51%. The mechanical properties of duplex stainless steel for welding strip are shown in Table 4 below.

[0039] Table 4: The yield strength of the duplex stainless steel cold-rolled coil for welding strip is greater than 450MPa, the tensile strength is greater than 650MPa, and the elongation is greater than or equal to 25%.

[0040] Example 3 1. Smelting Duplex stainless steel for welding strip is produced by electric furnace-AOD converter-LF refining process. The electric furnace melts nickel iron and scrap steel. AOD blows oxygen for decarburization, and reduction is carried out when the carbon content is 0.008%. Ferrosilicon is used for pre-reduction, and the addition amount is 36kg / ton of steel, and the reduction time is 5min. After reduction, the slag is poured, and the slag thickness is 100mm. Then 5.2kg / t steel aluminum blocks, 11kg / t steel lime and 3.8kg / t steel fluorite are added for desulfurization. The sulfur content after AOD treatment is 9ppm. After the LF enters the station and is electrified for slag, aluminum wire is fed in, and the aluminum content target value is 0.038%. After argon blowing and stirring for 15min, pure calcium wire is fed in, and the calcium content target value is 0.0021%. After weak blowing for 16min, the molten steel is cast on the continuous casting machine.

[0041] 2. Continuous casting The superheat of the tundish was controlled at 24°C, electromagnetic stirring was applied, and the current intensity was 1770A; the specifications of the duplex stainless steel ingot for welding strip were obtained: 220mm×1040mm×10200mm; the weight percentage of the duplex stainless steel composition for welding strip was: C 0.017%, Si 0.55%, Mn 1.58%, P 0.019%, S0.0007%, Cr 23.1%, Ni7.88%, Mo 3.06%, N0.135%, others are Fe and residual elements. The slab is ground after it comes off the line, first grinding the edge 200mm, grinding depth 2.0mm, and then the whole grinding, first grinding 2.5mm with 16# grinding wheel, and then grinding 0.5mm with 20# grinding wheel.

[0042] 3. Hot rolling Hot rolling is carried out according to the conventional process of duplex stainless steel. The process flow is: heating - rough rolling - finishing rolling by Steckel mill - coiling, and hot rolled black coil is obtained. The thickness of the black coil is 3.5mm.

[0043] 4. Cold rolling The production is carried out according to the process of hot annealing and pickling - online 6-roller rolling mill - hot annealing and pickling - chrome steel wire pickling - 20-roller rolling mill - cold annealing and pickling.

[0044] The target thickness of the welding strip is 2.8 mm after rolling with a 6-roll online rolling mill using duplex stainless steel.

[0045] Chromium steel wire pickling is carried out by sulfuric acid and mixed acid (nitric acid + hydrofluoric acid) in sequence. Sulfuric acid concentration is 266g / L, metal ion is 44g / L, temperature is 82℃. Nitric acid concentration is 62g / L, hydrofluoric acid concentration is 6.5g / L, metal ion is 22g / L, temperature is 39.5℃.

[0046] The 20-roll mill rolled the steel in 11 passes, with a target thickness of 0.5 mm. The pass reduction ratios are shown in Table 5.

[0047] Table 5: The metallographic structure diagram of the duplex stainless steel cold-rolled coil for welding strip obtained by the method of this embodiment is shown in Figure 3 ,from Figure 3 It can be seen that the austenite content is 53%. The mechanical properties of duplex stainless steel for welding strip are shown in Table 6 below.

[0048] Table 6: The yield strength of the duplex stainless steel cold-rolled coil for welding strip is greater than 450MPa, the tensile strength is greater than 650MPa, and the elongation is greater than or equal to 25%.

Claims

1. A continuous casting production process of duplex stainless steel cold-rolled coil for welding strip, characterized in that: The chemical composition of the duplex stainless steel is calculated by weight percentage: C≤0.018%, Si 0.45-0.65%, Mn 1.50-1.75%, P≤0.020%, S≤0.001%, Cr 23.0-23.5%, Ni 7.50-8.00%, Mo 3.00-3.50%, N 0.12-0.14%, and the rest are Fe and residual elements; the production process comprises the following steps: (1) Smelting Duplex stainless steel for welding strip is produced by electric furnace-AOD converter-LF refining process; the sulfur content after AOD converter treatment is ≤10ppm; the target value of aluminum content in LF refining process is 0.03-0.04%, and the target value of calcium content is 0.0015-0.0025%; (2) Continuous casting The superheat of the tundish is controlled at 20-30°C, electromagnetic stirring is applied, and the current intensity is 1770A to obtain a duplex stainless steel ingot for welding strip; (3) Hot rolling Hot rolling is carried out according to the conventional process of duplex stainless steel, and the process flow is: heating - rough rolling - finishing rolling by Steckel mill - coiling to obtain hot rolled black coil; (4) Cold rolling The duplex stainless steel cold-rolled coil for welding strip is produced according to the process of hot annealing and pickling - online 6-roller rolling mill - hot annealing and pickling - chrome steel wire pickling - 20-roller rolling mill - cold annealing and pickling.

2. The continuous casting production process of duplex stainless steel cold-rolled coil for welding strip according to claim 1, characterized in that: In step (1), the AOD converter is decarbonized by oxygen blowing, and when the carbon content is ≤0.01%, ferrosilicon is used for reduction, the amount of ferrosilicon added is 35-40 kg / ton of steel, and the reduction time is 5 min; after reduction, the slag is poured, the slag thickness is ≤100 mm, and then 5-6 kg / t of aluminum blocks, 10-12 kg / t of lime and 3-5 kg / t of fluorite are added for desulfurization.

3. The continuous casting production process of duplex stainless steel cold-rolled coil for welding strip according to claim 2, characterized in that: After the LF enters the station and is electrified to slag, aluminum wire is fed in. After argon blowing and stirring for 15 minutes, pure calcium wire is fed in. After weak blowing for 15-20 minutes, the molten steel is put into the continuous casting machine for casting.

4. The continuous casting production process of duplex stainless steel cold-rolled coil for welding strip according to claim 3, characterized in that: The specifications of the duplex stainless steel ingot used for the welding strip in step (2) are: 220 mm×1040 mm×(10000-10500) mm.

5. The continuous casting production process of duplex stainless steel cold-rolled coil for welding strip according to claim 4, characterized in that: The thickness of the hot-rolled black coil in step (3) is 3.5 mm.

6. The continuous casting production process of duplex stainless steel cold-rolled coil for welding strip according to any one of claim 5, characterized in that: In step (4), the target thickness of the welding strip after rolling with a duplex stainless steel online 6-roller mill is 2.8 mm.

7. The continuous casting production process of duplex stainless steel cold-rolled coil for welding strip according to claim 6, characterized in that: In step (4), the chromium steel wire is pickled with sulfuric acid and mixed acid (nitric acid + hydrofluoric acid), with the sulfuric acid concentration of 265-268 g / L, metal ions of 43-45 g / L, and temperature of 80-85°C; the nitric acid concentration of 61-63 g / L, the hydrofluoric acid concentration of 6.0-7.0 g / L, the metal ions of 21-23 g / L, and the temperature of 39-40°C.

8. The continuous casting production process of duplex stainless steel cold-rolled coil for welding strip according to claim 7, characterized in that: In step (4), the 20-roll mill is rolled for 11 passes, the rolling target thickness is 0.5 mm, and the pass reduction rate is 10.7-18%.

9. Duplex stainless steel cold-rolled coil for welding strip produced by the production process according to any one of claims 1 to 8.

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