Ultra-wide duplex stainless steel medium and thick plate and manufacturing method thereof

Abstract

The present invention relates to the technical field of duplex stainless steel plate production, and in particular to an ultra-wide duplex stainless steel medium and thick plate and a manufacturing method thereof. The chemical composition by weight is as follows: C: 0.02% to 0.10%, Mn: 1.1% to 1.9%, P≤0.010%, S: 0.005% to 0.015%, Ni: 2.0% to 3.5%, Cr: 13.9% to 16.9%, Mo: 0.20% to 0.75%, N: 0.001% to 0.030%, Cu: 0.001% to 0.010%, Zr: 1pm to 10ppm, V: 0.001% to 0.010%, Ti: 0.001% to 0.015%, Mg: 0.001% to 0.010%, Ce: 5ppm to 15ppm, and the balance is Fe and unavoidable impurities. It not only solves the problem of edge cracks and surface cracks in ultra-wide duplex stainless steel medium and thick plates, and improves the surface quality; it is also easy to process and form, and has excellent mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of duplex stainless steel plate production, and in particular to an ultra-wide duplex stainless steel medium and thick plate and a manufacturing method thereof. Background Art

[0002] Ferrite + martensite duplex stainless steel exhibits excellent toughness and corrosion resistance at both high and low temperatures, making it widely used in the petroleum, chemical, and nuclear power industries, where it is used to manufacture large pressure vessels and key equipment. Currently, domestic duplex stainless steel plate widths are primarily between 2000mm and 3000mm. The use of large-width duplex stainless steel medium and thick plates can reduce weld seams, minimize weld material flaw detection during the manufacturing process, lower equipment maintenance costs, and increase equipment safety. Furthermore, it significantly reduces factory prefabrication costs, shortens the procurement cycle for economical duplex stainless steel, and increases project construction speed, offering broad application prospects. Consequently, market demand for ultra-wide duplex stainless steel medium and thick plates is growing.

[0003] Currently, duplex stainless steel continuous castings have a high carbon content and contain nitrogen. At the same time, the matrix is ​​a duplex structure. Therefore, during hot working, they are rolled within the brittle phase precipitation temperature range. When the brittle phase ratio is high and the duplex grain boundary stress is large, hot rolling edge cracks and surface cracks are likely to occur, and the performance of the steel plate is unstable. Chinese patent document CN 103074552A discloses "Economical High-Performance Duplex Stainless Steel and Its Preparation Method." By replacing part of the high-priced nickel element with low-priced manganese and nitrogen elements, and replacing molybdenum with tungsten, the cost of duplex stainless steel can be greatly reduced, while ensuring that the smelted duplex stainless steel has good corrosion resistance and hot and cold working properties. Although the amount of edge cracking in duplex stainless steel is significantly reduced, the performance is unstable and the surface quality of the steel plate is not high. Chinese patent publication CN101724789A discloses "Austenitic stainless steel medium and thick plate and its manufacturing method." The method involves rolling the plate in the recrystallization zone at 1250-1050°C in 4-10 passes, with the first pass reducing the plate by no less than 30%, and the subsequent passes reducing the plate by 15-30%. The plate is then water-cooled at 20-40°C / s to a non-recrystallization zone of 700-950°C. The plate is then rolled in this temperature range for 3-5 passes, with a cumulative reduction greater than 40%, and then water-cooled to room temperature. This method is not suitable for producing extra-thick austenitic stainless steel plate exceeding 40 mm in thickness, and its solution temperature is far below the minimum solution temperature of 1040°C for austenitic stainless steel specified in the GB / T24511-2017 standard. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, the present invention provides an ultra-wide duplex stainless steel medium and thick plate and a manufacturing method thereof. This not only solves the problem of edge and surface cracks in ultra-wide duplex stainless steel medium and thick plates, improving surface quality, but also facilitates processing and forming, and exhibits excellent mechanical properties.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] An ultra-wide duplex stainless steel medium and thick plate, the chemical composition by weight percentage is:

[0007] C: 0.02%~0.10%, Mn: 1.1%~1.9%, P≤0.010%, S: 0.005%~0.015%, Ni: 2.0%~3.5%, Cr: 13.9%~16.9%, Mo: 0.20%~0.75%, N: 0.001%~0.030%, Cu: 0.001%~0.010%, Zr: 1pm~10ppm, V: 0.001%~0.010%, Ti: 0.001%~0.015%, Mg: 0.001%~0.010%, Ce: 5ppm~15ppm, the balance is Fe and unavoidable impurities.

[0008] The specifications of the finished steel plates are 4500-5000mm in width and 6-60mm in thickness.

[0009] The average mechanical properties of the finished steel plates are: room temperature tensile yield strength ≥392MPa, room temperature tensile strength ≥550MPa, room temperature elongation ≥20%; high temperature tensile yield strength ≥311MPa, high temperature tensile strength ≥455Mpa, room temperature is 15-30℃, high temperature is 320℃; -30℃ impact energy ≥54J, crack scrap rate ≤1%.

[0010] A method for manufacturing an ultra-wide duplex stainless steel medium and thick plate, the method specifically comprising the following steps:

[0011] Step 1, smelting:

[0012] High-quality scrap steel and molten iron are used as raw materials in the EAF electric furnace, and the mass percentage of molten iron is controlled at 30% to 45%.

[0013] The chromium and nickel contents in the AOD converter are strictly controlled: Cr: 13.9% to 16.9%, Ni: 2.0% to 3.5%.

[0014] The slag is removed as soon as the converter is tapped, and the slag is removed to 11-21 cm. The LF is refined outside the furnace and fed with high calcium wire. The content of P and S elements is strictly controlled, P≤0.010%, S: 0.005%-0.015%.

[0015] The VOD vacuum treatment process takes 10 to 20 minutes, with argon protection throughout the process, and the calming time before pouring is 2 to 6 minutes.

[0016] Step 2: Casting:

[0017] (1) Casting:

[0018] After breaking the vacuum, continuous casting machine is used for casting, the stacking slow cooling time is 24 to 48 hours, and the stacking is unstacking below 400℃.

[0019] (2) Electroslag remelting:

[0020] The continuous casting billet is used as the electrode to produce the electroslag billet with a thickness of 200 to 500 mm. The argon protection method is used throughout the production process, and the argon flow rate is 20 to 40m 3 / h.

[0021] The current during the electroslag remelting process is 6000~30000A, the voltage is 70~120V, the slag thickness is 150~260mm, and the melting rate is 800~1190kg / h.

[0022] Step 3: Heating the ingot:

[0023] The ingot that has been ground and sprayed with anti-oxidation coating is sent into a walking beam heating furnace for heating. The spraying thickness is 0.2 to 0.3 mm. The ingot is sequentially processed in the preheating section, heating section and soaking section before being taken out of the furnace.

[0024] When the slab thickness is ≤300mm, the temperature range of the preheating section is 700~850℃.

[0025] When the slab thickness is in the range of 300-400 mm, the temperature range of the preheating section is 700-860°C.

[0026] When the slab thickness is between 400 and 500 mm, the temperature range of the preheating section is 700 to 900°C.

[0027] The temperature range of the heating section for all thickness slabs is 1170-1230℃; the temperature range of the soaking section is 1180-1250℃.

[0028] The soaking time of the slab in the heating furnace is controlled at 3 to 5 hours.

[0029] Step 4: High-pressure water descaling:

[0030] Before rolling, use high-pressure water to descale the cast billet after it leaves the furnace for 3 to 10 seconds. The descaling machine pressure is 10 to 25 MPa. During rolling, the cooling water flow rate of the roller is controlled at 200 to 500 m 3 / h.

[0031] Step 5: Rolling:

[0032] (1) Rough rolling stage:

[0033] The starting rolling temperature is ≥1150℃, the first rolling reduction rate is 18-25%, when continuing rolling, the subsequent rolling reduction in the rough rolling stage is 12-20%, the roller speed is 45-65r / min, and the rolling passes are 5-9 times.

[0034] (2) Finishing rolling stage:

[0035] The starting temperature of finishing rolling is ≥1050℃, and finishing rolling is carried out after steel transfer. The final rolling temperature is ≥950℃, the rolling reduction rate is 10-18%, and the target thickness is rolled. The roller speed is 20-40r / min. When the pass reduction is less than 5mm, it is controlled at 5mm reduction. Finishing rolling realizes the transformation of austenite phase to ferrite.

[0036] Step 6) Tempering treatment:

[0037] The quenching temperature is 900℃~1100℃, and the holding time is 2~8min / mm.

[0038] Quenching unit water volume 150~260m 3 / min, water pressure 5-11 bar, upper and lower water ratio 0.35-0.65, swing watering in the low-pressure area, roller speed 0.1-1.0 m / s, this quenching process can effectively control the ferrite content to 25-40%, and the rest is martensite.

[0039] The tempering temperature is 680℃~780℃, and the holding time is 1.5~7.0min / mm.

[0040] Compared with the prior art, the present invention has at least the following technical effects or advantages:

[0041] 1. The composition of the present invention is designed to improve the toughness, high-temperature austenite stability and machinability of the material through low C, Mn and high Ni content. Mo is used to improve the hardenability of steel and ensure the matrix strength of steel. At the same time, it forms stable carbon and nitrides with carbon and nitrogen elements to play a precipitation strengthening role. The introduction of Ce, Mg and Cr elements can play the role of inclusion modification and nucleation point formation, which can refine the grains and enhance the strength, and ultimately solve the problem of strength-toughness matching and machinability of ultra-wide duplex stainless steel.

[0042] 2. The present invention adopts continuous casting machine for casting after breaking vacuum, stacking slow cooling time is 24 to 48 hours, and stacking is performed below 400°C; the continuous casting billet is used as an electrode to produce electroslag billets with a thickness of 200 to 500 mm, the current in the electroslag remelting process is 6000 to 30000A, the voltage is 70 to 120V, the slag thickness is 150 to 260mm, and the melting rate is 800 to 1190kg / h.

[0043] This invention further improves steel purity through continuous casting and electroslag remelting technology, eliminates internal defects such as segregation and porosity, reduces non-metallic inclusions, and homogenizes the as-cast structure. The low segregation and porosity in this invention can improve the thickness variability caused by the presence of martensite in duplex stainless steel. It can also reduce stress concentration in the uneven structure caused by segregation, solving the problem of difficult machining and edge cracking of ultra-wide duplex stainless steel. The non-metallic inclusion content of Class A is ≤0.5, Class B is ≤0.5, Class C is ≤0.5, and Class D is ≤0.5. The total non-metallic inclusion content is ≤1.5. A low non-metallic inclusion content can reduce creep, and a total non-metallic inclusion content of ≤1.5 can improve high-temperature stability.

[0044] 3. The present invention sends the cast blanks that have been ground and sprayed with an anti-oxidation coating into a walking beam heating furnace for heating. The spraying thickness is 0.2-0.3 mm. The slab thickness is ≤300 mm and the preheating temperature is 700-850 ° C. If the slab thickness is 300 mm or less and ≤400 mm, the preheating temperature is 700-860 ° C. If the slab thickness is 400 mm or less and ≤500 mm, the preheating temperature is 700-900 ° C. Before rolling, the cast blanks are descaled for 3-10 seconds using high-pressure water. The descaling machine pressure is 10-25 MPa. During rolling, the roller cooling water flow rate is controlled to be 200-500 m 3 / h;

[0045] The surface spraying and insulation process of the billet significantly impacts rolling. Excessively high temperatures can cause severe oxidation of the billet, uneven grain size, and surface stress concentration, leading to cracks during rolling. Billets of varying thicknesses require different heating temperatures. Excessively low temperatures increase deformation resistance and result in excessively low temperatures during subsequent rolling, impacting the surface and edge quality of the product. Therefore, the present invention sprays the billet surface, with a spray thickness to billet thickness ratio of 0.00059-0.001, and strictly controls the insulation temperature and time, ensuring the rolling temperature of the steel plate and improving its surface quality.

[0046] 4. In the roughing stage of the present invention, the first pass has a rolling reduction of 18-25%. During continued rolling, the subsequent passes have a rolling reduction of 12-20%, the roller speed is 45-65 r / min, and the number of rolling passes is 5-9. In the finishing stage, the rolling reduction is 10-18%, and the target thickness is reached at a roller speed of 20-40 r / min.

[0047] The present invention adopts a comprehensive control of process parameters such as the deformation amount of rough rolling and finishing rolling passes and the transverse and longitudinal rolling processes. The rough rolling stage adopts a large deformation amount at a high temperature stage. The purpose is to use the high temperature and large deformation amount to maximize the dynamic recrystallization of austenite and form a larger proportion of large-angle grain boundaries. The finishing rolling temperature can promote the formation and recrystallization of more ferrite, and after steel conversion, the austenite and ferrite will not have a single-direction rolling deformation, which is conducive to improving toughness and reducing the occurrence of cracks.

[0048] 5. The quenching temperature of the present invention is 900℃~1100℃, the holding time is 2~8min / m. The water volume of the quenching unit is 150~260m 3 / min, water pressure 5-11 bar, upper and lower water ratio 0.35-0.65, swing watering in the low-pressure zone, roller speed 0.1-1.0 m / s. This quenching process can effectively control the ferrite content to 25-40%, with the remainder being martensite. The tempering temperature is 680°C-780°C, and the holding time is 1.5-7.0 min / min.

[0049] By adopting online heat treatment, quenching not only controls the recovery of austenite and martensite through temperature and holding time, but also ensures consistency between the upper and lower surfaces of the steel plate through the water ratio and water volume during the cooling process. Tempering controls the size and morphology of the precipitated phases, ensuring comprehensive performance. Secondary heating during offline heat treatment causes secondary oxidation on the steel plate surface, affecting surface quality. Furthermore, offline heat treatment can cause recovery and secondary recrystallization of the steel plate, changing the microstructure and distribution of the controlled rolling process, which is detrimental to the steel plate's strength and toughness.

[0050] In summary, the present invention ultimately produces wide-gauge duplex stainless steel medium and thick plates with a width of 4500mm-5000mm and a thickness of 6-60mm. The chemical composition, smelting and rolling processes solve the problems of edge cracks and surface cracks, phase ratio adaptability, etc. in ultra-wide and economical duplex stainless steel medium and thick plates. The unique surface spraying and dephosphorization process is combined to reduce the surface crack scrap rate from more than 10% in the initial stage to less than 1%, the ferrite content is 25-0%, and the rest is martensite. Online heat treatment replaces the traditional offline heat treatment process, and the average mechanical properties of the steel plates are: room temperature tensile yield strength ≥392MPa, room temperature strength ≥550MPa, room temperature elongation ≥20%; 320℃ high temperature tensile yield strength ≥311MPa, high temperature tensile strength ≥455MPa, -30℃ impact energy ≥54J. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is the metallographic structure diagram of Example 3 of the present invention. DETAILED DESCRIPTION

[0052] The present invention discloses an ultra-wide duplex stainless steel medium and thick plate and a method for manufacturing the same. Those skilled in the art may refer to the contents of this document and appropriately improve the process parameters to achieve the desired result. It should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0053] An ultra-wide duplex stainless steel medium and thick plate with a width of more than 5000 mm and a thickness of 6 to 60 mm, composed of the following chemical elements in percentage by weight:

[0054] C: 0.02%~0.10%, Mn: 1.1%~1.9%, P≤0.010%, S: 0.005%~0.015%, Ni: 2.0%~3.5%, Cr: 13.9%~16.9%, Mo: 0.20%~0.75%, N: 0.001%~0.030%, Cu: 0.001%~0.010%, Zr: 1pm~10ppm, V: 0.001%~0.010%, Ti: 0.001%~0.015%, Mg: 0.001%~0.010%, Ce: 5ppm~15ppm, the balance is Fe and unavoidable impurities.

[0055] The reasons for adopting the above components are as follows:

[0056] 1. Carbon: Carbon is the most effective and inexpensive element for improving the room temperature and high temperature strength of materials. It improves the strength of the matrix through solid solution and chemical combination. The present invention adopts a relatively low carbon content design, mainly to ensure the high temperature strength and high temperature long-time mold welding performance without affecting the welding performance of steel. Therefore, the carbon content of the present invention is 0.02% to 0.10%.

[0057] 2. Manganese: Mn can inhibit the effect of sulfur in steel and improve thermoplasticity. However, when the Mn content becomes high, the formation of MnS can easily cause pitting corrosion, reducing the corrosion resistance of stainless steel. When its content in stainless steel is less than 1%, it plays a role in changing the phase region. Therefore, Mn: 1.1%~1.9%.

[0058] 3. Phosphorus: P is considered a harmful element in stainless steel and should be controlled as low as possible. Taking the cost into consideration, the P content should be controlled below 0.010%.

[0059] 4. Sulfur: Sulfur (S) easily forms sulfide inclusions in steel, which reduces the impact toughness of the steel and impairs welding performance. It also aggravates defects such as central segregation and porosity and increases radiation embrittlement. However, an appropriate amount of sulfur is beneficial to the cutting effect of the steel plate. Therefore, the present invention requires S: 0.005% to 0.015%.

[0060] 5. Nickel: Nickel is a key element in austenitic stainless steel. It expands the austenite region while inhibiting the formation of ferrite. Combined with Cr, it ensures excellent resistance to oxidation and corrosion. Due to its high price, the Ni content should be kept to 2.0% to 3.5%.

[0061] 6. Chromium: Cr is a key element in austenitic stainless steel. It plays a key role in improving the steel's high-temperature oxidation and corrosion resistance. It is also a key element in the formation of M23C6 carbides. However, excessive addition of Cr will cause the carbides to coarsen, which in turn reduces the steel's high-temperature strength and toughness. In the present invention, the Cr content is controlled to 13.9% to 16.9%.

[0062] 7. Molybdenum: Mo improves the hardenability of steel and ensures the steel's matrix strength. Molybdenum is also a strong carbonitride-forming element. It forms stable carbonitrides with the carbon and nitrogen elements in the present invention, providing precipitation strengthening. Furthermore, molybdenum is an optimal element for improving tempering stability. Especially when combined with chromium and manganese, it reduces or inhibits the temper brittleness caused by these elements. Therefore, the present invention requires a Mo content of 0.20% to 0.75%.

[0063] 8. Nitrogen: N forms nitrides with elements such as Nb, V, and Ti, precipitates at grain boundaries, pins the grain boundaries and refines the grains, thereby improving the high-temperature strength of the grain boundaries. N: 0.001%-0.030%.

[0064] 9. Copper: Cu is an austenite-forming element. At the same time, the support of copper in the core of the steel plate can compensate for the loss of strength due to increased thickness. Cu: 0.001% ~ 0.010%.

[0065] 10 Zirconium: Zirconium can play a deoxidation role in the smelting process, forming nano-scale ZrO2, which has the effect of refining grains and is beneficial to the low-temperature toughness of steel. Therefore, the content of ZrO2 added to the steel is controlled at 1pm~10ppm.

[0066] 11. V: The present invention adds a large amount of vanadium, mainly to utilize it to form stable refractory carbides with carbon and nitrogen, so that the steel can still maintain a fine-grained structure at high temperatures, ensuring the high-temperature performance of the steel. In addition, since vanadium fixes carbon in vanadium carbides, the hydrogen resistance of the steel under high temperature and high pressure is greatly improved. V: 0.001% ~ 0.010%.

[0067] 12. Ti: Precipitates as carbides at grain boundaries, inhibiting the precipitation of Cr at the grain boundaries and preventing the formation of "chromium-depleted zones" near the grain boundaries, thereby increasing the steel plate's resistance to intergranular corrosion. However, excessive Ti content can cause embrittlement of welded joints during welding, reducing the material's plasticity and toughness. Therefore, the Ti content should be between 0.001% and 0.015%.

[0068] 13. Mg: During the smelting process, magnesium combines with large-sized inclusions and modifies them into soft and fine magnesia spinel. The fine spinel inclusions have a smaller mismatch with carbides and are more likely to become nucleation cores for carbides, thereby refining the primary carbides. Therefore, the present invention requires that the Mg content in the steel be controlled at 0.001% to 0.010%.

[0069] 14. Ce: Cerium element modifies inclusions during the smelting process, converting them into soft and fine inclusions. The fine rare earth inclusions can serve as nucleation points for high-temperature ferrite, refine the dendritic structure, and thereby reduce microsegregation, reduce the size of primary carbides, and make the distribution of primary carbides more uniform. Therefore, the present invention requires that the Ce content in the steel be controlled at 5ppm to 15ppm.

[0070] The average mechanical properties of ultra-wide duplex stainless steel medium and thick plates are: room temperature tensile yield strength ≥392MPa, room temperature tensile strength ≥550MPa, room temperature elongation ≥20%; high temperature tensile yield strength ≥311MPa, high temperature tensile strength ≥455Mpa, room temperature is 15-30℃, high temperature is above 450℃; -30℃ impact energy ≥54J, crack scrap rate ≤1%.

[0071] A method for manufacturing ultra-wide duplex stainless steel medium and thick plates, the method specifically comprising the following steps:

[0072] Step 1, smelting:

[0073] High-quality scrap steel and molten iron are used as raw materials in the EAF electric furnace, and the mass percentage of molten iron is controlled at 30% to 45%.

[0074] The chromium and nickel content in the AOD converter is strictly controlled.

[0075] The slag is removed as soon as the converter is tapped, and the slag is removed to 11-21 cm. The LF is refined outside the furnace and fed with a high calcium wire, and the content of P and S elements is strictly controlled.

[0076] The VOD vacuum treatment process takes 10 to 20 minutes, with argon protection throughout the process, and the calming time before pouring is 2 to 6 minutes.

[0077] Step 2: Casting:

[0078] (1) Casting: After breaking the vacuum, continuous casting machine is used for casting. The stacking slow cooling time is 24 to 48 hours, and the stacking is unstacked below 400℃ to prevent cracks inside the ingot due to rapid cooling.

[0079] (2) Electroslag remelting: In order to further improve the purity of steel, eliminate internal defects such as segregation and porosity, reduce non-metallic inclusions, and homogenize the cast structure, the addition of the electroslag remelting process is crucial to the structure content and stability.

[0080] The present invention uses continuous casting billets as electrodes to produce electroslag billets with a thickness of 200 to 500 mm. Argon protection is used throughout the production process, with an argon flow rate of 20 to 40 m 3 / h. The current during the electroslag remelting process is 6000-30000A, the voltage is 70-120V, the slag thickness is 150-260mm, and the melting rate is 800-1190kg / h.

[0081] Step 3: Heating the ingot:

[0082] The ingot that has been ground and sprayed with anti-oxidation coating is sent into a walking beam heating furnace for heating. The spraying thickness is 0.2 to 0.3 mm. The ingot is sequentially processed in the preheating section, heating section and soaking section before being taken out of the furnace.

[0083] When the slab thickness is ≤300mm, the temperature range of the preheating section is 700~850℃.

[0084] When the slab thickness is in the range of 300-400 mm, the temperature range of the preheating section is 700-860°C.

[0085] When the slab thickness is between 400 and 500 mm, the temperature range of the preheating section is 700 to 900°C.

[0086] The temperature range of the heating section for all thickness slabs is 1170-1230℃; the temperature range of the soaking section is 1180-1250℃.

[0087] The soaking time of the slab in the heating furnace is controlled at 3 to 5 hours.

[0088] Step 4: High-pressure water descaling:

[0089] Before rolling, high-pressure water is used to descale the billet after it leaves the furnace for 3 to 10 seconds. The descaling machine pressure is 10 to 25 MPa. During rolling, the cooling water flow rate of the roller is controlled at 200 to 500 m 3 / h.

[0090] Step 5) Rolling:

[0091] A rough rolling stage:

[0092] The starting rolling temperature is ≥1150℃, the first rolling reduction rate is 18-25%, and when rolling continues, the subsequent rolling reduction in the rough rolling stage is 12-20%, the roller speed is 45-65r / min, and the rolling passes are 5-9 times to achieve dynamic recrystallization and refinement of austenite.

[0093] B Rough rolling stage:

[0094] The starting temperature of finishing rolling is ≥1050℃, and finishing rolling is carried out after steel transfer. The purpose of steel transfer is to ensure that the shape of rough-rolled austenite grains is changed to avoid excessive deformation of austenite grains in one direction. The final rolling temperature is ≥950℃, the rolling reduction rate is 10-18%, and the target thickness is rolled. The roller speed is 20-40r / min. When the pass reduction is less than 5mm, it can be controlled according to 5mm reduction. The rough rolling realizes the transformation of austenite phase to ferrite.

[0095] Step 6) Tempering treatment:

[0096] The quenching temperature is 900℃~1100℃, and the holding time is 2~8min / m.

[0097] Quenching unit water volume 150~260m 3 / min, water pressure 5-11 bar, upper and lower water ratio 0.35-0.65, swing watering in the low-pressure area, roller speed 0.1-1.0 m / s, this quenching process can effectively control the ferrite content to 25-40%, and the rest is martensite.

[0098] The tempering temperature is 680℃~780℃, and the holding time is 1.5~7.0min / mm.

[0099] The plasticity, toughness and high temperature performance are regulated. During tempering under this process, the second phase precipitation in the steel compensates for the strength attenuation while obtaining stable performance, especially high temperature strength and toughness.

[0100] [Example]

[0101] An ultra-wide duplex stainless steel medium and thick plate and a manufacturing method thereof, the specific implementation methods are as follows:

[0102] Table 1 shows the chemical composition of the example steel; Table 2 shows the smelting process system of the example steel; Table 3 shows the heating and dephosphorization method of the example steel ingot; Table 4 shows the rolling method of the example steel; Table 5 shows the heat treatment method of the example steel; and Table 6 shows the properties of the example stainless steel.

[0103] Table 1 Chemical composition of steel in each example (wt%)

[0104] Example C Ce / ppm Mn Mg S Ni Cr Mo 1 0.02 5 1.1 0.001 0.005 2.0 13.9 0.20 2 0.03 15 1.9 0.002 0.013 3.4 14.2 0.25 3 0.04 7 1.3 0.003 0.007 2.2 16.1 0.30 4 0.05 13 1.4 0.004 0.011 3.0 14.8 0.40 5 0.06 9 1.5 0.005 0.009 2.6 15.1 0.75 6 0.07 10 1.6 0.006 0.010 2.8 15.4 0.50 7 0.08 11 1.7 0.007 0.008 2.4 15.7 0.60 8 0.09 12 1.8 0.008 0.012 3.2 14.5 0.65 9 0.10 8 1.2 0.009 0.006 2.1 16.5 0.70 10 0.02 6 1.1 0.010 0.015 3.5 16.9 0.45 Example N V Ti Cu Zr / ppm / / / 1 0.001 0.001 0.001 0.001 1 / / / 2 0.005 0.002 0.003 0.002 2 / / / 3 0.010 0.003 0.005 0.003 3 / / / 4 0.013 0.004 0.007 0.004 4 / / / 5 0.016 0.005 0.008 0.005 5 / / / 6 0.019 0.006 0.009 0.006 6 / / / 7 0.023 0.007 0.011 0.007 7 / / / 8 0.025 0.008 0.012 0.008 8 / / / 9 0.028 0.009 0.014 0.009 9 / / / 10 0.030 0.010 0.015 0.010 10 / / /

[0105] Note: Since P is a harmful element in steel, the P content can be controlled below 0.010% without special instructions.

[0106] Table 2 Smelting process system of example steel

[0107]

[0108] Table 3 Heating and dephosphorization method of steel castings according to the embodiment

[0109]

[0110] Table 4 Rolling method of example steel

[0111]

[0112]

[0113] The rolling passes are as follows: the first pass has a rolling reduction rate of 18-25%. When continuing rolling, the subsequent passes in the rough rolling stage have a rolling reduction of 12-20%, and the rolling passes are 5-9 times; after steel transfer, finishing rolling is carried out with a rolling reduction rate of 10-18% until the target thickness is reached. When the pass reduction is less than 5mm, it can be controlled at a reduction of 5mm.

[0114] Table 5 Heat treatment method of example steel

[0115]

[0116] Table 6 Stainless steel properties of the embodiment

[0117]

[0118]

[0119] It can be seen from the performance table of the embodiments of the present invention that the average mechanical properties of the steel plates produced according to the chemical composition and production process requirements of the steel of the present invention are: room temperature tensile yield strength ≥392 MPa, room temperature tensile strength ≥550 MPa, room temperature elongation ≥20%; high temperature tensile yield strength ≥311 MPa, high temperature tensile strength ≥455 MPa, -30°C impact energy ≥54 J, ferrite content: 25-40%, and crack scrap rate ≤1%.

[0120] This invention solves the problems of edge and surface cracks, phase ratio, and performance compatibility in ultra-wide, economical duplex stainless steel medium and thick plates. The surface crack rejection rate has been reduced from over 10% in the early stages to less than 1%, with a ferrite content of 25-0%, and the remainder being martensite.

[0121] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for manufacturing ultra-wide duplex stainless steel medium and thick plates, characterized in that: The chemical composition of the ultra-wide duplex stainless steel medium and thick plate is as follows by weight percentage: C: 0.04% to 0.10%, Mn: 1.1% to 1.9%, P ≤ 0.010%, S: 0.005% to 0.015%, Ni: 2.0% to 3.5%, Cr: 14.2% to 16.9%, Mo: 0.20% to 0.75%, N: 0.001% to 0.028%, Cu: 0.003% to 0.009%, Zr: 1pm to 10ppm, V: 0.001% to 0.010%, Ti: 0.001% to 0.015%, Mg: 0.003% to 0.009%, Ce: 5ppm to 15ppm, the balance is Fe and unavoidable impurities; The specifications of the finished steel plates are 4500-5000mm in width and 6-60mm in thickness. The average mechanical properties of the finished steel plates are as follows: room temperature tensile yield strength ≥392MPa, room temperature tensile strength ≥550MPa, room temperature elongation ≥20%; high temperature tensile yield strength ≥311MPa, high temperature tensile strength ≥455MPa, room temperature is 15-30℃, high temperature is 320℃; impact energy at -30℃ ≥54J, crack rejection rate ≤1%; The manufacturing method specifically comprises the following steps: Step 1) smelting: smelting according to the above ingredients; Step 2) Casting: A Casting: After breaking the vacuum, continuous casting machine is used for casting, the stacking slow cooling time is 24 to 48 hours, and the stacking is unstacking below 400℃; B Electroslag Remelting: The continuous casting billet is used as the electrode to produce electroslag billets with a thickness of 200 to 500 mm. The current during the electroslag remelting process is 6000 to 30000 A, the voltage is 70 to 120 V, the slag thickness is 150 to 260 mm, and the melting rate is 800 to 1190 kg / h. Step 3) Heating of the casting: The ingot that has been ground and sprayed with anti-oxidation coating is sent into the heating furnace for heating. The coating thickness is 0.22-0.28 mm. The ingot is processed in the preheating section, heating section and soaking section in sequence before being taken out of the furnace. Slab thickness ≤ 300mm, preheating temperature is 700~850℃; 300mm<slab thickness≤400mm, preheating temperature 700~860℃; 400mm<slab thickness≤500mm, preheating temperature 700~900℃; The temperature range of the heating section of slabs of all thicknesses is 1200-1220°C; the temperature range of the soaking section is 1180-1250°C; The soaking time of the slab in the heating furnace is 3.6 to 3.9 hours; Step 4) High-pressure water descaling: Before rolling, use high-pressure water to descale the cast billet after it leaves the furnace for 3 to 10 seconds. During rolling, control the flow rate of the roller cooling water to 200 to 500 m 3 / h; Step 5) Rolling: A rough rolling stage: The starting rolling temperature is 1180-1200℃, the first rolling reduction is 18-25%, and when rolling continues, the subsequent rolling reduction is 12-20% in the rough rolling stage, the roller speed is 45-65r / min, and the rolling passes are 5-9 times; B finishing rolling stage: The starting temperature of finishing rolling is 1065-1072℃, and finishing rolling is carried out after steel transfer. The final rolling temperature is 950-975℃. When the reduction per pass is less than 5mm, it is controlled as 5mm reduction. The rolling reduction rate is 10-18%, and the roller speed is 20-40 r / min; Step 6) Tempering treatment: The quenching temperature is 960℃~1000℃, and the holding time is 5.2~5.8min / mm; the tempering temperature is 680℃~780℃, and the holding time is 1.5~7.0min / mm.

2. The method for manufacturing an ultra-wide duplex stainless steel medium and thick plate according to claim 1, characterized in that: The step 1) is smelted by a three-step process of EAF electric furnace steelmaking, AOD converter decarburization, and VOD deoxidation; The EAF electric furnace uses scrap steel and molten iron as raw materials, and the mass percentage of molten iron is controlled at 30% to 45%; The chromium and nickel content in the AOD converter is controlled to 13.9% to 16.9% for Cr and 2.0% to 3.5% for Ni. Slag is removed as soon as the converter is tapped, to a depth of 11 to 21 cm. LF furnace refining feeds high calcium wire to control the content of P and S elements, P≤0.010%, S: 0.005%~0.015%; The VOD vacuum treatment process takes 10 to 20 minutes, with argon protection throughout the process, and the calming time before pouring is 2 to 6 minutes.

3. The method for manufacturing an ultra-wide duplex stainless steel medium and thick plate according to claim 1, characterized in that: In the step 2), the continuous casting billet is used as an electrode to produce an electroslag billet with a thickness of 200 to 500 mm. Argon protection is used throughout the production process, wherein the argon flow rate is 20 to 40 m 3 / h.

4. The method for manufacturing an ultra-wide duplex stainless steel medium and thick plate according to claim 1, characterized in that: In the step 4), the descaling machine has a pressure of 10 to 25 MPa.

5. The method for manufacturing an ultra-wide duplex stainless steel medium and thick plate according to claim 1, characterized in that: Step 6) quenching and tempering treatment: Quenching unit water volume 150~260m 3 / min, water pressure 5-11 bar, upper and lower water ratio 0.35-0.65, swing watering in low pressure area, roller speed 0.1-1.0 m / s.

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