12crni series stainless steel plate, method for manufacturing the same, and application thereof in welded pipe

Abstract

This invention belongs to the field of metallurgical technology, specifically relating to a 12CrNi-based stainless steel medium plate, its manufacturing method, and its application in welded pipes. The 12CrNi-based stainless steel medium plate provided by this invention, by weight, comprises: C: ≤0.03%, N: ≤0.03%, Si: ≤0.40%, Mn: 1.00~2.50%, P: ≤0.03%, S: ≤0.01%, Cr: 11.0~12.5%, Ni: 0.5~1.5%, Ti: 0.10~0.35%, with the balance being Fe and unavoidable impurities. The 12CrNi-based stainless steel medium plate material of this invention has the advantages of easy welding, high strength, and good economy, and can be widely used in wear-resistant welded pipes.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a 12CrNi series stainless steel medium plate, its manufacturing method, and its application in welded pipes. Background Technology

[0002] Welded pipes are widely used in mining, petrochemical, and power energy industries due to their high surface hardness and low cost. Currently, welded pipes are mainly composed of ordinary carbon steel base pipes with a wear-resistant surface layer. When used in corrosive environments, they may corrode, reducing their service life and increasing maintenance costs.

[0003] 12CrNi series stainless steel is a material with excellent corrosion resistance and oxidation resistance, and it also boasts advantages such as high strength, good machinability, and weldability. Furthermore, due to its low alloy content, it offers significant economic advantages and is widely used in building panels, rail transportation, and home appliances and bathroom fixtures. Developing a 12CrNi series stainless steel medium plate for welded pipes can reduce product maintenance costs and promote high-quality social development. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a 12CrNi series stainless steel medium plate, its manufacturing method, and its application in welded pipes.

[0005] Specifically, the present invention is achieved through the following technical solutions: A type of 12CrNi stainless steel medium plate, by weight, comprises: C: ≤0.03%, N: ≤0.03%, Si: ≤0.40%, Mn: 1.00~2.50%, P: ≤0.03%, S: ≤0.01%, Cr: 11.0~12.5%, Ni: 0.5~1.5%, Ti: 0.10~0.35%, with the balance being Fe and unavoidable impurities.

[0006] The aforementioned 12CrNi series stainless steel medium plate has a Creq / Nieq ≤ 7.5; where Creq = Cr + 1.5Si + 0.5Ti; Nieq = Ni + 30C + 30N + 0.5Mn.

[0007] A method for preparing a 12CrNi-based stainless steel medium plate includes: (1) The pretreated molten iron was successively smelted in a converter, refined in an AOD furnace, and refined in an LF furnace. The composition of the molten steel obtained was as shown in the above 12CrNi series stainless steel medium plate. (2) The molten steel is continuously cast to obtain a continuously cast billet; (3) Cut the continuous casting billet according to the finished product specifications. After cutting, send it to the annealing furnace for annealing to obtain continuous casting slab billet. (4) The continuously cast slab billet is heated, rolled, and straightened to obtain a hot-rolled steel plate; (5) After annealing and pickling the hot-rolled steel plate, the 12CrNi stainless steel medium plate is obtained.

[0008] In the above-mentioned method for preparing 12CrNi series stainless steel medium plates, during continuous casting, the superheat in the crystallizer is controlled to be ≤35℃, the steel pulling speed is 0.8~1.3m / min, the water flow rate of the wide die is 4500±50L / min, and the water flow rate of the narrow die is 450±50L / min.

[0009] In the above-mentioned method for preparing 12CrNi stainless steel medium plate, in step (3), the annealing temperature is 600℃±10℃ and the time is 4h±0.5h.

[0010] In the above-mentioned method for preparing 12CrNi stainless steel medium plate, in step (4), the heating temperature is 1180℃±20℃ and the time is 0.8~1.2min / mm.

[0011] In the above-mentioned method for preparing 12CrNi stainless steel medium plates, in step (4), the final rolling temperature is (T2-20)℃±10℃. Where T2 is the characteristic value, calculated as follows: T2 = 467 + 38Cr + 21Si + 360Ti - 1200(C + N) - 57Mn - 68Ni.

[0012] In the above-mentioned method for preparing 12CrNi stainless steel medium plate, in step (5), the annealing heat treatment temperature is [T1+3 / 4(T2-T1)]℃±10℃, and the annealing time is 4±0.2 min / mm.

[0013] Where T1 and T2 are characteristic values, calculated as follows: T1=850 +6Cr+10Si+70Ti-500(C +N)-98Mn -110Ni; T2 = 467 + 38Cr + 21Si + 360Ti - 1200(C + N) - 57Mn - 68Ni.

[0014] A 12CrNi-based stainless steel medium plate is prepared using the above-described preparation method.

[0015] The above-mentioned 12CrNi series stainless steel medium plates are used in the preparation of welded pipes.

[0016] The technical solution of the present invention has the following beneficial effects: (1) The 12CrNi series stainless steel medium plate of the present invention has a yield strength Rp0.2≥380MPa, a tensile strength Rm≥510MPa, an elongation after fracture A50≥20%, and a room temperature impact absorption energy density≥50J / cm 2 ; (2) The 12CrNi series stainless steel medium plate material prepared according to the method of the present invention has the advantages of easy welding, high strength and good economy, and can be widely used in wear-resistant welded pipes. Detailed Implementation

[0017] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0018] This invention comprises two parts: alloy composition design and manufacturing process design. Its core is to achieve a performance balance of "low cost, high wear resistance, high toughness, and easy welding" through composition synergy and process optimization.

[0019] Specifically, the 12CrNi series stainless steel medium plate provided by the present invention comprises, by weight: C: ≤0.03%, N: ≤0.03%, Si: ≤0.40%, Mn: 1.00~2.50%, P: ≤0.03%, S: ≤0.01%, Cr: 11.0~12.5%, Ni: 0.5~1.5%, Ti: 0.10~0.35%, with the balance being Fe and unavoidable impurities.

[0020] C and N: Carbon and nitrogen are the main harmful elements in ferritic stainless steel. High levels of C and N readily combine with Cr to form Cr₂. 23 C6 and CrN lead to "intergranular corrosion" and "room temperature brittleness". This invention controls C and N at a low level of ≤0.030%, which can avoid the above defects, while leaving room for the role of Ti element.

[0021] Si: Silicon is a passivating element that has a positive effect on corrosion resistance, but it also reduces the plasticity and toughness of steel. Therefore, this invention adopts a low-silicon design, and the Si content should be controlled at a low level of ≤0.40%.

[0022] Mn: Manganese is a strong austenite-forming element that can partially replace nickel, reducing the nickel content required in steel and thus lowering costs. Additionally, manganese can improve hardenability, increase hardness through solid solution strengthening, and improve the microstructure of weld seams, thereby enhancing weldability. However, excessive manganese can reduce toughness and lead to brittle cracking during installation and use. Therefore, this invention limits Mn content to 1.0%~2.5%.

[0023] Cr: Chromium is the most important alloying element in stainless steel. It is one of the main alloying elements in stainless steel for its oxidation resistance and corrosion resistance. In order to ensure the corrosion resistance of the product in atmospheric environment, the present invention limits Cr to 11%~12.5%.

[0024] Ni: Nickel is one of the core austenitizing elements, which is beneficial to the product's strength, toughness and weldability. However, too much Ni will lead to a significant increase in product cost. To balance cost and performance, this invention limits Ni to 0.5-1.5%.

[0025] P: Phosphorus is an impurity element. If the content is too high, it will cause the material to become "cold brittle". Therefore, this invention requires that the content of P element be ≤0.03%.

[0026] S: Sulfur is an impurity element. If the content is too high, it will cause the material to become "hot brittle". Therefore, the present invention requires that the content of sulfur element be ≤0.01%.

[0027] Ti: Titanium acts as a stabilizing element, combining with C and N elements in the product beforehand, thus preventing the formation of Cr during subsequent welding processes. 23 C6, CrN, etc., create precipitates in Cr-depleted grain boundary regions, reducing the tendency for intergranular corrosion and improving product weldability. However, excessive Ti content can lead to "fish-like" inclusions during continuous casting, resulting in inclusion-like defects. Therefore, this invention requires Ti to be limited to 0.10%~0.35%. In some preferred embodiments, to ensure the weldability of the material, the present invention limits Creq / Nieq to ≤ 7.5, where Creq and Nieq are the Cr equivalent and Ni equivalent, respectively, and their calculation formulas are shown in Equations 1 and 2.

[0028] Creq = Cr + 1.5Si + 0.5Ti (Equation 1) Nieq = Ni + 30C + 30N + 0.5Mn (Equation 2) Material property values ​​T1 and T2 can be obtained based on the material composition, and the calculation methods are shown in Equations 3 and 4. These material property values ​​represent the phase transformation characteristics of the material and have a certain influence on the formulation of subsequent rolling and normalizing processes.

[0029] T1 = 850 + 6Cr + 10Si + 70Ti - 500(C + N) - 98Mn - 110Ni (Formula 3) T2 = 467+38Cr+21Si+360Ti-1200(C+N) -57Mn-68Ni (Equation 4) On the other hand, the method for preparing 12CrNi-based stainless steel medium plates provided by the present invention includes: smelting The pretreated molten iron is sequentially smelted in a converter, refined in an AOD furnace, and refined in an LF furnace to obtain molten steel. The molten steel, by weight, comprises: C: ≤0.03%, N: ≤0.03%, Si: ≤0.40%, Mn: 1.00~2.50%, P: ≤0.03%, S: ≤0.01%, Cr: 11.0~12.5%, Ni: 0.5~1.5%, Ti: 0.10~0.35%, with the balance being Fe and unavoidable impurities.

[0030] Further preferred, Creq / Nieq ≤ 7.5.

[0031] The converter smelting, AOD furnace refining, and LF furnace refining involved in this invention are all carried out in accordance with existing technologies, and this invention does not impose any specific limitations on them.

[0032] Continuous casting Molten steel is continuously cast to obtain a continuously cast billet.

[0033] In some preferred embodiments, the superheat in the crystallizer is controlled to be ≤35℃, the steel pulling speed is 0.8~1.3m / min, the water flow rate of the wide die is 4500±50L / min, and the water flow rate of the narrow die is 450±50L / min. By controlling the superheat, steel pulling speed, and cooling water flow rate, the proportion of surface defects in the continuously cast billet can be effectively reduced.

[0034] Cutting After continuous casting is completed, the continuously cast billet is cut according to the finished product specifications. After cutting, it is sent to the annealing furnace for annealing to obtain the continuously cast slab billet.

[0035] The 12CrNi stainless steel of this invention exhibits high internal stress during the cooling process, making it prone to brittleness. Hot cutting and low-temperature annealing can effectively reduce product brittleness and decrease the risk of subsequent hot rolling cracking.

[0036] In some preferred embodiments, the continuous casting billet is cut within 12 hours after continuous casting is completed.

[0037] In some preferred embodiments, the annealing temperature is 600℃±10℃ and the time is 4h±0.5h.

[0038] Hot rolling The continuously cast slab is heated, rolled, and straightened to obtain a hot-rolled steel plate.

[0039] In some preferred embodiments, the heating temperature is 1180℃±20℃ and the time is 0.8~1.2min / mm, thereby ensuring that the continuously cast billet is thoroughly heated to reduce the load of subsequent hot rolling.

[0040] In some preferred embodiments, the final rolling temperature is (T2-20)℃±10℃.

[0041] This invention controls the final rolling temperature at (T2-20)℃±10℃, which ensures that the material is basically in the austenitic single-phase region, avoids ferrite transformation during hot rolling, and reduces the risk of edge cracking.

[0042] Annealing and pickling The hot-rolled steel plate is subjected to annealing heat treatment and pickling to obtain the 12CrNi series stainless steel medium plate.

[0043] The purpose of annealing heat treatment is to relieve stress and improve the microstructure and properties of the material. In some preferred embodiments, the annealing heat treatment temperature is [T1+3 / 4(T2-T1)]℃±10℃, and the annealing time should be 4±0.2 min / mm.

[0044] In this process, the material is in the ferrite + austenite dual-phase region, which ensures that the microstructure is strengthened through phase transformation after heat treatment, improving product strength, while still retaining some ferrite structure to preserve toughness and ductility. After annealing, pickling removes the surface iron oxide scale to obtain a clean hot-rolled steel sheet.

[0045] The 12CrNi series stainless steel medium plate material prepared according to the method of the present invention has the advantages of easy welding, high strength and good economy, and can be widely used in wear-resistant welded pipes.

[0046] Example The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments, unless otherwise specified, are performed according to conventional methods and conditions.

[0047] Example 1 (1) The pretreated molten iron was successively smelted in a converter, refined in an AOD furnace, and refined in an LF furnace. The composition of the resulting molten steel is shown in Table 1: Table 1. Steel composition (wt%) in Example 1

[0048] The calculated Creq / Nieq value is 5.39, which meets the requirement of being less than 7.5; the characteristic values ​​T1 are 721℃ and T2 are 835℃.

[0049] (2) The molten steel is continuously cast, the superheat in the crystallizer is controlled at 20°C, the steel pulling speed is 1.1m / min, the water flow rate of the wide mold is 4500L / min, and the water flow rate of the narrow mold is 430L / min, so as to obtain the continuously cast billet.

[0050] (3) The billet shall be cut within 7 hours after continuous casting is completed. After cutting, it shall be transported to a low-temperature annealing furnace for annealing at a temperature of 600℃ for 4 hours.

[0051] (4) The continuously cast slab is heated, rolled, and straightened to obtain a hot-rolled steel plate. The thickness of the cast slab is 200 mm. According to the calculation, the hot rolling heating temperature is 1180℃, and the holding time should be 160~240 min. The actual holding time is 200 min. The thickness of the rolled slab is 20 mm. According to the calculation, the final rolling temperature should be set at 815℃±10℃. The actual final rolling temperature is 810℃.

[0052] (5) The hot-rolled steel plate is subjected to annealing heat treatment and pickling to obtain the 12CrNi stainless steel medium plate. The annealing temperature should be 807℃±10℃ and the time should be 80min±4min. The actual annealing temperature is 810℃ and the time is 82min.

[0053] Three finished slabs were produced with the following properties: yield strength Rp0.2: 398 MPa, tensile strength Rm: 550 MPa, elongation after fracture A50: 27%; room temperature impact absorption energy density: 87 J / cm³. 2 .

[0054] Example 2 (1) The pretreated molten iron was successively smelted in a converter, refined in an AOD furnace, and refined in an LF furnace. The composition of the resulting molten steel is shown in Table 2. Table 2. Steel composition (wt%) in Example 2

[0055] The calculated Creq / Nieq value is 4.92, which meets the requirement of being less than 7.5; the characteristic values ​​T1 are 694℃ and T2 are 819℃.

[0056] (2) The molten steel is continuously cast, the superheat in the crystallizer is controlled at 25°C, the steel pulling speed is 1.0 m / min, the water flow rate of the wide mold is 4500 L / min, and the water flow rate of the narrow mold is 450 L / min, so as to obtain the continuously cast billet.

[0057] (3) The billet shall be cut within 9 hours after continuous casting is completed. After cutting, it shall be transported to a low-temperature annealing furnace for annealing at a temperature of 600℃ for 4 hours.

[0058] (4) The continuously cast slab billet is heated, rolled and straightened to obtain hot-rolled steel plate.

[0059] The slab thickness is 200mm. Calculations show that the hot rolling temperature should be 1180℃, and the holding time should be 160~240min, with an actual holding time of 230min. The rolled slab thickness is 16mm. Calculations show that the final rolling temperature should be set at 799℃±10℃, with an actual final rolling temperature of 815℃.

[0060] (5) The hot-rolled steel plate is subjected to annealing heat treatment and pickling to obtain the 12CrNi stainless steel medium plate. The annealing temperature should be 789℃±10℃ and the time should be 64min±3min. The actual annealing temperature is 795℃ and the time is 66min.

[0061] Five finished boards were produced, with the following properties: yield strength Rp0.2: 420 MPa, tensile strength Rm: 567 MPa, elongation after fracture A50: 25%; room temperature impact absorption energy density: 89 J / cm³. 2 .

[0062] Example 3 (1) The pretreated molten iron was successively smelted in a converter, refined in an AOD furnace, and refined in an LF furnace. The composition of the resulting molten steel is shown in Table 3. Table 3. Composition of molten steel in Example 3 (wt%)

[0063] The calculated Creq / Nieq value is 4.4, which meets the requirement of being less than 7.5; the characteristic values ​​T1 are 678℃ and T2 are 810℃.

[0064] (2) The molten steel is continuously cast, the superheat in the crystallizer is controlled at 30°C, the steel pulling speed is 1.2m / min, the water flow rate of the wide mold is 4500L / min, and the water flow rate of the narrow mold is 450L / min, so as to obtain the continuously cast billet.

[0065] (3) The billet shall be cut within 10 hours after continuous casting is completed. After cutting, it shall be transported to a low-temperature annealing furnace for annealing at 600℃ for 4 hours.

[0066] (4) The continuously cast slab billet is heated, rolled and straightened to obtain hot-rolled steel plate.

[0067] The slab thickness is 200mm. Calculations show that the hot rolling temperature should be 1180℃, and the holding time should be 160~240min, with an actual holding time of 225min. The rolled slab thickness is 25mm. Calculations show that the final rolling temperature should be set at 790℃±10℃, with an actual final rolling temperature of 800℃.

[0068] (5) After annealing and pickling the hot-rolled steel plate, the 12CrNi stainless steel medium plate is obtained. The annealing temperature should be 777℃±10℃ and the time should be 100min±5min. The actual annealing temperature is 785℃ and the time is 100min.

[0069] Five finished boards were produced with the following properties: yield strength Rp0.2: 410 MPa, tensile strength Rm: 556 MPa, elongation after fracture A50: 29%; room temperature impact absorption energy density: 97 J / cm³. 2 .

[0070] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0071] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0072] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A 12CrNi series stainless steel medium plate, characterized in that, By weight, it includes: C: ≤0.03%, N: ≤0.03%, Si: ≤0.40%, Mn: 1.00~2.50%, P: ≤0.03%, S: ≤0.01%, Cr: 11.0~12.5%, Ni: 0.5~1.5%, Ti: 0.10~0.35%, with the balance being Fe and unavoidable impurities.

2. The 12CrNi series stainless steel medium plate according to claim 1, characterized in that, Creq / Nieq≤7.5; where Creq=Cr+1.5Si+0.5Ti; Nieq=Ni+30C+30N+0.5Mn.

3. A method for preparing a 12CrNi-based stainless steel medium plate, characterized in that, include: (1) The pretreated molten iron is sequentially smelted in a converter, refined in an AOD furnace, and refined in an LF furnace, and the resulting molten steel has the composition as described in claim 1 or 2. (2) The molten steel is continuously cast to obtain a continuously cast billet; (3) Cut the continuous casting billet according to the finished product specifications. After cutting, send it to the annealing furnace for annealing to obtain continuous casting slab billet. (4) The continuously cast slab billet is heated, rolled, and straightened to obtain a hot-rolled steel plate; (5) After annealing and pickling the hot-rolled steel plate, the 12CrNi stainless steel medium plate is obtained.

4. The preparation method according to claim 3, characterized in that, During continuous casting, the superheat in the crystallizer is controlled to be ≤35℃, the steel pulling speed is 0.8~1.3m / min, the water flow rate of the wide mold is 4500±50L / min, and the water flow rate of the narrow mold is 450±50L / min.

5. The preparation method according to claim 3, characterized in that, In step (3), the annealing temperature is 600℃±10℃ and the time is 4h±0.5h.

6. The preparation method according to claim 3, characterized in that, In step (4), the heating temperature is 1180℃±20℃ and the heating time is 0.8~1.2min / mm.

7. The preparation method according to claim 3, characterized in that, In step (4), the final rolling temperature is (T2-20)℃±10℃; Where T2 is the characteristic value, calculated as follows: T2 = 467 + 38Cr + 21Si + 360Ti - 1200(C + N) - 57Mn - 68Ni.

8. The preparation method according to claim 3, characterized in that, In step (5), the annealing heat treatment temperature is [T1+3 / 4(T2-T1)]℃±10℃, and the annealing time is 4±0.2 min / mm. Where T1 and T2 are characteristic values, calculated as follows: T1=850 +6Cr+10Si+70Ti-500(C +N)-98Mn -110Ni; T2 = 467 + 38Cr + 21Si + 360Ti - 1200(C + N) - 57Mn - 68Ni.

9. A 12CrNi series stainless steel medium plate, characterized in that, It is prepared by the preparation method according to any one of claims 3 to 8.

10. The application of the 12CrNi stainless steel medium plate according to any one of claims 1 to 2 and 9 in the preparation of welded pipes.

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