00Cr13 ferritic stainless steel exempted from post-weld heat treatment and manufacturing method thereof

Abstract

The present invention discloses a 00Cr13 ferritic stainless steel exempt from post-weld heat treatment and a manufacturing method thereof, belonging to the field of stainless steel technology. It comprises the following components by mass content: Scheme 1: C: ≤ 0.01%; Cr: 13.4-13.8%; Mn ≤ 0.4%; Si ≤ 0.3%; Ti: 0.15-0.2%; Al: 0.05-0.1%; N: ≤ 0.008%; Ni: ≤ 0.1%; Scheme 2: C: ≤ 0.01%; Cr: 13.4-13.8%; Mn ≤ 0.4%; Si ≤ 0.3%; Ti: 0.1-0.15%; Al: 0.15-0.2%; N: ≤ 0.008%; Ni: ≤ 0.1%; and its manufacturing method is also disclosed. The 00Cr13 ferritic stainless steel provided by the present invention does not require complex heat treatment after welding, and a single-phase ferrite structure can be obtained by direct cooling after welding.

Description

Technical Field

[0001] The present invention belongs to the technical field of stainless steel, and in particular relates to a 00Cr13 ferritic stainless steel free of post-weld heat treatment and a manufacturing method thereof. Background Art

[0002] Ferritic stainless steel is widely used in Sinopec pipelines. Since martensite tends to form during cooling during welding, generating internal stress and causing cracking in the material, the primary consideration when welding ferritic stainless steel is the post-weld heat treatment of the stainless steel. To prevent the formation of martensite or secondary phases during the cooling process, traditional methods require high-temperature annealing of the weld (such as insulation treatment at 800 to 950°C). This adds an additional 0.5 to 1 hour of annealing time per meter of pipe welded, increasing energy costs by approximately 15%-20%. Furthermore, localized heat treatment of complex components (such as tees and flanges) can easily lead to uneven residual stress distribution, causing deformation or cracking. This poses common challenges, such as difficulty or high cost, in post-weld heat treatment. Summary of the Invention

[0003] The present invention provides a 00Cr13 ferritic stainless steel that does not require post-weld heat treatment, and a method for manufacturing the same. By modifying the composition of conventional 00Cr13 ferritic stainless steel and, based on the influence of the constituent elements, eliminating the γ phase and expanding the α phase, the material is cooled from a temperature above the phase transition point to obtain a single-phase ferrite structure. The 00Cr13 ferritic stainless steel of the present invention undergoes no phase transition when cooled at various cooling rates after welding, eliminating the need for complex post-weld heat treatment and achieving a single-phase ferrite structure that meets the requirements for use in oil pipelines and automotive exhaust systems. This shortens production cycles, reduces costs, avoids heat treatment defects, and is suitable for a variety of industrial fields.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A 00Cr13 ferritic stainless steel exempt from post-weld heat treatment, characterized in that the 00Cr13 ferritic stainless steel comprises the following components by mass: C: ≤0.01%; Cr: 13.4-13.8%; Mn ≤0.4%; Si ≤0.3%; Ti: 0.1-0.2%; Al: 0.05-0.2%; N: ≤0.008%; Ni: ≤0.1%, and the remainder being Fe and unavoidable impurities.

[0006] Furthermore, the 00Cr13 ferritic stainless steel includes the following components by mass: C 0.01 wt%; Cr13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.175 wt%; Al 0.075 wt%; N 0.008 wt%; Ni 0.1 wt%; the balance being Fe and unavoidable impurities.

[0007] Furthermore, the 00Cr13 ferritic stainless steel includes the following components by mass: C 0.01 wt%; Cr13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.125 wt%; Al 0.175 wt%; N 0.008 wt%; Ni 0.1 wt%; the balance being Fe and unavoidable impurities.

[0008] Furthermore, the 00Cr13 ferritic stainless steel includes the following components by mass:

[0009] C 0.01 wt%; Cr 13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.175 wt%; Al 0.175wt%; N 0.008 wt%; Ni 0.1 wt%; the balance is Fe and inevitable impurities.

[0010] The present invention also provides a method for manufacturing 00Cr13 ferritic stainless steel that is exempt from post-weld heat treatment, comprising: smelting 00Cr13 ferritic stainless steel according to designed components, and forging the smelted 00Cr13 ferritic stainless steel into plates; wherein: smelting is performed in a medium-frequency induction furnace, and in order to control Al burnout, Al is added after all other alloys are melted, and smelting is continued for 10 to 15 minutes before casting is started to cast the ingot into a round ingot; then, the round ingot is trimmed of its head and tail, kept at 1190°C to 1200°C for 2 to 2.5 hours, and forged into a square billet of a certain thickness and width after a punching and drawing operation; then, the square billet is kept at 1080°C to 1120°C for 1 to 1.5 hours, hot rolled 6 to 8 times, and the final rolling temperature is ensured to be ≥850°C; and finally, air-cooled to room temperature after rolling.

[0011] Furthermore, the final thickness of the plate is 3 mm.

[0012] Furthermore, the method further includes the following steps: degreasing, solutionizing, pickling, straightening, cutting off the head and tail of the plate, and taking samples for inspection.

[0013] Furthermore, after a punching and drawing operation, the billet is forged into a 75mm thick and 100mm wide square billet.

[0014] Furthermore, the manufactured 00Cr13 ferritic stainless steel does not require complex heat treatment after welding, and a single-phase ferrite structure can be obtained by direct cooling after welding.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects:

[0016] In order to prevent the occurrence of phase transformation and martensite formation during the cooling process of welding, the material of ferritic stainless steel pipe fittings must meet the requirement that the microstructure remains single-phase ferrite after direct cooling after welding. The present invention provides a new type of ferritic stainless steel that overcomes the welding heat treatment difficulties faced in the existing pipeline welding process. By optimizing the chemical composition and microstructure of stainless steel, it is possible to ensure that the weld and heat-affected zone have good performance without the need for complex heat treatment procedures after welding, thereby effectively reducing the time cost, labor cost and energy consumption of pipeline welding, improving the construction efficiency and quality of pipeline welding, and expanding the application scope of ferritic stainless steel in the field of pipeline engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below with reference to the accompanying drawings.

[0018] Figure 1 The metallographic structures of Example 1 after welding at different cooling rates to room temperature are shown;

[0019] Figure 2 The metallographic structures of Example 2 after welding at different cooling rates to room temperature are shown;

[0020] Figure 3 This is the post-weld metallographic structure of Comparative Example 1 (conventional ferritic stainless steel);

[0021] Figure 4 1 and 2 are thermal expansion curves of Example 1 and Example 2;

[0022] Figure 5 Thermo-Calc phase diagrams for Examples 1 and 2;

[0023] Figure 6 The Vickers hardness of Example 1 and Example 2 at different cooling rates after welding. DETAILED DESCRIPTION

[0024] A 00Cr13 ferritic stainless steel that does not require post-weld heat treatment and its manufacturing method are described. The composition design principles are shown in Table 1. Analysis of the designed composition shows that controlling the carbon and nitrogen contents below 0.02% effectively eliminates the driving force for austenitization, and controlling the Cr content to 13.4%-13.8% maintains the corrosion resistance of 00Cr13 ferritic stainless steel. Furthermore, titanium stabilizes the carbon / nitrogen ratio, inhibiting carbide precipitation, while aluminum expands the ferrite phase and improves high-temperature stability. Furthermore, the steel is free of high-cost elements such as Mo and Nb, and its Ni content is ≤0.1%. The material cost is 25%-30% lower than that of Mo-containing steels, making it suitable for cost-sensitive applications such as civil pipelines and building structures.

[0025] Table 1 Composition and action mechanism of 00Cr13 ferritic stainless steel

[0026]

[0027] (1) Product: 00Cr13 ferritic stainless steel includes the following components by mass:

[0028] Option 1: C: ≤0.01%; Cr: 13.4-13.8%; Mn ≤0.4%; Si ≤0.3%; Ti: 0.15-0.2%; Al: 0.05-0.1%; N: ≤0.008%; Ni: ≤0.1%, the rest is Fe and unavoidable impurities;

[0029] Option 2: C: ≤0.01%; Cr: 13.4-13.8%; Mn ≤0.4%; Si ≤0.3%; Ti: 0.1-0.15%; Al: 0.15-0.2%; N: ≤0.008%; Ni: ≤0.1%, the rest is Fe and unavoidable impurities;

[0030] (2) Method: A furnace of 00Cr13 ferritic stainless steel was smelted according to the designed composition. 50 kg of the smelted 00Cr13 ferritic stainless steel was forged into plates with a thickness of 75 mm and a width of 100 mm. First, the smelting was carried out in a medium frequency induction furnace. To control the burnout of Al, Al was added after all other alloys were melted. The smelting was continued for 10 to 15 minutes before casting was started. The plates were cast into 50 kg round ingots. The ingots were then trimmed and kept at 1190 to 1200°C for 2 to 2.5 hours. After a one-step and one-draw operation, they were forged into square billets with a thickness of 75 mm and a width of 100 mm. The square billets were then kept at 1080 to 1120°C for 1 to 1.5 hours and hot rolled 6 to 8 times to ensure that the final rolling temperature was ≥850°C. Finally, the plates were air-cooled to room temperature after rolling. The final thickness of the plates was 3 mm. The plates are degreased, solution treated, pickled, straightened, heads and tails cut off, and samples taken for inspection.

[0031] (1) Example 1: The mass percentages are as follows: C 0.01 wt%; Cr 13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.175 wt%; Al 0.075 wt%; N 0.008 wt%; Ni 0.1 wt%; the balance being Fe and unavoidable impurities.

[0032] (2) Example 2: The mass percentages are as follows: C 0.01 wt%; Cr 13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.125 wt%; Al 0.175 wt%; N 0.008 wt%; Ni 0.1 wt%; the balance being Fe and unavoidable impurities.

[0033] (3) Comparative Example 1 (conventional ferritic stainless steel): The mass percentages are as follows: C 0.025 wt%, Cr 12.5 wt%, Mn 0.4 wt%, Si 0.3 wt%, Ti 0.1 wt%, Al 0.05 wt%, N 0.020 wt%, Ni 0.6 wt%, and the rest are Fe and impurities.

[0034] (4) Other comparative examples:

[0035] Comparative Example 2: C 0.025 wt%; Cr 13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.175 wt%; Al 0.075 wt%; N 0.008 wt%; Ni 0.1 wt%; the balance being Fe and unavoidable impurities.

[0036] Comparative Example 3: C 0.01 wt%; Cr 12.5 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.175 wt%; Al 0.075 wt%; N 0.008 wt%; Ni 0.1 wt%; the balance being Fe and unavoidable impurities.

[0037] Comparative Example 4: C 0.01 wt%; Cr 13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.1 wt%; Al 0.075 wt%; N 0.008 wt%; Ni 0.1 wt%; the balance being Fe and unavoidable impurities.

[0038] Comparative Example 5: C 0.01 wt%; Cr 13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.175 wt%; Al 0.075 wt%; N 0.008 wt%; Ni 0.2 wt%; the balance being Fe and unavoidable impurities.

[0039] Comparative Example 6 (also an alternative, with higher element cost than the embodiment): C 0.01 wt%; Cr 13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.175 wt%; Al 0.175 wt%; N 0.008 wt%; Ni 0.1 wt%; the balance being Fe and unavoidable impurities.

[0040] Comparative Example 7: C 0.01 wt%; Cr 13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.125 wt%; Al 0.075 wt%; N 0.008 wt%; Ni 0.1 wt%; the balance being Fe and unavoidable impurities.

[0041] The specific preparation process for each Example and Comparative Example is as follows: 1 heat of 00Cr13 ferritic stainless steel was smelted according to the designed composition. 50 kg of the smelted 00Cr13 ferritic stainless steel was forged into plates 75 mm thick and 100 mm wide. First, smelting was performed in a medium-frequency induction furnace. To control Al burnout, Al was added after all other alloys were completely melted. Smelting was continued for 12 minutes before casting began, resulting in a 50 kg round ingot. The ingot was then trimmed and held at 1195°C for 2 hours. After a series of forging and drawing operations, it was forged into a 75 mm thick, 100 mm wide billet. The billet was then held at 1100°C for 1.2 hours, hot-rolled 6 to 8 times, and finally air-cooled to room temperature after rolling. The resulting plates had a final thickness of 3 mm. (The same smelting and forging processes were used in all Examples and Comparative Examples.)

[0042] The welding adopts conventional welding conditions and is not restricted by welding conditions (the welding rod is a ferritic stainless steel welding rod and its material is the same as the stainless steel material being welded). This ensures that the weld of the material does not need to be heat treated and austenite phase transformation does not occur after welding.

[0043] The test results of the prepared samples are as follows: Figure 1 This is the metallographic diagram of Example 1 after welding at different cooling rates to room temperature. Figure 2 1 is a metallographic diagram of Example 2 after welding at different cooling rates to room temperature. The metallographic structure shows that the steel structure is composed of ferrite. Figure 3This is the post-weld organization diagram of Comparative Example 1 (conventional ferritic stainless steel). The metallographic structure shows that the steel structure consists of ferrite and lath-shaped martensite.

[0044] Figure 4 The results of thermal expansion tests of Example 1 and Example 2 are shown respectively. After the materials of Example 1 and Example 2 are heated to above Ac3 temperature (1050°C), no sudden change in expansion coefficient due to austenite-martensite phase transformation occurs during the cooling process. Combined with the results of Thermo-Calc phase diagram simulation (see Figure 5 ), proving that it maintains a single-phase ferrite structure within the cooling rate range of the weld heat affected zone (HAZ) (5-100℃ / s).

[0045] Measure the mechanical properties of the product: measure its Vickers hardness results as follows Figure 6 The hardness of the sample air-cooled to room temperature after welding is shown in the figure. It can be seen that the mechanical properties before and after heating and cooling are similar. The tensile strengths of Example 1 and Example 2 were measured to be 324 MPa and 334 MPa, respectively, which can meet the requirements for use in oil pipelines and automobile exhaust systems.

[0046] Table 2 shows the test results of the microstructure and performance of 00Cr13 ferritic stainless steel with different compositions. Compared with the present invention, it can be seen from Comparative Example 2 that excessive C content will lead to the expansion of the austenite phase region, and austenite transformation will occur during cooling; it can be seen from Comparative Example 3 that insufficient Cr equivalent cannot completely eliminate the austenite region, and the retained austenite is partially transformed into martensite after cooling; it can be seen from Comparative Example 5 that Ni promotes the formation of austenite, and the retained austenite is partially transformed into martensite during cooling; Comparative Examples 4 and 7 show that no phase transformation occurs, but when the Ti content is insufficient, the C / N ratio cannot be fully fixed, the grain boundaries are coarse, and performance may be degraded; Comparative Example 6 is still a feasible solution, but the cost is higher than that of the present invention (the price of Al is higher).

[0047] Table 2 Test results of microstructure and properties of 00Cr13 ferritic stainless steel under different compositions

[0048]

[0049] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. An application of 00Cr13 ferritic stainless steel that can obtain a single-phase ferrite structure by direct cooling after welding without complicated heat treatment, characterized in that: The 00Cr13 ferritic stainless steel includes the following components by mass: C: ≤ 0.01%; Cr: 13.4-13.8%; Mn ≤ 0.4%; Si ≤ 0.3%; Ti: 0.1-0.2%; Al：0.15-0.2%； N: ≤0.008%; Ni: 0.1%, the rest is Fe and unavoidable impurities; The 00Cr13 ferritic stainless steel does not require complicated heat treatment after welding, and a single-phase ferrite structure can be obtained by direct cooling after welding.

2. The use according to claim 1, characterized in that The 00Cr13 ferritic stainless steel includes the following components by mass: C 0.01 wt%; Cr 13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.125 wt%; Al 0.175 wt%; N 0.008 wt%; Ni 0.1 wt%; the balance being Fe and unavoidable impurities.

3. The use according to claim 1, characterized in that The 00Cr13 ferritic stainless steel is replaced by the following components by mass: C 0.01 wt%; Cr 13.6 wt%; Mn 0.4 wt%; Si 0.3 wt%; Ti 0.175 wt%; Al 0.175 wt%; N 0.008 wt%; Ni 0.1 wt%; the balance is Fe and inevitable impurities.

4. The use according to any one of claims 1 to 3, characterized in that The manufacturing method of 00Cr13 ferritic stainless steel comprises: smelting 00Cr13 ferritic stainless steel according to the designed composition, forging the smelted 00Cr13 ferritic stainless steel into plates; wherein: smelting is performed in a medium frequency induction furnace, and to control the burnout of Al, Al is added after all other alloys are melted, and smelting is continued for 10 to 15 minutes before casting is started to cast the 00Cr13 ferritic stainless steel into a round ingot; then, the round ingot is trimmed, kept at 1190° C. to 1200° C. for 2 to 2.5 hours, and forged into a square billet of a certain thickness and width by a punching and drawing operation; then, the square billet is kept at 1080° C. to 1120° C. for 1 to 1.5 hours, hot rolled 6 to 8 times, and the final rolling temperature is ensured to be ≥850° C.; and finally, air-cooled to room temperature after rolling.

5. The use according to claim 4, characterized in that The final thickness of the plate is 3 mm.

6. The use according to claim 4, characterized in that The process also includes the following steps: degreasing, solutionizing, pickling, straightening, cutting off the head and tail of the plate, and taking samples for inspection.

7. The use according to claim 4, characterized in that After a one-step-and-one-pull operation, it is forged into a square billet with a thickness of 75mm and a width of 100mm.

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