A heat treatment method for improving the microstructure of as-cast high-boron stainless steel
By employing a heat treatment method involving multiple heating and holding cycles followed by slow cooling, the problem of uneven boride distribution in high-boron stainless steel was solved, its ductility and toughness were improved, and the mechanical properties of as-cast high-boron stainless steel were enhanced.
Patent Information
- Application Number
- CN202411213891.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-31
- Publication Date
- 2026-02-27
- Estimated Expiration
- 2044-08-31
AI Technical Summary
High boron content forms low-melting-point eutectic borides distributed along grain boundaries in stainless steel, leading to reduced plasticity and toughness, increased manufacturing difficulty, and increased susceptibility to cracking, especially during hot rolling.
A heat treatment method involving multiple heating and holding and slow cooling is adopted, including holding at 350-400℃ for 3-4 hours, then heating to 800-900℃, then holding at 800-900℃ for 1-2 hours, then heating to 960-1120℃ and holding for 40-80 hours, and finally slow cooling to room temperature, controlling the volume fraction of boride to ≤45%.
It significantly reduces the volume fraction of borides in the microstructure of cast high-boron stainless steel, thereby improving mechanical properties, especially elongation and yield strength.
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Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of stainless steel for shielding materials of controllable nuclear fusion reactors, and relates to a heat treatment method for improving the organization of cast high-boron stainless steel. BACKGROUND
[0002] Controllable nuclear fusion has many advantages and has immeasurable market prospects and social significance. Developing radiation-resistant high-boron stainless steel for nuclear fusion reactors is not only an urgent need for the compact nuclear fusion energy experimental device BEST currently to be built by the country, but also a solution for subsequent larger engineering demonstration reactors and commercial reactors.
[0003] The solid solubility of boron in austenite is 0.02wt%, and a high content of boron forms low-melting-point eutectic borides distributed along the grain boundaries in the stainless steel. The brittle and hard phase borides greatly reduce the plasticity and toughness of the stainless steel, and the steel plate cracks seriously during hot rolling, especially the edge cracks, so the manufacturing difficulty of high-boron stainless steel prepared by the melting method is extremely high. How to optimize the proportion and distribution of borides in the cast high-boron stainless steel prepared by the melting method has become an extremely important technical problem. SUMMARY
[0004] The application aims to provide a heat treatment method for improving the organization of cast high-boron stainless steel, which can solve the serious problem of boride proportion in the cast high-boron stainless steel.
[0005] To achieve the above-mentioned application purposes, the technical solution adopted by the application is as follows:
[0006] A heat treatment method for improving the organization of cast high-boron stainless steel, comprising the following steps:
[0007] (1) The high-boron stainless steel ingot is heated to 350-400 DEG C and then loaded into the furnace, and after heat preservation for 3-4 hours, the temperature is raised to 800-900 DEG C, and after heat preservation for 1-2 hours, the furnace is discharged and water-cooled; the operation is repeated 3-4 times.
[0008] (2) The furnace temperature is 800-900 DEG C, and then the furnace is loaded, and after heat preservation for 1-2 hours, the temperature is raised to 960-1000 DEG C, and after heat preservation for 2-3 hours, the temperature is raised to 1050-1120 DEG C, and after heat preservation for 40-80 hours, the furnace is slowly cooled.
[0009] Further, in step (1), the temperature is raised to 800-900 DEG C at a rate of 50-100 DEG C / h.
[0010] Further, in step (2), the temperature is raised to 960-1000 DEG C at a rate of 100-200 DEG C / h.
[0011] Further, in step (2), the temperature is raised to 1050-1120 DEG C at a rate of 400-600 DEG C / h.
[0012] Further, in step (2), the furnace is slowly cooled to a furnace temperature of 800-900 DEG C, and then the furnace is discharged and water-cooled to room temperature.
[0013] Further, the high-boron stainless steel has a chemical composition by mass percentage of C: 0.03-0.08%, Si: 0.3-0.35%, Mn: 1.1-1.8%, P≤0.012%, S≤0.003%, Ni: 12-15%, Cr: 17-20%, Ti≤0.08%, B: 1.8-2.25%, N≤0.005%, O≤0.003%, Nb≤0.01%, Co≤0.05%, and the balance of Fe and other inevitable impurities.
[0014] Further, after the heat treatment, the high-boron stainless steel has an austenite and boride dual-phase structure, wherein the volume fraction of the boride is ≤45%.
[0015] Compared with the prior art, the application has the following beneficial effects: the application can reduce the volume fraction of boride in the as-cast high-boron stainless steel, and the as-cast high-boron stainless steel has an austenite and boride dual-phase structure, wherein the volume fraction of the boride is ≤45%, and the mechanical properties are greatly improved. BRIEF DESCRIPTION OF DRAWINGS
[0016] Figure 1 Figure 1 is a typical microstructure diagram of the as-cast high-boron stainless steel (before heat treatment) of the application;
[0017] Figure 2 Figure 2 is a microstructure diagram of the high-boron stainless steel after heat treatment in Example 1 of the application;
[0018] Figure 3 Figure 3 is a microstructure diagram of the high-boron stainless steel after heat treatment in Example 2 of the application. DETAILED DESCRIPTION
[0019] The application will be further described in detail below in combination with the drawings and examples.
[0020] Example 1
[0021] The high-boron stainless steel ingot used in this example has a height of 150 mm, a width of 150 mm, and a length of 230 mm, and has a composition of C: 0.03%, Si: 0.3%, Mn: 1.1%, P: 0.012%, S: 0.003%, Ni: 12%, Cr: 17%, Ti: 0.08%, B: 1.8%, N: 0.005%, O: 0.003%, Nb: 0.01%, Co: 0.05%, and the balance of Fe and other inevitable impurities.
[0022] The high-boron stainless steel ingot is heated to 350°C and then loaded into the furnace, and heated to 800°C at a rate of 50°C / h after holding for 3h, and then taken out of the furnace and water cooled after holding for 1h; the high-boron stainless steel ingot is heated to 350°C and then loaded into the furnace, and heated to 800°C at a rate of 50°C / h after holding for 3h, and then taken out of the furnace and water cooled after holding for 1.5h; the high-boron stainless steel ingot is heated to 350°C and then loaded into the furnace, and heated to 800°C at a rate of 50°C / h after holding for 3h, and then taken out of the furnace and water cooled after holding for 1.5h; the high-boron stainless steel ingot is heated to 800°C and then loaded into the furnace, and heated to 960°C at a rate of 100°C / h after holding for 1.5h, and then heated to 1050°C at a rate of 400°C / h after holding for 2h, and then slowly cooled in the furnace, and taken out of the furnace and water cooled to room temperature after the furnace temperature is reduced to 800°C.
[0023] The microstructure of the high-boron stainless steel after the heat treatment of Example 1 is shown in Figure 1. Figure 2 As shown in Figure 1, the volume fraction of boride in the high-boron stainless steel after the heat treatment of Example 1 is 45%. Figure 2 As shown in Table 1, the room temperature mechanical properties of the high-boron stainless steel after the heat treatment of Example 1 are as follows.
[0024] Table 1 Room temperature tensile properties of the high-boron stainless steel in Example 1
[0025] Heat treatment regime Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 1 530 300 6.2
[0026] Example 2:
[0027] The high-boron stainless steel ingot used in this example has a height of 150mm, a width of 150mm, and a length of 230mm, and has the following composition: C: 0.04%, Si: 0.31%, Mn: 1.2%, P: 0.01%, S: 0.002%, Ni: 13%, Cr: 18%, Ti: 0.07%, B: 1.85%, N: 0.004%, O: 0.003%, Nb: 0.01%, Co: 0.04%, and the balance being Fe and other inevitable impurities.
[0028] The high-boron stainless steel ingot is heated to 360°C and then loaded into the furnace, and heated to 820°C at a rate of 50°C / h after holding for 3h, and then taken out of the furnace and water cooled after holding for 1h; the high-boron stainless steel ingot is heated to 360°C and then loaded into the furnace, and heated to 820°C at a rate of 50°C / h after holding for 3h, and then taken out of the furnace and water cooled after holding for 1.5h; the high-boron stainless steel ingot is heated to 360°C and then loaded into the furnace, and heated to 820°C at a rate of 50°C / h after holding for 3h, and then taken out of the furnace and water cooled after holding for 1h; the high-boron stainless steel ingot is heated to 820°C and then loaded into the furnace, and heated to 970°C at a rate of 100°C / h after holding for 1h, and then heated to 1050°C at a rate of 450°C / h after holding for 2.5h, and then slowly cooled in the furnace, and taken out of the furnace and water cooled to room temperature after the furnace temperature is reduced to 840°C.
[0029] The microstructure of the high-boron stainless steel after the heat treatment of Example 2 is shown in Figure 2. Figure 3 As shown in Figure 2, the volume fraction of boride in the high-boron stainless steel after the heat treatment of Example 2 is 45%.Figure 3 It can be seen that the volume fraction of boride in the ingot after heat treatment in this embodiment is 44%, and the room temperature mechanical property data is shown in Table 2.
[0030] Table 2 Room temperature tensile properties of high boron stainless steel in Example 2
[0031] Heat treatment regime Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 2 555 330 6.5
[0032] Example 3:
[0033] The high boron stainless steel ingot used in this embodiment has a height of 150 mm, a width of 150 mm, and a length of 230 mm, and its composition is C: 0.05%, Si: 0.32%, Mn: 1.3%, P: 0.009%, S: 0.002%, Ni: 14%, Cr: 19%, Ti: 0.06%, B: 1.9%, N: 0.003%, O: 0.003%, Nb: 0.01%, Co: 0.04%, and the balance is Fe and other unavoidable impurities.
[0034] The high boron stainless steel ingot is heated to 840°C at a rate of 50°C / h after being heated to 370°C and holding for 3.5h, and then water-cooled after holding for 1h; the high boron stainless steel ingot is heated to 840°C at a rate of 50°C / h after being heated to 370°C and holding for 3.5h, and then water-cooled after holding for 1h; the high boron stainless steel ingot is heated to 840°C at a rate of 50°C / h after being heated to 370°C and holding for 3.5h, and then water-cooled after holding for 1h; the high boron stainless steel ingot is heated to 980°C at a rate of 120°C / h after being heated to 840°C and holding for 1h, and then water-cooled after holding for 2h and being heated to 1060°C at a rate of 500°C / h, and then slowly cooled in the furnace after holding for 50h, and then water-cooled to room temperature after the furnace temperature is reduced to 860°C.
[0035] The volume fraction of boride in the high boron stainless steel ingot after heat treatment in Example 3 is 44%, and the room temperature mechanical property data is shown in Table 3.
[0036] Table 3 Room temperature tensile properties of high boron stainless steel in Example 3
[0037] Heat treatment regime Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 3 565 334 6.5
[0038] Example 4:
[0039] The high-boron stainless steel ingot used in this embodiment has a height of 150 mm, a width of 150 mm, and a length of 230 mm, and has a composition of C: 0.06%, Si: 0.33%, Mn: 1.4%, P: 0.008%, S: 0.003%, Ni: 15%, Cr: 20%, Ti: 0.05%, B: 1.95%, N: 0.003%, O: 0.003%, Nb: 0.01%, Co: 0.04%, and the balance of Fe and other inevitable impurities.
[0040] The high-boron stainless steel ingot was heated to 860°C at a rate of 80°C / h after being kept at 380°C for 4 h, and then water-cooled after being kept at 860°C for 1 h. The high-boron stainless steel ingot was heated to 860°C at a rate of 80°C / h after being kept at 380°C for 4 h, and then water-cooled after being kept at 860°C for 1 h. The high-boron stainless steel ingot was heated to 860°C at a rate of 80°C / h after being kept at 380°C for 4 h, and then water-cooled after being kept at 860°C for 1 h. The high-boron stainless steel ingot was heated to 990°C at a rate of 150°C / h after being kept at 860°C for 1.5 h, and then water-cooled after being kept at 990°C for 2.5 h and then being heated to 1070°C at a rate of 550°C / h and kept at 1070°C for 55 h.
[0041] The volume fraction of borides in the high-boron stainless steel ingot after the heat treatment of Example 4 was 43%, and the room-temperature mechanical property data are shown in Table 4.
[0042] Table 4 Room-temperature tensile properties of the high-boron stainless steel in Example 4
[0043] Heat treatment regime Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 4 563 345 7
[0044] Example 5:
[0045] The high-boron stainless steel ingot used in this embodiment has a height of 150 mm, a width of 150 mm, and a length of 230 mm, and has a composition of C: 0.07%, Si: 0.34%, Mn: 1.5%, P: 0.007%, S: 0.003%, Ni: 15%, Cr: 19%, Ti: 0.06%, B: 2%, N: 0.004%, O: 0.003%, Nb: 0.01%, Co: 0.04%, and the balance of Fe and other inevitable impurities.
[0046] High-boron stainless steel ingots were loaded into the furnace at 390℃, held at that temperature for 4 hours, then heated to 860℃ at a rate of 90℃ / h, held for 1 hour, and then removed from the furnace and water-cooled. Water cooling after furnace exit; High boron stainless steel ingots are loaded into the furnace at 390℃, held for 4 hours, then heated to 860℃ at a rate of 90℃ / h, held for 1 hour, and then water-cooled after furnace exit; When the furnace temperature is 880℃, the ingots are loaded into the furnace, held for 2 hours, then heated to 1000℃ at a rate of 150℃ / h, held for 3 hours, then heated to 1080℃ at a rate of 550℃ / h, held for 60 hours, and then slowly cooled with the furnace. When the furnace temperature drops to 900℃, the ingots are water-cooled to room temperature after furnace exit.
[0047] The volume percentage of borides in the high-boron stainless steel ingot after heat treatment in Example 5 was 41%, and the room temperature mechanical properties are shown in Table 5.
[0048] Table 5. Room temperature tensile properties of high boron stainless steel in Example 5
[0049] Heat treatment regime Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 5 570 350 7.5
[0050] Example 6:
[0051] The high-boron stainless steel ingot used in this embodiment has a height of 150mm, a width of 150mm, and a length of 230mm. Its composition is C: 0.08%, Si: 0.35%, Mn: 1.6%, P: 0.009%, S: 0.003%, Ni: 15%, Cr: 20%, Ti: 0.06%, B: 2.1%, N: 0.003%, O: 0.003%, Nb: 0.01%, Co: 0.04%, with the balance being Fe and other unavoidable impurities.
[0052] High-boron stainless steel ingots are first loaded into the furnace at 400℃, held at that temperature for 3.5 hours, then heated to 900℃ at a rate of 100℃ / h, held for 2 hours, and then removed from the furnace and water-cooled. After 2 hours, the high-boron stainless steel ingots are removed from the furnace and water-cooled. The ingots are loaded into the furnace at 400℃, held for 3.5 hours, and then heated to 900℃ at a rate of 100℃ / h. After holding for 2 hours, they are removed from the furnace and water-cooled. The ingots are loaded into the furnace at 900℃, held for 2 hours, and then heated to 1000℃ at a rate of 200℃ / h. After holding for 3 hours, they are heated to 1100℃ at a rate of 600℃ / h. After holding for 70 hours, they are slowly cooled in the furnace. When the furnace temperature drops to 900℃, they are removed from the furnace and water-cooled to room temperature.
[0053] The volume percentage of borides in the high-boron stainless steel ingot after heat treatment in Example 6 was 39%, and the room temperature mechanical properties are shown in Table 6.
[0054] Table 6. Room temperature tensile properties of high boron stainless steel in Example 6
[0055] Heat treatment regime Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 6 577 368 8.5
[0056] Example 7:
[0057] The high-boron stainless steel ingot used in this embodiment has a height of 150mm, a width of 150mm, and a length of 230mm. Its composition is C: 0.08%, Si: 0.35%, Mn: 1.8%, P: 0.009%, S: 0.003%, Ni: 15%, Cr: 20%, Ti: 0.06%, B: 2.25%, N: 0.003%, O: 0.003%, Nb: 0.01%, Co: 0.04%, with the balance being Fe and other unavoidable impurities.
[0058] High-boron stainless steel ingots are charged into a preheated furnace at 400℃, held at that temperature for 4 hours, then heated to 900℃ at a rate of 100℃ / h, held for 2 hours, and then removed from the furnace and water-cooled. After being removed from the furnace, the high-boron stainless steel ingots are water-cooled. They are loaded into the furnace at 400℃, held for 4 hours, and then heated to 900℃ at a rate of 100℃ / h. After holding for 2 hours, they are removed from the furnace and water-cooled. They are also loaded into the furnace at 900℃, held for 2 hours, heated to 1000℃ at a rate of 200℃ / h, held for 3 hours, and then heated to 1120℃ at a rate of 600℃ / h. After holding for 80 hours, they are slowly cooled in the furnace. When the furnace temperature drops to 900℃, they are removed from the furnace and water-cooled to room temperature.
[0059] The volume percentage of borides in the high-boron stainless steel ingot after heat treatment in Example 7 was 37%, and the room temperature mechanical properties are shown in Table 7.
[0060] Table 7. Room temperature tensile properties of high boron stainless steel in Example 7
[0061] Heat treatment regime Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 7 573 360 8.8
[0062] Typical microstructure of the as-cast high-boron stainless steel before heat treatment according to this invention is shown in the figure below. Figure 1 As shown, the microstructure of the heat-treated as-cast high-boron stainless steel is as follows. Figure 2 , 3The results show that the borides in the as-cast high boron stainless steel are mainly continuous and elongated, while the borides in the heat treated high boron stainless steel are mainly short and discontinuous. The proportion of borides in the as-cast high boron stainless steel and the heat treated high boron stainless steel is reduced to 45% and 44%, respectively.
Claims
1. A heat treatment method for improving the microstructure of as-cast high-boron stainless steel, characterized in that, Includes the following steps: (1) The high boron stainless steel ingot is loaded into the furnace at 350-400℃, held for 3-4 hours, then heated to 800-900℃, held for 1-2 hours, and then removed from the furnace and water-cooled; this operation is repeated 3-4 times. (2) When the furnace temperature is 800-900℃, put it into the furnace and keep it at that temperature for 1-2 hours. Then raise the temperature to 960-1000℃, keep it at that temperature for 2-3 hours, raise the temperature to 1050-1120℃, keep it at that temperature for 40-80 hours, and then slowly cool it with the furnace. When the furnace temperature is 800-900℃, take it out of the furnace and cool it to room temperature with water. The chemical composition of the high-boron stainless steel is as follows (by mass percentage): C: 0.03–0.08%, Si: 0.3–0.35%, Mn: 1.1–1.8%, P≤0.012%, S≤0.003%, Ni: 12–15%, Cr: 17–20%, Ti≤0.08%, B: 1.8–2.25%, N≤0.005%, O≤0.003%, Nb≤0.01%, Co≤0.05%, with the balance being Fe and other unavoidable impurities.
2. The heat treatment method for improving the microstructure of cast high-boron stainless steel according to claim 1, characterized in that: In step (1), the temperature is increased to 800-900℃ at a rate of 50-100℃ / h.
3. The heat treatment method for improving the microstructure of cast high-boron stainless steel according to claim 2, characterized in that: In step (2), the temperature is increased to 960-1000℃ at a rate of 100-200℃ / h.
4. The heat treatment method for improving the microstructure of as-cast high-boron stainless steel according to claim 3, characterized in that: In step (2), the temperature is increased to 1050-1120℃ at a rate of 400-600℃ / h.
5. The heat treatment method for improving the microstructure of cast high-boron stainless steel according to claim 4, characterized in that: After being treated by the above heat treatment method, the microstructure of high boron stainless steel is a duplex microstructure of austenite and borides, wherein the volume fraction of borides is ≤45%.
Citation Information
Patent Citations
High-boron-content stainless steel and preparation method thereof
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Production method of high-boron austenitic stainless steel sheet with high plasticity and high toughness
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