Heat treatment method for improving as-cast high-boron stainless steel structure

Abstract

The invention discloses a heat treatment method for improving the structure of as-cast high-boron stainless steel, and belongs to the technical field of stainless steel for shielding materials of controllable nuclear fusion reactors. The method comprises the following steps: (1) charging a high-boron stainless steel ingot at the temperature of 350-400 DEG C in a furnace, keeping the temperature for 3-4 hours, heating to 800-900 DEG C, keeping the temperature for 1-2 hours, discharging from the furnace, and performing water cooling; repeating the operation for 3-4 times; and (2) when the furnace temperature is 800-900 DEG C, feeding into the furnace, keeping the temperature for 1-2 hours, heating to 960-1000 DEG C, keeping the temperature for 2-3 hours, heating to 1050-1120 DEG C, keeping the temperature for 40-80 hours, and slowly cooling along with the furnace. According to the method, the volume ratio of the boride in the as-cast high-boron stainless steel structure can be reduced, the volume ratio of the boride structure in the obtained high-boron stainless steel is smaller than or equal to 45%, and the mechanical property is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel used as shielding material for controlled nuclear fusion reactors, and relates to a heat treatment method for improving the structure of cast high-boron stainless steel. Background Art

[0002] Controlled nuclear fusion has many advantages and has immeasurable market prospects and social significance. The development of 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 that the country is currently building, but also a solution for subsequent larger engineering demonstration reactors and commercial reactors.

[0003] The solid solubility of boron in austenite is 0.02wt%. High boron content forms low-melting-point eutectic borides distributed along the grain boundaries in stainless steel. Brittle hard phase borides cause the plasticity and toughness of stainless steel to be greatly reduced, and the steel plate cracks severely during hot rolling, especially at the edges. Therefore, the manufacturing difficulty of high-boron stainless steel prepared by smelting method is extremely high. How to optimize the proportion and distribution of borides in smelting cast high-boron stainless steel has become an extremely important technical problem. Summary of the invention

[0004] The present invention aims to provide a heat treatment method for improving the structure of as-cast high-boron stainless steel, which can solve the problem that the proportion of boride in the as-cast high-boron stainless steel is serious.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] A heat treatment method for improving the structure of cast high-boron stainless steel comprises the following steps:

[0007] (1) Place the high-boron stainless steel ingot in a temperature furnace at 350-400°C, heat it for 3-4 hours, then heat it to 800-900°C, heat it for 1-2 hours, then take it out of the furnace and cool it with water; repeat this operation 3-4 times;

[0008] (2) When the furnace temperature is 800-900℃, enter the furnace, keep it warm for 1-2 hours, then raise the temperature to 960-1000℃, keep it warm for 2-3 hours, then raise the temperature to 1050-1120℃, keep it warm for 40-80 hours, then slowly cool it with the furnace.

[0009] Furthermore, in step (1), the temperature is increased to 800-900° C. at a rate of 50-100° C. / h.

[0010] Furthermore, in step (2), the temperature is increased to 960-1000° C. at a rate of 100-200° C. / h.

[0011] Furthermore, in step (2), the temperature is increased to 1050-1120° C. at a rate of 400-600° C. / h.

[0012] Furthermore, in step (2), when the furnace temperature is slowly cooled to 800-900°C, the product is taken out of the furnace and water-cooled to room temperature.

[0013] Furthermore, the mass percentage composition of the high-boron stainless steel chemical composition is 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 is Fe and other inevitable impurities.

[0014] Furthermore, after heat treatment by the above method, the microstructure of the high-boron stainless steel is a dual-phase microstructure of austenite and boride, wherein the volume fraction of the boride is ≤45%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: the present invention can reduce the volume proportion of borides in the cast high-boron stainless steel structure, and the structure of the obtained high-boron stainless steel is a dual-phase structure of austenite and boride, wherein the volume fraction of boride is ≤45%, and the mechanical properties are greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 : is a typical microstructure diagram of the as-cast high-boron stainless steel (before heat treatment) of the present invention;

[0017] Figure 2 This is a microstructure diagram of high-boron stainless steel after heat treatment in Example 1 of the present invention;

[0018] Figure 3 This is the microstructure diagram of the high-boron stainless steel after heat treatment in Example 2 of the present invention. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0020] Embodiment 1:

[0021] The specifications of the high boron stainless steel ingot used in this embodiment are 150 mm in height, 150 mm in width, and 230 mm in length, and its composition is 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 is Fe and other inevitable impurities.

[0022] The high-boron stainless steel ingot is loaded into the furnace at 350℃, kept warm for 3h, heated to 800℃ at a rate of 50℃ / h, kept warm for 1h, and then taken out of the furnace for water cooling; The high-boron stainless steel ingot is loaded into the furnace at 350℃, kept warm for 3h, heated to 800℃ at a rate of 50℃ / h, kept warm for 1h, and then taken out of the furnace for water cooling; The high-boron stainless steel ingot is loaded into the furnace at 350℃, kept warm for 3h, heated to 800℃ at a rate of 50℃ / h, kept warm for 3h, and then taken out of the furnace for water cooling; The high-boron stainless steel ingot is loaded into the furnace at 350℃, kept warm for 3h, heated to 800℃ at a rate of 50℃ / h, kept warm for 1.5h, and then taken out of the furnace for water cooling; When the furnace temperature is 800℃, it is heated into the furnace, kept warm for 1.5h, heated to 960℃ at a rate of 100℃ / h, kept warm for 2h, heated to 1050℃ at a rate of 400℃ / h, kept warm for 40h, and slowly cooled with the furnace. When the furnace temperature drops to 800℃, it is taken out of the furnace and cooled to room temperature with water.

[0023] The microstructure of the high boron stainless steel after heat treatment in Example 1 is shown in Figure 2 ,Depend on Figure 2 It can be seen that the volume proportion of boride in the ingot after heat treatment in this embodiment is 45%, and the room temperature mechanical properties data are shown in Table 1.

[0024] Table 1 Room temperature tensile properties of high boron stainless steel in Example 1

[0025] Heat treatment system Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 1 530 300 6.2

[0026] Embodiment 2:

[0027] The specifications of the high boron stainless steel ingot used in this embodiment are 150 mm in height, 150 mm in width, and 230 mm in length, and its composition is 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 is Fe and other inevitable impurities.

[0028] The high-boron stainless steel ingot is loaded into the furnace at 360°C, kept warm for 3h, heated to 820°C at a rate of 50°C / h, kept warm for 1h, and then taken out of the furnace and water-cooled; the high-boron stainless steel ingot is loaded into the furnace at 360°C, kept warm for 3h, heated to 820°C at a rate of 50°C / h, kept warm for 1.5h, and then taken out of the furnace and water-cooled; the high-boron stainless steel ingot is loaded into the furnace at 360°C, kept warm for 3h, heated to 820°C at a rate of 50°C / h, kept warm for 3h, and then taken out of the furnace and water-cooled; when the furnace temperature is 820°C, it is heated into the furnace, kept warm for 1h, heated to 970°C at a rate of 100°C / h, kept warm for 2.5h, heated to 1050°C at a rate of 450°C / h, kept warm for 45h, and slowly cooled with the furnace. When the furnace temperature drops to 840°C, it is taken out of the furnace and water-cooled to room temperature.

[0029] The microstructure of the high boron stainless steel after heat treatment in Example 2 is shown in Figure 3 ,Depend on Figure 3 It can be seen that the volume proportion of boride in the ingot after heat treatment in this embodiment is 44%, and the room temperature mechanical properties data are shown in Table 2.

[0030] Table 2 Room temperature tensile properties of high boron stainless steel in Example 2

[0031] Heat treatment system Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 2 555 330 6.5

[0032] Embodiment 3:

[0033] The specifications of the high boron stainless steel ingot used in this embodiment are 150 mm in height, 150 mm in width, and 230 mm in length, 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 inevitable impurities.

[0034] The high-boron stainless steel ingot is charged into the furnace at 370°C, kept warm for 3.5 hours, heated to 840°C at a rate of 50°C / h, and taken out of the furnace for water cooling after being kept warm for 1 hour; The high-boron stainless steel ingot is charged into the furnace at 370°C, kept warm for 3.5 hours, heated to 840°C at a rate of 50°C / h, and taken out of the furnace for water cooling after being kept warm for 1 hour; The high-boron stainless steel ingot is charged into the furnace at 370°C, kept warm for 3.5 hours, heated to 840°C at a rate of 50°C / h, and taken out of the furnace for water cooling after being kept warm for 1 hour; When the furnace temperature is 840°C, it is heated into the furnace, kept warm for 1 hour, heated to 980°C at a rate of 120°C / h, kept warm for 2 hours, heated to 1060°C at a rate of 500°C / h, and kept warm for 50 hours, and slowly cooled with the furnace, and when the furnace temperature drops to 860°C, it is taken out of the furnace and water-cooled to room temperature.

[0035] The volume proportion of boride in the high-boron stainless steel ingot after heat treatment in Example 3 is 44%, and the room temperature mechanical properties data are shown in Table 3.

[0036] Table 3 Room temperature tensile properties of high boron stainless steel in Example 3

[0037] Heat treatment system Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 3 565 334 6.5

[0038] Embodiment 4:

[0039] The specifications of the high boron stainless steel ingot used in this embodiment are 150 mm in height, 150 mm in width, and 230 mm in length, and its composition is 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 is Fe and other inevitable impurities.

[0040] The high-boron stainless steel ingot is loaded into the furnace at 380°C, and after keeping it for 4 hours, the temperature is increased to 860°C at a rate of 80°C / h, and after keeping it for 1 hour, it is taken out of the furnace and water-cooled; the high-boron stainless steel ingot is loaded into the furnace at 380°C, and after keeping it for 4 hours, the temperature is increased to 860°C at a rate of 80°C / h, and after keeping it for 1 hour, it is taken out of the furnace and water-cooled; the high-boron stainless steel ingot is loaded into the furnace at 380°C, and after keeping it for 4 hours, the temperature is increased to 860°C at a rate of 80°C / h, and after keeping it for 1 hour, it is taken out of the furnace and water-cooled; when the furnace temperature is 860°C, it is heated and entered into the furnace, and after keeping it for 1.5 hours, it is heated to 990°C at a rate of 150°C / h, and after keeping it for 2.5 hours, it is heated to 1070°C at a rate of 550°C / h, and after keeping it for 55 hours, it is slowly cooled with the furnace, and when the furnace temperature drops to 900°C, it is taken out of the furnace and water-cooled to room temperature.

[0041] The volume proportion of boride in the high-boron stainless steel ingot after heat treatment in Example 4 is 43%, and the room temperature mechanical properties data are shown in Table 4.

[0042] Table 4 Room temperature tensile properties of high boron stainless steel in Example 4

[0043] Heat treatment system Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 4 563 345 7

[0044] Embodiment 5:

[0045] The specifications of the high boron stainless steel ingot used in this embodiment are 150 mm in height, 150 mm in width, and 230 mm in length, and its composition is 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 is Fe and other inevitable impurities.

[0046] The high-boron stainless steel ingot is placed in a warm-charging furnace at 390°C. After being kept warm for 4 hours, the temperature is increased to 860°C at a rate of 90°C / h. After being kept warm for 1 hour, it is taken out of the furnace and water-cooled. The high-boron stainless steel ingot is placed in a warm-charging furnace at 390°C. After being kept warm for 4 hours, the temperature is increased to 860°C at a rate of 90°C / h. After being kept warm for 1 hour, it is taken out of the furnace and water-cooled. The high-boron stainless steel ingot is placed in a warm-charging furnace at 390°C. After being kept warm for 4 hours, the temperature is increased to 860°C at a rate of 90°C / h. After being kept warm for 1 hour, it is taken out of the furnace and water-cooled. Water-cooling after taking out of the furnace; high boron stainless steel ingot is charged into the furnace at 390℃, kept at this temperature for 4h, heated to 860℃ at a rate of 90℃ / h, kept at this temperature for 1h and taken out of the furnace and water-cooling; it is heated into the furnace at 880℃, kept at this temperature for 2h, heated to 1000℃ at a rate of 150℃ / h, kept at this temperature for 3h, heated to 1080℃ at a rate of 550℃ / h, kept at this temperature for 60h and slowly cooled with the furnace. When the furnace temperature drops to 900℃, it is taken out of the furnace and water-cooled to room temperature.

[0047] The volume proportion of boride in the high-boron stainless steel ingot after heat treatment in Example 5 is 41%, and the room temperature mechanical properties data are shown in Table 5.

[0048] Table 5 Room temperature tensile properties of high boron stainless steel in Example 5

[0049] Heat treatment system Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 5 570 350 7.5

[0050] Embodiment 6:

[0051] The specifications of the high boron stainless steel ingot used in this embodiment are 150 mm in height, 150 mm in width, and 230 mm in length, and 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%, and the balance is Fe and other inevitable impurities.

[0052] The high-boron stainless steel ingot is placed in a warm furnace at 400℃. After being kept warm for 3.5 hours, the temperature is increased to 900℃ at a rate of 100℃ / h. After being kept warm for 2 hours, it is taken out of the furnace and water-cooled. The high-boron stainless steel ingot is placed in a warm furnace at 400℃. After being kept warm for 3.5 hours, the temperature is increased to 900℃ at a rate of 100℃ / h. After being kept warm for 2 hours, it is taken out of the furnace and water-cooled. The high-boron stainless steel ingot is placed in a warm furnace at 400℃. After being kept warm for 3.5 hours, the temperature is increased to 900℃ at a rate of 100℃ / h. After being kept warm for 2 hours, it is taken out of the furnace and water-cooled. After 2 hours, it is taken out of the furnace and cooled with water; the high boron stainless steel ingot is charged into the furnace at 400℃, kept warm for 3.5 hours, heated to 900℃ at a rate of 100℃ / h, kept warm for 2 hours, and taken out of the furnace and cooled with water; when the furnace temperature is 900℃, it is heated into the furnace, kept warm for 2 hours, heated to 1000℃ at a rate of 200℃ / h, kept warm for 3 hours, heated to 1100℃ at a rate of 600℃ / h, kept warm for 70 hours, and slowly cooled with the furnace. When the furnace temperature drops to 900℃, it is taken out of the furnace and cooled to room temperature with water.

[0053] The volume proportion of boride in the high-boron stainless steel ingot after heat treatment in Example 6 is 39%, and the room temperature mechanical properties data are shown in Table 6.

[0054] Table 6 Room temperature tensile properties of high boron stainless steel in Example 6

[0055] Heat treatment system Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 6 577 368 8.5

[0056] Embodiment 7:

[0057] The specifications of the high boron stainless steel ingot used in this embodiment are 150 mm in height, 150 mm in width, and 230 mm in length, and 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%, and the balance is Fe and other inevitable impurities.

[0058] The high-boron stainless steel ingot is placed in a warm furnace at 400℃, kept warm for 4 hours, and then heated to 900℃ at a rate of 100℃ / h. After being kept warm for 2 hours, it is taken out of the furnace and water-cooled; The high-boron stainless steel ingot is placed in a warm furnace at 400℃, kept warm for 4 hours, and then heated to 900℃ at a rate of 100℃ / h. After being kept warm for 2 hours, it is taken out of the furnace and water-cooled; The high-boron stainless steel ingot is placed in a warm furnace at 400℃, kept warm for 4 hours, and then heated to 900℃ at a rate of 100℃ / h. After being kept warm for 2 hours, it is taken out of the furnace and water-cooled. The ingot is then taken out of the furnace and water-cooled; the high boron stainless steel ingot is charged into the furnace at 400℃, kept at this temperature for 4h, then heated to 900℃ at a rate of 100℃ / h, kept at this temperature for 2h, and taken out of the furnace and water-cooled; the ingot is charged into the furnace at 900℃, kept at this temperature for 2h, then heated to 1000℃ at a rate of 200℃ / h, kept at this temperature for 13h, then heated to 1120℃ at a rate of 600℃ / h, kept at this temperature for 80h, and slowly cooled with the furnace. When the furnace temperature drops to 900℃, it is taken out of the furnace and water-cooled to room temperature.

[0059] The volume proportion of boride in the high-boron stainless steel ingot after heat treatment in Example 7 is 37%, and the room temperature mechanical properties data are shown in Table 7.

[0060] Table 7 Room temperature tensile properties of high boron stainless steel in Example 7

[0061] Heat treatment system Tensile strength MPa Yield strength MPa Elongation % No heat treatment 505 290 4.8 Example 7 573 360 8.8

[0062] The typical microstructure of the cast high-boron stainless steel before heat treatment of the present invention is as follows: Figure 1 As shown in the figure, the microstructure of the cast high boron stainless steel after heat treatment is as follows Figure 2 , 3As shown in the figure, before heat treatment, the boride in the cast high-boron stainless steel is dominant, while after heat treatment, the boride is significantly reduced, and the morphology changes from slender and continuous boride dendrites to thick and short boride. After calculation, the proportion of boride is reduced to 45% and 44%, respectively.

Claims

1. A heat treatment method for improving the structure of cast high-boron stainless steel, characterized in that: The following steps are involved: (1) Place the high-boron stainless steel ingot in a warm furnace at 350-400°C, keep it warm for 3-4 hours, then heat it up to 800-900°C, keep it warm for 1-2 hours, then take it out of the furnace and cool it with water; repeat this operation 3-4 times; (2) When the furnace temperature is 800-900℃, enter the furnace, keep it warm for 1-2 hours, then raise the temperature to 960-1000℃, keep it warm for 2-3 hours, then raise the temperature to 1050-1120℃, keep it warm for 40-80 hours, then slowly cool it with the furnace.

2. The heat treatment method for improving the structure of as-cast high-boron stainless steel according to claim 1, characterized in that: In step (1), the temperature is increased to 800-900°C at a rate of 50-100°C / h.

3. The heat treatment method for improving the structure of as-cast high-boron stainless steel according to claim 2, characterized in that: In step (2), the temperature is increased to 960-1000°C at a rate of 100-200°C / h.

4. The heat treatment method for improving the structure of as-cast high-boron stainless steel according to claim 3, characterized in that: In step (2), the temperature is increased to 1050-1120°C at a rate of 400-600°C / h.

5. The heat treatment method for improving the structure of as-cast high-boron stainless steel according to claim 4, characterized in that: In step (2), the furnace is slowly cooled to a temperature of 800-900°C, and then the product is taken out of the furnace and water-cooled to room temperature.

6. The heat treatment method for improving the structure of as-cast high-boron stainless steel according to any one of claims 1 to 5, characterized in that: The mass percentage composition of the high-boron stainless steel chemical composition is 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 is Fe and other inevitable impurities.

7. The heat treatment method for improving the structure of as-cast high-boron stainless steel according to claim 6, characterized in that: After being treated by the above heat treatment method, the microstructure of the high-boron stainless steel is a dual-phase microstructure of austenite and boride, wherein the volume fraction of the boride is ≤45%.

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