Duplex stainless steel ingot and preparation method thereof

Abstract

The invention relates to a duplex stainless steel ingot and a preparation method thereof, and the preparation method comprises the following steps: injecting molten steel obtained by smelting into an ingot mold, and carrying out thermal demolding after the surface temperature of the ingot mold is reduced to 600-620 DEG C; the temperature of the heating furnace is controlled to be larger than or equal to 700 DEG C + / -20 DEG C; the heating speed is controlled to heat the heating furnace, and after the temperature in the heating furnace rises to 970-1030 DEG C, the heat preservation time is set according to the included angle of the polygon corresponding to the cross section of the steel ingot and the distance between the two opposite sides for heat preservation; the heating speed is controlled again to heat the heating furnace, and after the temperature in the heating furnace rises to 1100-1180 DEG C, heat preservation is conducted for 3-4 h; and the steel ingot is taken out and subjected to water cooling. The method solves the problem that a large-size steel ingot is easy to crack, so that the crack-free steel ingot can be obtained, a qualified blank is provided for forging production, and the method can be used for producing large equipment parts.

Description

Technical Field

[0001] The present invention belongs to the technical field of forging, and particularly relates to a duplex stainless steel ingot and a preparation method thereof. Background Art

[0002] Improper design of the ingot mold and improper operations of ingot demolding and cooling can both lead to excessive internal stress in the ingot, resulting in stress concentration during the pouring process and thus prone to cracking. During the solidification and cooling stages of large-sized ingots, the greater the temperature difference between the inner surface and the outer surface, the greater the tissue stress and thermal stress generated, and correspondingly, the easier it is to generate cracks.

[0003] Therefore, to ensure that the surface of large-sized ingots does not crack, it is necessary to conduct research on ingot anti-cracking from aspects such as ingot mold design, demolding and cooling, etc. Summary of the Invention

[0004] To solve all or part of the above problems, the purpose of the present invention is to provide a duplex stainless steel ingot and a preparation method thereof.

[0005] According to one aspect of the present invention, a preparation method of a duplex stainless steel ingot is provided, including:

[0006] Injecting the molten steel obtained by smelting into the ingot mold, standing for 3 to 4 hours, and performing hot demolding after the surface temperature of the ingot mold drops to between 600°C and 620°C. The ingot mold is a regular even-sided polygon;

[0007] Controlling the temperature of the heating furnace ≥ 700°C ± 20°C, and loading the demolded ingot into the heating furnace;

[0008] Controlling the heating rate to heat the heating furnace, and after the temperature in the heating furnace rises to 970°C to 1030°C, setting the heat preservation time according to the included angle of the polygon corresponding to the cross-section of the ingot and the distance between two opposite sides for heat preservation;

[0009] Controlling the heating rate to 80°C / h again to heat the heating furnace, and after the temperature in the heating furnace rises to 1100°C to 1180°C, heat preserving for 3h to 4h;

[0010] Taking out the ingot and performing water cooling on the ingot.

[0011] Further, by mass percentage, the molten steel includes: C ≤ 0.025%, Si ≤ 0.80%, Mn ≤ 1.30%, P ≤ 0.025%, S ≤ 0.005%, Cr: 25.2 - 25.8%, Ni: 6.8 - 7.5%, Mo: 3.4 - 3.8%, N: 0.28 - 0.32%, with the balance being Fe, and 2 ≤ Si / (Al * 10) ≤ 4, Mn / Si ≥ 1.4.

[0012] Further, heating the heating furnace by controlling the heating rate, and after the temperature in the heating furnace rises to 970°C - 1030°C, setting the holding time according to the included angle of the polygon corresponding to the cross-section of the ingot and the distance between two opposite sides for heat preservation, further includes:

[0013] Heat the heating furnace by controlling the heating rate ≥ 100°C / h, and raise the temperature in the heating furnace to 970°C - 1030°C;

[0014] After the temperature in the heating furnace rises to 970°C - 1030°C, set the holding time according to the included angle of the polygon corresponding to the cross-section of the ingot and the distance between two opposite sides for heat preservation.

[0015] Further, after the temperature in the heating furnace rises to 970°C - 1030°C, setting the holding time according to the included angle of the polygon corresponding to the cross-section of the ingot and the distance between two opposite sides for heat preservation is specifically:

[0016] After the temperature in the heating furnace rises to 970°C - 1030°C, when 90° ≤ the included angle ≤ 135°, control the value of the holding time of the heating furnace to be equal to 1 - 2 times the distance divided by six, and the unit of the holding time is minutes; when 135° ≤ the included angle ≤ 150°, control the value of the holding time of the heating furnace to be equal to 2 - 3 times the distance divided by eight, and the unit of the holding time is minutes.

[0017] Further, taking out the ingot and performing water cooling on the ingot is specifically:

[0018] Control the circulating water temperature below 50°C, place the ingot single-piece in water for water cooling, take out the ingot after it is placed in water for 1h - 2h, and control the surface temperature of the taken-out ingot below 200°C.

[0019] Further, before injecting the molten steel obtained by smelting into the ingot mold, standing for 3 - 4 hours, and performing hot demolding after the surface temperature of the ingot mold drops to between 600°C - 620°C, the method further includes:

[0020] Smelt the molten steel by using the electric arc furnace + argon oxygen refining furnace + secondary refining process.

[0021] Further, the ingot mold is a regular quadrilateral, a regular octagon or a regular dodecagon.

[0022] The present invention also provides a duplex stainless steel ingot, which is prepared by using the preparation method described in any one of the above.

[0023] Further, the stainless steel ingot has a duplex of ferrite and austenite.

[0024] As can be seen from the above technical solutions, a duplex stainless steel ingot and its preparation method provided by the present invention have the following beneficial effects:

[0025] The present invention solves the problems such as easy cracking of large-sized steel ingots, so that a crack-free steel ingot can be obtained, providing qualified billets for forging production; the steel ingot prepared by the present invention has good internal quality and forging performance and can be used for producing large equipment components. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flowchart of a preparation method of a duplex stainless steel ingot according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] In order to fully understand the purpose, features and effects of the present invention, the present invention will be described in detail through the following specific embodiments. Except for the following content, the process methods of the present invention all adopt conventional methods or devices in the art. Unless otherwise specified, the following noun terms all have the meanings commonly understood by those skilled in the art.

[0028] When a numerical range is disclosed herein, the above range is considered continuous and includes the minimum value and the maximum value of the range, as well as each value between such minimum value and maximum value. Further, when the range refers to an integer, it includes each integer between the minimum value and the maximum value of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0029] As Figure 1 shown, it shows a preparation method of a duplex stainless steel ingot according to an embodiment of the present invention, including the following steps:

[0030] Step S001: Pour the molten steel obtained by smelting into an ingot mold, stand for 3 to 4 hours, and perform hot demolding after the surface temperature of the ingot mold drops to between 600°C and 620°C. The ingot mold is a regular even-sided polygon;

[0031] Step S002: Control the heating furnace temperature ≥ 700°C ± 20°C, and load the demolded steel ingot into the heating furnace;

[0032] Step S003: Control the heating rate to heat the heating furnace, and after the temperature in the heating furnace rises to 970°C to 1030°C, set the holding time according to the included angle of the polygon corresponding to the cross-section of the steel ingot and the distance between two opposite sides for holding;

[0033] Step S004: Control the heating rate to 80°C / h again to heat the heating furnace, and after the temperature in the heating furnace rises to 1100°C to 1180°C, hold for 3 h to 4 h;

[0034] Step S005: Take out the ingot and perform water cooling on the ingot.

[0035] In the embodiment of the present invention, research work is carried out on duplex stainless steel ingots for large equipment components, focusing on solving problems such as easy cracking of large-sized ingots, so as to obtain crack-free ingots and provide qualified blanks for forging production.

[0036] Among them, the duplex stainless steel ingot is a special-shaped ingot, and the cross-sectional shape is a regular even-sided polygon, such as a regular quadrilateral, a regular octagon or a regular dodecagon. Corresponding to different ingot sizes, the ingot mold of this embodiment is a regular even-sided polygon, such as a regular quadrilateral, a regular octagon or a regular dodecagon. And the anti-cracking of the duplex stainless steel ingot is related to the included angle α of the polygon corresponding to the cross-section of the ingot and the distance H between two opposite sides of the polygon corresponding to the cross-section of the ingot. Therefore, the holding time set after the first heating of the heating furnace in the embodiment of the present invention is determined according to the included angle of the polygon corresponding to the cross-section of the ingot and the distance between two opposite sides.

[0037] The ingots prepared in the embodiment of the present invention have good internal quality and forging properties and can be used to produce large equipment components.

[0038] Among them, by mass percentage, the molten steel in step S001 includes: C≤0.025%, Si≤0.80%, Mn≤1.30%, P≤0.025%, S≤0.005%, Cr: 25.2 - 25.8%, Ni: 6.8 - 7.5%, Mo: 3.4 - 3.8%, N: 0.28 - 0.32%, the balance is Fe, and 2≤Si / (Al*10)≤4, Mn / Si≥1.4.

[0039] C, Si, Mn, and N are all main elements in duplex stainless steel, but excessive amounts will cause a reduction in the hot working performance of the steel. Therefore, their ranges need to be controlled. In the embodiment of the present invention, the C content is controlled below 0.025%, the Si content is controlled below 0.80%, the Mn content is controlled below 1.30%, and the N content is controlled at 0.28 - 0.32%. At the same time, in order to reduce the inclusion level, it is necessary to satisfy Mn / Si≥1.4.

[0040] Cr is an important element in stainless steel and plays a key role in its corrosion resistance. However, in order to ensure that the proportion of austenite and ferrite phases in duplex stainless steel is 45 - 55%, the Cr content in the embodiment of the present invention is controlled at 25.20 - 25.80%.

[0041] Ni and Mo are key alloying elements in duplex stainless steel, which can improve the corrosion resistance of the steel and endow the steel with good high-temperature properties. However, both Ni and Mo belong to precious metal elements, and excessive content will increase the manufacturing cost. Therefore, in the embodiments of the present invention, the Ni content is controlled within 6.8-7.5%, and the Mo content is controlled within 3.4-3.8%.

[0042] Both Si and Al have the ability to deoxidize during the smelting process of duplex stainless steel. However, excessive content will reduce the steel purity and also affect the hot working plasticity of the steel. Therefore, although the Al content is not restricted separately, the relationship between the Si and Al contents needs to be considered, and thus it is necessary to satisfy 2 ≤ Si / (Al*10) ≤ 4.

[0043] Among them, step S003 controls the heating rate to heat the heating furnace, and after the temperature in the heating furnace rises to 970°C - 1030°C, setting the holding time for holding according to the included angle of the polygon corresponding to the cross-section of the ingot and the distance between two opposite sides further includes:

[0044] Controlling the heating rate ≥ 100°C / h to heat the heating furnace and raising the temperature in the heating furnace to 970°C - 1030°C;

[0045] After the temperature in the heating furnace rises to 970°C - 1030°C, set the holding time for holding according to the included angle of the polygon corresponding to the cross-section of the ingot and the distance between two opposite sides.

[0046] In this step, after the temperature in the heating furnace rises to 970°C - 1030°C, setting the holding time for holding according to the included angle of the polygon corresponding to the cross-section of the ingot and the distance between two opposite sides is specifically:

[0047] After the temperature in the heating furnace rises to 970°C - 1030°C, when 90° ≤ included angle ≤ 135°, control the value of the holding time of the heating furnace to be equal to 1 - 2 times the distance divided by six, and the unit of the holding time is minutes; when 135° ≤ included angle ≤ 150°, control the value of the holding time of the heating furnace to be equal to 2 - 3 times the distance divided by eight, and the unit of the holding time is minutes.

[0048] Among them, step S005 takes out the ingot and performs water cooling on the ingot specifically as follows: controlling the circulating water temperature below 50°C, placing the ingot single in water for water cooling, taking out the ingot after it has been placed in water for 1h - 2h, and controlling the surface temperature of the taken-out ingot below 200°C.

[0049] Among them, before step S001 injects the smelted steel liquid into the ingot mold, stands for 3 - 4 hours, and performs hot demolding after the surface temperature of the ingot mold drops to between 600°C - 620°C, the preparation method of this embodiment further includes: smelting the steel liquid by using an electric arc furnace + argon oxygen refining furnace + secondary refining process.

[0050] An embodiment of the present invention also provides a duplex stainless steel ingot, which is prepared by using the preparation method described in any one of the above embodiments.

[0051] The duplex stainless steel ingot of this embodiment has a duplex structure of ferrite and austenite.

[0052] The duplex stainless steel ingot of this embodiment has good internal quality and forging properties, and can be used to produce large equipment components.

[0053] The preparation method of the embodiment of the present invention will be described below through Example 1, Example 2 and Example 3. The chemical compositions of the molten steel in Example 1, Example 2 and Example 3 are shown in Table 1 below:

[0054] Table 1: Chemical composition table of molten steel in Example 1, Example 2 and Example 3

[0055]

[0056] Example 1:

[0057] Smelted by the process of "EAF (electric arc furnace smelting) + AOD (argon oxygen decarburization furnace smelting) + LF (ladle furnace refining)". After the chemical composition of the smelted molten steel is qualified, it is poured into an ingot mold and left standing for 4 hours. When the surface temperature of the ingot mold drops to 600 °C, hot stripping is carried out; the ingot mold is a regular quadrilateral, the inner angle α between two adjacent sides is 90 °, the distance H between two opposite sides is 800 mm, the furnace temperature of the heating furnace is 710 °C when charging, and after charging, it is heated to 1020 °C at a speed of 100 °C / h. The holding time is calculated by 1.2 * 800 / 6, and the holding time is 140 min; then it is heated to 1150 °C at a speed of 80 °C / h again, and after holding for 3.5 h, it is taken out of the furnace and water-cooled; the steel ingot is placed in circulating water for 2 h, and the surface temperature of the steel ingot after taking out is controlled at 190 °C, and the steel ingot does not crack. The steel ingot obtained in this example is a regular quadrilateral, α = 90 °, and weighs 8.4 tons.

[0058] Example 2:

[0059] Smelted by the process of "EAF (electric arc furnace smelting) + AOD (argon oxygen decarburization furnace smelting) + LF (ladle furnace refining)". After the chemical composition of the molten steel obtained by smelting is qualified through detection, it is poured into an ingot mold and left standing for 3 hours. After the surface temperature of the ingot mold drops to 600 °C, hot demolding is carried out; the ingot mold is a regular octagon, the interior angle α between two adjacent sides is 135 °, the distance H between two opposite sides is 500 mm. When charging, the furnace temperature of the heating furnace is 690 °C, and after charging, it is heated to 1020 °C at a rate of 100 °C / h. The holding time is calculated by 2.2 * 500 / 8, and the holding time is 138 min; then it is heated to 1140 °C at a rate of 80 °C / h again, and after holding for 3 h, it is taken out of the furnace and cooled with water; the steel ingot is placed in circulating water for 1.5 h, and the surface temperature of the steel ingot after being taken out is controlled at 170 °C, and the steel ingot does not crack. The steel ingot obtained in this example is a regular octagon, α = 135 °, and weighs 3 tons.

[0060] Example 3:

[0061] Smelted by the process of "EAF (electric arc furnace smelting) + AOD (argon oxygen decarburization furnace smelting) + LF (ladle furnace refining)". After the chemical composition of the molten steel obtained by smelting is qualified through detection, it is poured into an ingot mold and left standing for 3.5 hours. After the surface temperature of the ingot mold drops to 620 °C, hot demolding is carried out; the ingot mold is a regular dodecagon, the interior angle α between two adjacent sides is 150 °, the distance H between two opposite sides is 600 mm. When charging, the furnace temperature of the heating furnace is 715 °C, and after charging, it is heated to 1020 °C at a rate of 100 °C / h. The holding time is calculated by 2.2 * 600 / 8, and the holding time is 165 min; then it is heated to 1140 °C at a rate of 80 °C / h again, and after holding for 3 h, it is taken out of the furnace and cooled with water; the steel ingot is placed in circulating water for 1.5 h, and the surface temperature of the steel ingot after being taken out is controlled at 180 °C, and the steel ingot does not crack. The steel ingot obtained in this example is a regular dodecagon, α = 150 °, and weighs 4.5 tons.

[0062] The present invention has been disclosed in the above with preferred embodiments. However, those skilled in the art should understand that these embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. It should be noted that all equivalent changes and substitutions to these embodiments should be regarded as covered within the scope of the claims of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined in the claims.

Claims

1. A method for preparing a duplex stainless steel ingot, characterized in that: include: The molten steel obtained by smelting is injected into an ingot mold, and allowed to stand for 3 to 4 hours, and hot demoulding is performed after the surface temperature of the ingot mold drops to between 600°C and 620°C, wherein the ingot mold is a regular even-numbered polygon; Control the heating furnace temperature to ≥700℃±20℃, and load the demoulded steel ingot into the heating furnace; The heating furnace is heated by controlling the heating speed, and after the temperature in the heating furnace is raised to 970° C. to 1030° C., the heat preservation time is set according to the angle of the polygon corresponding to the cross section of the steel ingot and the distance between two opposite sides for heat preservation; The heating furnace is heated again at a heating rate of 80° C. / h, and after the temperature in the heating furnace is raised to 1100° C. to 1180° C., it is kept warm for 3 h to 4 h; The steel ingot is taken out and water-cooled.

2. The preparation method according to claim 1, characterized in that: Measured by mass percentage, the molten steel includes: C≤0.025%, Si≤0.80%, Mn≤1.30%, P≤0.025%, S≤0.005%, Cr: 25.2~25.8%, Ni: 6.8~7.5%, Mo: 3.4~3.8%, N: 0.28~0.32%, and the balance Fe, and 2≤Si / (Al*10)≤4, Mn / Si≥1.

4.

3. The preparation method according to claim 1, characterized in that: The step of controlling the heating speed to heat the heating furnace, and after the temperature in the heating furnace rises to 970° C. to 1030° C., setting the holding time for holding according to the angle of the polygon corresponding to the cross section of the steel ingot and the distance between two opposite sides further comprises: Controlling the heating speed to be ≥100°C / h to heat the heating furnace, and raising the temperature in the heating furnace to 970°C to 1030°C; After the temperature in the heating furnace is raised to 970° C. to 1030° C., the insulation time is set according to the angle of the polygon corresponding to the cross section of the steel ingot and the distance between two opposite sides for insulation.

4. The preparation method according to claim 3, characterized in that: After the temperature in the heating furnace is raised to 970° C. to 1030° C., the insulation time is set according to the angle of the polygon corresponding to the cross section of the steel ingot and the distance between two opposite sides for insulation: After the temperature in the heating furnace rises to 970°C~1030°C, when 90°≤the angle≤135°, the insulation time of the heating furnace is controlled to be equal to 1~2 times the distance divided by six, and the unit of the insulation time is minutes; when 135°≤the angle≤150°, the insulation time of the heating furnace is controlled to be equal to 2~3 times the distance divided by eight, and the unit of the insulation time is minutes.

5. The preparation method according to claim 1, characterized in that: The method of taking out the steel ingot and water cooling the steel ingot is as follows: The circulating water temperature is controlled below 50°C, and a single steel ingot is placed in water for water cooling. The steel ingot is taken out after being placed in water for 1 to 2 hours, and the surface temperature of the taken out steel ingot is controlled below 200°C.

6. The preparation method according to claim 1, characterized in that: Before the molten steel obtained by smelting is injected into the ingot mold and allowed to stand for 3 to 4 hours and the surface temperature of the ingot mold is reduced to between 600° C. and 620° C. and then hot demoulding is performed, the method further comprises: The molten steel is obtained by smelting using electric arc furnace + argon oxygen refining furnace + external refining process.

7. The preparation method according to claim 1, characterized in that: The ingot mold is a regular quadrilateral, a regular octagon or a regular dodecagon.

8. A duplex stainless steel ingot, characterized in that: The preparation method is described in any one of claims 1 to 7.

9. The duplex stainless steel ingot according to claim 8, characterized in that: The stainless steel ingot has a dual phase of ferrite and austenite.

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