Smelting device and casting method for inhibiting formation of nitrogen holes and looseness of high-nitrogen stainless steel

Abstract

The invention belongs to the technical field of high-nitrogen stainless steel casting, and discloses a smelting device and a casting method for inhibiting formation of nitrogen holes and looseness of high-nitrogen stainless steel, and the smelting device comprises a casting mold with a casting mold cooling device capable of hierarchically controlling cooling strength, a crucible with a water-cooling induction coil, a furnace cover, a furnace body and an enclosed closed furnace chamber, the side portion of the casting mold is divided into an air cooling module, a helium cooling module and a water cooling module from top to bottom and provided with an air cooling copper plate, a helium cooling copper plate and a water cooling copper plate respectively, the helium cooling copper plate is connected with an air inlet pipe and an exhaust pipe, the water cooling copper plate is connected with a water inlet pipe and a water outlet pipe, and the air inlet pipe, the exhaust pipe, the water inlet pipe and the water outlet pipe are connected with the outside through flange plates. The right end of the air inlet pipe is connected with a pressure gauge and an air bottle, a water-cooling copper plate base is arranged at the bottom of the ingot casting mold and communicated with a water-cooling copper plate on the side portion, and the longitudinal section of the casting mold is in an inverted cone shape.

Description

Technical Field

[0001] The invention belongs to the technical field of high-nitrogen stainless steel casting, and relates to a smelting device and a casting method for inhibiting the formation of nitrogen pores and porosity in high-nitrogen stainless steel. Background Art

[0002] High nitrogen stainless steel is not only strong and tough, but also wear-resistant and corrosion-resistant. It is also non-ferromagnetic and has good biocompatibility. It is widely used in many fields such as marine engineering, energy and chemical industry, national defense aviation, biomedicine, etc.

[0003] As one of the important alloying elements in high nitrogen stainless steel, the solubility and segregation degree of nitrogen greatly affect the strength, toughness, wear and corrosion resistance of high nitrogen stainless steel. At the same time, nitrogen is easy to form nitrogen bubbles due to segregation during the solidification process. The floating speed of nitrogen bubbles in molten steel is lower than the solidification speed of molten steel, and they are easily captured by grains to form defects such as nitrogen pores and looseness, which affect the quality of ingots. How to reasonably control the solidification rate and provide sufficient escape conditions for nitrogen bubbles has become a key challenge in the high nitrogen stainless steel casting process.

[0004] For high-nitrogen stainless steel casting process, although rapid cooling at the bottom can accelerate solidification, it will prematurely close the bubble escape channel; although slow cooling at the top is conducive to shrinkage compensation, it prolongs the production cycle. Reasonable control of the solidification rate and giving nitrogen bubbles time to float up can largely eliminate the influence of nitrogen pores. By adding a mold cooling device that can control the cooling intensity in layers to the outside of the mold, the heat exchange conditions of the mold and each part of the ingot are controlled to inhibit the formation of nitrogen pores. This design not only provides sufficient time and space for nitrogen bubbles to float up, but also suppresses porosity defects through continuous shrinkage compensation of the top molten steel, thereby significantly improving the quality of the ingot. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a high nitrogen stainless steel smelting device and a casting method thereof, which can effectively suppress nitrogen pores and loose defects of high nitrogen stainless steel ingots, have a simple process, and efficiently improve the ingot quality.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A smelting device for suppressing nitrogen pores and porosity of high-nitrogen stainless steel comprises a casting mold with a casting mold cooling device capable of controlling cooling intensity in layers, a crucible with a water-cooled induction coil, a furnace cover, a furnace body and a closed furnace chamber surrounded by the two. The side of the casting mold is divided into an air-cooling module, a helium-cooling module and a water-cooling module from top to bottom, and air-cooling copper plates, helium-cooling copper plates and water-cooling copper plates are respectively installed. The helium-cooling copper plate is connected to an air inlet pipe and an exhaust pipe, the water-cooling copper plate is connected to a water inlet pipe and a drain pipe, a flow control valve is arranged at the connection between the four pipes and the flange, a pressure difference sensor is arranged between the air inlet pipe and the exhaust pipe, a temperature difference sensor is arranged between the water inlet pipe and the drain pipe, the right end of the air inlet pipe is connected to an air inlet pipe pressure gauge and a gas cylinder, and the longitudinal section of the casting mold is in an inverted cone.

[0008] Except for the riser, the mold cooling device capable of controlling the cooling intensity in layers is a parallel structure into which different cooling media are introduced.

[0009] The air-cooled copper plate, the helium-cooled copper plate and the water-cooled copper plate are connected by sealing bolts with sealing rubber rings, and there is no gap between them to ensure continuity.

[0010] The helium-cooled copper plate has an air inlet and an air outlet on its side, which are connected to the air inlet pipe and the air outlet pipe through flanges respectively; the water-cooled copper plate has a water inlet and a water outlet on its side, which are connected to the water inlet pipe and the water outlet pipe through flanges respectively.

[0011] A casting method for a high nitrogen stainless steel smelting device, comprising the following steps:

[0012] 1) When the molten steel reaches the casting temperature, casting begins. Liquid water is introduced into the lower mold cooling device. Due to the supersaturation of nitrogen in some areas of the molten steel during the solidification process and the volume deficit caused by the density difference between the solid and liquid phases, nitrogen bubbles and looseness are formed. According to the temperature difference sensor, the flow rate and flow velocity of the water inlet pipe are controlled by the flow control valve within a safe range;

[0013] 2) When casting to the middle layer, helium is introduced into the cooling device of the middle layer mold. The cooling intensity of helium is lower than that of liquid water. The solidification rate of the ingot is slower than that of the lower layer. Nitrogen bubbles are formed in the middle layer and float upward. The nitrogen bubbles formed in the lower layer continue to float upward in the middle layer. The porosity caused by the volume deficit of the lower layer can be supplemented by the molten steel in the middle layer to inhibit the formation of porosity. According to the pressure difference sensor, the flow rate and flow velocity of the air inlet pipe are controlled within a safe range through the flow control valve;

[0014] 3) When casting to the upper layer, the upper mold cooling device introduces air into the furnace. The cooling intensity of the air is less than that of helium and liquid water. The solidification rate of the ingot is slower than that of the middle and lower layers. Nitrogen bubbles are formed and float in the upper layer, and the nitrogen bubbles formed in the middle and lower layers continue to float in the upper layer. Similarly, the porosity caused by volume deficit in the middle and lower layers can be compensated by the molten steel in the upper layer to inhibit the formation of porosity.

[0015] The mold cooling device with layered control of cooling intensity is determined from bottom to top by the actual proportion of nitrogen holes and porosity in the ingot. The height of the lower water cooling device (the proportion of nitrogen holes and porosity height is less than 10% of the actual height of the ingot) accounts for 40%-60% of the mold height, the height of the middle helium cooling device (the proportion of nitrogen holes and porosity height is less than 50% of the actual height of the ingot) accounts for 20%-40% of the mold height, and the height of the upper air cooling device accounts for 10%-30% of the mold height.

[0016] The taper range of the casting mold is 2.5%-3.5%.

[0017] The aspect ratio of the casting mold is in the range of 2.8-3.2.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This method uses a mold cooling device that can control the cooling intensity in layers to control the cooling intensity at different positions of the mold, thereby achieving layer-by-layer solidification from bottom to top. A "V"-shaped molten pool is formed inside the mold during the solidification process, giving nitrogen bubbles sufficient time and space to float up, and ensuring that there is sufficient shrinkage-feeding molten steel at the top during the solidification process, thereby inhibiting the formation of nitrogen pores and porosity, effectively improving the solidification quality of the ingot, and the device is simple and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the structure of the present invention.

[0021] In the figure: 1 furnace cover; 2 riser; 3 air-cooling cavity; 4 air-cooling copper plate; 5 sealing bolt; 6 helium-cooling copper plate; 7 flange; 8 flow control valve; 9 air inlet pipe; 10 differential pressure sensor; 11 air inlet pipe pressure gauge; 12 gas cylinder; 13 exhaust pipe; 14 water pump; 15 water inlet pipe; 16 drain pipe; 17 temperature difference sensor; 18 water-cooling copper plate; 19 helium-cooling cavity; 20 water-cooling cavity; 21 mold tray; 22 mold; 23 furnace body; 24 water-cooling induction coil; 25 crucible; 26 smelting furnace pressure gauge; 27 charging bin. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further explained in detail below through specific embodiments in combination with the accompanying drawings.

[0023] like Figure 1The invention discloses a smelting device for suppressing nitrogen pores and looseness of high-nitrogen stainless steel, comprising a furnace cover 1, a furnace body 21, a crucible 25, and a casting mold 22. A water-cooled induction coil 24 is arranged outside the crucible 25. An air-cooled copper plate 4, a helium-cooled copper plate 6, and a water-cooled copper plate 18 are wrapped outside the casting mold. The copper plates are connected by bolts 5 with sealing rubber rings. The helium-cooled copper plate 6 is connected to an intake pipe 9 and an exhaust pipe 13. The water-cooled copper plate 18 is connected to a water inlet pipe 15 and a drain pipe 16. The four pipes are connected to the outside of the furnace body through a flange 7. A pressure difference sensor 10 is connected between the intake pipe 9 and the exhaust pipe 13. A temperature difference sensor 17 is connected between the water inlet pipe 15 and the drain pipe 16. The right end of the intake pipe 9 is connected to an intake pipe pressure gauge 11 and a gas cylinder 12. The water inlet pipe 15 is connected to a water pump 14. The longitudinal section of the crucible 25 is in an inverted cone shape.

[0024] A water-cooled induction coil 24 is provided outside the crucible 25, and the crucible 25 shares a system with the water-cooled module of the casting mold 22, and can rotate toward the casting mold 22;

[0025] The furnace cover 1 is provided with a smelting furnace pressure gauge 26 and a charging bin 27, and the charging bin 27 is located directly above the crucible 25;

[0026] The embodiment of the present invention also discloses a casting method for suppressing nitrogen pores and porosity of high nitrogen stainless steel, using the above-mentioned high nitrogen stainless steel smelting device, comprising the following steps:

[0027] S1: When the molten steel reaches the casting temperature, casting begins, liquid water is introduced into the water-cooled copper plate 18 of the lower mold cooling device, and the water-cooling chamber 20 is filled with liquid water of a certain flow rate and flow rate. According to the monitoring of the temperature difference sensor 17, the flow rate and flow rate of the water inlet pipe 15 are controlled by the flow control valve 8 within a safe range;

[0028] S2: When casting to the middle layer, helium is introduced into the helium-cooled copper plate 6 of the middle layer mold cooling device, and the helium-cooled cavity 19 is filled with helium with a certain flow rate and flow velocity. According to the pressure difference sensor 10, the flow rate and flow velocity of the inlet pipe 9 are controlled within a safe range through the flow control valve 8;

[0029] S3: When casting to the upper layer, the air in the furnace is introduced into the air-cooling copper plate 4 of the upper mold cooling device, and the air-cooling cavity 3 is filled with air. The cooling intensity of the introduced air is less than that of the introduced helium and liquid water. Until the ingot is completely solidified in the mold 22, the introduction of the cooling medium is stopped.

[0030] Example 1

[0031] This embodiment is used to smelt a high nitrogen stainless steel ingot with a maximum weight of 25 kg, and the steel type is 654 alloy.

[0032] The smelting device used is for suppressing nitrogen pores and looseness of high-nitrogen stainless steel. The height of the riser 2 is 80mm, the thickness of the air-cooled 4, helium-cooled 6 and water-cooled copper plate 18 is 25mm, the major diameters of the air-cooled 3, helium-cooled 19 and water-cooled chamber 20 are 63, 50 and 37mm, respectively, the thickness of the mold tray 21 is 50mm, the internal diameters of the air inlet pipe 9 and the exhaust pipe 13 are 40mm, the internal diameters of the water inlet pipe 15 and the drain pipe 16 are 50mm, the taper of the mold 22 is 3%, and the aspect ratio is 3.

[0033] The method for smelting and casting high nitrogen stainless steel includes the following steps:

[0034] S1: Calculate the mass of the raw materials for smelting steel, add them into the crucible 25, calculate the required alloy mass, and put them into the charging bin 27.

[0035] S2: After the smelting is completed, the molten steel reaches the casting temperature and enters the casting stage. The crucible 25 is rotated to cast the molten steel into the casting mold 22. Liquid water is introduced into the water-cooled copper plate 18 of the lower casting mold cooling device. The water-cooled cavity 20 is filled with liquid water. According to the monitoring of the temperature difference sensor 17, the flow rate of the water inlet pipe 15 is controlled by the flow control valve 8 at 80-100 m 3 / h range.

[0036] S3: When casting to the middle layer, helium is introduced into the helium-cooled copper plate 6 of the middle layer mold cooling device, and the helium-cooled cavity 19 is filled with helium. According to the monitoring of the pressure difference sensor 10, the flow rate of the intake pipe 9 is controlled by the flow control valve 8 within the range of 7-9L / min.

[0037] S4: When casting to the upper layer, the air in the furnace is introduced into the air-cooling copper plate 4 of the upper mold cooling device, and the air-cooling cavity 3 is filled with air until the ingot is completely solidified in the mold 22, and the introduction of cooling medium is stopped.

[0038] S5: After the high nitrogen stainless steel has been cooled, the furnace chamber pressure is released to normal pressure, the furnace cover 1 is opened, the ingot is taken out, and the next cycle of smelting and casting can be carried out.

Claims

1. A smelting device for inhibiting the formation of nitrogen pores and looseness in high nitrogen stainless steel, characterized in that: The invention comprises an ingot mold with a mold cooling device capable of controlling cooling intensity in layers, a crucible (25) with a water-cooled induction coil (24), a furnace cover (1), a furnace body (23), and a closed furnace chamber surrounded by the two. The side of the mold is divided into an air-cooled module, a helium-cooled module, and a water-cooled module from top to bottom, and is respectively provided with an air-cooled copper plate (4), a helium-cooled copper plate (6), and a water-cooled copper plate (18). The helium-cooled copper plate (6) is connected to an air inlet pipe (9) and an exhaust pipe (13), and the water-cooled copper plate (18) is connected to an inlet pipe (15) and a drain pipe (16). A flow control valve (8) is provided at the connection between the four pipes and the flange (7), a pressure difference sensor (10) is provided between the air inlet pipe (9) and the exhaust pipe, and a temperature difference sensor (17) is provided between the water inlet pipe (15) and the drain pipe. The right end of the air inlet pipe (9) is connected to an air inlet pipe pressure gauge (11) and a gas cylinder (12), and the longitudinal section of the mold is in an inverted cone shape. The crucible (25) is located obliquely above the casting mold (22), and is wound with a water-cooled induction coil (24) on the outside, and its water cooling system shares a system with the water cooling module in the cooling module; A smelting furnace pressure gauge (26) and a charging bin (27) are provided on the upper portion of the furnace cover (1), and the charging bin is located directly above the crucible (25).

2. A smelting device for inhibiting the formation of nitrogen pores and looseness in high nitrogen stainless steel according to claim 1, characterized in that: Except for the riser (2), the mold cooling device capable of controlling the cooling intensity in layers is a parallel structure into which different cooling media are introduced.

3. A smelting device for inhibiting the formation of nitrogen pores and looseness in high nitrogen stainless steel according to claim 1, characterized in that: The air-cooled copper plate (4), the helium-cooled copper plate (6) and the water-cooled copper plate (18) and the casting mold (22) form an air-cooled cavity (3), a helium-cooled cavity (19) and a water-cooled cavity (20), and the three are connected by sealing bolts (5) with sealing rubber rings.

4. A smelting device for inhibiting the formation of nitrogen pores and looseness in high nitrogen stainless steel according to claim 1, characterized in that: The helium-cooled copper plate (6) is provided with an air inlet and an air outlet on its side, which are respectively connected to the air inlet pipe (9) and the exhaust pipe (13) via flanges (7); the water-cooled copper plate (18) is provided with a water inlet and a water outlet on its side, which are respectively connected to the water inlet pipe (15) and the drain pipe (16) via flanges (7).

5. A casting method for inhibiting the formation of nitrogen pores and porosity in high nitrogen stainless steel, using a smelting device for inhibiting the formation of nitrogen pores and porosity in high nitrogen stainless steel according to any one of claims 1 to 4, characterized in that Here are the steps: S1: When the molten steel reaches the casting temperature, casting begins, liquid water is introduced into the lower mold cooling device, and the flow rate and flow velocity of the water inlet pipe (15) are controlled within a safe range through the flow control valve (8) according to the temperature difference sensor (17); S2: When casting to the middle layer, helium is introduced into the middle layer mold cooling device, and the flow rate and flow velocity of the air inlet pipe (9) are controlled within a safe range through the flow control valve (8) according to the pressure difference sensor (10); S3: When casting to the upper layer, the upper mold cooling device introduces air into the furnace. The cooling intensity of the air introduced is less than that of the helium and liquid water introduced. The introduction of cooling medium is stopped until the ingot is completely solidified.

6. A casting method for inhibiting the formation of nitrogen pores and porosity in high nitrogen stainless steel as claimed in claim 5, characterized in that: The mold cooling device can control the cooling intensity in layers. From bottom to top, the height of the lower water cooling device accounts for 40%-60% of the mold height, the height of the middle helium cooling device accounts for 20%-40% of the mold height, and the height of the upper air cooling device accounts for 10%-30% of the mold height.

7. A casting method for inhibiting the formation of nitrogen pores and porosity in high nitrogen stainless steel according to claim 5 or 6, characterized in that: The taper range of the mold is 2.5%-3.5%.

8. A casting method for inhibiting the formation of nitrogen pores and porosity in high nitrogen stainless steel as claimed in claim 7, characterized in that: The aspect ratio of the molds ranged from 2.8-3.2.

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