A method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification

Abstract

A kind of zero inclusion stainless steel electron beam melting directional solidification preparation method belongs to stainless steel smelting technical field.The alloy is quantitatively supplemented according to the Cr content of stainless steel: when the alloy base material component of electron beam melting can be adjusted in the process of induction melting, the Cr element is supplemented in the process of induction melting;when the alloy base material of electron beam melting is standard alloy component, the alloy component is adjusted back through the form of alloy package in the process of electron beam melting;in the process of electron beam melting, Ca-Mg composite reaction agent is added to realize the conversion and removal of large-size inclusions in stainless steel;the directional solidification electron beam scanning mode is designed to realize the preparation of zero-inclusion stainless steel product.The present application solves the problems of long process, complex process control, and poor removal effect of large-size inclusions in the process of slagging and multi-stage melting by using electron beam melting directional solidification technology, adding Ca-Mg reaction agent and variable radius annular scanning mode, and the product can reach the cleanliness level of zero-inclusion product.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel smelting, and relates to a method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification. Background Art

[0002] Stainless steel, due to its excellent corrosion resistance and electropolishing properties, is widely used in medical guidewires, catheters, guidewires, mass flow controllers, gas filters, and solar cell screen printing. During the preparation of stainless steel microwires, coarse inclusions often lead to breakage during grinding. Stainless steel components are also corroded by contact with liquid or gaseous media. Non-metallic inclusions in stainless steel can damage the passive film, accelerating corrosion. In the semiconductor field, ultra-pure stainless steel, a key material, is widely used in equipment requiring high cleanliness, such as vacuum systems and gas delivery systems. Therefore, existing technical standards strictly regulate the content of impurities and harmful elements in stainless steel to improve biocompatibility, corrosion resistance, and high-precision processing performance, placing even higher demands on the purity of stainless steel. Al and C, as deoxidizers with strong deoxidizing properties in stainless steel, are commonly used in stainless steel deoxidation methods. However, the Al content in low-carbon stainless steels, such as 304L and 316L, is strictly limited, and the carbon content is also low to prevent the formation of large carbides. Therefore, at present, the inclusion size and impurity element content in steel are mostly reduced by optimizing the smelting process to achieve ultra-pure and low-inclusion preparation of stainless steel, especially low-carbon stainless steel.

[0003] The currently available methods for producing high-purity stainless steel include slag conditioning, vacuum decarburization furnace (VD) melting, electroslag remelting (ESR), and consumable remelting (VAR). According to the testing methods and standards in GB / T10561, "Determination of Non-Metallic Inclusions in Steel," stainless steel products produced by the more mature slag-forming or refining processes in China currently have a rating chart of Class A / B / C / D inclusions less than or equal to 1.0. By optimizing induction melting and vacuum arc remelting, the non-metallic inclusion content in stainless steel ingots can be reduced to Class D 0.5 and all other inclusions to Class 0. However, the addition of alkali metals in argon-oxygen refining furnaces and vacuum deoxidation and decarburization furnaces requires a high slag system ratio and is difficult to operate. Remelting ingots using ESR or VAR requires forging to create remelting electrodes, resulting in a lengthy process and low overall yield. In actual production, this process is also limited in its effectiveness at removing large inclusions. In the Chinese invention patent CN 118422038 A, stainless steel produced using an electron beam melting method still contains smaller inclusions, failing to achieve zero inclusions. Furthermore, no quantitative compensation is provided for elemental losses during the electron beam melting process, nor is a specific melting process specified for stainless steel impurity removal. Summary of the Invention

[0004] In response to the above problems, the present invention proposes a method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification. Specifically, it is a new method for promoting the removal of inclusions in stainless steel by electron beam melting and directional solidification in combination with in-situ addition of Ca-Mg composite reactants. The electron beam melting and directional solidification technology is used to prepare stainless steel with high purity, effectively alleviating the problem of deep removal of inclusions in stainless steel. The present invention addresses the problem of Cr volatilization during electron beam melting and directional solidification, adjusts the composition by over-matching the elements, and designs two composition adjustment methods to meet the over-matching requirements. By adding an alloy package to the stainless steel base material, the Ca-Mg reactant is successfully melted synchronously during the electron beam melting and directional solidification process, promoting the transformation and decomposition of inclusions in the stainless steel, deeply removing inclusions in the stainless steel, and reducing the content of impurity elements such as O and S. Specifically, during the smelting process, a variable radius circular scanning method is adopted to make the molten pool tend to be shallow and flat, inducing the growth of columnar crystals to ensure that the inclusions float fully. At the same time, the change in scanning radius induces the inclusions on the surface of the molten pool to be discharged to the edge of the ingot, promoting the decomposition and removal of inclusions in the stainless steel. The non-metallic inclusion content of the ingot is reduced, the O+N content is less than 15ppmw, and the inclusions of Class A, Class B, Class C, Class D, and Class DS are all level 0. The product has reached the "zero inclusion" product cleanliness level.

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

[0006] A method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification, which realizes the high-purity zero-inclusion preparation of stainless steel by electron beam melting and directional solidification. In view of the volatilization loss of alloy caused by local high temperature during electron beam melting, the present invention quantitatively supplements the alloy according to the Cr content of the stainless steel. When the composition of the alloy base material of the electron beam melting can be adjusted during the induction melting process, the Cr element over-matching method of the induction melting process is adopted; when the alloy base material of the electron beam melting is a standard alloy composition, the Cr element in-situ supplementation method of the electron beam melting directional solidification preparation process is adopted to ensure the accuracy of the electron beam melting alloy composition. During the electron beam melting process, a Ca-Mg composite reactant is added in the form of an alloy bag to further realize the transformation and removal of large-sized inclusions in the stainless steel. An electron beam scanning method that meets the requirements of directional solidification is designed to achieve the shallow flatness of the molten pool shape and the aggregation, floating, decomposition and removal of inclusions and lateral slag discharge, while effectively controlling the volatilization of alloy elements. Finally, the preparation of zero-inclusion stainless steel products is achieved. Specifically comprising the following steps:

[0007] The first step is to prepare a composite stainless steel base material and a stainless steel ingot head;

[0008] Step 1.1, preparation of stainless steel base material and Cr element overmatching method;

[0009] Determine the target composition of the stainless steel ingot after electron beam melting and directional solidification, where the Cr content is x. In order to make up for the Cr loss during the electron beam melting and directional solidification process, two Cr supplementation methods are designed according to the different compositions of the stainless steel base material. Specifically:

[0010] (1) Cr element overmatching method in induction melting process: When the composition of the stainless steel base material can be adjusted during the induction melting preparation process, the stainless steel base material with an overmatching alloy composition of Cr content of (105%~120%)*x is customized.

[0011] (2) In-situ supplementation method of Cr element in the electron beam melting and directional solidification process: When the Cr element is not over-matched in the stainless steel base material during the induction melting process, that is, the stainless steel base material is a stainless steel base material with a standard alloy composition, the Cr element needs to be supplemented in the electron beam melting and directional solidification process, and the supplementation amount is (10%~30%)*x.

[0012] Step 1.2, processing stainless steel ingot and melting stainless steel base material; specifically:

[0013] Based on the diameter of the stainless steel ingot produced by electron beam melting and directionally solidification, cut a section of the overmatched or standard alloy stainless steel base material prepared in step 1.1 to be processed into a stainless steel ingot head. The length of the processed stainless steel ingot head must be ≥ 10 cm. The remaining overmatched or standard alloy stainless steel base material after cutting the stainless steel ingot head section serves as the smelted stainless steel base material, with a mass of M.

[0014] Furthermore, the stainless steel ingot head and the smelted stainless steel base material are ultrasonically cleaned using deionized water and alcohol respectively, and then dried to obtain a clean stainless steel ingot head and a clean smelted stainless steel base material.

[0015] Step 1.3, preparation of composite stainless steel base material, specifically:

[0016] In step 1.3.1, based on the mass M of the smelting stainless steel base material, prepare dry, clean Ca and Mg elements with a total mass of (0.1%-5%)*M, with a mass ratio of Ca to Mg of 0.1-10, to obtain a Ca-Mg reactant for smelting.

[0017] In step 1.3.2, prepare iron foil with a purity of 99.95% and wipe it with acetone and then alcohol to remove oil and dust from its surface. Cut some iron foil strips for later use and use the rest to make the alloy package.

[0018] Step 1.3.3, depending on the classification of the stainless steel base material in step 1.1, the types of components in the alloy package have the following two different situations, specifically:

[0019] (1) When using a stainless steel base material with an alloy component, wrap the Ca-Mg reactant calculated in step 1.3.1 with iron foil to form an alloy bag. The width of the alloy bag is no greater than the diameter of the molten stainless steel base material, and the length of the alloy bag is the same as the length of the molten stainless steel base material.

[0020] (2) When using a stainless steel base material with a standard alloy composition, prepare a Cr element with a mass of (10%~30%)*x*M based on the Cr supplementation amount specified in step 1.1 and the smelted stainless steel base material M in step 1.2. The Cr element must be clean and free of contamination, with a purity of ≥99.95%. Finally, the Cr element is fully mixed with the Ca-Mg reactant calculated in step 1.3.1 to form an alloy package. The width of the alloy package is no greater than the diameter of the smelted stainless steel base material, and the length of the alloy package is consistent with the length of the smelted stainless steel base material.

[0021] Step 1.3.4, the alloy package and the smelted stainless steel base material obtained in step 1.2 are tied and fixed with iron foil strips, such as Figure 1 As shown, the alloy package is fixed above the molten stainless steel base material to obtain the composite stainless steel base material required for electron beam melting.

[0022] Step 1.4: Install the composite stainless steel base material and stainless steel ingot into the electron beam melting furnace. Specifically:

[0023] In step 1.4.1, select a crucible for electron beam melting based on the diameter of the stainless steel ingot obtained in step 1.2. The crucible diameter should be 0.5 mm to 8 mm larger than the diameter of the stainless steel remelting ingot. Clean the selected crucible with acetone and then alcohol before use.

[0024] Step 1.4.2, install the stainless steel ingot head obtained in step 1.2 on the ingot pulling mechanism of the electron beam melting furnace to realize the ingot spinning and ingot pulling functions.

[0025] Step 1.4.3: Adjust the positions of the ingot pulling crucible and the stainless steel ingot head so that they are aligned and the stainless steel ingot head does not rub or collide with the ingot pulling crucible during the ingot spinning and pulling process.

[0026] In step 1.4.4, the composite stainless steel base material obtained in step 1.3 is installed in the raw material box of the electron beam melting furnace and connected to the feeding device so that it can realize the feeding function from the raw material box to the ingot pulling crucible, the material withdrawal function from the ingot pulling crucible to the raw material box, and the swinging function in the forward and backward directions.

[0027] The second step is the electron beam melting directional solidification process;

[0028] Step 2.1: After the vacuum degree of the furnace body and the electron gun body reaches the target vacuum degree, start the electron gun and preheat it;

[0029] Step 2.2: Electrons emitted by the electron gun bombard the stainless steel ingot head, causing its entire surface to melt. Specifically:

[0030] After completing the preparations in step 2.1, adjust the electron gun beam current to 0, start the high voltage, and slowly increase the electron gun power to 3-15 kW after the high voltage stabilizes. The electrons emitted by the electron gun bombard the stainless steel ingot head. The beam spot radius of the electron gun is adjusted to 10 mm, and the scanning radius of the beam spot in the ingot pulling crucible is adjusted to the R / 2 position, where R is the radius of the ingot pulling crucible in mm; scan the stainless steel ingot head at a scanning frequency of 20 Hz and a circular scanning path until its surface is completely melted, and a molten pool is formed in the ingot pulling crucible.

[0031] Step 2.3, electron beam scanning process adjustment; specifically:

[0032] After the stainless steel ingot is melted in step 2.2, the electron beam melting power is adjusted to between (0.2*R-2) kW and (0.3*R+5) kW. The electron beam scanning process is adjusted to a variable-radius circular scan. Other parameters remain unchanged. The minimum radius of the electron beam scan is controlled between 0 and 0.6R, and the maximum radius is controlled between 0.4R and 0.9R. The scanning radius variation frequency is 5Hz. This process not only avoids local overheating and component loss caused by scanning the electron beam at a single location, but also promotes the directional growth of columnar crystals through a shallow, flat melt pool.

[0033] Step 2.4, start feeding and ingot pulling. During this process, the mass of the composite stainless steel base material in the raw material box continues to decrease, and the mass of the remelted stainless steel ingot head continues to increase; specifically:

[0034] In step 2.4.1, after completing step 2.3, activate the spindle rotation function. The stainless steel ingot head, driven by the ingot pulling mechanism, rotates at a rate between 1 and 10 rpm. Simultaneously, the feeder delivers the composite stainless steel base material above the molten pool. A portion of the electron beam spot, scanning in a variable-radius circular pattern across the molten pool, impinges on the composite stainless steel base material, causing the alloy cladding within the composite stainless steel base material to melt simultaneously with the stainless steel base material. Simultaneously, activate the swing function to ensure complete melting of the composite stainless steel base material and smooth droplet deposition into the molten pool of the ingot pulling crucible.

[0035] In step 2.4.2, the composite stainless steel base material is stably melted under the action of electron beam scanning. The ingot pulling function is then activated, and the rate at which the stainless steel ingot head is pulled down matches the melting rate of the composite stainless steel base material. The position of the molten pool in the ingot pulling crucible remains unchanged. During this process, the mass of the composite stainless steel base material continuously decreases, while the mass of the stainless steel ingot head continuously increases, resulting in a remelted stainless steel ingot head.

[0036] Step 2.5: After smelting is completed, adjust the parameters of the electron beam equipment; specifically:

[0037] Once the remelted stainless steel ingot has grown to the target size, disable the spinning, pulling, and swinging functions in step 2.4. Enable the material return function, gradually moving the composite stainless steel base material away from the top of the pulling crucible and back into the raw material bin. Simultaneously, maintaining the electron beam scanning method in step 2.3, reduce the electron beam power to 4-8 kW within 5-10 minutes. Then, reduce the electron beam scanning radius to within 0.3R, and reduce the electron beam power to 0 kW within 5-10 minutes. Turn off the electron gun and allow the equipment and stainless steel ingot to fully cool.

[0038] Step 26: After the stainless steel ingot head and the electron gun have cooled for 2 hours, the vacuum system is turned off, and the stainless steel ingot head is taken out. The part remelted by electron beam melting and directional solidification technology is a high-purity stainless steel ingot. The ingot composition meets the standard alloy composition range and can achieve the cleanliness level of zero-inclusion products.

[0039] Furthermore, the step 2.1 is specifically as follows: after the first step is completed, check that all doors of the electron beam melting furnace are tightly closed. Turn on the vacuum pump group, and the vacuum degree of the furnace body is required to be less than 5×10 -3 Pa, the vacuum degree of the electron gun body is required to be less than 1×10 -3 Pa, start the electron gun after reaching the target vacuum degree, adjust the electron gun beam current to 500-1000 mA, and preheat for 20-50 min.

[0040] The present invention prepares high-purity stainless steel ingots by electron beam melting and directional solidification technology, and has the following beneficial effects:

[0041] (1) The present invention utilizes Cr element overmatching to adjust the composition of Cr element loss in the process of preparing stainless steel ingots by electron beam melting and directional solidification. In step 1.1, a Cr element overmatching method in the induction melting process and a Cr element in-situ supplementation method in the electron beam melting and directional solidification process are designed. The Cr element overmatching amount is quantitatively determined, ensuring the composition stability in the electron beam melting and directional solidification process.

[0042] (2) In order to achieve zero-inclusion preparation of stainless steel ingots, an alloy package containing Ca-Mg reactants is prepared in step 1.3. It is melted synchronously with the stainless steel base material during the directional solidification process of electron beam melting. It can transform large-sized Al2O3 inclusions in stainless steel into small-sized CaO, MgO, and CaO·MgO, and at the same time promote the removal of S element, thereby deeply removing inclusions in stainless steel.

[0043] (3) In step 2.3, a variable radius annular scanning electron beam melting method for the preparation of zero-inclusion stainless steel was determined. By constructing a high-temperature, shallow molten pool on the surface, directional solidification was achieved. The density difference between inclusions and the melt and the Marangoni effect promoted the floating and aggregation of inclusions during the melting process, as well as the decomposition of inclusions and lateral slag removal, thereby enhancing the removal of inclusions in stainless steel, especially low-carbon stainless steel.

[0044] In summary, the present invention utilizes electron beam melting and directional solidification technology, combined with the addition of a Ca-Mg reactant and a variable-radius annular scanning method, to address the long slag-making and multi-stage melting processes of existing methods, complex process control, and limited removal of large inclusions. The stainless steel ingots produced using this method have zero inclusion levels for Class A, Class B, Class C, Class D, and Class DS inclusions, achieving a zero-inclusion cleanliness level. This provides a new approach for the high-purity production of stainless steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the assembly of composite stainless steel base material required for electron beam melting and directional solidification;

[0046] Figure 2 The distribution of inclusions in the high-purity 304LE stainless steel ingot prepared in Example 1;

[0047] Figure 3 This is the distribution of inclusions in the high-purity 316LE stainless steel ingot prepared in Example 2. DETAILED DESCRIPTION

[0048] The present invention is further described below with reference to specific implementation cases.

[0049] Example 1

[0050] A method for preparing zero-inclusion 304LE stainless steel by electron beam melting and directional solidification, specifically comprising the following steps:

[0051] The first step is to prepare the composite stainless steel base material and stainless steel ingot;

[0052] Step 1.1, preparation of stainless steel base material and Cr element overmatching method;

[0053] The target composition of the stainless steel ingot after electron beam melting and directional solidification was determined, which was recorded as follows in mass percentage: C: 0.03%, Si: 0.7%, Mn: 1.8%, Ni: 10.0%, Cr: 19.0%. In order to make up for the Cr loss during the electron beam melting and directional solidification process, the Cr element overmatching method in the induction melting process was adopted. That is, the composition of the stainless steel base material can be adjusted during the induction melting preparation. Therefore, a stainless steel base material with an overmatched alloy composition of 21.0% Cr content was customized.

[0054] Step 1.2, processing stainless steel ingot and melting stainless steel base material; specifically:

[0055] Based on the diameter of the stainless steel ingot produced by electron beam melting and directionally solidified casting, cut a section of the overmatched stainless steel base material prepared in Step 1.1 to form a stainless steel ingot head. The ingot head has a diameter of 100 mm and a length of 16 cm. The remaining overmatched stainless steel base material after cutting the ingot head serves as the smelted stainless steel base material, weighing 15 kg.

[0056] The stainless steel ingot head and the smelted stainless steel base material are ultrasonically cleaned using deionized water and alcohol respectively, and then dried to obtain a clean stainless steel ingot head and a clean smelted stainless steel base material.

[0057] Step 1.3, preparation of composite stainless steel base material, specifically:

[0058] In step 1.3.1, based on the mass of 15 kg of the smelted stainless steel base material, prepare 150 g of dry, clean Ca and Mg elements in a Ca:Mg ratio of 1:1 to obtain the Ca-Mg reactant for smelting.

[0059] In step 1.3.2, prepare iron foil with a purity of 99.95% and wipe it with acetone and then alcohol to remove oil and dust from its surface. Cut some iron foil strips for later use and use the rest to make the alloy package.

[0060] In step 1.3.3, the Ca-Mg reactant mass calculated in step 1.3.1 is wrapped with iron foil to form an alloy bag. The width of the alloy bag is no greater than the diameter of the molten stainless steel base material, and the length of the alloy bag is the same as the length of the molten stainless steel base material.

[0061] Step 1.3.4, and tie the above alloy package and the clean molten stainless steel base material prepared in step 1.2 with iron foil strips, as shown in Figure 1 As shown, the alloy package is fixed above the molten stainless steel base material to obtain the composite stainless steel base material required for electron beam melting.

[0062] Step 1.4: Install the composite stainless steel base material and stainless steel ingot into the electron beam melting furnace. Specifically:

[0063] In step 1.4.1, based on the diameter of the stainless steel ingot obtained in step 1.2, select a crucible for electron beam melting. The crucible diameter should be larger than the diameter of the stainless steel remelting ingot, which is 103 mm. Wipe the selected crucible with acetone and then alcohol, blow dry, and install it in the electron beam melting furnace.

[0064] Step 1.4.2, install the stainless steel ingot head obtained in step 1.2 on the ingot pulling mechanism of the electron beam melting furnace to realize the ingot spinning and ingot pulling functions.

[0065] Step 1.4.3: Adjust the positions of the ingot pulling crucible and the stainless steel ingot head so that they are aligned and the stainless steel ingot head does not rub or collide with the ingot pulling crucible during the ingot spinning and pulling process.

[0066] In step 1.4.4, the composite stainless steel base material obtained in step 1.3 is installed in the raw material box of the electron beam melting furnace and connected to the feeding device so that it can realize the feeding function from the raw material box to the ingot pulling crucible, the material withdrawal function from the ingot pulling crucible to the raw material box, and the swinging function in the forward and backward directions.

[0067] The second step is the electron beam melting directional solidification process;

[0068] Step 2.1: After the vacuum of the furnace body and the electron gun body reaches the target vacuum, start the electron gun and preheat. In this embodiment, after the first step is completed, check that all the doors of the electron beam melting furnace are tightly closed. Start the vacuum pump group. The vacuum degree of the furnace body is required to be less than 5×10 -3 Pa, the vacuum degree of the electron gun body is required to be less than 1×10 -3 Pa, start the electron gun after reaching the target vacuum degree, adjust the electron gun beam current to 700 mA, and preheat for 300 min.

[0069] Step 2.2: Electrons emitted by the electron gun bombard the stainless steel ingot head, causing its entire surface to melt. Specifically:

[0070] After completing the preparations in step 2.1, adjust the electron gun beam current to 0, start the high voltage, and slowly increase the electron gun power to 8 kW after the high voltage stabilizes. The electrons emitted by the electron gun bombard the stainless steel ingot head. The beam spot radius of the electron gun is adjusted to 10 mm, and the scanning radius of the beam spot in the ingot pulling crucible is adjusted to 50 mm. Scan the stainless steel ingot head at a scanning frequency of 20 Hz and a circular scanning path until its surface is completely melted and a molten pool is formed in the ingot pulling crucible.

[0071] Step 2.3, electron beam scanning process adjustment; specifically:

[0072] After the stainless steel ingot is melted in step 2.2, the electron beam melting power is adjusted to 14 kW, and the electron beam scanning process is adjusted to a variable-radius circular scan. Other parameters remain unchanged. The minimum electron beam scanning radius is 25 mm, the maximum radius is 40 mm, and the scanning radius variation frequency is 5 Hz. This prevents local overheating and component loss caused by scanning the electron beam at a single location, while also promoting the directional growth of columnar crystals through the shallow, flat melt pool.

[0073] Step 2.4, start feeding and ingot pulling. During this process, the mass of the composite stainless steel base material in the raw material box continues to decrease, and the mass of the remelted stainless steel ingot head continues to increase; specifically:

[0074] In step 2.4.1, after completing step 2.3, activate the spindle rotation function. The stainless steel ingot head, driven by the ingot pulling mechanism, rotates at a rate of approximately 3 rpm. Simultaneously, the feeder delivers the composite stainless steel base material above the molten pool. A portion of the electron beam spot, scanning the molten pool in a variable-radius circular pattern, impinges on the composite stainless steel base material, causing the alloy cladding and the stainless steel base material to melt simultaneously. Simultaneously, activate the swing function to ensure complete melting of the composite stainless steel base material and smooth droplet deposition into the molten pool of the ingot pulling crucible.

[0075] In step 2.4.2, the composite stainless steel base material is stably melted under the action of electron beam scanning. The ingot pulling function is then activated. The rate at which the stainless steel ingot head is pulled down matches the melting rate of the composite stainless steel base material, while the position of the molten pool in the ingot pulling crucible remains unchanged. During this process, the mass of the composite stainless steel base material continuously decreases, while the mass of the stainless steel ingot head continuously increases.

[0076] Step 2.5: After smelting is completed, adjust the parameters of the electron beam equipment; specifically:

[0077] Once the remelted stainless steel ingot has grown to the target size, disable the spinning, pulling, and swinging functions in step 2.4. Enable the material return function, gradually moving the composite stainless steel base material away from the top of the pulling crucible and back into the raw material bin. Simultaneously, maintaining the electron beam scanning method in step 2.3, reduce the electron beam power to 8 kW within 5 minutes. Then, reduce the electron beam scanning radius to less than 10 mm, and reduce the electron beam power to 0 kW within 5 minutes. Turn off the electron gun and allow the equipment and stainless steel ingot to fully cool.

[0078] Step 2.6: After the stainless steel ingot and electron gun have cooled for 2 hours, the vacuum system is turned off and the stainless steel ingot is taken out. The remelted part through electron beam melting and directional solidification technology is a high-purity 304LE stainless steel ingot. The ingot composition meets the standard alloy composition range and can achieve the zero-inclusion product cleanliness level. Figure 2 As shown, from Figure 2 It can be seen that at this magnification, the number of non-metallic inclusions is small and the size is extremely small, almost unobservable.

[0079] Example 2

[0080] A method for preparing zero-inclusion 316LE stainless steel by electron beam melting and directional solidification, comprising the following steps:

[0081] The first step is to prepare the composite stainless steel base material and stainless steel ingot;

[0082] Step 1.1, preparation of stainless steel base material and Cr element overmatching method;

[0083] The target composition of the stainless steel ingot after electron beam melting and directional solidification was determined, with the mass percentages being: C: 0.03%, Si: 1.0%, Mn: 1.7%, Ni: 13.0%, Cr: 17.0%, and Mo: 2.5%. To compensate for the Cr loss during electron beam melting and directional solidification, an in-situ Cr addition method was employed during the electron beam melting and directional solidification preparation process. The stainless steel base material was a standard alloy stainless steel base material with a Cr content of 19%. Therefore, 3% Cr was added during the electron beam melting and directional solidification process.

[0084] Step 1.2, processing stainless steel ingot and melting stainless steel base material; specifically:

[0085] Based on the diameter of the stainless steel ingot produced by electron beam melting and directionally solidified casting, cut a section of the standard alloy composition stainless steel base material prepared in Step 1.1 to form a stainless steel ingot head. The stainless steel ingot head has a diameter of 220 mm and a length of 20 cm. The remaining standard alloy composition stainless steel base material after cutting the stainless steel ingot head serves as the smelting stainless steel base material, weighing 50 kg.

[0086] The stainless steel ingot head and the smelted stainless steel base material are ultrasonically cleaned using deionized water and alcohol respectively, and then dried to obtain a clean stainless steel ingot head and a clean smelted stainless steel base material.

[0087] Step 1.3, preparation of composite stainless steel base material, specifically:

[0088] In step 1.3.1, based on the mass of 50 kg of the smelted stainless steel base material, prepare 500 g of dry, clean Ca and Mg elements in a Ca:Mg ratio of 1:1 to obtain the Ca-Mg reactant for smelting.

[0089] In step 1.3.2, prepare iron foil with a purity of 99.95% and wipe it with acetone and then alcohol to remove oil and dust from its surface. Cut some iron foil strips for later use and use the rest to make the alloy package.

[0090] In step 1.3.3, based on the Cr supplementation amount specified in step 1.1 and the mass of the smelted stainless steel base material in step 1.2, prepare 1.5 kg of pure Cr. This pure Cr must be clean and free of contamination, with a purity of ≥ 99.95%. Furthermore, thoroughly mix this Cr with the mass of Ca-Mg reactant calculated in step 1.3.1 to form an alloy bag. The width of the alloy bag should not exceed the diameter of the smelted stainless steel base material, and the length of the alloy bag should be the same as the length of the smelted stainless steel base material.

[0091] Step 1.3.4, and tie the above alloy package and the clean molten stainless steel base material prepared in step 1.2 with iron foil strips, as shown in Figure 1 As shown, the alloy package is fixed above the molten stainless steel base material to obtain the composite stainless steel base material required for electron beam melting.

[0092] Step 1.4: Install the composite stainless steel base material and stainless steel ingot into the electron beam melting furnace. Specifically:

[0093] In step 1.4.1, select a pulling crucible for electron beam melting based on the diameter of the stainless steel ingot obtained in step 1.2. The pulling crucible diameter should be 225 mm larger than the diameter of the stainless steel remelting ingot. Wipe the selected pulling crucible with acetone and then alcohol, blow dry, and install it in the electron beam melting furnace.

[0094] Step 1.4.2, install the stainless steel ingot head obtained in step 1.2 on the ingot pulling mechanism of the electron beam melting furnace to realize the ingot spinning and ingot pulling functions.

[0095] Step 1.4.3: Adjust the positions of the ingot pulling crucible and the stainless steel ingot head so that they are aligned and the stainless steel ingot head does not rub or collide with the ingot pulling crucible during the ingot spinning and pulling process.

[0096] In step 1.4.4, the composite stainless steel base material obtained in step 1.3 is installed in the raw material box of the electron beam melting furnace and connected to the feeding device so that it can realize the feeding function from the raw material box to the ingot pulling crucible, the material withdrawal function from the ingot pulling crucible to the raw material box, and the swinging function in the forward and backward directions.

[0097] The second step is the electron beam melting directional solidification process;

[0098] Step 2.1: After the vacuum degree of the furnace body and the electron gun body reaches the target vacuum degree, start the electron gun and preheat it. In this embodiment: After the first step is completed, check that all the doors of the electron beam melting furnace are tightly closed. Start the vacuum pump group. The vacuum degree of the furnace body is required to be less than 5×10 -3 Pa, the vacuum degree of the electron gun body is required to be less than 1×10 -3 Pa, start the electron gun after reaching the target vacuum degree, adjust the electron gun beam current to 700 mA, and preheat for 30 min.

[0099] Step 2.2: Electrons emitted by the electron gun bombard the stainless steel ingot head, causing its entire surface to melt. Specifically:

[0100] After completing the preparations in step 2.1, adjust the electron gun beam current to 0, start the high voltage, and slowly increase the electron gun power to 12 kW after the high voltage stabilizes. The electrons emitted by the electron gun bombard the stainless steel ingot head. The beam spot radius of the electron gun is adjusted to 10 mm, and the scanning radius of the beam spot in the ingot pulling crucible is adjusted to 110 mm. Scan the stainless steel ingot head at a scanning frequency of 20 Hz and a circular scanning path until its surface is completely melted and a molten pool is formed in the ingot pulling crucible.

[0101] Step 2.3, electron beam scanning process adjustment; specifically:

[0102] After the stainless steel ingot is melted in step 2.2, the electron beam melting power is adjusted to 25 kW, and the electron beam scanning process is adjusted to a variable-radius circular scan. Other parameters remain unchanged, with the minimum electron beam scanning radius controlled to 33 mm, the maximum radius to 88 mm, and the scanning radius variation frequency to 5 Hz. This prevents local overheating and component loss caused by scanning the electron beam at a single location, while also promoting the directional growth of columnar crystals through the shallow, flat melt pool.

[0103] Step 2.4, start feeding and ingot pulling. During this process, the mass of the composite stainless steel base material in the raw material box continues to decrease, and the mass of the remelted stainless steel ingot head continues to increase; specifically:

[0104] In step 2.4.1, after completing step 2.3, activate the spindle rotation function. The stainless steel ingot head, driven by the ingot pulling mechanism, rotates at a rate of approximately 1 rpm. Simultaneously, the feeder delivers the composite stainless steel base material above the molten pool. A portion of the electron beam spot, scanning the molten pool in a variable-radius circular pattern, impinges on the composite stainless steel base material, causing the alloy cladding and the stainless steel base material to melt simultaneously. Simultaneously, activate the swing function to ensure complete melting of the composite stainless steel base material and smooth droplet deposition into the molten pool of the ingot pulling crucible.

[0105] In step 2.4.2, the composite stainless steel base material is stably melted under the action of electron beam scanning. The ingot pulling function is then activated. The rate at which the stainless steel ingot head is pulled down matches the melting rate of the composite stainless steel base material, while the position of the molten pool in the ingot pulling crucible remains unchanged. During this process, the mass of the composite stainless steel base material continuously decreases, while the mass of the stainless steel ingot head continuously increases.

[0106] Step 2.5: After smelting is completed, adjust the parameters of the electron beam equipment; specifically:

[0107] Once the remelted stainless steel ingot has reached the target size, disable the spinning, pulling, and swinging functions in step 2.4. Enable the material return function, gradually moving the composite stainless steel base material away from the top of the pulling crucible and back into the raw material bin. Simultaneously, maintaining the electron beam scanning method in step 2.3, reduce the electron beam power to 5 kW within 8 minutes. Then, reduce the electron beam scanning radius to less than 15 mm, and reduce the electron beam power to 0 kW within 8 minutes. Turn off the electron gun and allow the equipment and stainless steel ingot to fully cool.

[0108] Step 2.6: After the stainless steel ingot and electron gun have cooled for 2 hours, the vacuum system is turned off and the stainless steel ingot is taken out. The remelted part through electron beam melting and directional solidification technology is a high-purity stainless steel ingot. The ingot composition meets the standard alloy composition range and can achieve the zero-inclusion product cleanliness level. Figure 3 As shown, from Figure 3It can be seen that at this magnification, the number of non-metallic inclusions is small and the size is extremely small, almost unobservable.

[0109] The above results show that Examples 1 and 2 provide electron beam melting directional solidification preparation technologies, which are suitable for preparing various types of zero-inclusion product grades of stainless steel materials, solving the problem of deep removal of inclusions that is difficult to achieve with existing technical means such as slag refining and multi-link smelting, and can achieve high-quality, zero-inclusion preparation of stainless steel.

[0110] The above-described embodiments merely represent implementation methods of the present invention, but should not be construed as limiting the scope of the patent of the present invention. It should be noted that those skilled in the art may make several modifications and improvements without departing from the concept of the present invention. For example, other "zero-inclusion" stainless steel materials prepared by electron beam melting, directional solidification, and reactant addition methods are all within the scope of protection of the present invention.

Claims

1. A method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification, characterized in that: High-purity, zero-inclusion stainless steel is produced through electron beam melting and directional solidification; specifically: First, the alloy is quantitatively supplemented according to the Cr content of the stainless steel. When the composition of the alloy base material of the electron beam melted alloy can be adjusted during the induction melting process, the Cr element over-matching method of the induction melting process is adopted; when the alloy base material of the electron beam melted alloy has a standard alloy composition, the Cr element in-situ supplementation method of the electron beam melting directional solidification preparation process is adopted to ensure the accuracy of the electron beam melted alloy composition. The two Cr element supplementation methods are specifically as follows: (1) Determine the target composition of stainless steel ingot after electron beam melting and directional solidification, where the Cr content is x， Cr overmatching method during induction melting: When the stainless steel base material can be adjusted in composition during induction melting, the customized Cr content is (105%~120%)* x Over-alloy composition of stainless steel base material; (2) In-situ Cr element supplementation method during electron beam melting and directional solidification: When the stainless steel base material is not over-matched with Cr during the induction melting process, that is, the stainless steel base material is a standard alloy composition stainless steel base material, the Cr element needs to be supplemented during the electron beam melting and directional solidification process. The supplementation amount is (10%~30%)* x ; Secondly, during the electron beam melting process, a Ca-Mg composite reactant is added in the form of an alloying ladle to transform and remove large inclusions in the stainless steel. An electron beam scanning method is designed to meet the requirements of directional solidification while effectively controlling the volatilization of alloying elements. Finally, the preparation of zero-inclusion stainless steel products is achieved.

2. The method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification according to claim 1, characterized in that: The method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification The following steps are involved: The first step is to prepare a composite stainless steel base material and a stainless steel ingot head; Step 1.1, preparation of stainless steel base material and Cr element overmatching method; In order to make up for the Cr loss during electron beam melting and directional solidification, two Cr supplementation methods were designed according to the different compositions of stainless steel base materials, and stainless steel base materials with over-alloy composition and standard alloy composition were obtained respectively. Step 1.2, processing stainless steel ingot and melting stainless steel base material; specifically: According to the diameter of the stainless steel ingot produced by electron beam melting and directionally solidified, a section of the stainless steel base material with overmatched alloy composition or standard alloy composition prepared in step 1.1 is cut off to process the stainless steel ingot head, and the remaining stainless steel base material with overmatched alloy composition or standard alloy composition is used as the smelting stainless steel base material with a mass of M ; Step 1.3, making composite stainless steel base material, specifically: Step 1.3.1, according to the quality of the smelting stainless steel base material M , prepare the total mass (0.1%-5%)* M Ca and Mg elements are obtained to obtain Ca-Mg reactant for smelting; Step 1.3.2: Prepare iron foil, cut some iron foil strips for later use, and use the rest to make alloy packages; Step 1.3.3, determine the type of components in the alloy package based on the different classifications of the stainless steel base material in step 1.1; Step 1.3.4, fix the alloy package and the molten stainless steel base material obtained in step 1.2 with iron foil strips, and fix the alloy package on top of the molten stainless steel base material to obtain the composite stainless steel base material required for electron beam melting; Step 1.4: Select an electron beam melting ingot pulling crucible and install the composite stainless steel base material and stainless steel ingot head into the electron beam melting furnace; The second step is the electron beam melting directional solidification process; Step 2.1: After the vacuum degree of the furnace body and the electron gun body reaches the target vacuum degree, start the electron gun and preheat it; Step 2.2: Electrons emitted by the electron gun bombard the stainless steel ingot head, causing the entire surface of the stainless steel ingot head to melt, and a molten pool is formed in the ingot pulling crucible; Step 2.3: After the stainless steel ingot is melted, adjust the electron beam scanning process; Step 2.4, starting feeding and ingot pulling. During this process, the mass of the composite stainless steel base material in the raw material box continues to decrease, and the mass of the remelted stainless steel ingot head continues to increase, thereby obtaining a remelted stainless steel ingot head. Step 2.5: After the smelting is completed, the parameters of the electron beam equipment are adjusted to allow the equipment and the stainless steel ingot to cool down sufficiently; the stainless steel ingot is taken out, and the part remelted by the electron beam melting directional solidification technology is a high-purity stainless steel ingot. The ingot composition meets the standard alloy composition range and can achieve the cleanliness level of zero-inclusion products.

3. The method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification according to claim 2, characterized in that: In the first step: In step 1.2, the length of the processed stainless steel ingot is ≥10 cm; In step 1.3.1, the mass ratio of Ca to Mg is 0.1-10; In step 1.3.2, the purity of the iron foil is 99.95%; In step 1.3.3, the types of components in the alloy package may be of two different types, specifically: (1) When a stainless steel base material with a complex alloy component is used, the Ca-Mg reactant obtained in step 1.3.1 is wrapped with iron foil to form an alloy bag; the width of the alloy bag is not greater than the diameter of the molten stainless steel base material, and the length of the alloy bag is consistent with the length of the molten stainless steel base material; (2) When using a stainless steel base material with a standard alloy composition, the amount of Cr added in step 1.1 and the amount of Cr added in step 1.2 are used to melt the stainless steel base material. M , preparation quality is (10%~30%)* x * M The Cr element is required to have a purity of ≥99.95%; finally, the Cr element is fully mixed with the Ca-Mg reactant obtained in step 1.3.1 to form an alloy bag; the width of the alloy bag is no greater than the diameter of the molten stainless steel base material, and the length of the alloy bag is consistent with the length of the molten stainless steel base material.

4. The method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification according to claim 2, characterized in that: The step 1.4 is specifically as follows: Step 1.4.1: Based on the diameter of the stainless steel ingot obtained in step 1.2, select a crucible for electron beam melting. The crucible diameter should be 0.5 mm to 8 mm larger than the diameter of the stainless steel remelting ingot. Step 1.4.2, installing the stainless steel ingot head obtained in step 1.2 on the ingot pulling mechanism of the electron beam melting furnace to realize the ingot spinning and ingot pulling functions; Step 1.4.3, adjust the positions of the ingot pulling crucible and the stainless steel ingot head so that they are aligned and the stainless steel ingot head does not rub or collide with the ingot pulling crucible during the ingot spinning and pulling process; In step 1.4.4, the composite stainless steel base material obtained in step 1.3 is installed in the raw material box of the electron beam melting furnace and connected to the feeding device so that it can realize the feeding function from the raw material box to the ingot pulling crucible, the material withdrawal function from the ingot pulling crucible to the raw material box, and the swinging function in the forward and backward directions.

5. The method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification according to claim 2, characterized in that: The step 2.1 is specifically as follows: after the first step is completed, check that all doors of the electron beam melting furnace are tightly closed; start the vacuum pump group, and the vacuum degree of the furnace body is required to be less than 5×10 -3 Pa, the vacuum degree of the electron gun body is required to be less than 1×10 -3 Pa, start the electron gun after reaching the target vacuum degree, adjust the electron gun beam current to 500-1000 mA, and preheat for 20-50 min.

6. The method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification according to claim 2, characterized in that: The step 2.2 is specifically as follows: The electron gun beam current is adjusted to 0, and the high voltage is started. After the high voltage stabilizes, the electron gun power is increased to 3-15 kW. The electrons emitted by the electron gun bombard the stainless steel ingot head. The beam spot radius of the electron gun is adjusted to 10 mm, and the scanning radius of the beam spot in the ingot pulling crucible is adjusted to the R / 2 position, where R is the radius of the ingot pulling crucible in mm. The stainless steel ingot head is scanned at a scanning frequency of 20 Hz and a circular scanning path so that its surface is completely melted, and a molten pool is formed on the stainless steel ingot head in the ingot pulling crucible.

7. The method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification according to claim 6, characterized in that: The step 2.3 is specifically as follows: The electron beam melting power was adjusted to between (0.2*R-2) kW and (0.3*R+5) kW, and the electron beam scanning process was adjusted to variable radius circular scanning. Other parameters remained unchanged. The minimum radius of the electron beam scanning was controlled between 0-0.6R, the maximum radius was controlled between 0.4R-0.9R, and the scanning radius change frequency was 5 Hz.

8. The method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification according to claim 7, characterized in that: The step 2.4 is specifically as follows: Step 2.4.1: After completing step 2.3, start the spindle rotation function. The stainless steel ingot head rotates under the drive of the ingot pulling mechanism at a spindle speed of 1-10 rpm. At the same time, the feeding device feeds the composite stainless steel base material above the molten pool. Part of the electron beam spot, which performs a variable radius circular scan in the molten pool, bombards the composite stainless steel base material, causing the alloy package and the stainless steel base material in the composite stainless steel base material to melt synchronously. At the same time, start the swing function to ensure that the composite stainless steel base material is completely melted and the droplets drip smoothly into the molten pool of the ingot pulling crucible. In step 2.4.2, the composite stainless steel base material is stably melted under the action of electron beam scanning, and the ingot pulling function is turned on. The rate at which the stainless steel ingot head is pulled down matches the melting rate of the composite stainless steel base material, and the position of the molten pool in the ingot pulling crucible remains unchanged. During this process, the mass of the composite stainless steel base material continues to decrease, while the mass of the stainless steel ingot head continues to increase.

9. The method for preparing zero-inclusion stainless steel by electron beam melting and directional solidification according to claim 8, characterized in that: The step 2.5 is specifically as follows: After the remelted stainless steel ingot head is increased to the target size, turn off the ingot spinning, ingot pulling and material swinging functions in step 2.4, turn on the material return function, and gradually move the composite stainless steel base material away from the top of the ingot pulling crucible and return it to the raw material box; at the same time, keep the electron beam scanning mode in step 2.3 unchanged, reduce the electron beam power to 4-8 kW within 5-10 minutes, then reduce the electron beam scanning radius to within 0.3R, and reduce the electron beam power to 0 kW within 5-10 minutes; turn off the electron gun to allow the equipment and stainless steel ingot head to cool down fully.

Images