Vacuum consumable remelting smelting method capable of reducing content of oxide inclusions

Abstract

A vacuum consumable remelting smelting method capable of reducing the content of oxide inclusions. The remelting speed is determined according to the inner diameter of a crystallizer; by controlling the remelting speed, oxide inclusions are removed in the manner of strengthening the reduction of oxides by C; and the reaction product is CO. Furthermore, by using a large arc distance of remelting and a large ring width of a liquid level, the reaction of O removal by means of C is promoted under the condition of a low melting speed. In cooperation with a high vacuum, more O in a remelted alloy is removed from a smelting system in the form of CO by means of evacuation, thereby alleviating the problem of oxide inclusion residues.

Description

A vacuum consumable remelting smelting method for reducing oxide inclusion content

[0001] This disclosure claims priority to a Chinese patent application filed with the Patent Office of China on July 21, 2023, with application number 202310901393.2 and invention name “A Vacuum Consumable Remelting Method for Reducing Oxide Inclusion Content,” the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present invention relates to the technical field of alloy smelting, in particular to a vacuum consumable remelting smelting method for reducing oxide inclusion content. Background Art

[0003] High-quality alloys are typically first cast into electrodes using vacuum induction smelting, then remelted into ingots in a vacuum consumable arc furnace. This improves the alloy's plasticity, high-temperature endurance, and fatigue strength. During smelting, the arc length is typically controlled to ensure a stable smelting process, and the final capping process is optimized to reduce shrinkage cavities. A low-voltage, high-current DC power supply is typically used.

[0004] Vacuum Arc Remelting (VAR) uses a DC power supply to generate an arc between an electrode and the bottom plate of a copper crucible placed in a water jacket under vacuum conditions. The arc heating generates high heat, melting the electrode. The electrode continuously descends and melts, forming a molten pool in the water-cooled copper crucible. The molten metal completes rapid solidification, crystallization, and solidification into an ingot.

[0005] Vacuum arc melting is generally used for refining easily oxidizable metals and alloys such as stainless steel, superalloys, titanium, zirconium, tantalum, niobium, tungsten, and molybdenum. It reduces the loss of active elements (such as Al and Ti), allows for controllable ingot solidification, and significantly improves the cleanliness, uniformity, fatigue resistance, and fracture toughness of the ingot. This results in better microstructure consistency and uniformity, fewer inclusions, and further improved alloy purity. Vacuum arc melting is well-suited for melting specialty steels and active and refractory metals such as titanium, molybdenum, and niobium.

[0006] In conventional vacuum consumable remelting, inclusions are primarily removed by floating to the surface of the molten pool, where they then migrate to the surrounding area and are expelled to the surface of the remelted ingot, thereby reducing the inclusion content. However, oxide inclusions removed during this removal process remain in the form of compounds and are not truly removed from the smelting system.

[0007] Therefore, there is an urgent need for a vacuum consumable remelting smelting method that reduces the oxide inclusion content, so as to reduce the oxide inclusions in the alloy ingots obtained by the vacuum consumable remelting smelting method and obtain high-quality alloys.

[0008] Summary of the Invention

[0009] In view of this, the present invention provides a vacuum consumable remelting smelting method for reducing the oxide inclusion content, the main purpose of which is to reduce or even remove oxide inclusions in the alloy to obtain high-quality alloy.

[0010] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0011] An embodiment of the present invention provides a vacuum consumable remelting smelting method for reducing the content of oxide inclusions. The remelting speed is determined according to the inner diameter of the crystallizer. By controlling the remelting speed, oxide inclusions are removed in a manner that strengthens the reduction of oxides by the C element. The reaction product is CO.

[0012] In some embodiments, the average remelting kg per hour = the inner diameter of the crystallizer in millimeters × (0.4-0.7) to reduce the total amount of material in the arc zone plasma, thereby increasing the time for carbon deoxidation and reduction of oxides and reducing the number of inclusions in the consumable remelted ingot.

[0013] In some embodiments, the arc spacing of the remelting is controlled to be maintained in the range of 15-19 mm to expand the volume of the arc zone, ensuring that during the vacuum consumable remelting process, oxide inclusions are mainly removed in the form of reduction by C element, and the reaction product is CO.

[0014] In some embodiments, the molten pool liquid surface ring width is controlled to be (mold inner diameter×0.06+19)±2.5, in mm, to increase the liquid surface area exposed by the molten pool.

[0015] In some embodiments, the arc spacing of the consumable remelting is calibrated by measuring the arc spacing by forcing the electrodes to drop rapidly to a short circuit.

[0016] In some embodiments, the method for measuring the arc spacing is: record the stroke position of the electrode rod before operation, then force the electrode to drop quickly until a short circuit occurs, that is, the remelting arc disappears, and record the corresponding electrode rod stroke position at this moment; subtract the stroke position before operation from the stroke position at the moment of short circuit occurrence, and the difference is the arc spacing.

[0017] In some embodiments, the timing of measurement is selected when the height of the remelted ingot reaches a range from 1 / 2 to 2 / 3 of the diameter of the crystallizer.

[0018] In some embodiments, the speed at which the electrode is forced to descend is 1.3 mm / s to 1.7 mm / s.

[0019] In some embodiments, the remelting vacuum is controlled below 0.5 Pa.

[0020] In some embodiments, the average remelting kg per hour = the inner diameter of the crystallizer in millimeters × (0.44-0.65) to reduce the total amount of material in the arc zone plasma.

[0021] Compared with the prior art, the vacuum consumable remelting smelting method for reducing oxide inclusion content of the present invention has at least the following beneficial effects:

[0022] The role of C in reducing oxide inclusions in consumable remelting is enhanced, and the deoxidation product CO is removed from the smelting system in the form of gas, reducing the amount of oxide inclusions remaining in the remelted ingot. Specifically:

[0023] (1) The remelting rate in the steady-state stage is set at a low level in order to prolong the total deoxidation reaction time and promote the reduction of more oxide inclusions by C elements;

[0024] (2) Based on (1), setting the arc spacing of consumable remelting to a specific size can further provide favorable conditions for the escape of CO gas, the reaction product of C reduction of oxide inclusions;

[0025] (3) On the basis of (1), setting the molten pool liquid surface ring width to a larger size can further provide more favorable conditions for the escape of CO gas, a reaction product of C-reduced oxide inclusions; if superimposed on (2), it will further provide more favorable conditions for the escape of CO gas, a reaction product of C-reduced oxide inclusions;

[0026] (4) Furthermore, by reducing the smelting vacuum, more ideal metallurgical thermodynamic conditions can be provided for the reduction of C oxide inclusions.

[0027] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 shows the inclusion situation of 15Cr-15Ni-Fe after forging by vacuum consumable remelting in Example 1 of the present invention; wherein, Figure 1 (a) shows the inclusion situation of the head of the alloy prepared in Example 1; Figure 1 (b) shows the inclusion situation of the middle part of the alloy prepared in Example 1; Figure 1 (c) shows the inclusion situation of the tail of the alloy prepared in Example 1.

[0029] Figure 2 shows the inclusions of the vacuum consumable remelted 316 stainless steel after forging in Example 2 of the present invention; wherein, Figure 2 (a) shows the inclusions at the head of the alloy prepared in Example 2; and Figure 2 (b) shows the inclusions at the tail of the alloy prepared in Example 2.

[0030] Figure 3 shows the inclusions of the vacuum consumable remelted 304 stainless steel after forging in Example 3 of the present invention; wherein, Figure 3 (a) shows the inclusions at the head of the alloy prepared in Example 3; and Figure 3 (b) shows the inclusions at the tail of the alloy prepared in Example 3.

[0031] Figure 4 shows the different types of inclusions after forging of 304 stainless steel in vacuum consumable remelting in Example 1; Figure 4 (a) shows the inclusions in the alloy head prepared in Example 1, D 细 =0.5; Figure 4 (b) shows the inclusions in the alloy head prepared in Comparative Example 1, D 粗 =0.5; Figure 4 (c) shows the inclusions at the head of the alloy prepared in Comparative Example 1, DS = 0.5; Figure 4 (d) shows the inclusions at the tail of the alloy prepared in Comparative Example 1, D 细 =1.0; Figure 4 (e) shows the inclusions at the tail of the alloy prepared in Comparative Example 1, D 粗 =0.5; Figure (f) in Figure 4 shows the inclusion situation at the tail of the alloy prepared in Comparative Example 1, DS=0.5.

[0032] Figure 5 shows the different types of inclusions after forging of 304 stainless steel in vacuum consumable remelting in comparative example 2; Figure 5 (a) shows the inclusions in the alloy head prepared in comparative example 2, D 细 =1.0; Figure 5 (b) shows the inclusions in the alloy head prepared in Comparative Example 2, D 粗 =0.5; Figure 5 (c) shows the inclusions at the head of the alloy prepared in Comparative Example 2, DS = 0.5; Figure 5 (d) shows the inclusions at the tail of the alloy prepared in Comparative Example 2, D 细 =1.0; Figure 5 (e) shows the inclusions at the tail of the alloy prepared in Comparative Example 2, D 粗 =0.5; Figure (f) in Figure 5 shows the inclusion situation at the tail of the alloy prepared in Comparative Example 2, DS=0.5.

[0033] Figure 6 shows the different types of inclusions after forging of 316 stainless steel in vacuum consumable remelting in Example 3; Figure 6 (a) shows the inclusions in the head of the alloy prepared in Example 3, D 细 =1.5; Figure 6 (b) shows the inclusions at the tail of the alloy prepared in Comparative Example 3, D 细 =1.5.

[0034] Figure 7 shows the different types of inclusions after forging of 316 stainless steel in vacuum consumable remelting in Example 4; Figure 7 (a) shows the inclusions in the head of the alloy prepared in Example 4, D 粗 =0.5; Figure 7 (b) shows the inclusions in the alloy head prepared in Comparative Example 4, D 细=1.0; Figure 7 (c) shows the inclusions at the tail of the alloy prepared in Comparative Example 4, D 粗 =0.5; Figure 7 (d) shows the inclusions at the tail of the alloy prepared in Comparative Example 4, D 细 =1.0. DETAILED DESCRIPTION

[0035] To further illustrate the technical means and effects employed by the present invention to achieve its intended objectives, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention is provided in conjunction with the accompanying drawings and preferred embodiments. In the following description, different references to "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0036] In conventional vacuum consumable remelting, inclusions are primarily removed by floating to the surface of the molten pool, where they then migrate and are eliminated from the remelting ingot surface area. Oxide inclusions in this removal process remain in compound form and are not truly removed from the smelting system.

[0037] The concept of the present invention is as follows: only by turning oxygen into gas can it be completely separated from the smelting system, so that there is no problem of oxides mixed in the metal. To this end, the oxide inclusions smelted by the method of the present invention are mainly removed in the form of reduction by the C element, and the reaction product CO is removed from the smelting system by vacuum extraction. In order to obtain a better CO reaction to deoxidize and reduce the content of alloy inclusions, the inventors found that the melting rate selection of the alloy vacuum consumable remelting has a clear correspondence with the crystallizer diameter. Under normal conditions, for stainless steel vacuum consumable remelting, when the crystallizer diameter is 508mm, the remelting rate is basically selected as 508×(1.1-0.9)kg / h, that is, 559kg / h-457kg / h; when the crystallizer diameter is 350mm, the remelting rate can be selected as 350×(1.1-0.9)kg / h, that is, 385kg / h-315kg / h. The present invention discloses an average remelting kg per hour = the value of the inner diameter of the crystallizer in millimeters × (0.4-0.7), wherein the units of measurement kg / h on the left side of the equation and the units of measurement mm on the right side are ignored, and only the specific values ​​are considered. The process principle is that the level of the remelting rate directly determines the total smelting time of the alloy, which is equivalent to the duration of the alloy vacuum refining and deoxidation. In the present invention, the average remelting kg per hour = the value of the inner diameter of the crystallizer in millimeters × (0.4-0.7) can extend the total smelting time by 28%-57% compared to × (1.1-0.9), more effectively increasing the time for carbon deoxidation and reduction of oxides, and ensuring that the number of inclusions in the consumable remelted ingot is effectively reduced. The purpose of the average remelting kg per hour > the value of the inner diameter of the crystallizer in millimeters × 0.4 is to avoid the situation where an excessively low melting rate limits the necessary input of melting power, which will deteriorate the surface quality of the consumable remelted ingot, and setting a lower limit for the remelting rate can also ensure the activity of the molten pool during the remelting process and ensure the metallurgical dynamic conditions for carbon deoxidation and reduction of oxides.

[0038] Furthermore, the inventors discovered that the lower the actual vacuum value in the reaction arc zone, the better.

[0039] During the vacuum consumable remelting process, the vacuum level displayed by the vacuum gauge used to monitor the equipment's operating status is inconsistent with the actual vacuum level in the reaction arc zone. The actual vacuum level in the reaction arc zone is typically much higher than the value indicated by the vacuum gauge. Reports indicate that the vacuum level is approximately between 133 Pa and 1330 Pa, but this lacks further evidence to support its credibility. Although the vacuum level in the reaction arc zone cannot be accurately measured, the inventors have discovered that its value is primarily affected by the total amount of plasma material in the arc zone and the volume of the arc zone. Therefore, to achieve the objectives of the present invention, the present invention reduces the total amount of plasma material in the arc zone and expands the volume of the arc zone to ensure that oxide inclusions are primarily removed by elemental carbon reduction during vacuum consumable remelting, with the reaction product being CO. Reducing the total amount of plasma material in the arc zone is achieved by controlling the average remelting kg per hour to the value of the mold inner diameter in millimeters × (0.4-0.7), while expanding the arc zone volume is achieved by maintaining the arc spacing within the range of 15-19 mm.

[0040] Conventional vacuum consumable remelting arc spacing control mainly has two options. One is to use voltage control to maintain the arc spacing. This operation is a long arc operation and generally controls the arc spacing between 20-30mm. The other is to use droplet control to maintain the arc spacing. This operation is a short arc operation and generally controls the arc spacing between 5-12.5mm.

[0041] The inventors of the present invention have found that under the condition of average remelting kg per hour = crystallizer inner diameter in millimeters × (0.4-0.7), controlling the arc spacing to be greater than 19 mm for smelting cannot obtain remelted ingots with low inclusion content. After further analysis and research, it was found that when the arc spacing is greater than 19 mm, due to the large arc spacing, the heat radiated outward by the molten pool liquid surface is also large, which in turn leads to a serious cooling of the molten pool liquid surface and an uneven distribution of liquid surface temperature, especially a significant decrease in the fluidity of the alloy liquid near the crystallizer cooling wall. During the remelting process, slag formed by oxide inclusions that have not yet been reduced to CO gas by C will float on the metal liquid surface. Driven by the heat flow, the floating slag will flow to the surrounding areas (i.e., the inner wall of the crystallizer) and may be captured by the crystallizer wall, that is, stay on the surface of the consumable ingot and be peeled off during the peeling process. However, due to the large arc spacing of the consumable remelting arcs and the poor fluidity of the alloy liquid near the wall of the crystallizer, the floating slag will be fixed by the paste-like alloy liquid before it reaches the wall of the crystallizer and eventually solidify and remain in the consumable ingot, resulting in the random distribution of oxides in the remelted consumable ingot, increasing the inclusion content of the remelted ingot. At the same time, when the arc spacing is greater than 19mm, a large amount of metal droplets splashed during the remelting process will adhere to the inner wall of the crystallizer. As the smelting process progresses, the alloy liquid level rises and eventually covers the metal splashes adhered to the inner wall of the crystallizer. Due to the strong cooling effect of the crystallizer, the metal splashes adhered in the early stage will not be heated by the alloy liquid and remelted, so the residual metal splashes seriously deteriorate the surface quality of the remelted ingot, resulting in an increase in the amount of peeling and turning of the consumable ingot.

[0042] The inventors found that it was difficult to obtain good remelting ingot quality when the arc spacing was controlled to be less than 15mm. Further research was conducted and it was found that within this parameter range, if the raw material electrode is thoroughly deoxidized, the remelting operation can be carried out smoothly and excellent consumable ingot surface quality can be obtained. However, for raw material electrodes with general deoxidation effects (especially stainless steel), it is not appropriate to carry out consumable remelting in an interval of less than 15mm. The reason is that the escape of CO gas, a deoxidation product generated by the combination of a large amount of oxygen and carbon in the alloy under vacuum conditions, will be suppressed by the short arc spacing, resulting in poor exhaust. The suppressed CO amount gradually accumulates, and after exceeding the critical escape condition, the CO gas will escape explosively. The large amount of CO gas that escapes in a short time causes the remelting arc to change from a diffuse distribution to an aggregate distribution, the remelting electrode is directly connected to the crystallizer, the natural fluctuations of the smelting voltage and current disappear, the arc heat no longer heats the remelting electrode evenly, and eventually forces the alloy liquid level to cool down or even solidify, and the remelting process fluctuates significantly. During the cooling and even solidification process of the alloy liquid, the slag floating on the liquid surface will be randomly encapsulated by the solidifying alloy, resulting in an increase in inclusions in the consumable ingot. Furthermore, since CO will be regenerated after the explosive escape and gradually accumulate under the suppression of the short arc until it exceeds the critical condition and escapes again in a short period of time, the entrapment of inclusions will also occur periodically during the consumable remelting process, resulting in a decrease in the quality of the finished product.

[0043] In order to overcome the defects of poor fluidity and easy slag rolling at the edge of the molten pool crystallizer in long arc distance and explosive escape of CO in short arc distance, the inventors selected a specific arc distance of 15-19mm as the selected range of operating parameters. On the basis of setting the remelting speed in the steady-state stage at a lower level, it can not only avoid the problems of poor surface quality of consumable ingots and inclusions remaining near the edge of the consumable ingot but unable to be removed by peeling caused by long arc operation, but also effectively avoid the periodic interruption of remelting caused by short arc operation and the random wrapping of inclusions by low-temperature alloy liquid.

[0044] Preferably, the width of the melt pool surface ring = (mold inner diameter × 0.06 + 19) ± 2.5 (unit: mm) to increase the exposed area of ​​the melt pool, which can better ensure that the number of inclusions in the consumable remelting ingot is reduced during the vacuum consumable remelting process. To achieve a smooth ingot surface and a shallow melt pool shape, the width of the melt pool surface ring (the annular metal surface visible by camera with the inner wall of the mold as the outer diameter and the outer contour of the remelting electrode as the inner diameter) is usually selected to be 20-25mm. When the mold diameter is less than 200mm, 20mm can be selected, and when the mold diameter is greater than 400mm, 25mm can be selected. The inventors found that under the conditions that the average remelting kg per hour = the value of the crystallizer inner diameter in millimeters × (0.4-0.7) and the arc spacing is 15-19 mm, when the molten pool liquid surface ring width is less than (crystallizer inner diameter × 0.06+19)-2.5 (unit: mm) (for example, a crystallizer inner diameter of 160 mm corresponds to 26.1 mm, and a crystallizer inner diameter of 508 mm corresponds to 46.98 mm), the vacuum self-consumption process is affected by the reduction of the exposed area of ​​the molten pool, the degree of C de-O is suppressed, which is not conducive to the carbon reduction reaction, and the inclusion level of the remelted ingot is not low. When the width of the molten pool liquid surface ring is greater than (mold inner diameter × 0.06 + 19) + 2.5 (unit: mm) (for example, a mold inner diameter of 160 mm corresponds to 31.1 mm, and a mold inner diameter of 508 mm corresponds to 51.98 mm), the molten pool solidifies near the edge of the mold during the vacuum self-consumption process due to the uneven temperature. The floating inclusions on the molten pool liquid surface are captured by the viscous paste metal, and the inclusion level of the remelted ingot is not low.

[0045] Further preferably, the arc spacing is measured by forcing the electrode to descend quickly to a short circuit, the electrode descent speed is controlled in the range of 1.3mm / s-1.7mm / s, and the measurement is performed when the height of the remelting ingot reaches the range of 1 / 2 to 2 / 3 of the crystallizer diameter.

[0046] Conventional consumable remelting operations have relatively loose control over arc spacing, and arc spacing measurements are rarely performed. Even when arc spacing measurements are performed, they are performed at the hot capping stage at the end of smelting, and there are no special regulations for the speed of manually forcing the electrode to descend. The above-mentioned arc spacing measurement method has three shortcomings: First, the timing of measuring arc spacing at the end of smelting is too late to detect abnormalities in arc length control parameters early; second, the melting power is low at the end of smelting, and the measurement of arc spacing will force the molten pool temperature to drop, resulting in abnormal solidification inclusions being entrapped; third, the electrode descent speed is not specially controlled, which may result in improper timing or inaccurate data for reading the electrode rod stroke position.

[0047] The difference of the present invention is that it has very high requirements for the control of the arc spacing, and corresponding means must be used to measure and control the arc spacing. The present invention specifically designs a process method for measuring the arc spacing when the height of the remelting ingot reaches the range of 1 / 2 crystallizer diameter to 2 / 3 crystallizer diameter. The advantage of this process method is that the arc spacing can be measured as early as possible, and when the process operation is not ideal, it can be discovered and corrected in advance, and the arc spacing control can be more accurate; secondly, the arc spacing is measured in the early stage of smelting, and the characteristics of the relatively large smelting current and relatively high molten pool temperature at this stage can be utilized to avoid the problem of abnormal solidification of molten steel and inclusions caused by short circuit and heat loss during the arc distance measurement. Moreover, at this stage, the distance between the molten pool and the bottom plate of the crystallizer is close, the cooling intensity is high, and the crystal structure is basically in a vertical direction, which can effectively push the inclusions to float up, further reducing the risk of increased inclusions caused by arc spacing measurement.

[0048] The method for measuring the arc spacing is to record the stroke position of the electrode rod before the operation, and then force the electrode to drop quickly until a short circuit occurs (i.e., the remelting arc disappears), and record the corresponding electrode rod stroke position at this moment. Subtract the stroke position before the operation from the stroke position at the moment the short circuit occurs, and the difference is the arc spacing. After adopting the specific electrode rapid descent operation described in the present invention, the electrode descent speed is 1.3mm / s-1.7mm / s. Using this speed descent, on the one hand, the arc spacing can be quickly measured, avoiding the interference of the electrode descent output by the automatic control on the accuracy of the measurement data; on the other hand, the moment when the remelting arc disappears can be more clearly judged, avoiding the judgment of the timing of accurate reading of the electrode rod stroke position due to excessive descent.

[0049] Preferably, the vacuum degree of the consumable remelting is controlled below 0.5 Pa.

[0050] In order to obtain better CO reaction conditions to deoxidize and reduce the inclusion content of the alloy, the lower the smelting vacuum value, the better. Under the condition of a vacuum degree of less than 0.5Pa, the actual vacuum value of the reaction arc zone will also decrease accordingly. The aforementioned use of a lower remelting speed can reduce the total amount of material in the arc zone plasma, and controlling the remelting arc spacing to maintain within the range of 15-19mm can greatly expand the volume of the arc zone, thereby cooperating to obtain good CO reaction conditions. Increasing the exposed liquid surface area of ​​the molten pool can further cooperate to obtain more ideal CO reaction conditions. In addition, a remelting vacuum degree below 0.5Pa will also provide favorable conditions for the CO reaction in the exposed molten pool liquid surface ring area. Through the comprehensive use of four measures of low remelting speed, medium and high arc spacing, large exposed molten pool area and high vacuum, the optimal purpose of promoting the remelting CO deoxidation reaction to efficiently remove inclusions is achieved.

[0051] In the process provided by the present invention, the technical mechanism is as follows:

[0052] (1) The remelting rate in the steady-state stage is set at a lower level in order to extend the total deoxidation reaction time and promote the reduction of more oxide inclusions by C elements;

[0053] (2) Based on (1), setting the arc spacing of consumable remelting to a specific size can further provide favorable conditions for the escape of CO gas, the reaction product of C reduction of oxide inclusions;

[0054] (3) On the basis of (1), setting the molten pool liquid surface ring width to a larger size can further provide more favorable conditions for the escape of CO gas, a reaction product of C-reduced oxide inclusions; if superimposed on (2), it will further provide more favorable conditions for the escape of CO gas, a reaction product of C-reduced oxide inclusions;

[0055] (4) Furthermore, by reducing the smelting vacuum, more ideal metallurgical thermodynamic conditions can be provided for the reduction of C oxide inclusions.

[0056] The advantages of the present invention are: strengthening the role of C in reducing oxide inclusions in consumable remelting, removing the deoxidation product CO from the smelting system in the form of gas, and reducing the amount of oxide inclusions remaining in the remelted ingot.

[0057] The present invention is further described below by means of specific embodiments:

[0058] Example 1

[0059] A new 15Cr-15Ni-Fe stainless steel was smelted in a 3-ton vacuum consumable remelting furnace. The remelting electrode diameter was Φ410mm, the mold inner diameter was Φ508mm, and the melt pool surface ring width was 49mm. After the furnace was closed, the equipment was evacuated, and a three-stage vacuum pump was used to reduce the vacuum to 0.16Pa before arc melting was initiated. After the melt pool was established and stabilized, when the remelting ingot height reached 260mm and the vacuum was maintained at 0.3Pa, the electrode was manually forced to descend rapidly at a rate of 1.5mm / s. A measured arc gap of 15mm was maintained and maintained. The current was manually adjusted to maintain a steady-state melt rate of 4.0kg / min, or 240kg / h. The ratio of "hourly melt rate / mold inner diameter" was 0.47. Feeding was performed when the remaining electrode weight was less than 240kg. The melt was terminated by power outage when the remaining electrode weight was 55kg.

[0060] The surface of the consumable remelted ingot was smooth and forged to a finished size of Φ210 mm × 11110 mm. 10 mm thick sections were cut from the head, tail, and center of the forged bar, 0.5 m from the top, and 0.5 m from the tail. Inclusion evaluation samples were taken at the 1 / 2 radius position and the inclusion levels at these three locations were checked using the GB / T 10561 standard. None of the three samples contained Class A, B, C, or D inclusions. Class A includes sulfides, Class B includes aluminas, Class C includes silicates, and Class D includes spherical oxides. The inclusion profile of vacuum consumable remelted 15Cr-15Ni-Fe after forging is detailed in Table 1 and Figure 1.

[0061] Table 1. Inclusion rating of vacuum consumable remelted 15Cr-15Ni-Fe after forging

[0062] Example 2

[0063] 316 stainless steel was smelted in a 0.2-ton vacuum consumable remelting furnace. The remelting electrode diameter was Φ105mm, the mold inner diameter was Φ160mm, and the molten pool liquid surface ring width was 27.5mm. After the furnace was closed, the equipment was evacuated, and a three-stage vacuum pump was used to reduce the vacuum to 0.25Pa before arc melting was started. After the molten pool was established and stabilized, when the remelting ingot height reached 93mm and the vacuum was maintained at 0.35Pa, the electrode was manually forced to descend rapidly at a rate of 1.7mm / s. The arc spacing was measured and maintained at 19mm. The current was manually adjusted to maintain a steady-state melting rate of 107kg / h, and the calculated "hourly melting rate / mold inner diameter" ratio was 0.65. When the remaining electrode length was less than 200mm, the electrode was fed back in, and the power was turned off and the melting ended when the remaining electrode length was 40mm.

[0064] The surface of the consumable remelted ingot is smooth. The ingot is forged to a finished size of Φ80 mm × 5100 mm. Due to the small size of the ingot, 10 mm thick sections are cut from the head and tail of the finished forged bar, with the head located 0.25 m from the top and the tail located 0.25 m from the end. Inclusion evaluation samples are taken at the 1 / 2 radius position and the inclusion levels at both locations are checked using the GB / T 10561 standard. No Class A, B, or C inclusions were found, but very few Class D inclusions were found, resulting in a fine grade of 0.5. Class A includes sulfides, Class B includes aluminas, Class C includes silicates, and Class D includes spherical oxides. The inclusion profile of vacuum consumable remelted 316 stainless steel after forging is shown in Table 2 and Figure 2.

[0065] Table 2. Inclusion ratings of vacuum consumable remelted 316 stainless steel after forging

[0066] Example 3

[0067] 304 stainless steel was smelted in a 0.2-ton vacuum consumable remelting furnace. The remelting electrode diameter was Φ98mm, the inner diameter of the crystallizer was Φ160mm, and the width of the molten pool liquid level ring was 31mm. After the furnace was closed, the equipment was evacuated, and a three-stage vacuum pump was used to reduce the vacuum to 0.25Pa before arc melting was started. After the molten pool was established and stabilized, when the remelting ingot height reached 107mm and the vacuum was maintained at 0.35Pa, the electrode was manually forced to descend rapidly at a rate of 1.3mm / s. The arc spacing was measured and maintained at 17mm. Manual current was used to maintain a steady-state melting rate of 70kg / h, and the calculated "hourly melting rate / mold inner diameter" ratio was 0.44. When the remaining length of the electrode was less than 200mm, shrinkage was carried out, and the power was turned off and the melting ended when the remaining length of the electrode was 40mm.

[0068] The surface of the consumable remelted ingot is smooth. The ingot is forged to a finished size of Φ80 mm × 5100 mm. The head is 0.25 m from the top of the ingot, and the tail is 0.25 m from the end. Due to the small size of the ingot, 10 mm thick sections are cut from the head and tail of the forged bar. Inclusion evaluation samples are prepared at the 1 / 2 radius position. Inclusion levels at both locations are inspected using the GB / T 10561 standard. No Class A, B, or C inclusions were found, but very few Class D inclusions were found, rated as Fine 0.5. Class A includes sulfides, Class B includes aluminas, Class C includes silicates, and Class D includes spherical oxides. Details of the inclusion profile of vacuum consumable remelted 304 stainless steel after forging can be found in Table 3 and Figure 3. Since all locations in Examples 1-3 contain only one type of inclusion, only one image is provided for each location.

[0069] Table 3. Inclusion rating of vacuum consumable remelted 304 stainless steel after forging

[0070] Comparative Example 1

[0071] 304 stainless steel was smelted in a 0.2-ton vacuum consumable remelting furnace. The remelting electrode diameter was Φ98mm, the inner diameter of the crystallizer was Φ160mm, and the width of the molten pool liquid surface ring was 31mm. After the furnace was closed, the equipment was evacuated, and a three-stage vacuum pump was used to reduce the vacuum to 0.25Pa before arc melting. The molten pool was established and stabilized. When the height of the remelting ingot reached 107mm, the vacuum was maintained at 0.35Pa. The electrode was manually forced to descend rapidly at a rate of 1.3mm / s. The arc spacing was measured and maintained at 17mm. Manual current was used to maintain the steady-state melting rate at 128kg / h, and the calculated "hourly melting rate / crystallizer inner diameter" ratio was 0.80. When the remaining length of the electrode was less than 200mm, shrinkage was carried out. When the remaining length of the electrode was 40mm, the power was turned off and the melting was terminated.

[0072] The surface of the consumable remelted ingot is smooth. The consumable ingot is forged and the finished product size is Φ80mm×5100mm. The head is 0.25m away from the top of the rod, and the tail is 0.25m away from the tail of the rod. Due to the small ingot shape, 10mm thick slices are cut from the head and tail of the forged finished bar. Inclusion evaluation samples are made at the 1 / 2 radius position. The inclusion levels at the three positions are checked using the GB / T 10561 standard. No A, B, or C inclusions were found during the inspection. D and DS inclusions were found, and the ratings are D, D, and D, respectively. 细 =0.5~1.0 level, D 粗 = 0.5, DS = 0.5. Category A refers to sulfides, Category B to aluminas, Category C to silicates, and Category D to spherical oxides. DS refers to point-like inclusions larger than 13 μm. For details on the inclusions in the vacuum consumable remelting 304 stainless steel after forging in Comparative Example 1, see Table 4 and Figure 4.

[0073] Table 4. Inclusion rating of vacuum consumable remelted 304 stainless steel after forging

[0074] Comparative Example 2

[0075] 304 stainless steel was smelted in a 0.2-ton vacuum consumable remelting furnace. The remelting electrode diameter was Φ98mm, the inner diameter of the crystallizer was Φ160mm, and the width of the molten pool liquid surface ring was 31mm. After the furnace was closed, the equipment was evacuated, and a three-stage vacuum pump was used to reduce the vacuum to 0.25Pa before arc melting. The molten pool was established and stabilized. When the height of the remelting ingot reached 107mm, the vacuum was maintained at 0.35Pa. The electrode was manually forced to descend rapidly at a rate of 1.3mm / s. The arc spacing was measured and maintained at 17mm. Manual current was used to maintain a steady-state melting rate of 50kg / h, and the calculated "hourly melting rate / mold inner diameter" ratio was 0.31. When the remaining length of the electrode was less than 200mm, shrinkage was carried out. When the remaining length of the electrode was 40mm, the power was turned off and the melting was terminated.

[0076] The surface quality of the consumable remelted ingot is poor. The consumable ingot is forged and the finished product size is Φ80mm×5100mm. The head is 0.25m away from the top of the rod, and the tail is 0.25m away from the tail of the rod. Due to the small ingot shape, 10mm thick slices are cut from the head and tail of the forged finished bar. Inclusion evaluation samples are made at the 1 / 2 radius position. The inclusion levels at the three positions are checked using the GB / T 10561 standard. No A, B, or C inclusions were found during the inspection. D and DS inclusions were found, and the ratings are D, D, and D, respectively. 细 =1.0 level, D 粗= 0.5, DS = 0.5. Category A refers to sulfides, Category B to aluminas, Category C to silicates, and Category D to spherical oxides. DS refers to point-like inclusions larger than 13 μm. For details on the inclusions in the vacuum consumable remelting 304 stainless steel after forging in Comparative Example 2, see Table 5 and Figure 5.

[0077] Table 5. Inclusion rating of vacuum consumable remelted 304 stainless steel after forging

[0078] Comparative Example 3

[0079] 316 stainless steel was smelted in a 0.2-ton vacuum consumable remelting furnace. The remelting electrode diameter was Φ98mm, the inner diameter of the crystallizer was Φ160mm, and the width of the molten pool liquid surface ring was 31mm. After the furnace was closed, the equipment was evacuated, and a three-stage vacuum pump was used to reduce the vacuum to 0.5Pa before arc melting. The molten pool was established and stabilized. When the height of the remelting ingot reached 107mm, the vacuum was maintained at 1Pa. The electrode was manually forced to descend rapidly at a rate of 1.3mm / s. The arc spacing was measured to be 17mm and maintained. Manual current was used to maintain the steady-state melting rate at 70kg / h, and the calculated "hourly melting rate / crystallizer inner diameter" ratio was 0.44. When the remaining length of the electrode was less than 200mm, it was supplemented and smelting was terminated when the remaining length of the electrode was 40mm.

[0080] The surface of the consumable remelted ingot is smooth. The consumable ingot is forged and the finished product size is Φ80mm×5100mm. The head is 0.25m away from the top of the rod, and the tail is 0.25m away from the tail of the rod. Due to the small ingot shape, 10mm thick slices are cut from the head and tail of the forged finished bar. Inclusion evaluation samples are made at the 1 / 2 radius position. The inclusion levels at the three positions are checked using the GB / T 10561 standard. No A, B, C, or DS inclusions were found during the inspection. D inclusions were found and the ratings are D, D, and D respectively. 细 = 1.5. Category A refers to sulfides, Category B to aluminas, Category C to silicates, and Category D to spherical oxides. DS refers to point inclusions larger than 13 μm. For details on the inclusions in the vacuum consumable remelting 304 stainless steel after forging in Comparative Example 3, see Table 6 and Figure 6.

[0081] Table 6. Inclusion rating of vacuum consumable remelted 304 stainless steel after forging

[0082] Comparative Example 4

[0083] 316 stainless steel was smelted in a 0.2-ton vacuum consumable remelting furnace. The remelting electrode diameter was Φ80mm, the inner diameter of the crystallizer was Φ160mm, and the width of the molten pool liquid level ring was 40mm. After the furnace was closed, the equipment was evacuated, and a three-stage vacuum pump was used to reduce the vacuum to 0.15Pa before arc melting. The molten pool was established and stabilized. When the height of the remelting ingot reached 107mm, the vacuum was maintained at 0.35Pa. The electrode was manually forced to descend rapidly at a rate of 1.3mm / s. The arc spacing was measured and maintained at 17mm. Manual current was used to maintain the steady-state melting rate at 70kg / h, and the calculated "hourly melting rate / mold inner diameter" ratio was 0.44. When the remaining length of the electrode was less than 200mm, shrinkage was carried out. When the remaining length of the electrode was 40mm, the power was turned off and the melting was terminated.

[0084] The surface of the consumable remelted ingot is smooth. The consumable ingot is forged and the finished product size is Φ80mm×5100mm. The head is 0.25m away from the top of the rod, and the tail is 0.25m away from the tail of the rod. Due to the small ingot shape, 10mm thick slices are cut from the head and tail of the forged finished bar. Inclusion evaluation samples are made at the 1 / 2 radius position. The inclusion levels at the three positions are checked using the GB / T 10561 standard. No A, B, C, or DS inclusions were found during the inspection. D inclusions were found and the ratings are D, D, and D respectively. 细 =1.0 level, D 粗 = 0.5. Category A refers to sulfides, Category B to aluminas, Category C to silicates, and Category D to spherical oxides. DS refers to point inclusions larger than 13 μm. For details on the inclusions in the 304 stainless steel forged from vacuum consumable remelting in Comparative Example 4, see Table 7 and Figure 7.

[0085] Table 7. Inclusion rating of vacuum consumable remelted 304 stainless steel after forging

[0086] Although the embodiments and comparative examples are all about stainless steel, those skilled in the art will appreciate that the method of the present invention is not only applicable to stainless steel, but also to carbon steel or Ni-based alloys suitable for vacuum consumable arc melting.

[0087] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiment based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A vacuum consumable remelting method for reducing oxide inclusion content, characterized in that: The remelting speed is determined according to the inner diameter of the crystallizer. By controlling the remelting speed, the oxide inclusions are removed in a manner that strengthens the reduction of oxides by the C element, and the reaction product is CO.

2. The vacuum consumable remelting method for reducing oxide inclusion content according to claim 1, characterized in that: The average remelting kg per hour = the inner diameter of the crystallizer in millimeters × (0.4-0.7) to reduce the total amount of material in the plasma in the arc zone, thereby increasing the time for carbon deoxidation and reduction of oxides and reducing the number of inclusions in the consumable remelted ingot.

3. The vacuum consumable remelting method for reducing oxide inclusion content according to claim 1, characterized in that: The arc spacing of the remelting is controlled to be maintained within the range of 15-19 mm to expand the volume of the arc zone, ensuring that during the vacuum consumable remelting smelting process, the oxide inclusions are mainly removed in the form of reduction by the C element, and the reaction product is CO.

4. The vacuum consumable remelting method for reducing oxide inclusion content according to claim 1, characterized in that: The width of the molten pool liquid surface ring is controlled to be (inner diameter of the crystallizer × 0.06 + 19) ± 2.5, in mm, to increase the liquid surface area exposed by the molten pool.

5. The vacuum consumable remelting method for reducing oxide inclusion content according to claim 3, characterized in that: The arc spacing of the consumable remelting is calibrated by measuring the method of forcing the electrodes to drop quickly to a short circuit.

6. The vacuum consumable remelting method for reducing oxide inclusion content according to claim 5, characterized in that: The method for measuring the arc spacing is: record the stroke position of the electrode rod before operation, then force the electrode to drop quickly until a short circuit occurs, that is, the remelting arc disappears, and record the corresponding electrode rod stroke position at this moment; subtract the stroke position before operation from the stroke position when the short circuit occurs, and the difference is the arc spacing.

7. The vacuum consumable remelting method for reducing oxide inclusion content according to claim 5, characterized in that: The arc spacing is measured when the height of the remelting ingot reaches a range between 1 / 2 and 2 / 3 of the mold diameter.

8. The vacuum consumable remelting method for reducing oxide inclusion content according to claim 5, characterized in that: The electrode is forced to descend at a speed of 1.3 mm / s-1.7 mm / s.

9. The vacuum consumable remelting method for reducing oxide inclusion content according to claim 1, characterized in that: The remelting vacuum degree is controlled below 0.5Pa.

10. The vacuum consumable remelting method for reducing oxide inclusion content according to claim 1, characterized in that: Average remelting kg per hour = mold inner diameter in millimeters × (0.44-0.65) to reduce the total amount of material in the arc zone plasma.

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