416 free-cutting stainless steel and manufacturing method thereof

Abstract

The invention discloses 416 free-cutting stainless steel and a manufacturing method thereof. The 416 free-cutting stainless steel comprises the following chemical components in percentage by mass: less than or equal to 0.15% of C, less than or equal to 1.00% of Si, less than or equal to 1.25% of Mn, less than or equal to 0.060% of P, more than or equal to 0.15% of S, 12.0-14.0% of Cr, less than or equal to 0.20% of Ni and the balance of Fe and inevitable impurities. Preferably, the content of C is 0.10%-0.12%, the content of Si is 0.30%-0.60%, the content of Mn is 0.85%-1.15%, the content of P is smaller than or equal to 0.030%, the content of S is 0.18%-0.22%, the content of Cr is 12.20%-12.70%, and the content of Ni is 0.08%-0.20%. The manufacturing method comprises the steps of medium-frequency induction furnace smelting, electroslag remelting and cooling treatment, according to the manufacturing method, melting, refining and sulfur alloying treatment are completed in a medium-frequency induction furnace to prepare an electrode bar, electroslag remelting is conducted under the argon protection condition, and an electroslag ingot is obtained; the method is suitable for production of the 416 chalcogenide free-cutting stainless steel, and the 416 free-cutting stainless steel prepared through the method is uniform in structure and suitable for application occasions with requirements for the cutting machining performance and the comprehensive performance of materials.

Description

Technical Field

[0001] This invention relates to the field of stainless steel manufacturing technology, and more specifically, to a 416 free-machining stainless steel and its manufacturing method. Background Technology

[0002] 416 stainless steel, domestically designated Y1Cr13, is a typical sulfur-based free-machining stainless steel. It is primarily used in the manufacture of motors, electrical components, and other parts requiring high machinability. This type of steel is produced by adding a certain amount of sulfur, which combines with manganese to form manganese sulfide inclusions. The distribution of manganese sulfide in the steel improves chip breaking performance during machining, thereby enhancing the material's machinability. Currently, sulfur-based free-machining stainless steel is typically produced using an electric furnace + ladle refining process, followed by continuous casting and rolling, or by casting into square ingots after smelting, and then forging and rolling to obtain the finished material. While this process is widely used in industrial production, it still has certain shortcomings in actual production and application. When smelted steel is directly cast into ingots, sulfur has a strong tendency to segregate in the molten steel, and sulfides tend to segregate significantly in the ingot, especially forming a sulfide-rich zone in the middle of the ingot. This enrichment is difficult to completely eliminate during subsequent forming processes, which not only hinders the uniform distribution of sulfides but also leads to a significant decrease in transverse properties during the material's service life, thus affecting the material's overall mechanical properties and reliability. In addition, when using continuous casting and rolling to form billets, although the distribution of sulfides on a macroscopic scale is relatively uniform compared to traditional ingot casting processes, sulfides are easily elongated along the rolling direction during rolling deformation, forming strip-shaped or long strip-shaped inclusions. This morphological change can easily cause defects such as "split ends" in subsequent processing, and excessively fine and long sulfide morphologies can weaken their beneficial effect on chip breaking during cutting, reduce the material's machinability, and further deteriorate the steel's transverse mechanical properties.

[0003] Therefore, the existing conventional smelting and forming processes for 416 sulfide-based free-machining stainless steel still have certain limitations in terms of the uniformity of sulfide distribution, morphology control, and transverse properties of the material, and need to be further improved and optimized. Summary of the Invention

[0004] One of the technical problems to be solved by the present invention is to provide a 416 free-machining stainless steel to solve the problem in the prior art that the uneven distribution of sulfides and the difficulty in controlling the morphology of inclusions make it difficult to balance the material's machinability and transverse mechanical properties.

[0005] To overcome the shortcomings of the prior art, the present invention provides a 416 free-machining stainless steel whose chemical composition, by mass percentage, satisfies the following: C ≤ 0.15%, Si ≤ 1.00%, Mn ≤ 1.25%, P ≤ 0.060%, S ≥ 0.15%, Cr 12.0–14.0%, Ni ≤ 0.20%, with the balance being Fe and unavoidable impurities.

[0006] Compared with existing technologies, the 416 free-cutting stainless steel of this invention has the following advantages: By synergistically controlling the content of key elements such as carbon, chromium, sulfur, and manganese, the 416 free-cutting stainless steel of this invention ensures the stability of the stainless steel matrix structure while allowing sulfur to participate in the microstructure regulation in a suitable form, thus providing a compositional basis for the formation and evolution of sulfide inclusions. The coordinated control of sulfur and manganese content is beneficial to the formation of manganese sulfide inclusions, while the reasonable limitation of carbon, chromium, and nickel content ensures the corrosion resistance and matrix strength requirements of the steel. Under the combined effect of the above compositional system, sulfide inclusions in the steel are more likely to obtain a morphology conducive to chip breaking during subsequent processing, while avoiding adverse effects on the transverse properties of the material due to sulfide segregation or abnormal morphology. Therefore, the 416 free-cutting stainless steel of this invention achieves a good balance between machining performance and overall material performance, effectively solving the technical problems described in the background art.

[0007] In one possible implementation, its chemical composition, by mass percentage, satisfies the following: C 0.10–0.12%, Si 0.30–0.60%, Mn 0.85–1.15%, P ≤ 0.030%, S 0.18–0.22%, Cr 12.20–12.70%, Ni 0.08–0.20%, with the balance being Fe and unavoidable impurities.

[0008] Compared with existing technologies, by further limiting the sulfur content to 0.18–0.22% and controlling the manganese content to the range of 0.85–1.15%, stable formation and distribution of manganese sulfide inclusions are achieved. At the same time, by limiting the carbon, chromium and nickel elements to the above-mentioned optimized range, the inconsistency of performance caused by composition fluctuations is avoided while ensuring the stability of the matrix structure, further improving the stability of the material's machinability and taking into account the overall performance of the material.

[0009] Another technical problem to be solved by the present invention is to provide a 416 free-machining stainless steel to solve the problem that in the prior art, sulfur-based free-machining stainless steel suffers from severe sulfide segregation and difficulty in controlling the morphology of inclusions during smelting and forming, which affects the material's machinability and transverse properties.

[0010] To overcome the shortcomings of the prior art, the present invention provides a method for manufacturing the aforementioned 416 free-machining stainless steel, comprising the following steps: S1: Medium-frequency induction furnace smelting: Using raw steel or process pure iron, chromium stainless steel return material, low-carbon ferrochrome, pyrite, metallic manganese and ferrosilicon as raw materials, the melting, refining and sulfur alloying processes are completed in sequence in the medium-frequency induction furnace, and then the steel is tapped and cast to obtain electrode rods. S2: Electroslag remelting: The electrode rod is placed in a crystallizer and electroslag remelted under argon protection to obtain an electroslag ingot. S3: Cooling treatment: The electroslag ingot is cooled to room temperature by passing it through a crystallizer, then under a hood.

[0011] Compared with the prior art, the manufacturing method of 416 free-machining stainless steel of the present invention has the following advantages: The manufacturing method of the present invention combines medium-frequency induction furnace smelting with electroslag remelting process, forming a synergistic control mechanism in the smelting and solidification stages: In step S1, the medium-frequency induction furnace smelting stage completes melting, refining and sulfur alloying treatment, so that sulfur can be stably and effectively introduced into the molten steel system, providing a compositional basis for free-machining performance; while the electroslag remelting process in step S2 utilizes slag-metal reaction, molten pool purification and controlled solidification conditions to further control inclusions in the molten steel, thereby reducing the segregation of sulfides in the ingot and improving their distribution state; The above steps in the manufacturing method of the present invention work together to improve the uniformity of the resulting electroslag ingot structure, and the steel has good hot working performance in subsequent processing, and is conducive to obtaining inclusion morphologies suitable for machining, solving the technical problem in the prior art that it is difficult to balance the uniformity of structure and the machinability of sulfur-based free-machining stainless steel.

[0012] In one possible implementation, step S1 includes: S11: Melting period: Melting is carried out at maximum power, and metallic manganese is added at the end of the melting process; S12: Slag Formation and Precipitation Deoxidation: After melting and cleaning, the bottom slag is removed and reducing slag is formed. The reducing slag consists of 55% CaF2 and 45% CaO by mass percentage, and the amount of slag is 3-5% of the weight of the molten steel. Calcium silicate blocks are inserted into the molten steel at a rate of 2-2.5 kg / t for precipitation deoxidation, and the temperature of the molten steel is controlled at 1540-1560℃.

[0013] Compared with existing technologies, by limiting the composition of the reducing slag to 55% CaF2 and 45% CaO, and controlling the slag amount to 3-5% of the weight of the molten steel, the slag simultaneously possesses good fluidity and deoxidation and inclusion adsorption capabilities, which is beneficial for the removal of non-metallic inclusions in the molten steel. At the same time, by adding 2-2.5 kg / t of calcium silicate blocks for precipitation deoxidation, under the molten steel temperature of 1540-1560℃, the deoxidation products are easily floated into the slag, thereby reducing the oxygen content in the molten steel and improving the cleanliness of the molten steel. This provides stable, low-oxygen molten steel conditions for subsequent refining and sulfur alloying treatment, which in turn helps to improve the stability of composition control and the effect of inclusion control.

[0014] In one possible implementation, in step S1, the refining includes: adjusting the temperature of the molten steel to 1550–1580°C, using aluminum powder for diffusion deoxidation, adding silicon-calcium powder to maintain the white slag state after the formation of white slag, the white slag time being 30–40 min, and adjusting the chemical composition of the molten steel during the refining process.

[0015] Compared with existing technologies, the above-mentioned technical solution further reduces residual oxygen in molten steel by controlling the refining temperature within the range of 1550–1580℃ and using aluminum powder for diffusion deoxidation. Furthermore, by maintaining the white slag state for 30–40 minutes, the slag possesses a continuous adsorption and purification capacity for inclusions, thereby promoting the removal of fine inclusions and homogenization of composition. The combination of the above refining conditions in this embodiment helps stabilize the composition of molten steel and improve its purity, providing conditions for the effective introduction and stable presence of sulfur in the subsequent sulfur alloying process, and improving the uniformity of the final steel structure.

[0016] In one possible implementation, step S1, the sulfur alloying treatment includes: removing about 50% of the refining slag from the surface of the molten steel; adding quartz sand to the molten steel at a weight of about 2% of the molten steel, and adding fluorite to adjust the fluidity of the slag; wrapping pyrite in aluminum foil and inserting it into the middle of the molten steel, stirring for 10–15 min, and then taking a sample to analyze the composition of the molten steel.

[0017] Compared with existing technologies, this embodiment reduces the adsorption effect of the original slag on sulfur by removing about 50% of the refining slag before sulfur alloying. It also stabilizes the slag-metal reaction conditions during the sulfur alloying stage by adding about 2% quartz sand and fluorite to the molten steel to adjust the slag fluidity. By inserting pyrite wrapped in aluminum foil into the middle of the molten steel and stirring for 10–15 min, sulfur can be uniformly introduced into the molten steel system and the sulfur recovery rate can be improved. This achieves stable control of the sulfur content in the steel, which is beneficial to the formation and distribution control of sulfide inclusions in subsequent processes, and ultimately improves the machinability of the material.

[0018] In one possible implementation, the temperature of the molten steel during the tapping and casting process is 1590–1620°C.

[0019] Compared with the prior art, by adopting the above technical solution, this embodiment limits the steel casting temperature to the range of 1590–1620℃, so that the molten steel maintains good fluidity during the casting process. At the same time, it avoids component loss caused by excessively high temperature or casting instability caused by excessively low temperature. This is conducive to obtaining electrode rods with uniform composition and dense structure. The above temperature control provides stable and consistent initial conditions for the subsequent electroslag remelting process, which is conducive to improving the controllability of the remelting process and the stability of the final steel quality.

[0020] In one possible implementation, in step S2: the diameter of the crystallizer is Φ360 mm, and the electroslag remelting is carried out under argon protection conditions, with the current of the electroslag remelting stage being 7000–8500 A and the voltage being 56–60 V.

[0021] Compared with existing technologies, the above technical solution, by using a crystallizer with a diameter of Φ360 mm, enables the electroslag ingot to form a stable molten pool during the remelting process; and by carrying out electroslag remelting under argon protection, the risk of secondary oxidation of molten steel in a high-temperature environment is reduced; at the same time, by controlling the remelting current within the range of 7000–8500 A and the voltage within the range of 56–60 V, the molten pool temperature and solidification rate are kept stable, which is conducive to the continuous progress of the electroslag remelting process and the uniform solidification of molten steel, thereby improving the microstructure uniformity of the electroslag ingot and reducing the possibility of internal defects.

[0022] In one possible implementation, in step S2, the slag material used in the electroslag remelting is, by weight percentage: fluorite 46%, alumina 21%, quartz sand 24%, fused magnesia 5%, and quicklime 4%.

[0023] Compared with existing technologies, the above technical solution, by proportioning fluorite, alumina, quartz sand, fused magnesia, and active lime in the electroslag remelting slag according to the aforementioned weight percentages, enables the slag system to simultaneously possess good conductivity, fluidity, and inclusion adsorption capacity. Under the slag system conditions of this embodiment, the reaction between slag and metal during electroslag remelting is more stable, which is beneficial for the removal of inclusions in the molten steel and the controlled existence of sulfides, thereby further improving the purity and microstructure consistency of the electroslag ingot and providing a guarantee for obtaining stable free-machining stainless steel.

[0024] In one possible implementation, step S3 includes the following cooling process: after electroslag remelting, the electroslag ingot is cooled in a crystallizer for 20–40 min and then removed from the ingot, and then cooled under a hood for at least 36 h before being air-cooled.

[0025] Compared with the prior art, the above technical solution reduces the internal temperature gradient of the electroslag ingot by cooling it in the crystallizer for 20–40 min before removing it from the ingot; and by hood cooling for no less than 36 h, the electroslag ingot completes the phase transformation process under relatively gentle cooling conditions, thereby reducing internal stress and lowering the risk of defects such as cracks. The cooling method provided by the above embodiments of the present invention is beneficial to maintaining the integrity and uniformity of the electroslag ingot structure, providing favorable conditions for subsequent forging processing and obtaining stable material properties. Detailed Implementation

[0026] First, those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0027] This invention provides a 416 free-machining stainless steel whose chemical composition, by mass percentage, satisfies the following: C ≤ 0.15%, Si ≤ 1.00%, Mn ≤ 1.25%, P ≤ 0.060%, S ≥ 0.15%, Cr 12.0–14.0%, Ni ≤ 0.20%, with the balance being Fe and unavoidable impurities.

[0028] As a preferred embodiment, its chemical composition, by mass percentage, satisfies the following: C 0.10–0.12%, Si 0.30–0.60%, Mn 0.85–1.15%, P ≤ 0.030%, S 0.18–0.22%, Cr 12.20–12.70%, Ni 0.08–0.20%, with the balance being Fe and unavoidable impurities.

[0029] This invention provides a method for manufacturing the aforementioned 416 free-machining stainless steel, comprising the following steps: S1: Medium-frequency induction furnace smelting: Using raw steel or process pure iron, chromium stainless steel return material, low-carbon ferrochrome, pyrite, metallic manganese and ferrosilicon as raw materials, the melting, refining and sulfur alloying processes are completed in sequence in the medium-frequency induction furnace, and then the steel is tapped and cast to obtain electrode rods. S2: Electroslag remelting: The electrode rod is placed in a crystallizer and electroslag remelted under argon protection to obtain an electroslag ingot. S3: Cooling treatment: The electroslag ingot is cooled to room temperature by passing it through a crystallizer, then under a hood.

[0030] As a preferred embodiment, step S1 includes: S11: Melting period: Melting is carried out at maximum power, and metallic manganese is added at the end of the melting process; S12: Slag Formation and Precipitation Deoxidation: After melting and cleaning, the bottom slag is removed and reducing slag is formed. The reducing slag consists of 55% CaF2 and 45% CaO by mass percentage, and the amount of slag is 3-5% of the weight of the molten steel. Calcium silicate blocks are inserted into the molten steel at a rate of 2-2.5 kg / t for precipitation deoxidation, and the temperature of the molten steel is controlled at 1540-1560℃.

[0031] As a preferred embodiment, in step S1, the refining includes: adjusting the temperature of the molten steel to 1550–1580℃, using aluminum powder for diffusion deoxidation, adding silicon-calcium powder to maintain the white slag state after the formation of white slag, the white slag time being 30–40 minutes, and adjusting the chemical composition of the molten steel during the refining process.

[0032] As a preferred embodiment, in step S1, the sulfur alloying treatment includes: removing about 50% of the refining slag from the surface of the molten steel; adding quartz sand to the molten steel at a rate of about 2% of the weight of the molten steel, and adding fluorite to adjust the fluidity of the slag; wrapping pyrite in aluminum foil and inserting it into the middle of the molten steel, stirring for 10–15 min, and then taking a sample to analyze the composition of the molten steel.

[0033] As a preferred embodiment, the temperature of the molten steel during the tapping and casting process is 1590–1620℃.

[0034] As a preferred embodiment, in step S2: the diameter of the crystallizer is Φ360 mm, and the electroslag remelting is carried out under argon protection conditions, with the current of the electroslag remelting stage being 7000–8500 A and the voltage being 56–60 V.

[0035] As a preferred embodiment, in step S2, the slag material used for electroslag remelting is, by weight percentage: fluorite 46%, alumina 21%, quartz sand 24%, fused magnesia 5%, and active lime 4%.

[0036] As a preferred embodiment, in step S3, the cooling process includes: after electroslag remelting, the electroslag ingot is cooled in the crystallizer for 20–40 min and then removed from the ingot, and then cooled under a hood for no less than 36 h before being air-cooled.

[0037] In the 416 free-machining stainless steel and its manufacturing method described in this invention, the preferred embodiments closely revolve around the inventive objective of improving the distribution and morphology control of sulfides in sulfur-based free-machining stainless steel, forming a synergistic whole: by synergistically limiting the range of key chemical components such as carbon, manganese, sulfur, chromium, and nickel, a compositional basis is provided for the formation and stable existence of manganese sulfide inclusions, and the adverse effects of sulfide segregation on the transverse properties of the material are avoided while ensuring the stability of the stainless steel matrix; furthermore, by organically combining medium-frequency induction furnace smelting, electroslag remelting, and controlled cooling processes, sulfur can be stably introduced during the smelting stage and further regulated during remelting and solidification, effectively improving the distribution and morphology control of sulfide inclusions in the steel. The distribution and morphological characteristics of the sulfides; furthermore, the deoxidation, refining and sulfur alloying treatment in the medium-frequency induction furnace stage provides electrode rods with uniform composition and high cleanliness for electroslag remelting. During the electroslag remelting process, the purification and morphology optimization of inclusions are achieved through the coordinated control of slag composition, electrical parameters and solidification conditions. Combined with the subsequent mild cooling process, the steel is more likely to obtain a sulfide morphology mainly in the form of "spindle" in subsequent processing. The above composition design and process conditions support and promote each other as a whole, enabling the present invention to achieve a good balance between machinability and comprehensive mechanical properties of materials, thereby effectively solving the technical problems of uneven sulfide distribution, difficult morphology control and performance balance in sulfur-based free-machining stainless steel in the background art.

[0038] The 416 free-machining stainless steel and its manufacturing method of the present invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0039] Example 1 This embodiment provides a 416 free-machining stainless steel, which is manufactured by the following method. The chemical composition of the finished product, by mass percentage, is: C 0.115%, Si 0.447%, Mn 0.968%, P 0.008%, S 0.21%, Cr 12.46%, Ni 0.165%, with the balance being Fe and unavoidable impurities.

[0040] The manufacturing method of this 416 free-machining stainless steel includes the following steps: S1: Medium-frequency induction furnace smelting Raw materials such as raw steel, recycled chromium stainless steel, low-carbon ferrochrome, pyrite, metallic manganese, and ferrosilicon are selected and smelted in a medium-frequency induction furnace.

[0041] S11: Melting period The furnace charge is melted using maximum power, and metallic manganese is added to the molten steel at the end of the melting process.

[0042] S12: Slag Formation and Sedimentation Deoxidation After the molten steel is melted and cleared, the bottom slag is removed and a reducing slag is made. The reducing slag consists of 55% CaF2 and 45% CaO by mass percentage, and the amount of slag is 4% of the weight of the molten steel. Then, silicon-calcium blocks are inserted into the molten steel at 2.25 kg / t for precipitation and deoxidation, and the temperature of the molten steel is controlled at 1550℃.

[0043] S13: Refining The temperature of the molten steel was adjusted to 1565℃, and aluminum powder was used for diffusion deoxidation. After the formation of white slag, calcium silicate powder was added to maintain the white slag state. The white slag time was 35 minutes, and the chemical composition of the molten steel was adjusted during the refining process.

[0044] S14: Sulfur alloying About 50% of the refining slag on the surface of the molten steel was removed. Quartz sand was added to the molten steel at a weight of 2% of the molten steel, and fluorite was added to adjust the fluidity of the slag. Pyrite was wrapped in aluminum foil and inserted into the middle of the molten steel. After stirring for 12 minutes, a sample was taken to analyze the composition of the molten steel.

[0045] S15: Steel tapping and casting After adjusting the temperature of the molten steel to 1605℃, the steel was tapped out and cast to obtain an electrode rod. In this embodiment, the composition of the electrode rod is controlled as follows: When the electrode rod is smelted in the medium-frequency induction furnace and cast into a steel rod, the chemical composition of the electrode rod is controlled. The chemical composition, by mass percentage, includes: C 0.10–0.12%, Cr 12.20–12.70%, Ni 0.08–0.20%, Si 0.30–0.55%, Mn 0.90–1.15%, P ≤0.030%, S 0.20–0.23%, with the balance being Fe and unavoidable impurities.

[0046] S2: Electroslag Remelting The electrode rod was placed in a crystallizer with a diameter of Φ360 mm and electroslag remelting was carried out under argon protection. The slag material used was as follows by weight percentage: fluorite 46%, alumina 21%, quartz sand 24%, fused magnesia 5%, and quicklime 4%. The current during the electroslag remelting stage was 7750 A and the voltage was 58 V, and an electroslag ingot was obtained.

[0047] S3: Cooling treatment After electroslag remelting, the electroslag ingot is cooled in the crystallizer for 30 minutes and then removed from the ingot. It is then hooded and cooled for 36 hours, and finally air-cooled to room temperature.

[0048] Example 2 This embodiment provides a 416 free-machining stainless steel, which is manufactured by the following method. The chemical composition of the finished product, by mass percentage, is: C 0.11%, Si 0.53%, Mn 1.03%, P 0.010%, S 0.20%, Cr 12.41%, Ni 0.147%, with the balance being Fe and unavoidable impurities.

[0049] Its manufacturing method is basically the same as that of Example 1, except that: In step S12, the amount of the reducing slag is 3% of the weight of the molten steel, the amount of silicon-calcium blocks added during precipitation deoxidation is 2 kg / t, and the temperature of the molten steel is controlled at 1540℃. In step S13, the refining temperature is 1550℃ and the white residue time is 30 min; In step S14, the sulfur alloying stirring time is 10 min; In step S15, the temperature of the molten steel during tapping and casting is 1590℃; In step S2, the current during the electroslag remelting stage is 7000 A and the voltage is 56 V; In step S3, the electroslag ingot is cooled in the crystallizer for 20 minutes and then removed from the ingot.

[0050] Example 3 This embodiment provides a 416 free-machining stainless steel, which is produced by the following manufacturing method. The chemical composition of the finished product, by mass percentage, is: C 0.116%, Si 0.46%, Mn 1.04%, P 0.011%, S 0.22%, Cr 12.52%, Ni 0.139%, with the balance being Fe and unavoidable impurities.

[0051] Its manufacturing method is basically the same as that of Example 1, except that: In step S12, the amount of reducing slag is 5% of the weight of the molten steel, the amount of silicon-calcium blocks added during precipitation deoxidation is 2.5 kg / t, and the temperature of the molten steel is controlled at 1560℃. In step S13, the refining temperature is 1580℃ and the white residue time is 40 min; In step S14, the sulfur alloying stirring time is 15 min; In step S15, the temperature of the molten steel during tapping and casting is 1620℃; In step S2, the current during the electroslag remelting stage is 8500 A and the voltage is 60 V; In step S3, the electroslag ingot is cooled in the crystallizer for 40 min and then removed from the ingot.

[0052] In Examples 1-3 above, the 416 free-machining stainless steel obtained was smelted using a combination of medium-frequency induction furnace and electroslag remelting. During the medium-frequency induction furnace smelting stage, sulfur had a high and stable recovery rate, consistently above 85%. After electroslag remelting, the sulfur recovery rate further exceeded 90%, ensuring stable sulfur content control in the resulting steel. Furthermore, through the purification and solidification control effects of the electroslag remelting process, the sulfide inclusions in the electroslag ingots obtained in these examples were evenly distributed, exhibiting good consistency between macroscopic and microstructures, and the steel displayed good hot workability during subsequent processing. After forging the electroslag ingots obtained in these examples, the sulfide inclusions in the forging were predominantly spindle-shaped. This inclusion morphology exhibited good chip-breaking characteristics during machining, ensuring both good machinability and performance.

[0053] In summary, this invention achieves a synergistic relationship between composition control and microstructure regulation by employing medium-frequency induction furnace smelting and electroslag remelting processes in the manufacturing of 416 free-machining stainless steel. In the medium-frequency induction furnace smelting stage, reasonable melting, refining, and sulfur alloying operations allow sulfur to enter the molten steel system stably and effectively, enabling controllable introduction of sulfur content into the free-machining stainless steel. Furthermore, in the electroslag remelting process, slag-metal reaction, molten pool purification, and controlled solidification conditions further regulate inclusions in the molten steel, optimizing the distribution and morphology of sulfide inclusions. The coordinated steps of these manufacturing methods ensure that the resulting steel maintains a stable chemical composition while also exhibiting good microstructure uniformity and hot working properties. This also facilitates the formation of inclusion morphologies suitable for machining during subsequent processing, making the 416 free-machining stainless steel of this invention suitable for applications requiring both high machinability and comprehensive material performance.

[0054] In the description of this invention, the references to "one embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0055] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A type of 416 free-machining stainless steel, characterized in that, Its chemical composition, by mass percentage, meets the following requirements: C ≤ 0.15%, Si ≤ 1.00%, Mn ≤ 1.25%, P ≤ 0.060%, S ≥ 0.15%, Cr 12.0–14.0%, Ni ≤ 0.20%, with the balance being Fe and unavoidable impurities.

2. The 416 free-machining stainless steel according to claim 1, characterized in that, Its chemical composition, by mass percentage, satisfies the following: C 0.10–0.12%, Si 0.30–0.60%, Mn 0.85–1.15%, P ≤ 0.030%, S 0.18–0.22%, Cr 12.20–12.70%, Ni 0.08–0.20%, with the balance being Fe and unavoidable impurities.

3. A method for manufacturing 416 free-machining stainless steel as described in claim 1 or 2, characterized in that, Includes the following steps: S1: Medium-frequency induction furnace smelting: Using raw steel or process pure iron, chromium stainless steel return material, low-carbon ferrochrome, pyrite, metallic manganese and ferrosilicon as raw materials, the melting, refining and sulfur alloying processes are completed in sequence in the medium-frequency induction furnace, and then the steel is tapped and cast to obtain electrode rods. S2: Electroslag remelting: The electrode rod is placed in a crystallizer and electroslag remelted under argon protection to obtain an electroslag ingot. S3: Cooling treatment: The electroslag ingot is cooled to room temperature by passing it through a crystallizer, then under a hood.

4. The manufacturing method according to claim 3, characterized in that, Step S1 includes: S11: Melting period: Melting is carried out at maximum power, and metallic manganese is added at the end of the melting process; S12: Slag Formation and Precipitation Deoxidation: After melting and cleaning, the bottom slag is removed and reducing slag is formed. The reducing slag consists of 55% CaF2 and 45% CaO by mass percentage, and the amount of slag is 3-5% of the weight of the molten steel. Calcium silicate blocks are inserted into the molten steel at a rate of 2-2.5 kg / t for precipitation deoxidation, and the temperature of the molten steel is controlled at 1540-1560℃.

5. The manufacturing method according to claim 4, characterized in that, In step S1, the refining includes: adjusting the temperature of the molten steel to 1550–1580℃, using aluminum powder for diffusion deoxidation, adding silicon-calcium powder to maintain the white slag state after the formation of white slag, the white slag time being 30–40 min, and adjusting the chemical composition of the molten steel during the refining process.

6. The manufacturing method according to claim 3, characterized in that, In step S1, the sulfur alloying treatment includes: removing about 50% of the refining slag from the surface of the molten steel; adding quartz sand to the molten steel at a weight of about 2% of the molten steel, and adding fluorite to adjust the fluidity of the slag; wrapping pyrite in aluminum foil and inserting it into the middle of the molten steel, stirring for 10–15 min, and then taking a sample to analyze the composition of the molten steel.

7. The manufacturing method according to claim 3, characterized in that, The temperature of the molten steel during the tapping and casting process is 1590–1620℃.

8. The manufacturing method according to claim 3, characterized in that, In step S2: the diameter of the crystallizer is Φ360 mm, and the electroslag remelting is carried out under argon protection. The current during the electroslag remelting stage is 7000–8500 A and the voltage is 56–60 V.

9. The manufacturing method according to claim 8, characterized in that, In step S2, the slag material used in the electroslag remelting is, by weight percentage: fluorite 46%, alumina 21%, quartz sand 24%, fused magnesia 5%, and active lime 4%.

10. The manufacturing method according to claim 3, characterized in that, In step S3, the cooling process includes: after electroslag remelting, the electroslag ingot is cooled in the crystallizer for 20–40 min and then removed from the ingot, and then cooled under a hood for no less than 36 h before being air-cooled.