Soft magnetic stainless steel wire rod suitable for cold heading machining and preparation method of soft magnetic stainless steel wire rod

Abstract

The invention belongs to the technical field of steel manufacturing, and discloses a soft magnetic stainless steel wire rod suitable for cold heading machining and a preparation method of the soft magnetic stainless steel wire rod. The soft magnetic stainless steel comprises the following components in percentage by weight: less than or equal to 0.02% of C, 1.0%-2.5% of Si, 0.10%-0.40% of Mn, less than or equal to 0.035% of P, less than or equal to 0.0020% of S, less than or equal to 0.60% of Ni, 12.0%-18.0% of Cr, 0.20%-1.00% of Cu, 0.010%-0.100% of Al, 0.001%-0.010% of RE, 0.050%-0.100% of Nb, 0.050%-0.100% of Ti, 0.050%-0.100% of V, less than or equal to 0.0025% of O and the balance of iron and inevitable impurities. Through reasonable component design and production process control, the soft magnetic stainless steel wire rod which has excellent plasticity, good corrosion resistance and excellent magnetic performance is obtained, the soft magnetic stainless steel wire rod is suitable for cold heading forming machining and can replace common turning machining, and the cold machining efficiency and the cold machining yield are greatly improved. The manufacturing method is simple in process, high in rolling yield and suitable for batch production.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel manufacturing, and relates to a stainless steel and a manufacturing method thereof, in particular to a soft magnetic stainless steel wire rod suitable for cold heading processing and a manufacturing method thereof. Background Art

[0002] Soft magnetic materials have high magnetic permeability, high saturation magnetic induction intensity, and low coercivity. Soft magnetic materials are easy to magnetize and demagnetize, which enables them to quickly reach saturation under the action of an external magnetic field and quickly lose magnetism after the external magnetic field disappears. Therefore, they are widely used in the manufacture of magnetic conductors, transformers, cores of relays, electromagnetic valves for household appliances, solenoid valves for automotive control systems, etc. Common soft magnetic materials are industrial pure iron or non-oriented silicon steel, etc. However, these materials have poor corrosion resistance and low service life, which makes stainless steel soft magnetic materials attract public attention. The production of soft magnetic stainless steel materials is difficult, and there are few manufacturers in China that can produce them currently. The most common grade is 430FR, which is a ferritic stainless steel. Adding element S to improve machinability results in fast cutting speed and high processing efficiency. However, adding sulfur also seriously reduces the corrosion resistance of the material, affects the hot working performance at the same time, has a low rolling yield, large cutting processing loss of the product, and low processing yield. With the development of society, the consumption of soft magnetic stainless steel is increasing day by day. Based on the processing efficiency and magnetic properties of soft magnetic stainless steel, further requirements are put forward for the corrosion resistance of the material, the processing yield of the material, and the economic cost.

[0003] In recent years, there have been more and more studies on soft magnetic stainless steel in the field. Patent CN115786804A, a low-Cr series soft magnetic stainless steel and a control method for its structure, discloses a ferritic stainless steel. Through the optimized design of the process, a uniform ferritic structure is formed after hot rolling, improving magnetic properties and plasticity. However, no effective control of the molten steel purity is proposed, so the corrosion resistance and material plasticity will be affected. Patent CN115287544A, a soft magnetic stainless steel wire rod with excellent welding performance and a manufacturing method thereof, fixes carbon and nitrogen by adding Nb and Ti, and adds Al to improve the purity of the molten steel, thereby enhancing the welding performance. However, it cannot stably improve the material plasticity and uniform structure. Excessive Al may also form more Al-containing inclusions, resulting in too high inclusion grade, thus affecting plasticity. Patent CN106636909A, a corrosion-resistant soft ferritic stainless steel, deoxidizes by adding Al and RE to improve the purity of the molten steel. However, too much Al will seriously affect casting and rolling, and at the same time bring too many Al-containing inclusions, affecting plasticity and being not suitable for mass production. Moreover, a large amount of Ti is added, which brings difficulty to rolling and will seriously reduce the rolling yield. Therefore, further exploration is still needed in the field on how to obtain soft magnetic stainless steel with excellent magnetic properties while having excellent plasticity and good corrosion resistance.

[0004] Based on this, the present invention is proposed. The present invention obtains a soft magnetic stainless steel wire rod having excellent plasticity, good corrosion resistance and excellent magnetic properties through reasonable component design and production process control, which is suitable for cold heading forming and can replace the traditional turning processing of soft magnetic stainless steel, greatly improving the cold processing efficiency and cold processing yield rate. Summary of the invention

[0005] The technical problems solved by the present invention are: 1) improving the plasticity of soft magnetic stainless steel to make it suitable for cold heading processing, replacing turning processing, and improving cold processing efficiency and yield rate; 2) improving the magnetic properties and corrosion resistance of soft magnetic stainless steel.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions.

[0007] The invention discloses a soft magnetic stainless steel wire rod suitable for cold heading processing. The chemical composition thereof comprises, by weight percentage, C≤0.02%, Si: 1.0%-2.5%, Mn: 0.10%-0.40%, P≤0.035%, S≤0.0020%, Ni≤0.60%, Cr: 12.0%-18.0%, Cu: 0.20%-1.00%, Al: 0.010%-0.100%, RE: 0.001%-0.010%, Nb: 0.050%-0.100%, Ti: 0.050%-0.100%, V: 0.050%-0.100%, O≤0.0025%, and the rest is iron and unavoidable impurities.

[0008] Preferred chemical composition: C≤0.018%, Si: 1.2%~2.3%, Mn: 0.20%~0.30%, P≤0.032%, S≤0.0018%, Ni≤0.40%, Cr: 12.5%~17.0%, Cu: 0.30%~0.80%, Al: 0.020%~0.080%, RE: 0.002%~0.008%, Nb: 0.060%~0.090%, Ti: 0.060%~0.090%, V: 0.060%~0.090%, O≤0.0020%, and the rest are iron and unavoidable impurities.

[0009] A method for preparing the soft magnetic stainless steel wire rod suitable for cold heading processing comprises the following steps: electric arc furnace smelting, AOD refining, LF refining, die casting, blanking, continuous rolling and annealing.

[0010] Further, electric arc furnace smelting steel: the electric arc furnace melts the scrap steel, selects the scrap stainless steel with P≤0.035%, and obtains crude molten steel.

[0011] Further, during the smelting process in the AOD furnace, first add ferrosilicon for deoxidation to reduce the oxygen content in the molten steel to within 60 ppm, then add aluminum blocks for deoxidation to reduce the oxygen content in the molten steel to within 25 ppm. During the smelting process, argon gas is blown for stirring throughout, replacing nitrogen gas. Even further, for AOD refining: it is divided into a decarburization period, a reduction period, and a refining period. Decarburization period: Make a high-alkalinity slag, control the alkalinity at 2.5 - 3.5, control the temperature at 1700°C - 1750°C, for a time of 10 min - 20 min, and the decarburization end point C ≤ 0.010%. Reduction period: Make a low-alkalinity slag, control the alkalinity at 1.5 - 2.5, control the temperature at 1650°C - 1700°C, for a time of 10 min - 15 min. In the reduction period, first add ferrosilicon (5 Kg - 6 Kg per ton of molten steel) for deoxidation to reduce the oxygen content in the molten steel to within 60 ppm, then add aluminum blocks (2 Kg - 3 Kg per ton of molten steel) for deoxidation to reduce the oxygen content in the molten steel to within 25 ppm. During the smelting process, argon gas is blown for stirring throughout, replacing nitrogen gas, and the tapping temperature is 1620°C - 1680°C.

[0012] Further, 10 - 15 minutes before tapping in LF smelting, feed a rare earth wire to reduce the oxygen content in the molten steel to within 20 ppm and adjust RE: 0.001% - 0.010%. Even further, for LF refining: Except for the element RE, fine-tune the content of each element to reach the target range, then adjust the temperature of the molten steel to 1620 - 1650°C, start feeding the rare earth wire, adjust RE: 0.001% - 0.010%, after the wire feeding is completed, softly blow argon gas for 10 min - 15 min, and then adjust the temperature again to 1600°C - 1630°C, and then lift the ladle for tapping. More preferably, the rare earth wire is a kind of iron-sheathed cored wire with a diameter of 9 - 12 mm, and the inside is wrapped with a mixture of rare earth and iron. In each meter of the wire, iron accounts for 55% - 60%, and rare earth accounts for 40% - 45%; more preferably, the iron sheet thickness is 0.6 mm. More preferably, the wire feeding speed is controlled at 100 m / min - 150 m / min.

[0013] Further, for ingot casting: Control the superheat at 50°C - 80°C during ingot casting, and cast into square ingots with cross-sectional dimensions in the range of 350 mm × 350 mm - 600 mm × 600 mm. If the size is too large, it will lead to a greater requirement for rolling pressure and generally rolling for blooming cannot be achieved; if the size is too small, the reduction ratio is too small to effectively break the as-cast structure, which is not conducive to the final uniform structure of the wire rod.

[0014] Further, blooming: The blooming heating temperature is divided into three sections. The first section: heating from room temperature to 600±50°C at a rate of 100±10°C / h and holding for 2±0.1 h; the second section: heating from 600±50°C to 900±50°C at a rate of 80±10°C / h and holding for 2±0.1 h; the third section: heating from 900±50°C to 1100±10°C at a rate of 80±10°C / h and holding for 2 h to 4 h; the blooming passes are controlled within 9 to 15 passes, and the reduction per pass is less than or equal to 50 mm, which can effectively reduce the surface cracking problem. Blooming to small square billets of 160 mm×160 mm to 190 mm×190 mm, and then directly feeding into the continuous rolling mill. Such billet shape design can effectively break the as-cast structure and is beneficial to the homogenization of the final wire rod structure. More preferably, the maximum reduction per pass is 40 to 50 mm. By adopting the above heating parameter settings, it can be ensured that the billet can be heated slowly and evenly to the final target temperature, held for a period of time, and the residence time in the furnace will not be too long to avoid overburning the billet structure and causing rolling cracking; if the residence time in the furnace is too short, it will not be heated through, which will also cause rolling cracking; the final temperature will not be too high or too low, further reducing the cracking risk.

[0015] Further, continuous rolling: An induction heating device is provided between the blooming mill and the continuous rolling mill to heat the surface of the billet. The heating controls the starting rolling temperature of continuous rolling at 1100°C to 1150°C and the finishing rolling temperature at 850°C to 900°C. A low finishing rolling temperature can reduce the abnormal coarsening of the core grains.

[0016] Further, annealing: The wire rod is heated to 790±10°C at a rate of 100±10°C / h, held at 790±10°C for 8 h to 10 h, then cooled to 500±20°C at a rate of 70±10°C / h, and finally air-cooled to room temperature. The long-term low-temperature annealing makes the material structure more uniform and further improves the plasticity. If the temperature is too low, the material stress cannot be eliminated thoroughly; if the temperature is too high, the grains are prone to be uneven. By adopting the above technical solution, the uniformity of the material structure can be effectively ensured and the plasticity of the material can be further improved.

[0017] The functions of the chemical components in the present invention are explained below.

[0018] Carbon (C): Carbon is an austenite-forming element and should be as low as possible in ferritic stainless steel. Carbon mainly exists in the form of carbides in ferritic stainless steel. Carbides are prone to accumulate at grain boundaries, seriously affecting the plasticity and corrosion resistance of the material. The C content in the present invention is controlled at ≤0.02%.

[0019] Silicon (Si): Silicon is a strong deoxidizer that reduces the oxygen content in steel and improves inclusions in steel. At the same time, silicon can significantly improve the magnetic properties of materials, increase the magnetic permeability. Higher silicon is usually required in soft magnetic stainless steel. However, excessive silicon will also reduce the cold working performance of stainless steel and its resistance to chloride ion corrosion. In this invention, the Si content is controlled at 1.0% - 2.5%.

[0020] Phosphorus (P): Phosphorus is a harmful element, and in stainless steel, it is generally required to be as low as possible. In this invention, P is controlled at ≤0.035%.

[0021] Sulfur (S): Sulfur can improve the machinability of materials in stainless steel. A small amount of sulfur is added to common soft magnetic stainless steel to achieve the purpose of rapid processing. However, the addition of sulfur will also significantly reduce the corrosion resistance and plasticity. The material is prone to cracking during extrusion deformation, and the service life of the material will also be reduced. In this invention, cold heading processing is used instead of turning processing, so sulfur is not needed, and at the same time, the adverse effects of sulfur are avoided. In this invention, S is controlled at ≤0.0020%.

[0022] Nickel (Ni): Nickel is an austenite-forming element and should be as low as possible in ferritic stainless steel. In this invention, nickel is controlled at ≤0.60%.

[0023] Chromium (Cr): Chromium is the main element in stainless steel and is the main reason for the stainlessness of stainless steel. When the chromium content in steel exceeds 10.5, a dense oxide film can be formed on the material surface by reacting with air to protect the matrix from corrosion. The higher the chromium content, the better the corrosion resistance. However, too high chromium content will affect the magnetic properties of materials, resulting in high coercivity and also affecting the hot plasticity, and the cost is relatively high; chromium is also a ferrite-forming element. In this invention, the chromium content is controlled at 12.0% - 18.0%.

[0024] Copper (Cu): Copper can improve the plasticity of materials in stainless steel. Copper is also an austenite-forming element, so it should not be too much in ferritic steel. Excessive copper will also significantly reduce the hot working performance of materials. In this invention, copper is controlled at 0.20% - 1.00%.

[0025] Aluminum (Al): Aluminum mainly plays a role in deoxidizing in stainless steel, improving the purity of molten steel. Aluminum is similar to silicon and can improve the magnetic properties of ferritic stainless steel. At the same time, aluminum can also form fine AlN precipitation phases with nitrogen, which can inhibit grain growth and thus improve the plasticity of materials. However, excessive aluminum will also form various brittle precipitation phases, seriously affecting the material properties. In this invention, aluminum is controlled at 0.01% - 0.10%.

[0026] Rare earth (RE): Rare earth has active chemical properties and can easily combine with elements such as sulfur, oxygen, and hydrogen in molten steel. It is an excellent desulfurizer that can efficiently purify molten steel and improve the quality of molten steel. A small amount of rare earth can also significantly improve the mechanical properties and plasticity of stainless steel, refine grains, and homogenize the structure. However, the solubility of rare earth elements in steel is very low, generally not exceeding 0.5%; in this invention, the rare earth is controlled within 0.001% - 0.010%.

[0027] Niobium (Nb): Niobium has a strong affinity for carbon and nitrogen in steel, forming extremely stable compounds to eliminate the adverse effects of carbon and nitrogen. Excessive Nb will form large particle precipitates, deteriorating the performance of the material. In this invention, it is controlled within 0.050% - 0.100%.

[0028] Titanium (Ti): Titanium has similar properties to niobium. By forming stable compounds such as titanium carbide and titanium nitride, it refines grains, improves the strength and plasticity of the material, further eliminates the adverse effects of carbon and nitrogen, and can also improve the corrosion resistance of the material and effectively prevent intergranular corrosion. Excessive titanium strengthens the matrix and reduces plasticity. In this invention, it is controlled within 0.050% - 0.100%.

[0029] Vanadium (V): Vanadium also has similar properties to niobium and titanium. It can act simultaneously with niobium and titanium to maximize the plasticity of the material, refine grains, and further improve the corrosion resistance of the material. However, too high a vanadium content will have the opposite effect. In this invention, it is controlled within 0.050% - 0.100%.

[0030] Oxygen (O): Oxygen is a gaseous element and also an impurity element. It usually exists in the form of solid solution and inclusions in stainless steel, which will reduce the plasticity and corrosion resistance of the material. Generally, the lower the better. In this invention, it is controlled within ≤0.0025%.

[0031] Compared with the prior art, a soft magnetic stainless steel wire rod suitable for cold heading processing in this invention has the following remarkable beneficial effects:

[0032] 1. In this invention, by adopting triple deoxidation methods of silicon deoxidation, aluminum deoxidation, and rare earth deoxidation, the total oxygen content is within 25 ppm. Then, through a reasonable smelting method, and controlling the rating of each coarse and fine series of inclusions A, B, C, and D within 1.0 level, the plasticity, corrosion resistance, and magnetic properties of the material are effectively improved.

[0033] 2. In this invention, three microalloying elements Nb, Ti, and V are added in a small amount, while fixing the residual C and N elements in the material, maximizing the elimination of the adverse effects of carbon and nitrogen, further improving the magnetic properties and corrosion resistance, and at the same time refining grains and further improving the plasticity of the material.

[0034] 3. In the manufacturing method of the present invention, large-sized square billets are cast by die casting, and then the billets are opened and continuously rolled into required wire rods. The large compression ratio enables the as-cast structure to be fully broken, recovered and recrystallized. In addition, the low final rolling temperature is controlled, so that the recrystallized structure is fine and uniform, which greatly improves the plasticity of the material.

[0035] 4. The present invention obtains soft magnetic stainless steel wire rods with excellent plasticity, good corrosion resistance and excellent magnetic properties through reasonable component design and production process control. The wire rods are suitable for cold heading and can replace common turning processing, greatly improving cold processing efficiency and cold processing yield. The manufacturing method of the present invention has a simple process, a high rolling yield, and is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a picture of the structure of Example 1 observed under a metallographic microscope;

[0037] Figure 2 This is a tissue image of Comparative Example 4 observed under a metallographic microscope;

[0038] Figure 3 This is a conventional 430FR structure picture observed under a metallographic microscope. DETAILED DESCRIPTION

[0039] In order to better clarify and understand the purpose, process scheme and advantages of the present invention, the technical scheme and implementation method of the present invention are further described clearly, completely and in detail through specific examples and in combination with the accompanying drawings. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical scheme of the present invention, and detailed implementation methods and specific operating processes are given, but they are only part of the embodiments of the present invention, not all of the embodiments. The specific implementation methods described are limited to explaining and interpreting the present invention, and do not limit the present invention. Based on the embodiments in the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0040] The experimental methods and conditions used in the embodiments of the present invention are conventional methods and conventional conditions unless otherwise specified. The materials, reagents or instruments used in the embodiments, unless otherwise specified, can be obtained from commercial sources or prepared by conventional methods. The reaction conditions embodied in the content of the invention of the present invention can achieve the reaction and obtain the product of the expected effect. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of the present invention.

[0041] Embodiment 1:

[0042] Provide a soft magnetic stainless steel wire rod suitable for cold heading processing. The main component composition of the soft magnetic stainless steel is shown in Table 2 and Table 4, and the rest is iron and inevitable impurities.

[0043] To produce a soft magnetic stainless steel wire rod suitable for cold heading processing with the above composition, the manufacturing method is as follows: melting steel in an electric arc furnace → AOD refining → LF refining → ingot casting → blooming → continuous rolling → annealing.

[0044] 1) Melting steel in an electric arc furnace: Use a 40-ton electric arc furnace to melt scrap steel, select scrap stainless steel with P: 0.030%, and obtain 36 tons of crude molten steel.

[0045] 2) AOD refining: Decarburization period: Make a high-alkalinity slag, control the alkalinity at 3.2, control the temperature at 1700°C - 1750°C, for 15 minutes, and the decarburization end point C: 0.005%; Reduction period: Make a low-alkalinity slag, control the alkalinity at 1.9, control the temperature at 1650°C - 1700°C, for 12 minutes. First, add 182 Kg of ferrosilicon for deoxidation during the reduction period, reduce the oxygen in the molten steel to 55 ppm, then add 83 Kg of aluminum blocks for deoxidation, reduce the oxygen in the molten steel to 22 ppm, stir with argon gas throughout the smelting process, and the tapping temperature is 1670°C.

[0046] LF refining: Except for the element RE, fine-tune the content of each element to reach the target range, then adjust the temperature of the molten steel to 1637°C, start feeding the rare earth wire, adjust to RE of 0.004% (in this example, cerium Ce is added), control the wire feeding speed at 120 m / min, soft blow argon for 13 minutes after the wire feeding is completed, adjust the temperature to 1621°C again, and lift the ladle to tap the steel. Preferably, the rare earth wire is a ferrous sheathed cored wire with a diameter of 9 - 12 mm, and the inside is wrapped with a mixture of rare earth and iron. Iron accounts for 55% - 60% and rare earth accounts for 40% - 45% per meter of the wire; more preferably, the thickness of the iron sheet is 0.6 mm.

[0047] Ingot casting: Control the superheat at 50°C - 80°C during ingot casting, and cast into a square ingot with a cross-sectional size in the range of 350 mm × 350 mm - 410 mm × 410 mm.

[0048] Blooming: The blooming heating temperature is divided into 6 sections. The first section: Heat from room temperature to 600°C at a rate of 100°C / h; The second section: Insulate at 600°C for 2 hours; The third section: Heat from 600°C to 900°C at a rate of 80°C / h; The fourth section: Insulate at 900°C for 2 hours; The fifth section: Heat from 900°C to 1100°C at a rate of 80°C / h; The sixth section: Insulate at 1100°C for 2.5 hours; Control the blooming passes at 11 passes, the maximum reduction per pass is 44 mm, no cracking problem appears on the surface, bloom to a small square billet of 160 mm × 160 mm, and then directly enter the continuous rolling mill.

[0049] Continuous rolling: An induction heating device is provided between the blooming mill and the continuous rolling mill to heat the surface of the billet. The heating controls the starting rolling temperature of the continuous rolling to be 1140 °C, the final rolling temperature to be 855 °C, the rolling specification to be a diameter of 10 mm, and the final rolling speed to be 42 m / s.

[0050] Annealing: The wire rod is heated to 790 °C at a speed of 100 °C / h, held at 790 °C for 8 h, then cooled to 500 °C at a speed of 70 °C / h, and finally cooled to room temperature in the air. The long-term low-temperature annealing makes the material structure more uniform and further improves the plasticity.

[0051] Example 2-3: A method for preparing a soft magnetic stainless steel wire rod suitable for cold heading processing disclosed in the present invention. The difference from Example 1 is that the parameter conditions of each step are shown in Table 1, and the component compositions of the obtained soft magnetic stainless steel are shown in Tables 2 and 4.

[0052] Comparative Examples 1-5: The differences between Comparative Examples 1 and 2 and the examples are that less aluminum and rare earth are added during the smelting process, thus affecting the final composition and properties; the differences between Comparative Examples 3 and 4 and the examples are that the addition amounts of microalloying elements are different, thus affecting the final composition and properties; the difference between Comparative Example 5 and the examples is that there are significant differences in the process control parameters (starting rolling temperature and final rolling temperature). The parameter conditions of each specific step are shown in Table 1, and the component compositions of the obtained soft magnetic stainless steel are shown in Tables 2 and 4.

[0053] Comparative Example 6: Taking the common 430FR steel as Comparative Example 6, in this example, the 430FR produced by Tsingshan Iron and Steel with the furnace number 241002AE02 is selected as an example for comparison. The component compositions of the stainless steel are shown in Tables 2 and 4.

[0054] Table 1 Summary of key process parameters of each example and comparative example

[0055]

[0056]

[0057] Table 2 Summary of component percentages of specific examples, comparative examples and common 430FR, (O element is shown in Table 4)

[0058]

[0059] The above Examples 1 to 3 and Comparative Example 5 meet the designed chemical composition: C≤0.02%, Si: 1.0% - 2.5%, Mn: 0.10% - 0.40%, P≤0.035%, S≤0.0020%, Ni≤0.60%, Cr: 12.0% - 18.0%, Cu: 0.20% - 1.00%, Al: 0.010% - 0.100%, RE: 0.001% - 0.010%, Nb: 0.050% - 0.100%, Ti: 0.050% - 0.100%, V: 0.050% - 0.100%, and the rest is iron and unavoidable impurities. In Comparative Example 1, the rare earth element RE was added less compared with the present invention. In Comparative Example 2, the element Al was added less compared with the present invention. Both RE and Al have the functions of deoxidizing and desulfurizing, so the oxygen content and sulfur content in Comparative Examples 1 and 2 are relatively high, and the inclusion rating is also relatively high. In Comparative Example 3, the elements Nb and V were added less compared with the present invention. In Comparative Example 4, the element V was added less compared with the present invention. Nb and V are both elements for refining and homogenizing grains. Adding too little or too much will not work. Excessive amounts of individual elements will not only not achieve the same effect but also increase the difficulty of rolling production. The common 430FR in Comparative Example 6 does not add elements Al, RE, Nb, Ti, and V, and higher amounts of S element and Mn element are added to improve machinability. S will seriously affect the plasticity, corrosion resistance, and magnetic properties of the material, and Mn will affect the magnetic properties of the material.

[0060] Test Example

[0061] Performance tests were carried out on each of the examples, comparative examples, and the common 430FR. The specific results are shown in Tables 3 and 4.

[0062] Among them, the test methods for strength and plasticity indexes are "GB / T 228.1 Metallic materials - Tensile testing - Part 1: Method of test at room temperature";

[0063] The test method for corrosion resistance index is "GB / T 10125 Corrosion tests in artificial atmospheres - Salt spray tests";

[0064] The test method for magnetic property indexes is "GB / T 13012 Methods for measurement of d.c. magnetic properties of soft magnetic materials";

[0065] The rolling yield = (weight of qualified products after rolling / total weight before rolling) × 100%; The cold processing yield = (weight of qualified products after cold processing / total weight before cold processing) × 100%;

[0066] The test method for oxygen content is "GB / T 11261 Steel and iron - Determination of oxygen content - Pulse heating inert gas fusion - Infrared absorption method";

[0067] The test method for inclusion grade is "GBT 10561 Methods for the determination of the content of non - metallic inclusions in steel";

[0068] The grain size test method is "GB / T6394 Metal Average Grain Size Determination Method".

[0069] Table 3 Summary of performance indicators and yield rates of specific embodiments and comparative examples

[0070]

[0071] Table 4 Summary of oxygen content, inclusion results, and grain size of specific examples and comparative examples

[0072]

[0073]

[0074] As can be seen from Table 3, the elongation and shrinkage of Examples 1 to 3 are relatively high, indicating good plasticity. The plasticity of Comparative Examples 1 to 5 and 430FR is relatively poor. Comparative Examples 1 to 2 are affected by the high level of inclusions. Comparative Examples 3 to 5 are mainly due to the reduced plasticity caused by uneven grains. 430FR is affected by the addition of high S elements. Examples 1 to 3 and Comparative Examples 3 to 5 can be rust-free for 80 hours in the neutral salt spray test, and have good corrosion resistance. Comparative Examples 1 to 2 are affected by inclusions and have poor corrosion resistance. 430FR is affected by S and has worse corrosion resistance. Examples 1 to 3 and Comparative Examples 1 to 5 have lower coercive force and higher saturation magnetic induction intensity, indicating good magnetic properties. Comparative Example 6 conventional 430FR has a higher Mn content and higher coercive force, so the magnetic properties are relatively poor. The rolling yield of Examples 1 to 3 and Comparative Examples 1 to 4 is relatively high, the rolling yield of Comparative Example 5 is very low due to unreasonable rolling process control parameters, and the rolling yield of Comparative Example 6 is relatively low due to the influence of S on the common 430FR. Examples 1 to 3 can be cold headed and have a high processing yield, while Comparative Examples 1 to 5 have a relatively low yield when used for cold headed processing due to low plasticity, but are still better than the turning yield of 430FR.

[0075] As can be seen from Table 4, the oxygen content of Examples 1 to 3 and Comparative Examples 3 to 5 is relatively low, so the inclusion level can meet ≤1.0 level. This is the effect of triple deoxidation of Si, Al, and RE, which is the main reason for good corrosion resistance; Comparative Examples 1 to 2 lack RE or Al deoxidation, resulting in high oxygen content and relatively high inclusion level, which also reduces corrosion resistance; Comparative Example 6 common 430FR has worse deoxidation effect, high oxygen content, higher inclusion level, and greater impact on corrosion resistance. The grain size of Examples 1 to 3 and Comparative Examples 1 to 2 is uniform at level 7, which is the effect of the combined action of Nb, Ti, and V, making the plasticity better. Comparative Examples 3 to 5 and 430FR have mixed crystals and poor plasticity.

[0076] Figure 1This is the metallographic structure of the material produced in Example 1, showing uniform structure; Figure 2 This is the metallographic structure of the material produced in Example 4, showing mixed crystal structure; Figure 3 This is the metallographic structure of conventional 430FR in comparative example 6, showing mixed crystal structure.

[0077] In summary, the soft magnetic stainless steel wire rod suitable for cold heading processing manufactured by the composition and process designed by the present invention has both excellent plasticity and good corrosion resistance, and at the same time has excellent magnetic properties. It is suitable for cold heading forming processing, can replace the common turning chip processing, greatly improves the cold processing efficiency and cold processing yield, and avoids the consequences of plasticity, corrosion resistance and magnetic properties deterioration caused by sulfur addition. The manufacturing method of the present invention has a simple process, a high rolling yield, and is suitable for mass production.

[0078] The above-described embodiments are only preferred solutions of the present invention and are not intended to limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

Claims

1. A soft magnetic stainless steel wire rod suitable for cold heading, characterized in that, Comprising by weight percentage: C ≤ 0.02%, Si: 1.0% - 2.5%, Mn: 0.10% - 0.40%, P ≤ 0.035%, S ≤ 0.0020%, Ni ≤ 0.60%, Cr: 12.0% - 18.0%, Cu: 0.20% - 1.00%, Al: 0.010% - 0.100%, RE: 0.001% - 0.010%, Nb: 0.050% - 0.100%, Ti: 0.050% - 0.100%, V: 0.050% - 0.100%, O ≤ 0.0025%, and the balance being iron and unavoidable impurities.

2. The soft magnetic stainless steel wire rod suitable for cold heading processing according to claim 1, characterized in that Comprising by weight percentage: C ≤ 0.018%, Si: 1.2% - 2.3%, Mn: 0.20% - 0.30%, P ≤ 0.032%, S ≤ 0.0018%, Ni ≤ 0.40%, Cr: 12.5% - 17.0%, Cu: 0.30% - 0.80%, Al: 0.020% - 0.080%, RE: 0.002% - 0.008%, Nb: 0.060% - 0.090%, Ti: 0.060% - 0.090%, V: 0.060% - 0.090%, O ≤ 0.0020%, and the balance being iron and unavoidable impurities.

3. A method for preparing a soft magnetic stainless steel wire rod suitable for cold heading as described in claim 1 or 2, characterized in that, Including the following steps: Steelmaking in an electric arc furnace, AOD refining, LF refining, ingot casting, blooming, continuous rolling, annealing.

4. The preparation method of a soft magnetic stainless steel wire rod suitable for cold heading processing according to claim 3, characterized in that, Melting scrap steel in an electric arc furnace, selecting scrap stainless steel with P ≤ 0.035% to obtain crude steel liquid.

5. The preparation method of a soft magnetic stainless steel wire rod suitable for cold heading processing according to claim 3, characterized in that, During the smelting process in an AOD furnace, first add ferrosilicon for deoxidation to reduce the oxygen in the molten steel to within 60 ppm, then add aluminum blocks for deoxidation to reduce the oxygen in the molten steel to within 25 ppm, and stir the molten steel with argon gas throughout the smelting process instead of blowing nitrogen gas.

6. The preparation method of a soft magnetic stainless steel wire rod suitable for cold heading according to claim 3, characterized in that, Feed rare earth wire during LF smelting to adjust RE: 0.001% - 0.010%.

7. The preparation method of a soft magnetic stainless steel wire rod suitable for cold heading according to claim 3, characterized in that, Control the superheat degree at 50°C - 80°C during ingot casting, and cast into square ingots with cross-sectional dimensions in the range of 350 mm × 350 mm - 600 mm × 600 mm.

8. The preparation method of a soft magnetic stainless steel wire rod suitable for cold heading according to claim 3, characterized in that, Bloom to square billets of 160 mm × 160 mm - 190 mm × 190 mm; the blooming heating temperature is divided into three sections. The first section: heat from room temperature to 600 ± 50°C at a rate of 100 ± 10°C / h and hold for 2 ± 0.1 h; The second section: heat from 600 ± 50°C to 900 ± 50°C at a rate of 80 ± 10°C / h and hold for 2 ± 0.1 h; the third section: heat from 900 ± 50°C to 1100 ± 10°C at a rate of 80 ± 10°C / h and hold for 2 h - 4 h; the number of blooming passes is controlled within 9 - 15 passes, and the reduction per pass is less than or equal to 50 mm.

9. The preparation method of a soft magnetic stainless steel wire rod suitable for cold heading according to claim 3, characterized in that, An induction heating device is provided between blooming and continuous rolling to heat the surface of the billet, and control the starting rolling temperature of continuous rolling at 1100°C - 1150°C and the final rolling temperature at 850°C - 900°C.

10. The preparation method of a soft magnetic stainless steel wire rod suitable for cold heading according to claim 3, characterized in that The annealing process is to heat the wire rod to 790 ± 10°C at a rate of 100 ± 10°C / h, hold at 790 ± 10°C for 8 h - 10 h, then cool at a rate of 70 ± 10°C / h to 500 ± 20°C, and finally cool in air.

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